20260114Application.pdf

RECEIVED
JANUARY 14, 2026
IDAHO PUBLIC
INTERMOUNTAIN° UTILITIES COMMISSION
GAS COMPANY
A Subsidiary of MDU Resources Group,Inc.
In the Community to Serve®
January 14, 2026
Ms. Monica Barrios-Sanchez
Commission Secretary
Idaho Public Utilities Commission
P.O. Box 83720
Boise, ID 83720-0074
RE: Case No. INT-G-26-01
Dear Ms. Barrios-Sanchez:
Attached for consideration by this Commission is an electronic submission of Intermountain Gas
Company's Application for Approval to Place into Effect a Change in Its Depreciation and
Amortization Rates.
If you should have any questions regarding the attached,please don't hesitate to contact me at (509)
528-9223.
Sincerely,
Is/Michael Parvinen
Michael Parvinen
Director, Regulatory Affairs
Intermountain Gas Company
Enclosure
cc: Preston Carter

Preston N. Carter, ISB No. 8462
Megann E. Meier, ISB No. 11948
GIVENS PURSLEY LLP
601 West Bannock Street
P.O. Box 2720
Boise, Idaho 83701-2720
Office: [phone]
Fax: [phone]
Attorneys for Intermountain Gas Company
BEFORE THE IDAHO PUBLIC UTILITIES COMMISSION
IN THE MATTER OF THE Case No. INT-G-26-01
APPLICATION OF INTERMOUNTAIN
GAS COMPANY FOR APPROVAL TO APPLICATION
PLACE INTO EFFECT A CHANGE IN
ITS DEPRECIATION AND
AMORTIZATION RATES
Intermountain Gas Company("Intermountain"or"Company"), a subsidiary of MDU
Resources Group,Inc. with general offices located at 555 South Cole Road,Boise,Idaho,pursuant
to the Rules of Procedure of the Idaho Public Utilities Commission("Commission"), requests
authority to place into effect a change in its depreciation and amortization rates.
Please address communications regarding this Application to:
Preston N. Carter
Megann E. Meier
Givens Pursley LLP
601 W. Bannock St.
Boise, Idaho 83702
[e-mail]
[e-mail]
[e-mail]
and
APPLICATION- 1

Michael Parvinen
Director—Regulatory Affairs
Intermountain Gas Company
Post Office Box 7608
Boise, ID 83707
[e-mail]
[e-mail]
In support of this Application, Intermountain alleges and states as follows.
I. INTRODUCTION
Intermountain is a gas utility, subject to the jurisdiction of the Commission, engaged in the
sale of and distribution of natural gas within the State of Idaho under authority of Commission
Certificate No. 219, issued December 2, 1955, as amended and supplemented by Order No. 6564,
dated October 3, 1962.
Intermountain provides natural gas service to the following Idaho communities and counties
and adjoining areas:
Ada County-Boise,Eagle,Garden City,Kuna,Meridian,and Star;
Bannock County-Arimo,Chubbuck,Inkom,Lava Hot Springs,McCammon,and Pocatello;
Bear Lake County-Georgetown,and Montpelier;
Bingham County-Aberdeen,Basalt,Blackfoot,Firth,Fort Hall,Moreland/Riverside, and Shelley;
Blaine County-Bellevue,Hailey,Ketchum,and Sun Valley;
Bonneville County-Ammon,Idaho Falls,Iona,and Ucon;
Canyon County-Caldwell,Greenleaf,Middleton,Nampa,Parma,and Wilder;
Caribou County-Bancroft,Grace,and Soda Springs;
Cassia County-Burley,Declo,Malta,and Raft River;
Elmore County-Glenns Ferry,Hammett,and Mountain Home;
Fremont County-Parker,and St.Anthony;
Gem County-Emmett;
Gooding County-Gooding and Wendell;
Jefferson County-Lewisville,Menan,Rigby,and Ririe;
Jerome County-Jerome;
Lincoln County- Shoshone;
Madison County-Rexburg,and Sugar City;
Minidoka County-Heybum,Paul,and Rupert;
Owyhee County-Bruneau, and Homedale;
Payette County-Fruitland,New Plymouth,and Payette;
Power County-American Falls;
Twin Falls County-Buhl,Filer,Hansen,Kimberly,Murtaugh,and Twin Falls;
Washington County-Weiser.
APPLICATION-2

Intermountain's properties in these locations consist of transmission pipelines, liquefied
natural gas storage facilities, compressor stations, distribution mains, services,meters and
regulators, and general plant and equipment.
II. BACKGROUND
Intermountain's currently effective combined depreciation and amortization rate of 2.40%
(comprised of the currently approved combined depreciation and amortization rate of 2.41%
weighted by December 31, 2024 assets)was approved by this Commission in Case No. INT-G-21-
01, Order No. 35134. The Company received authorization from the Commission in Case No. INT-
G-23-05, Order No. 36041 to update its depreciation and amortization rates with this Commission
every five years. This Application reflects an update to Intermountain's last study.
III. DEPRECIATION&AMORTIZATION STUDY
Intermountain contracted the services of Concentric Energy Advisors ("Concentric")to
perform an update of the depreciation and amortization study filed in Case No. INT-G-21-01.
The study is based on the Company's books and records as of December 31, 2024. Intermountain's
investment balance and reserve balance of depreciable property included in the study is
$933,798,386 and$412,785,793,respectively, as shown on Exhibit No. 1, Line 41, Col. (c) and
(d).
The results of the study performed by Concentric indicate that Intermountain's currently
approved depreciation and amortization rates are under-depreciating its assets. Therefore,
Intermountain requests an increase in its depreciation and amortization rates from a combined
2.40% (when the accrual rates per Order No. 35134 are weighted by December 31, 2024 assets)
to 2.49%. This increase is required in order to accrue the proper dollars over the remaining life of
the property. The effect of the higher rate would be to increase Intermountain's annual
APPLICATION-3

depreciation and amortization accrual by$877,030 as seen on Exhibit No. 1, Line 41, Col. 0).
Exhibit No. 1 contains a summary comparison of the current depreciation and amortization rates
and annual accruals,by plant function and by account,versus the rates proposed in this Application
and is attached and incorporated by reference.
The depreciation and amortization study performed by Concentric discusses the reasoning
and methodology for the proposed changes to Intermountain's depreciation and amortization rates.
The study is presented in Exhibit No. 2 and is attached and incorporated by reference.
IV. AMORTIZATION DETAIL
Pursuant to Case No. INT-G-99-2, Order No. 28331, six general plant accounts (Acct Nos.
391, 393, 394, 395, 397, and 398)were analyzed according to amortization accounting. Exhibit No.
3 provides additional detail for these accounts including the present and proposed lives and
investment balances. Exhibit No. 3 is attached and incorporated by reference.
V. EFFECTIVE DATE
Intermountain requests that the changes to its depreciation and amortization rates be
effective on the first day of the month following the issuance of the Commission's Order in this
matter.
VI. PRICE IMPACT
Intermountain does not seek a change in its prices as a result of this requested change in
depreciation and amortization rates.
VII. MODIFIED PROCEDURE
Intermountain requests that this matter be handled under modified procedure pursuant to
Rules 201-204 under the Commission's Rules of Procedure. Intermountain stands ready to respond
to any requests for information in this matter.
APPLICATION-4

VIII. REQUEST FOR RELIEF
Intermountain respectfully petitions the Idaho Public Utilities Commission as follows:
a. That Intermountain be authorized to increase its depreciation and amortization rates
from a combined 2.40% (when the accrual rates per Order No. 35134 are weighted by
December 31, 2024 assets) to 2.49% as shown on Exhibit No. 1, Line 41, Col. (h).
b. That Intermountain's current prices remain unchanged as a result of this Application.
c. That Intermountain be authorized to record these changes in its depreciation and
amortization rates effective on the first day of the month following the issuance of the
Commission's Order in this matter.
d. For such other relief as this Commission may determine proper.
Dated: January 14,2026.
GIVENS PURSLEY LLP
By /s/Preston N. Carter
Preston N. Carter
Givens Pursley LLP
Attorneys for Intermountain Gas Company
APPLICATION-5

CERTIFICATE OF SERVICE
I hereby certify that on January 14, 2026, I caused to be served a true and correct copy of
the foregoing document to the person(s) listed below by the method indicated:
Commission Staff Via Electronic Mail
Monica Barrios-Sanchez, Commission Secretary [e-mail]
Idaho Public Utilities Commission
11331 W. Chinden Blvd., Bldg. 8, Suite 201-A
Boise, ID 83714
/s/Chris Shoop
Chris Shoop—Regulatory Affairs Analyst
APPLICATION-6

EXHIBIT NO. 1
CASE NO. INT-G-26-01
INTERMOUNTAIN GAS COMPANY
Summary of Approved and Proposed Depreciation and Amortization Rates
(1 page)

Exhibit No. 1
Case No. INT-G-26-01
Intermountain Gas Company
Page 1 of 1
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2

EXHIBIT NO. 2
CASE NO. INT-G-26-01
INTERMOUNTAIN GAS COMPANY
Concentric Energy Advisors—Calculated Annual Depreciation Accrual Rates Applicable to
Gas Plant in Service as of December 31,2024
(235 pages)

I@ CONCENTRIC
2025 DEPRECIATION STUDY
CALCULATED ANNUAL DEPRECIATION ACCRUAL RATES
APPLICABLE TO GAS PLANT IN SERVICE AS OF DECEMBER 31,2024
Prepared for Intermountain Gas Company
January 2026
Headquarters Washington, D.C. Office
293 Boston Post Rd West, Ste 500 1300 19th St NW, Ste 620
Marlborough, MA,USA 01752 Washington, DC, USA 20036
508.263.6200 202.587.4470
Concentric Advisors, ULC
28 Quarry Park Blvd SE, Ste 350
Calgary,AB, Canada T2C 5P9
587.997.6489
Concentric Energy Advisors®and its logo are federally registered trademarks of Concentric Energy Advisors®. Any unauthorized use is prohibited.

16 CONCENTRIC
January 8,2026
Intermountain Gas Company
555 S Cole Road
Boise,Idaho 83709
Attention: Mr. Garret Senger
Chief Utilities Officer, Montana-Dakota Utilities
Dear Mr.Senger;
Pursuant to your request,we conducted a depreciation study related to the natural gas transmission,
distribution and general plant system of Intermountain Gas Company as of December 31, 2024. Our
study presents a description of the methods used in the estimation of service life, as well as our
recommendations for average service life estimates.
We gratefully acknowledge the assistance of Intermountain Gas Company personnel in the
completion of the review.
Should you have any questions or concerns, please do not hesitate to contact me directly at
587.997.6489
Yours truly,
Concentric Energy Advisors
Larry Kennedy Colin Burns
Senior Vice President Senior Project Manager
LEK/ta
Project:101010
28 QUARRY PARK BLVD SE • SUITE 350 • CALGARY,AB T2C 5P9 • 403-257-5946 0 CEADVISORS.COM

Intermountain Gas Company
16 2025 Depreciation Study
TABLE OF CONTENTS
1 EXECUTIVE SUMMARY ..................................................................................................................................... 1-1
1.1 Executive Summary............................................................................................................................ 1-2
2 BASIS OF THE STUDY......................................................................................................................................... 2-1
2.1 Scope.................................................................................................................................................. 2-1
2.2 Plan of Study....................................................................................................................................... 2-2
2.3 Depreciation....................................................................................................................................... 2-2
2,4 Information Provided by Intermountain Gas Company................................................................ 2-3
2.5 Data Reconciliation........................................................................................................................... 2-3
3 DEVELOPMENT OF THE REQUIRED DEPRECIATION RATES............................................................................. 3-1
3.1 Depreciation....................................................................................................................................... 3-1
3.1.1 Study Depreciation Methods and Procedures ...............................................................3-2
3.1.2 Truncation Cuts...................................................................................................................3-4
3.2 Estimation of Survivor Curves.............................................................................................................3-4
3.2.1 Survivor Curves ................................................................................................................... 3-4
3.2.2 Survivor Curve Judgments................................................................................................. 3-5
3.3 Major Account Analysis..................................................................................................................... 3-8
4 CALCULATION OF ANNUAL AND ACCRUED DEPRECIATION......................................................................4-1
4,1 Calculation of Annual and Accrued Amortization.........................................................................4-1
4,2 Monitoring of Book Accumulated Depreciation ............................................................................4-2
5 RESULTS OF THE STUDY..................................................................................................................................... 5-1
5.1 Qualification of Results....................................................................................................................... 5-1
5.2 Description of Detailed Tabulations................................................................................................. 5-1
6 RETIREMENT RATE ANALYSIS............................................................................................................................ 6-1
7 NET SALVAGE................................................................................................................................................... 7-1
8 DETAILED DEPRECIATION CALCULATIONS ....................................................................................................8-1
9 ESTIMATION OF SURVIVOR CURVES............................................................................................................... 9-1
9.1 Average Service Life.......................................................................................................................... 9-1
9.2 Survivor Curves.................................................................................................................................... 9-1
9.3 Iowa Type Curves............................................................................................................................... 9-3
9.4 Retirement Rate Method of Analysis................................................................................................ 9-8
9,5 Schedules of Annual Transactions in Plant Records ....................................................................... 9-8
9,6 Schedule of Plant Exposed to Retirement..................................................................................... 9-12
9.7 Original Life Tables............................................................................................................................ 9-14
9.& Smoothing the Original Survivor Curve .......................................................................................... 9-16
10 ESTIMATION OF NET SALVAGE...................................................................................................................... 10-1
Concentric Energy Advisors -Table of Contents- Page 1 1

Intermountain Gas Company
1@ 2025 Depreciation Study
SECTION 1
1 EXECUTIVE SUMMARY
Pursuant to the request of Intermountain Gas 2024, are amortized over the composite
Company ("IGC" or the "Company"), remaining life of each account.
Concentric Energy Advisors, ("Concentric") Concentric recommends the calculated annual
completed a depreciation study related to gas depreciation accrual rates set forth herein
transmission, distribution and general plant apply specifically to gas plant in service, as of
accounts. The purpose of the study is to December 31, 2024, summarized by Tables 1,
determine the annual depreciation accrual 1A, and 113, starting on page 5-2. Supporting
rates and amounts applicable to the original data and calculations are provided within the
cost of gas utility plant, as of December 31, study.
2024.
Concentric's study results in an annual
The depreciation rates are based on the depreciation expense accrual related to the
Straight-Line method using the Average Life recovery of original cost of investment of
Group ( ALG ) procedure and were applied on
$23.27 million when applied to depreciable
a Remaining Life basis. The calculations were plant study balances,as of December 31,2024,
based on attained ages and estimated average of $934 million and calculated in accordance
service life estimates for each depreciable with the ALG Procedure. The study results are
group of assets. Variances between the summarized at an aggregate functional group
calculated accrued depreciation and the book level as follows:
accumulated depreciation,as of December 31,
SUMMARY OF ORIGINAL COST,ACCRUAL PERCENTAGES AND AMOUNTS
Plant Group Original Cost Previously Approved Annual Recommended Annual
Accrual Accrual
Other Storage $43,407,348 $883,031 2.83% $964,980 2.22%
Transmission $83,221,231 $1,036,414 1.42% $1,424,592 1.71%
Distribution $742,569,566 $11,715,205 2.32% $18,445,981 2.48%
General Plant $64,514,295 $2,446,156 4.20% $2,434,127 3.77%
TOTAL $933,798,386 $16,080,806 2.417o $23,269,680 2.49%
Concentric Energy Advisors Page 1 1-1

Intermountain Gas Company
16 2025 Depreciation Study
1 ,1 Executive Summary
Annual Accrual By Plant Type Total Depreciable Plant r. Original Cost By Plant Type
64.6M(6.91
933 - 80M 8.912-,
2.43M— Plant Type (8.914_�
�,.. � Plant Type
Distribution Pla Distribution Plant
General Plant *Transmission Plant
Transmission Plant Accrual Rate By Plant Type General Plant
Gas Other Storage Gas Other Storage
•-1)19 Accrual Rate 2024 Proposed Accrual Rate 742.57M
18.45rI'79.52%)
0
u m o
m 4% N INix
Previously Approved N N N Previously Approved
Annual Accrual 2°% ' , :_ Depreciation Rate
16 0 8 M °°'° General Gas Other Distribution Transmission■ 2 . 41 %
>
Storage
*_ Proposed 2024 Plant Type
` Depreciation Expense Proposed 2024
P P Change In Annual Change in Depreciation Depreciation Rate
Accrual Accrual .9 Rate
T 23 ■ 27M2 . 49 %7 . 19M 0 . 08 %
Annual Accrual Amount - Top Five Accounts
7.26M
1.83M 1.81M
a 0.97 M
380.00 SERVICES 376.00 MAINS 381.20 ERT UNITS 381.00 METERS 367.00 MAINS
Account
Concentric Energy Advisors Page 1 1-2

Intermountain Gas Company
16 2025 Depreciation Study
SECTION 2
2 BASIS OF THE STUDY
2.1 Scope
This study sets forth the results of the depreciation study for the transmission, distribution, and
general gas plant assets of IGC,to determine the annual depreciation accrual rates and amounts for
book purposes applicable to the original cost of investment as of December 31, 2024.The rates and
amounts are based on the Straight-Line Method, incorporating the ALG Procedure applied on a
Remaining Life Basis.This study also describes the concepts,methods and judgments which underlie
the recommended annual depreciation accrual rates related to the IGC assets in service, as of
December 31, 2024.
The service life estimates resulting from the study were based on:
■ informed professional judgment which incorporated analyses of historical plant retirement data
recorded through December 31,2024;
■ a review of IGC company practice and outlook,as they relate to plant operation and retirement;
and
■ consideration of current practice in the Gas system industry,including knowledge of service life
estimates used for other Gas system companies.
The depreciation accrual rates presented herein are based on generally-accepted methods and
procedures for calculating depreciation. The estimated survivor curves used in this study are based
on studies incorporating actual data through 2024 for most accounts.
Amortization accounting is used for certain accounts because of the disproportionate plant
accounting effort required in these accounts. Many regulated utilities in North America have received
approval to adopt amortization accounting for these types of accounts.
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Intermountain Gas Company
1@ 2025 Depreciation Study
2.2 Plan of Study
This study is presented in the following order:
Section 1: Executive Summary, presents a brief summary of the depreciation study and results
Section 2: Contains statements with respect to the plan and the Basis of the Study
Section 3: Development of the Required Depreciation Rates, presents descriptions of the methods
used and factors considered in the service life study
Section 4: Calculation of Annual and Accrued Depreciation, presents the methods and procedures
used in the calculation of depreciation
Section 5: Results of Study, presents summaries by depreciable group of annual and accrued
depreciation in Tables 1, 1 A,and 1 B.
Section 6: Presents the results of the Retirement Rate Analysis
Section 7: Presents the results of the Net Salvage Study
Section 8: Presents the results of the Detailed Depreciation Calculations
Section 9: Estimation of Survivor Curves is an overview of Iowa curves and the Retirement Rate Analysis
Section 10: Estimation of Net Salvage
2.3 Depreciation
A full and comprehensive depreciation study includes the following components:
1. supported recommendations regarding Average Service Life estimates for each account;
2. supported recommendations regarding estimated Net Salvage requirements for each account;
3. selection of an appropriate grouping procedure;
4. detailed calculation of the depreciation rate utilizing the estimated Average Service Life and Net
Salvage requirements; and
5. a document explaining the procedures followed and justifying the results in a format suitable for
submission to senior management and regulatory authorities.
A diagram of the nine primary processes followed by Concentric in the development of the
depreciation study is provided below. Each of the steps is undertaken by Concentric using
proprietary software.
For most accounts,the annual and accrued depreciation were calculated by the Straight-Line Method
using the ALG Procedure. For certain general plant accounts, the annual and accrued depreciation
are based on amortization accounting. Both types of calculations were based on original cost,
attained ages and an estimate of service lives.
Consistent with the current IGC practice,amortization accounting continues to be recommended for
certain general plant accounts because of the disproportionate plant accounting effort required in
Concentric Energy Advisors Page 1 2-2

Intermountain Gas Company
1@ 2025 Depreciation Study
these accounts. Many regulated utilities in North America have received approval to adopt
amortization accounting for these accounts.
1) Project 2) Data 3) Statistical
Initiation Assembly and
U Meeting Review Analysis of Data
O
L
O 4) Field Review 5) Preliminary
II and Estimates and 6) Management
UManagement Depreciation Review
Q Conference Calculations I
N
7) Final Estimates
� and 8) Draft and 9) Regulatory
Calculations Final Reports Proceedings
2.4 Information Provided by Intermountain Gas Company
IGC has provided Concentric with the required information,as of December 31,2024,for all accounts
being studied. This information has been compiled from the plant accounting records and includes
the following:
■ Current balances by vintage year for each account (aged balances). The balances provide the
amount of investment sorted by installation year currently in operation. This file is only inclusive
of current plant in service and does not include any retirement information; and
■ retirement transactions for all accounts. The transactions include information regarding the
transaction year of the retirement,the installation year of the asset being retired,and the original
cost of the asset being retired.
■ detailed cost of removal and gross salvage transactions for all accounts requiring the recovery of
net salvage. The transactions include information regarding the transaction year of the
retirement, the costs associated with the retirement, and any gross salvage proceeds from the
sale or reuse of the property; and
■ Accumulated Depreciation balances as of December 31, 2024 for accounts studied.
2.5 Data Reconciliation
The above data was reviewed and reconciled to Company control schedules to ensure accuracy and
reasonableness in use of the calculations developed in this study. These checks include:
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Intermountain Gas Company
1@ 2025 Depreciation Study
■ that the surviving investment by account equals (or can be reconciled to) the Company's gross
plant in service and accumulated depreciation ledger balances;
■ that the surviving investment in each vintage is not negative. In other words,this check confirms
that the sum of retirements from any given vintage have not exceeded the amount of plant
additions to the vintage; and
■ that any adjusting transactions are properly accounted for within the databases.
Concentric Energy Advisors Page 1 2-4

Intermountain Gas Company
16 2025 Depreciation Study
SECTION 3
3 DEVELOPMENT OF THE REQUIRED DEPRECIATION RATES
3.1 Depreciation
The development of the depreciation calculations requires the input of an average service life, a
retirement dispersion curve (i.e. Iowa curve) and net salvage (if applicable) recommendations (i.e.,
collectively, the depreciation parameters). Additionally, to complete the depreciation calculations
the calculation methods must be established. Specifically, the selection of the depreciation method
must establish three types of additional input:
1. the choice of a depreciation method;
2. a basis upon which to apply the method,and
3. in the case of group assets,a procedure to use in grouping the assets.
In this study,the depreciation rates for IGC have been calculated in accordance with the Straight-Line
method,the ALG procedure and applied using the Remaining Life technique, with any accumulated
depreciation variances trued-up over the composite remaining life of each account.
Depreciation, as applied to depreciable gas plant, means the loss in service value not restored by
current maintenance,incurred in connection with the consumption or prospective retirement of gas
plant in the course of service from causes which are known to be in current operation and against
which the utility is not protected by insurance. Among the causes to be given consideration are wear
and tear, decay, action of the elements, inadequacy, obsolescence, changes in the art, changes in
demand and requirements of public authorities,and,in the case of gas companies,the exhaustion of
natural resources.'
When considering the action of the elements, the average service life calculations have considered
large catastrophic events that have occurred and impacted the life estimates of utilities across North
America. The average service life of utilities has been influenced by events including:
■ forest fires; ■ fires;
■ earthquakes; ■ lightning;
■ tornadoes; ■ intentional actions of third parties;
■ ice storms; ■ hoar frost; and
■ wind storms; ■ other natural forces of nature.
■ large scale flooding;
Depreciation, as used in accounting, is a method of distributing fixed capital costs, less net salvage,
over a period of time by allocating annual amounts to expense. Each annual amount of such
depreciation expense is part of that year's total cost of providing gas utility service. Normally, the
1 Federal Energy Regulatory Commission-Part 201-Uniform System of Accounts Prescribed for Gas Companies
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Intermountain Gas Company
1@ 2025 Depreciation Study
time over which the fixed capital cost is allocated to the cost of service,is equal to the time over which
an item renders service-that is the item's service life. The most prevalent method of allocation is to
distribute an equal amount of cost to each year of service life. This method is known as the Straight-
Line method of depreciation.
The calculation of annual and accrued depreciation based on the straight-line method requires the
estimation of survivor curves and is described in the following sections of this report. The
development of the proposed depreciation rates also requires the selection of group depreciation
procedures,as discussed below.
3.1 .1 Study Depreciation Methods and Procedures
When more than a single item of property is under consideration,a group procedure for depreciation
is appropriate because normally all of the items within a group do not have identical service lives but
have lives that are dispersed over a range of time. There are two primary group procedures,namely,
the Average Life Group ("ALG") and Equal Life Group ("ELG") procedures.
In the ALG Procedure,the rate of annual depreciation is based on the average service life of the group.
This rate is applied to the surviving balances of the group's cost. A characteristic of this procedure is
that the cost of plant retired prior to average life is not fully recouped at the time of retirement,
whereas the cost of plant retired subsequent to the average life is more than fully recouped. Over the
entire life cycle,the portion of cost not recouped prior to average life is balanced by the cost recouped
subsequent to average life.
In the ELG Procedure, also known as the Unit Summation Procedure, the property group is
subdivided according to service life. That is, each equal life group includes that portion of the
property which experiences the life of that specific group. The relative size of each equal life group
is determined from the property's life dispersion curve.The calculated depreciation for the property
group is the summation of the calculated depreciation based on the service life of each equal life unit.
For most accounts,the annual and accrued depreciation were calculated by the Straight-Line Method
using the ALG Procedure with an ALG procedure remaining life true-up. For certain General plant
accounts,the annual and accrued depreciation are based on amortization accounting. Both types of
calculations were based on original cost,attained ages and an estimate of service lives.
The ALG Procedure is a commonly used depreciation calculation that has been widely accepted in
jurisdictions throughout North America including for IGC in prior studies. Concentric recommends
its continued use.
Amortization accounting is used for certain general plant accounts because of the disproportionate
plant accounting effort required in these accounts. Many regulated utilities in North America have
received approval to adopt amortization accounting for these accounts.
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Continued monitoring and maintenance of the accumulated depreciation reserve at the account level
is recommended. Concentric has determined an amortization amount to correct the present variance
with the calculated accrued depreciation (theoretical reserve) over the greater of the composite
remaining life of each account.
The depreciation rates calculated in this study were calculated in a similar manner as used in the
prior full depreciation study - i.e., using the straight-line method, the ALG Procedure applied on a
remaining life basis.The vintaged remaining life approach weighs the calculations of remaining life
on an allocation of the actual book accumulated depreciation account by the Calculated Accumulated
Depreciation("CAD")factor determined for each vintage of plant in service. This method is described
as a CAD weighted calculation in the Depreciation Systems textbook by Frank K.Wolf and W.Chester
Fitch,published by the Iowa State University in 1994 under the title"Adjustments"within the Broad
Group Model.
When depreciation rates are calculated utilizing a remaining life technique,the depreciation rate is
established by dividing the undepreciated value of each group of assets (after consideration to the
net salvage requirements) by the composite remaining life of the group of assets. This calculation is
made for each vintage surviving investment as of the date of the study(December 31,2024),and then
composited into a calculation for the account or group as a whole. This calculation requires two
estimates:
1. The allocation of actual booked accumulated depreciation for each vintage within each account.
IGC does not track the booked accumulated depreciation reserve by vintage within each account.
Rather, the depreciation expense is calculated at an account level and booked to accumulated
depreciation at the same account level. Concentric notes that this is the practice employed by
virtually all regulated utilities. As such, the accumulated depreciation by account is allocated
within the account to each vintage, on the basis of the calculated accumulated depreciation by
vintage. The calculated accumulated depreciation is a function of the estimated survivor curve,
the average service life estimate,the net salvage estimates and the achieved age of each vintage.
2. The remaining life of each vintage with each account.
The estimated remaining life of each vintage is a direct function of the achieved age of each
vintage,the estimated survivor curve and the average service life estimate.
Once the above two estimates are determined (the allocated booked reserve by vintage and the
average remaining life of each vintage),an annual accrual requirement for each vintage is determined
by dividing the net book value for each vintage (considering the estimated future salvage
requirements)by the average remaining life of the vintage. The annual requirement for each vintage
is summed at the account level and divided into the sum of the accounts original cost surviving as of
December 31, 2024.
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This process results in each vintage's calculated net book value to be depreciated over an appropriate
remaining life. This vintage weighting on CAD approach to the remaining life calculations is widely
considered to be the most accurate. Concentric agrees and views this methodology as the correct
and most appropriate calculation.
3.1 .2 Truncation Cuts
It is commonly accepted within depreciation texts that some data points, particularly towards the
end of the Iowa curve,may be less reliable due to the lower amount of exposures that the retirements
are calculated on.It is widespread practice to place lesser weighting on these data points through the
use of a Truncation Cut (or "T-Cut"). This practice is described in detail in the text "Public Utility
Depreciation Practices" compiled and edited by the Staff Subcommittee on Depreciation of the
Finance and Technology Committee of the National Association of Regulatory Utility Commissioners
on page 122 where it is stated:
A T-cut is used to mathematically perform a function that is automatic in visual fitting(i.e.,
setting a point beyond which the observed data are considered irrelevant or unreliable and
are, therefore, ignored).
Careful selection of a T-cut can greatly enhance the reliability of the resulting analysis.
Conversely,since the use of a T-cut involves truncating the observed data, careless selection
can impair the reliability of subsequent work.
Concentric has utilized T-cuts throughout the Iowa curve selection where necessary.Where a T-cut
has been utilized, Concentric has indicated such in Section 3.3 below.
3.2 Estimation of Survivor Curves
3.2.1 Survivor Curves
The use of an average service life for a property group implies that the various units in the group
have different lives. Thus,the average life may be obtained by determining the separate lives of each
of the units, or by constructing a survivor curve by plotting the number of units which survive at
successive ages using the retirement rate method of analysis.
The range of survivor characteristics usually experienced by utility and industrial properties is
encompassed by a system of generalized survivor curves known as Iowa type curves. The Iowa
curves "...were sorted into three groups according to whether the mode was to the left, approximately
coincident with, or to the right of the average-life ordinate. The curves in each of these three groups
were then sub-classified in accordance with the height of the mode, taking also into consideration the
distance of the mode to the left or right of the average life."2 The Iowa curves are described as L-type
2 Robley Winfrey,Statistical Analyses of Industrial Property Retirements, Bulletin 125 revised (Engineering Research
Institute, Iowa State University, 1935) 65
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(i.e. left-moded), R-type (i.e. right-moded), and S-type (i.e. symmetrical). Further development
resulted in the introduction of 0-type (i.e. origin-moded curves) where the greatest frequency of
retirement occurs at the origin, or immediately after age zero. Individual type curves are further
depicted with numerical subscripts which represent the relative heights of the modes of the
frequency curves within each family.
The program that is used by Concentric for statistical smooth curve fitting utilizes an internal
"goodness-of-fit" criterion which is called the Residual Measure. This Residual Measure is based on
a least square's solution of the differences between the stub curve (or original data points) and
smooth survivor curve which also requires a balancing of the differences above and below the stub
curve.
The criterion of goodness-of-fit is the mean square of the differences between the points on the stub
and fitted smooth survivor curves. The Residual Measure, or standard error of estimate, shown in
the output format is the square root of this mean square. As such, the lower the Residual Measure
the better the statistical fit between the analyzed Iowa curve and the observed data points.
Concentric follows the widely used practice of fitting Iowa curves up to one percent of the maximum
exposures. This standard practice is utilized to minimize the influence of typically small retirements
applied to similarly small exposures which may unduly affect the Iowa curve fitting process.
However, Concentric will recognize the observed data points beyond the one percent of maximum
exposures if it is determined that the additional data is a valid consideration for life recommendation.
A discussion of the general concept of survivor curves and retirement rate method is presented in
Section 9.
3.2.2 Survivor Curve Judgments
The service life estimates used in the depreciation and amortization calculations were based on
informed professional judgment which incorporated a review of historical retirement patterns, a
review of management's plans, policies and outlook as obtained through a series of interviews with
management and subject matter experts, a general knowledge of the gas industry, and comparisons
of the service life estimates from Concentric's studies of other gas utilities. A detailed peer review is
compiled to establish a range of reasonableness for the Iowa curve and net salvage estimate for each
account.While the peer review is considered an appropriate test of the estimates,it should never be
viewed as definitive. Differences in characteristics such as the account structure,climate conditions,
regulatory environment,and area of service must always be considered when reviewing a peer study.
The following utilities with similar characteristics to Intermountain Gas were considered in the peer
review:
• APEX (Formerly A1taGas) - Selected for peer review as APEX has a transmission and
distribution network located in small and medium sized cities in Western Canada and is
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therefore subject to similar forces of retirement and cost of removal as IGC.Additionally,the
most recent depreciation study was completed by Concentric.
• ATCO Gas - Selected for peer review as ATCO Gas has an extensive distribution network
located in large municipalities in Western Canada and is therefore subject to similar forces of
retirement and cost of removal. Additionally, the most recent depreciation study was
completed by Concentric.
• Cascade Natural Gas Corporation(CNGC)-Selected for peer review as CNGC has an extensive
distribution network, as well as a transmission system, throughout the Pacific Northwest
United States, namely Oregon and Washington. They are subject to similar forces of
retirement and CNGC is also operated by MDU utilities, leading them to have similar
treatment for many of their assets. Additionally, the most recent depreciation study was
completed by Concentric.
• Centra Gas - Selected for peer review as Centra Gas has an extensive transmission and
distribution network throughout the province of Manitoba and is therefore subject to similar
forces of retirement and cost of removal. Additionally, the most recent depreciation study
was completed by Concentric.
• Fortis BC Gas("FEI")-Selected for peer review as FortisBC has an extensive transmission and
distribution network throughout the province of BC and is therefore subject to similar forces
of retirement and cost of removal. Additionally, the most recent depreciation study was
completed by Concentric.
• Great Plains Natural Gas (GPNG) - Selected for peer review as GPNG has a transmission and
distribution network located throughout western Minnesota and is therefore subject to
similar forces of retirement and cost of removal. GPNG is also operated by MDU utilities,
leading them to have similar treatment for many of their assets.Additionally,the most recent
depreciation study was completed by Concentric.
• Montana-Dakota Utilities Co. Gas Segment(MDU Gas) -Selected for peer review as MDU Gas
has an extensive distribution network servicing parts of Montana, North Dakota, South
Dakota, and Wyoming. It is therefore subject to similar forces of retirement and cost of
removal.Additionally,the most recent depreciation study was completed by Concentric.
The use of survivor curves to reflect the expected dispersion of retirement provides a consistent
method of estimating depreciation for gas plant. Iowa type survivor curves were used to depict the
estimated survivor curves for the plant accounts not subject to amortization accounting.
The procedure for estimating service lives consisted of compiling and analyzing historical data for
the plant accounts using widely accepted techniques,and forecasting the survivor characteristics for
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each depreciable group based on interpretations of the historical data analyses and the probable
future.
The forecasting of the probable future included conversations with operations and management
staff. The combination of historical experience and the estimated future yielded estimated survivor
curves from which the average service lives were derived. The resultant depreciation rates are
summarized in Tables 1, 1A,and 1B of this study(Section 5).
The depreciation rates should be reviewed periodically to reflect the changes that result from plant
and reserve account activity. A depreciation reserve deficiency or surplus will develop if future
capital expenditures vary significantly from those anticipated in this study.
The estimates of net salvage for the mass property accounts were based in part on historical data
related to actual retirement activity for the years 1975 through 2024,for accounts that were analyzed
with net salvage. Gross salvage and cost of removal as recorded to the depreciation reserve account
and related to experienced retirements were used. Percentages of the cost of plant retired were
calculated for each component of net salvage on an annual,three-year,five-year,and on a cumulative
moving average basis. The use of rolling average bands and trendlines in net salvage analysis is
widely recommended to better smooth the historical data.It is common for cost of removal amounts
to lead or lag the retirement transaction associated with the asset being removed from service. As
such, looking at a band of historical data allows a better understanding of the historical trends.
Concentric utilizes both a three-and a five-year rolling average to smooth both short-term trends as
well as smooth the impact of longer lasting program retirements.
The following discussion, dealing with all major accounts, presents an overview of the factors
considered by Concentric in the determination of the average service life. The survivor curve
estimates for the remainder of the accounts not discussed in the following sections were based on
similar considerations.
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3.3 Major Account Analysis
ACCOUNT 361 -OTHER STORAGE-STRUCTURES AND IMPROVEMENTS - NAMPA
Previously Concentric Previously Concentric
Investment$ Investment% Approved Recommended Approved Net Recommended
Curve Curve Salvage Net Salvage
$9,568,070 1.02% 38-S5 40-S5 -17% -10%
The investment in Other Storage - Structures and Improvements - Nampa is approximately $9.6
million, representing 1.02 percent of the total depreciable plant studied. The assets in this account
relate to the structures within the Nampa LNG facility.Some of these assets include an onsite welding
shop, a control room that contains offices for operators, and a reinforced concrete building that is
built to be explosion resistant.The retirements,additions,and other plant transactions for the period
1974 through 2024 were analyzed by the retirement rate method. This account did not utilize a T-
Cut and retirements of$1,519,319 were recorded for the period 2016 through 2024.
■ Actual —Iowa 38-S5(RM 0.8918) —Iowa 40-S5(RM 0.5513)
-------
80- 17M NONE
c
> 60
3
N
C
N 40
V
a
20
0
0 10 20 30 40 50 50 70
Age(Years)
The currently approved life parameter was an Iowa 38-S5, which produced a related Residual
Measure of 0.8918.The proposed Iowa 40-S5 produced a stronger visual and mathematical fit to the
historical retirement experience and produced a related Residual Measure of 0.5513, as seen in the
graph above and on page 6-2.As seen above,by adjusting the average service life by two years,but
leaving the mode of the Iowa curve the same, the survivor curve now better aligns with the Iowa
curve through the period of the largest retirement ratios,seen around age 40.
Conversations with IGC operations and management staff indicated that the buildings that are within
this account are built to a higher standard than normal, and that there is an abundance of safety
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features throughout the facility at Nampa that would lead to a longer service life on average for the
assets contained within this account.
A peer comparison of a similar gas utility with LNG production and storage produced an average
service life estimate of 28 years for an account with like assets. Although Concentric's
recommendation places IGC above this peer utility, as there is only one data point to reference,
Concentric does not believe it prudent to align directly with the one peer utility as this is just one of
the variables in an average service life selection. Based on the above discussion and considerations,
and on Concentric's experience,an Iowa 40-SS is a reasonable expectation for the investment in this
account. As such, Concentric recommends an Iowa 40-SS to continue to represent the future
expectations for the investment in this account.
Net Salvage Trend
Historical Percent-Rolling Average —Concentric Recommendation
-----Historical Net Salvage Percent Trendline
Year
r` ao rn O N N m a
i--I i 1 rl i 1 N N N N N
O O O O O O O O O
N N N N N N N N N
-12
-10
C
N
i -8
d
a
-6
u
o -4 ? -3 -3
_ 1 1
-1 -2 -2
-2 2
0 —
As shown in the graph above,the historical net salvage activity for this account shows a range from
negative one percent to negative three percent. This range represents a rolling average, and the
calculation is utilized in the same fashion for all accounts discussed below.As shown on page 7-2 of
this report, the most recent (last three years) three-year rolling bands all produce negative nine
percent,and the most recent(last five years) five-year rolling bands show a range from negative two
percent to negative 11 percent.The full depth band shows an amount of negative three percent.The
previously approved net salvage percentage was negative 17 percent,and a review of the same peer
gas utility revealed a negative 10 percent net salvage rate for their similar account.As the historical
data has not displayed the levels of cost of removal that were previously approved, and IGC
operational staff indicated to Concentric that those levels were no longer expected for the future,
Concentric recommends the use of a negative ten percent net salvage rate for this account moving
forward.
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ACCOUNT 362—OTHER STORAGE—GAS HOLDERS - NAMPA
Previously Concentric Previously Concentric
Investment$ Investment% Approved Recommended Approved Net Recommended
Curve Curve Salvage Net Salvage
$10,132,429 1.09% 35-R3.5 40-R4 -17% -15%
The investment in Other Storage-Gas Holders-Nampa is approximately$10.1 million,representing
1.09 percent of the total depreciable plant studied. The assets in this account relate to the LNG tanks
at the Nampa LNG facility.These tanks can hold over 700 million gallons of product and are cryogenic
with four feet of insulation around the walls.The tanks store the LNG in a liquid state which is cooled
to approximately negative 260 degrees Fahrenheit.The tanks do not refrigerate themselves,and they
are under roughly a pound of pressure at all times. The retirements, additions, and other plant
transactions for the period 1974 through 2024 were analyzed by the retirement rate method. This
account did not utilize a T-Cut and retirements of $157,388 were recorded for the period 2020
through 2024.
■ Actual —Iowa 35-R3.5(RM 3.1484) —Iowa 40-R4(RM 2.3545)
100
on
80
on
c
> 60
Ln
c
v 40
u
v
a
20
0
0 10 20 30 40 50 60 70
Age(Years)
The currently approved life parameter for this account is an Iowa 35-113.5 that produced a related
Residual Measure of 3.1484. The proposed life parameter for this account is an Iowa 40-R4 that
produced a related Residual Measure of 2.3545 that can be seen in the graph above and on page 6-7.
There have only been retirements since 2020 occurring within this account, and with the limited
amount of retirement experience,Concentric has placed less weight on the actuarial analysis for this
account. This account is deemed to be a stub curve as the exposures above never drop below 80
percent of plant surviving on the Y-axis.As there are more retirements in future depreciation studies,
Concentric would expect that this curve would align much closer to both of the Iowa curves presented
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in the graph above.With that in mind, Concentric is aware that a subtle life extension to the average
service life estimate may be necessary given information from the peer group studied and
conversations with IGC operational and management staff.
A peer comparison of a similar gas utility with LNG production and storage produced average service
life estimates of 57 and 60 years for their accounts with like assets.As above for Account 361,there
was a limited number of comparable peer utility accounts. However, these peer accounts
predominantly contain similar assets,with the largest investment being the tanks that hold LNG.The
conversations with IGC staff indicated to Concentric that although the Nampa facility was
commissioned in 1974,the tanks have been rebuilt only once since commissioning.Therefore,based
on the above discussion and considerations,and on Concentric's experience,an extension to an Iowa
40-R4 is a reasonable expectation for the investment in this account. As such, Concentric
recommends an Iowa 40-R4 to represent the future expectations for the investment in this account.
Net Salvage Trend
Historical Percent-Rolling Average —Concentric Recommendation
————-Historical Net Salvage Percent Trendline
Year
lD r, 00 a) O -1 N rn V
ci ci ci -1 N N N N N
O O O O O O O O O
-35 -
-29
-30 —
-25 —
c
-20 —_
L _14 -15 -15 _
-14
-15 —
V
L - �
N_ 10
-5 _ —
0
0
5
As shown in the graph above,the historical net salvage activity for this account shows a range from
zero percent to negative 29 percent. The full depth band shows negative 14 percent. As shown on
page 7-4 of this report,the most recent(last three years)three-year rolling bands show a range from
negative 14 percent to negative 15 percent, and the most recent (last five years) five-year rolling
bands show a range from negative 14 percent to negative 29 percent.As seen in the graph above,the
historical net salvage experience displays less in most years than the amount that is currently
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approved. The previously approved net salvage rate was negative 17 percent, and a review of the
same peer gas utility showed negative 20 percent for similar assets. As the historical data has not
displayed the levels of cost of removal that were previously approved, and IGC operational staff
indicated to Concentric that those levels were no longer expected for the future, Concentric
recommends the use of a negative 15 percent net salvage rate for this account moving forward.
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ACCOUNT 363-OTHER STORAGE-MEASURE & REG EQUIPMENT- NAMPA
Previously Concentric Previously Concentric
Investment$ Investment% Approved Recommended Approved Net Recommended
Curve Curve Salvage Net Salvage
$18,387,813 1.97% 47-R4 40-R2.5 -17% -10%
The investment in Other Storage - Measure and Reg Equipment - Nampa is approximately $18.4
million, representing 1.97 percent of the total depreciable plant studied. The assets in this account
relate to measuring and regulating at the Nampa LNG facility,such as methane detectors and oxygen
detectors, as well as assets utilized as part of the liquefaction, purification, and vaporization of the
LNG, such as mole sieves and skid valves. This account is combined for purposes of this writeup, as
all of the 363 subaccounts for Nampa were analyzed with the same Iowa curve and average service
life parameters.The high level results displaying these accounts broken out can be seen in Tables 1,
1A, and 113 within Section 5 of this report. Retirements, additions, and other plant transactions for
the period 1974 through 2024 were analyzed by the retirement rate method. This account did not
utilize a T-Cut and retirements of$1,475,462 were recorded for the period 2016 through 2024.
■ Actual —Iowa 47-S4(RM 1.1559) —Iowa 40-R2.5(RM 1.9241)
lOD
• •�•p• •tea
80
c
> 60
V)
c
v u 40
v
a X x
20
0
0 10 20 30 40 sa e0 70 80 90
Age(Years)
The currently approved life parameter for this account is an Iowa 47-S4, with a related Residual
Measure of 1.1559. The proposed life parameter is an Iowa 40-R2.5 which produced a related
Residual Measure of 1.9241 as seen above and on page 6-12.Although the proposed life parameter
produced a worse mathematical Residual Measure, the visual fit to the data is stronger. This is
displayed through age 20, where the Iowa 40-112.5 aligns much better with the early retirement
experience. Concentric also believes that the recommended Iowa R2.5 curve is a better indicator for
this account at this point in time than the Iowa S4 curve. This is due to the interim retirement
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experience that is expected with the R2.5 curve. Due to the nature of the assets within these 363
Measuring and Regulating Equipment accounts, Concentric believes that adjusting this curve to the
R2.5 will allow for better alignment of the future retirement experience. As indicated below, in the
peer analysis that Concentric performed, similar assets to these had with average service lives of no
longer than 40 years. Concentric notes that in the previous depreciation study,the recommendation
for this account based on the facts and investment at that time was an average service life of 37 years.
By proposing a 40-year average service life,Concentric believes this is a reasonable recommendation
that balances the current expectations for the future experience with a gradual and moderate
decrease in the approved average service life.
A peer comparison of a similar gas utility with LNG production and storage produced average service
life estimates of 27, 30, and 40 years for their accounts with like assets. However, Concentric notes
that this peer utility breaks out their Measuring and Regulating Equipment accounts in a different
fashion than IGC,and the 27-,30-,and 40-year average service life estimates are only the most similar
of these accounts. Conversations with IGC operations and management staff indicated that the
recommended 40-year life for this account is a good representation of the historical life and future
expectations.As such,the Iowa 40-R2.5 is recommended for this account based on the fit to historic
data,the indications from IGC and management staff,and the professional judgment of Concentric.
Net Salvage Trend
Historical Percent-Rolling Average —Concentric Recommendation
————-Historical Net Salvage Percent Trendline
Year
r, oo m O N m a
ci -1 -1 —1 N N N N N
O O O O O O O O O
N N N N N N N N N
-12
-10
a+
-8 -7 -7 -7 -7
6 -6 _
a " -6
-6
4
-2 -1 1
0
As shown in the graph above,the historical net salvage activity for this account shows a range from
negative one percent to negative seven percent. The full depth band shows negative six percent.As
shown on page 7-5 of this report, the most recent (last three years) three-year rolling bands all
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produce negative three percent,and the most recent (last five years) five-year rolling bands show a
range from negative three percent to negative 65 percent.As seen in the graph above,the historical
net salvage experience displays less in most years than the amount that is currently approved. The
previously approved net salvage rate was negative 17 percent, and a review of the same peer gas
utility showed a range from negative five percent to negative 20 percent for similar assets. As the
historical data has not displayed the levels of cost of removal that were previously approved,and IGC
operational staff indicated to Concentric that those levels were no longer expected for the future,
Concentric recommends the use of a negative 10 percent net salvage rate for this account moving
forward.
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ACCOUNT 367-TRANSMISSION-MAINS
Previously Concentric Previously Concentric
Investment$ Investment% Approved Recommended Approved Net Recommended
Curve Curve Salvage Net Salvage
$72,446,841 7.76% 63-R4 63-R4 -35% -35%
The investment in Transmission Mains is approximately $72 million, representing 7.76 percent of
the total depreciable plant studied. The assets within this account relate to the transmission pipeline
owned and operated by IGC.Retirements,additions,and other plant transactions for the period 1959
through 2024 were analyzed by the retirement rate method.This account did not utilize a T-Cut and
retirements of$1,735,797 were recorded for the period 2016 through 2024.
■ Actual —Iowa 63-R4(RM 1.066) —Iowa 63-R4(RM 1.066)
100
80
m
c
.Z 60
L
QU 0
() 'Y
Q�
d
20
0
0 20 40 60 80 100
A&(Years)
The currently approved and proposed life parameter for this account is an Iowa 63-114,with a related
Residual Measure of 1.066, as depicted above and on page 6-24. As there has not been any major
changes in the retirement experience since the last depreciation study, and there have not been
indications to Concentric that this will change in the future, Concentric recommends the continued
use of the Iowa 63-114 curve for this account.
A peer comparison of gas transmission utilities produced a range from 55 to 70 years with a mean
average service life recommendation of 65 years. Conversations with IGC operations and
management staff indicated that the recommended 63-year life for this account is a good
representation of the historical life and future expectations based on the current vintaging within
this account. Staff informed Concentric that there are no active transmission replacement programs
in place, and that there have been no major issues with corrosion. As such, the Iowa 63-114 is
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recommended for this account based on the fit to historic data, the indications from IGC operations
and management staff,and the professional judgment of Concentric.
Net Salvage Trend
Historical Percent-Rolling Average —Concentric Recommendation
— — —Historical Net Salvage Percent Trendline
Year
O ci N M V Ln l0 I, 00 Ol O ci N M -Cl- U1 W r` 00 a) O -i N (M It
O O O O O O O O O O -1 -1 -1 -1 -1 ­1 -1 -1 -1 r-i N N N N N
O O O O O O O O O O O O O O O O O O O O O O O O O
N N N N N N N N N N N N N N N N N N N N N N N N N
-40
-35
-30 - 7 7
_ 23 -23 -22
-� 25 �2
21 -20 -20-41. 30--20
a°1 19 -19 -18
-20 -18 17 -
•o
15 -12 -1
-10 -7
-8 9 -10�
-5 -2
0
As shown in the graph above,the historical net salvage activity for this account shows a range from
negative two percent to negative 27 percent.The full depth band shows negative 27 percent.As there
is data dating back to 1975 within this account, Concentric has only displayed the most recent and
relevant 25 years in the graph above for conciseness.As shown on page 7-6 of this report,the most
recent(last three years)three-year rolling bands show a range from negative 143 percent to negative
187 percent,and the most recent(last five years)five-year rolling bands show a range from negative
143 percent to negative 344 percent. The previously approved net salvage percentage was negative
35 percent,and a review of peer gas transmission utilities indicates a range from negative 20 percent
to negative 23 percent. Even though the graph above displays an all-in band amount of negative 27
percent, and the peer range for similar assets is below the recommendation, Concentric was not
informed by IGC staff that the salvage expectations would be materially different than the past.That,
coupled with the most recent three-and five-year moving averages indicated above,leads Concentric
to recommend the continued use of a negative 35 percent net salvage rate for this account moving
forward.
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Intermountain Gas Company
1@ 2025 Depreciation Study
ACCOUNT 376—DISTRIBUTION -MAINS
Previously Concentric Previously Concentric
Investment$ Investment% Approved Recommended Approved Net Recommended
Curve Curve Salvage Net Salvage
$331,142,799 35.46% 70-R3.5 70-R4 -48% -50%
The investment in Distribution Mains is approximately$331 million, representing 35.46 percent of
the total depreciable plant studied. The assets within this account relate to the distribution pipeline
owned and operated by IGC.The mains within the IGC system are a mix of plastic and steel pipe,with
predominantly plastic being installed when replacements or new connections are necessary.
Retirements, additions, and other plant transactions for the period 1959 through 2024 were
analyzed by the retirement rate method. This account did not utilize a T-Cut and retirements of
$9,996,194 were recorded for the period 2016 through 2024.
■ Actual —Iowa 70-113.5(RM 0.1833) —Iowa 70-R4(RM 0.1483)
100
NONE
80
ao
60 - 7N
Ln
c
.Z
Ln
c
GO)u 40
v
a
20
0
0 20 40 60 so 100 in
Age(Years)
The currently approved life parameter for this account is an Iowa 70-113.5, with a related Residual
Measure of 0.1833. The proposed life parameter is an Iowa 70-114 that produces a stronger visual
and mathematical fit to the retirement experience,producing a Residual Measure of 0.1483 as seen
above and on page 6-39. Based on the retirement experience and new information since the last
study, Concentric found no need to adjust the average service life parameter for this account.
However,by shifting the mode of the Iowa curve to an R4 curve,the survivor curve now better aligns
with the proposed Iowa curve through approximately age 65. This produces a better Residual
Measure and aligns with the curves proposed for other peer gas distribution Mains accounts.
Concentric Energy Advisors Page 1 3-18

Intermountain Gas Company
1@ 2025 Depreciation Study
A peer comparison of gas distribution utilities produced a range from 50 to 66 years with a mean
average service life recommendation of 61 years. Even though the recommendation is to continue
using an average service life estimate that is above the peer range,conversations with IGC operations
and management staff indicated that the recommended 70-year life for this account is a good
representation of the historical life and future expectations. Staff informed Concentric that there is
active replacement of early vintage plastic pipe through the System Safety and Integrity Plan (SSIP)
of approximately three to five miles a year.Additionally, staff told Concentric that the early vintage
pre-1970's steel pipe is also being replaced as part of the SSIP. The SSIP is still in a nascent stage,
however,plastic pipe is all that is expected to be installed moving forward within the system.As such,
the Iowa 70-R4 is recommended for this account based on the fit to historic data,the indications from
IGC operations and management staff,and the professional judgment of Concentric.
Net Salvage Trend
Historical Percent-Rolling Average —Concentric Recommendation
— — —Historical Net Salvage Percent Trendline
Year
O -1 N M � Ln lD r` 00 0) O -1 N M Ln LO I, 00 M O ­1 N rn V
O O O O O O O O O O -1 -1 -1 - ­1 -1 r-i -1 ­1 N N N N N
O O O O O O O O O O O O O O O O O O O O O O O O O
N N N N N N N N N N N N N N N N N N N N N N N N N
-70
-62
-58 -59 -59
-60 -52 -53 -52 -54 54 -56
-50 -51 -47
-50 -44
43 -43 -43 -43 -44 -43
w 39 41 \1 -39 40 41
u
-40
a
Ta
u
o -30 -
A
x
-20 -
-10 -
0 -
As shown in the graph above,the historical net salvage activity for this account shows a range from
negative 39 percent to negative 62 percent.The full depth band shows negative 62 percent.As there
is data dating back to 1975 within this account, Concentric has only displayed the most recent and
relevant 25 years in the graph above for conciseness.As shown on page 7-8 of this report,the most
recent(last three years)three-year rolling bands show a range from negative 68 percent to negative
112 percent,and the most recent(last five years)five-year rolling bands show a range from negative
90 percent to negative 106 percent. The previously approved net salvage percentage was negative
Concentric Energy Advisors Page 1 3-19

Intermountain Gas Company
1@ 2025 Depreciation Study
48 percent,and a review of peer gas distribution utilities indicates a range from negative 30 percent
to negative 70 percent. The historical rolling average has been above negative 50 percent since the
time of the last study and climbing,and IGC staff indicated that there have been no material changes
in the cost of removal practices since the last study. Concentric therefore recommends the use of a
negative 50 percent net salvage rate for this account moving forward which was also the
recommendation at the time of the last study(as of 2019),when the full depth band showed negative
54 percent.
Concentric Energy Advisors Page 1 3-20

Intermountain Gas Company
1@ 2025 Depreciation Study
ACCOUNT 378—MEASURING AND REGULATING STATION EQUIPMENT-GENERAL
Previously Concentric Previously Concentric
Investment$ Investment% Approved Recommended Approved Net Recommended
.& Curve Curve Salvage Net Salvage
$14,581,059 1.56% 43-R 1.5 45-SO -25% -30%
The investment in Measuring and Regulating Station Equipment is approximately $14.6 million,
representing 1.56 percent of the total depreciable plant studied. The assets within this account relate
to all equipment at regulating stations owned by IGC that are not involved in regulation at homes.
Retirements, additions, and other plant transactions for the period 1959 through 2024 were
analyzed by the retirement rate method. This account did not utilize a T-Cut and retirements of
$2,710,521 were recorded for the period 2016 through 2024.
■ Actual —Iowa 43-R1.5(RM O.SS95) —Iowa 4S-SO(RM 0.5615)
100
80
cw
c
> 60
c
v 40
u
v
a
20
0
0 w 20 30 40 so 60 70 e0 90 100
Age(Years)
The currently approved life parameter for this account is an Iowa 43-R1.5, with a related Residual
Measure of 0.5595.The proposed life parameter for this account is an Iowa 45-SO which produces a
Residual Measure of 0.5615 as seen in the graph above and on page 6-43.Although the mathematical
fit to data is not as strong with the proposed Iowa 45-SO, Concentric notes that in the middle section
of the survivor curve approximately between ages 15 and 40 (approximately 90 percent to 50
percent surviving) the proposed curve presents a better fit to the observed data. This is due to the
more gradual nature of the Iowa SO curve, which anticipates more interim retirements at each age
interval. Concentric believes at this point in time, the Iowa 45-SO aligns better to the observed
retirement experience,while being a strong expectation for the future,especially if there were to be
a continuation of what is currently seen in the age intervals indicated above.
Concentric Energy Advisors Page 1 3-21

Intermountain Gas Company
1@ 2025 Depreciation Study
A peer comparison of gas distribution utilities produced a range from 34 to 54 years with a mean
average service life recommendation of 45 years. Conversations with IGC operations and
management staff indicated that the recommended 45-year life for this account is a good
representation of the historical life and future expectations.Staff informed Concentric that the assets
within this account are rebuilt if able,or replaced,and the older parts will stay if they are still in good
shape,even as parts and pieces surrounding them are changed. Most of the replacements are due to
capacity and need, not due to maintenance issues. Based on the above, Concentric recommends the
use of the Iowa 45-SO for this account.
Net Salvage Trend
Historical Percent-Rolling Average —Concentric Recommendation
— — —Historical Net Salvage Percent Trendline
Year
(D c-I (,4 m zt Ln l0 n 00 a) O r-I N m �t N w n 00 a) O c-I N m
O O O O O O O O O O c-I r-I c-I a-I c-I r-I r-I r-I r-I c-I N N N N N
O O O O O O O O O O O O O O O O O O O O O O O O O
N N N N N N N N N N N N N N N N N N N N N N N N N
-45
40
-39 -38 -38
r6 -36 -35
-35 —33
-30
a -25 /-.22'Fa`—' 20
-1 �l�1414 -14 -14
_ -15
-10
8 -9 -9 -9 -g -10 }p'
-5
As shown in the graph above,the historical net salvage activity for this account shows a range from
negative eight percent to negative 39 percent. The full depth band shows negative 33 percent. As
there is data dating back to 1975 within this account, Concentric has only displayed the most recent
and relevant 25 years in the graph above for conciseness.As shown on page 7-9 of this report, the
most recent (last three years) three-year rolling bands show a range from negative 11 percent to
negative 34 percent, and the most recent (last five years) five-year rolling bands show a range from
negative 26 percent to negative 79 percent. The previously approved net salvage percentage was
negative 25 percent,and a review of peer gas distribution utilities indicates a range from negative 12
percent to negative 40 percent. The historical rolling average has been above negative 30 percent
since the time of the last study, and IGC staff indicated that there have been no material changes in
Concentric Energy Advisors Page 1 3-22

Intermountain Gas Company
1@ 2025 Depreciation Study
the cost of removal practices since the last study. Concentric therefore recommends the use of a
negative 30 percent net salvage rate for this account moving forward as Concentric believes this
better captures the future expectations while recognizing the last five years of historical experience.
Concentric Energy Advisors Page 1 3-23

Intermountain Gas Company
1@ 2025 Depreciation Study
ACCOUNT 380-SERVICES
Previously Concentric Previously Concentric
Investment$ Investment% Approved Recommended Approved Net Recommended
i Curve Curve Salvage Net Salvage
$256,371,253 27.45% 58-R3 58-R3 -74% -75%
The investment in Services is approximately $256 million, representing 27.45 percent of the total
depreciable plant studied. The assets in this account relate to pipe used for services in the IGC system.
Older vintage (majority pre-1970's) steel and Aldyl A services are replaced with plastic when
replacement is necessary. Retirements, additions, and other plant transactions for the period 1959
through 2024 were analyzed by the retirement rate method.This account did not utilize a T-Cut and
retirements of$12,403,098 were recorded for the period 2016 through 2024.
■ Actual —Iowa 58-R3(RM 0.6102) —Iowa 58-R3(RM 0.6102)
100
80
ao
c
> 60
V)
c
u 40
v
a
20
0
0 20 40 60 80 100
Age(Years)
The currently approved and proposed life parameter for this account is an Iowa 58-113,with a related
Residual Measure of 0.6102 as seen above and on page 6-49.As the previously approved curve still
presents a robust fit to the historical experience, Concentric found no need to deviate the new
recommendation. The Iowa curve matches the survivor curve through age 40 and approximately to
age 50, where the survivor curve begins to move away from the Iowa curve at that point. With the
replacement of older vintage steel and Aldyl A services with newer plastic services,it is a reasonable
expectation that this portion of the curve will begin to align with the Iowa curve again in the future
as older vintage assets are retired.
A peer comparison of gas distribution utilities produced a range from 45 to 62 years with a mean
average service life recommendation of 53 years. Conversations with IGC operations and
Concentric Energy Advisors Page 1 3-24

Intermountain Gas Company
1@ 2025 Depreciation Study
management staff indicated that the recommended 58-year life for this account is still a good
representation of the historical life and future expectations.As such,the Iowa 58-113 is recommended
to be continued for use for this account.
Net Salvage Trend
—Historical Percent-Rolling Average —Concentric Recommendation
Historical Net Salvage Percent Trendline
Year
O r-I N M � Ln l0 r` oo a) O r-i N M � Ln l0 r` oo a) O i-i N m
O O O O O O O O O O c 1 a 1 c-I a 1 ci a 1 ci a 1 ci .-i N N N N N
O O O O O O O O O O O O O O O O O O O O O O O O O
N N N N N N N N N N N N N N N N N N N N N N N N N
-100 92
-90 -84 -86
-80
-80 -74 76
-70 -60_
60 54 54 -53 53 -53 53 -52 -52 -52-52-52'-52 -52 -52
v
a
-50
c,
-40
x
-30
-20
-10 -
0 -
As shown in the graph above,the historical net salvage activity for this account shows a range from
negative 52 percent to negative 92 percent.The full depth band shows negative 92 percent.As there
is data dating back to 1975 within this account, Concentric has only displayed the most recent and
relevant 25 years in the graph above for conciseness.As shown on page 7-10 of this report,the most
recent(last three years)three-year rolling bands show a range from negative 182 percent to negative
236 percent,and the most recent(last five years)five-year rolling bands show a range from negative
159 percent to negative 217 percent. The previously approved net salvage percentage was negative
74 percent,and a review of peer gas distribution utilities indicates a range from negative 45 percent
to negative 160 percent.The historical rolling average has been above negative 74 percent since the
time of the last study,and IGC staff indicated that there have been no material changes in the cost of
removal practices since the last study. Staff informed Concentric that the services do not typically
come out upon removal,which was also the policy at the time of the last study. However, due to the
Concentric Energy Advisors Page 1 3-25

Intermountain Gas Company
1@ 2025 Depreciation Study
increase in net salvage seen in the graph between 2020 and 2024,Concentric recommends a gradual
and moderated increase to the use of a negative 75 percent net salvage rate for this account moving
forward. Concentric believes this better captures the future expectations while recognizing the last
five years of historical experience.
Concentric Energy Advisors Page 1 3-26

Intermountain Gas Company
1@ 2025 Depreciation Study
ACCOUNT 381 -METERS
Previously Concentric Previously Concentric
Investment$ Investment% Approved Recommended Approved Net Recommended
Curve Curve Salvage Net Salvage
$74,759,880 8.01% 48-R3 40-R3 0% 0%
The investment in Meters is approximately $74.8 million, representing 8.01 percent of the total
depreciable plant studied. The assets in this account relate to the AMR Meters and costs associated
with the installation of the meters,and any sampling performed.Since 2019,IGC has implemented a
new testing program whereby any meter that comes through the shop that is over 30 years old gets
retired. Retirements,additions,and other plant transactions for the period 1959 through 2024 were
analyzed by the retirement rate method. This account did not utilize a T-Cut and retirements of
$4,254,774 were recorded for the period 2016 through 2024.
■ Actual —Iowa 48-R3(RM 1.2291) —Iowa 40-R3(RM 2.4904)
100
4■�
80
■
cn ■
c ■
.Z ■
60
■
V ■
vi ■
c
u
40 ■■
a� ■
a ■
■
20
0
0 10 20 30 40 50 60 70 80 90
Age(Years)
The currently approved life parameter for this account is an Iowa 48-R3, with a related Residual
Measure of 1.2291. The proposed life parameter for this account is an Iowa 40-R3 that produces a
related Residual Measure of 2.4904. Concentric notes that the fit to the historical retirement
experience in the proposed curve is worse both visually and mathematically than the previously
approved curve. At this point in time however, the historical fit to the data has less importance to
Concentric in the selection of an average service life and Iowa curve. As indicated in the preceding
paragraph, IGC has, since the completion of the last depreciation study, undergone a change in the
retirement practices for their meters.This change now stipulates that any meter that is brought into
the meter shop that is over 30 years old will be retired rather than be refurbished and reinstalled in
service.
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Intermountain Gas Company
1@ 2025 Depreciation Study
IGC operational staff have indicated to Concentric that not every meter that is older than 30 years old
will get pulled for testing,therefore,Concentric expects to continue to see assets live longer than 30
years old in the future. Only moving forward, the graph depicted for this account will likely look
materially different in the future as the investment dollars that exist after age 30 have a strong
likelihood of rapidly diminishing. Currently, between ages 30 and 65, the percent surviving moves
from approximately 90 percent surviving down to approximately 25 percent surviving.As the change
in the testing and replacement program continues to be employed, Concentric would reasonably
expect that this same drop in percent surviving may occur, however the end result would have a
strong probability of being at an age earlier than 60. This would align much closer with the
recommended Iowa 40-R3,which passes through 25 percent surviving at approximately age 45.
Concentric still anticipates due to the nature of technology within this account that there will be
interim retirements and believes that the Iowa R3 curve still has a high likelihood of matching the
future retirement experience.
A peer comparison of gas distribution utilities produced a range from 18 to 40 years with a mean
average service life recommendation of 27 years.By adjusting the average service life of this account,
in addition to the reasons highlighted above, it also brings it back in line with the peer utilities
studied.There are three peer MDU Resources Group owned companies,and as of completion of this
study, their average service lives are in a range from 31 to 40 years. All three of these accounts
contain both meters and meter installations, making IGC's currently approved life a large outlier.
Conversations with IGC operational and management staff indicated to Concentric that the IGC
meters are 90% fixed network, with the other 10% needing a mobile car unit for the reading.
Approximately 30 to 40 percent of the meters that come through the shop get retired, and that
continues to be the expectation moving forward.Due to all of the above,Concentric recommends the
use of an Iowa 40-R3 parameter for use for this account.
There have not been large changes in the cost of removal experience in this account since the last
study,and as such, Concentric continues to propose no collection of net salvage through the rate for
this account.
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Intermountain Gas Company
1@ 2025 Depreciation Study
ACCOUNT 381.2- ERT UNITS
Previously Concentric Previously Concentric
Investment$ Investment% Approved Recommended Approved Net Recommended
i Curve Curve Salvage Net Salvage
$28,898,085 3.10% 15-R3 15-R3 -2% 0%
The investment in ERT Units is approximately$28.9 million, representing roughly three percent of
the total depreciable plant studied. The assets in this account relate to the ERT Units and their
installation costs. Retirements, additions, and other plant transactions for the period 2002 through
2024 were analyzed by the retirement rate method. This account did not utilize a T-Cut and
retirements of$21,476,081 were recorded for the period 2016 through 2024.
■ Actual —Iowa 15-R3(RM 1.1442) —Iowa 15-R3(RM 1.1442)
100
80
■
c
> 60
c
v 40
v
a
■
20
0
0 10 20 30 40
Age(Years)
The currently approved and proposed life parameter for this account is an Iowa 15-R3,with a related
Residual Measure of 1.1442 as seen in the graph above and on page 6-57. As this account contains
batteries that have a life of 20 years, which IGC continues to proactively replace early to ensure
reliability, Concentric found no need to adjust the average service life or Iowa curve parameters.
Concentric did not find a peer utility amongst the group considered that broke out ERT Units from
their Metering accounts.As such, Concentric has considered the same peer range for this account as
described above on page 3-29 for Account 381.00, however noting that this account is highly
technological.This drove Concentric to not place a heavy weight on the peer analysis for this account,
as the majority of the peer utilities studied have highly mechanical meters, along with installation
costs,driving the majority of investment in their accounts.Concentric has instead placed more weight
on the historical retirement experience and the information gleaned through conversations with IGC
Concentric Energy Advisors Page 1 3-29

Intermountain Gas Company
1@ 2025 Depreciation Study
operations and management staff.These conversations indicated that there is no need to change from
the currently approved life as the proactive early replacement of the batteries is continuing on. The
15-year average service life with the Iowa R3 curve should continue to capture any interim
retirement experience,and also align well with the lack of assets remaining in service past 20 years.
As such, Concentric continues to recommend the Iowa 15-R3 for this account.
Although there was a negative two net salvage percent proposed and approved last depreciation
study, there has not been sufficient cost of removal experience since. Concentric did not get any
indication from IGC operational and management staff that there will be large cost of removal
expectations in the future either. As such, Concentric proposes to have no collection of net salvage
through the rate for this account.
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Intermountain Gas Company
1@ 2025 Depreciation Study
ACCOUNT 383-REGULATORS
Previously Concentric Previously Concentric
Investment$ Investment% Approved Recommended Approved Net Recommended
i Curve Curve Salvage Net Salvage
$20,442,204 2.19% 50-R3 50-R3 0% 0%
The investment in Regulators is approximately$20.4 million, representing 2.19 percent of the total
depreciable plant studied. The assets in this account relate to the regulators on the homes within
IGC's service territory that regulate gas pressure at every meter and drop the distribution pressure
down from the distribution system to the customer level. Retirements, additions, and other plant
transactions for the period 1959 through 2024 were analyzed by the retirement rate method. This
account did not utilize a T-Cut and retirements of $829,848 were recorded for the period 2016
through 2024.
IS Actual —Iowa 50-R3(RM 1.9379) —Iowa 50-R3(RM 1.9379)
100
80 - ■�■■■
■
■
c ■
> 50
c
U 40
L
Q.l
d
20
0
0 10 20 30 40 50 60 70 80 90
Age(Years)
The currently approved and proposed life parameter for this account is an Iowa 50-113,with a related
Residual Measure of 1.9379, as seen in the graph above and on page 6-59. Concentric notes that the
currently approved and proposed life parameter does not produce a robust fit visually to the
historical retirement experience. However,at this time, based on similar technology as to what was
installed five years ago, Concentric does not find it prudent to extend the life of this account.
Conversations with IGC operations and management staff indicated to Concentric that the regulators
usually stay unless there is a load change that requires a different size as part of a customer request.
This does not happen that frequently,although the Boise area and Eastern Idaho as a whole continue
to show signs of potential growth to the system. This potential growth may require earlier than
Concentric Energy Advisors Page 1 3-31

Intermountain Gas Company
1@ 2025 Depreciation Study
anticipated retirements and replacements due to load changes,therefore causing the graph above to
fall more in line with the currently approved and proposed Iowa curve.
A peer comparison of gas distribution utilities produced a range from 35 to 58 years with a mean
average service life recommendation of 44 years.As there is only one peer above a 50-year average
service life, in addition to the discussion in the preceding paragraph, Concentric recommends that
the Iowa 50-R3 be continued for use for this account.
There have not been large changes in the cost of removal experience in this account since the last
study,and as such, Concentric continues to propose no collection of net salvage through the rate for
this account.
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Intermountain Gas Company
1@ 2025 Depreciation Study
ACCOUNT 385-INDUSTRIAL MEASURE & REG STATION EQUIPMENT
Previously Concentric Previously Concentric
Investment$ Investment Approved Recommended Approved Net Recommended
Curve Curve Salvage Net Salvage
$12,763,496 1.37% 40-R 1 40-R 1 -12% -12%
The investment in Industrial Measure and Reg Station Equipment is approximately $12.8 million,
representing 1.37 percent of the total depreciable plant studied. This account contains large meter
sets,that are either turbine based or utilize ultrasonic technology. Retirements,additions,and other
plant transactions for the period 1959 through 2024 were analyzed by the retirement rate method.
This account did not utilize a T-Cut and retirements of$3,598,033 were recorded for the period 2016
through 2024.
■ Actual —Iowa 40-R1(RM 0.7962) —Iowa 40-R1(RM 0.7962)
100
■
�
80 ■
c
> 60
Ln
c •
(UV40
u
a
�007 NEWS
20
0
0 10 20 30 40 s0 60 70 80 90
Age(Years)
The currently approved and proposed life parameter for this account is an Iowa 40-111,with a related
Residual Measure of 0.7962 as seen in the graph above and on page 6-63. The fit from the Iowa 40-
R1 curve to the historical retirement experience is robust, tracking along with the survivor curve
through age 50.Although a moderate extension of the average service life would result in a stronger
mathematical fit, Concentric does not believe at this time that the historical retirement experience
should outweigh the comments from IGC operations and management staff.The conversations with
staff indicated to Concentric that the current life still makes sense for this account,as there have been
no material changes to the account since the time of the last depreciation study. The materials and
technology used on these large meter sets are a mix of turbine and ultrasonic technologies,which are
more mechanical and digital in their measurement,respectively.
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Intermountain Gas Company
1@ 2025 Depreciation Study
There has been a slow rollout of the ultrasonic technology, but as it is more digitally inclined,
Concentric believes that keeping the average service life recommendation the same at this point in
time is prudent to not overestimate the influence of the mechanical technology that will start to be
transitioned away from in the future. IGC staff informed Concentric that if there is a load increase
that necessitates a change,it will be an ultrasonic meter that is installed.
A peer comparison of gas distribution utilities produced a range from 34 to 50 years with a mean
average service life recommendation of 42 years. Due to the above, Concentric recommends
continuing the use of the currently approved Iowa 40-R1 for this account.
Net Salvage Trend
Historical Percent-Rolling Average —Concentric Recommendation
— — —Historical Net Salvage Percent Trendline
Year
O i1 N M � Ln lO r` 00 M O ­1 N M � Ln l0 r` 00 M O .1 N co 'T
O O O O O O O O O O -4 -4 -4 -4 -4 -4 -4 a 1 a 1 a 1 N N N N N
O O O O O O O O O O O O O O O O O O O O O O O O O
N N N N N N N N N N N N N N N N N N N N N N N N N
-14
-12
-10
a -8
a,
a°1 6 5 -5 -5 -5 -5 6
2
-4
u 4 3 3
C
0 1 -2
iF 2 0 0 -1 1 1
0
0 2
2
4
As shown in the graph above,the historical net salvage activity for this account shows a range from
positive two percent to negative six percent.The full depth band shows negative six percent.As there
is data dating back to 1975 within this account, Concentric has only displayed the most recent and
relevant 25 years in the graph above for conciseness.As shown on page 7-11 of this report,the most
recent(last three years)three-year rolling bands show a range from negative 48 percent to negative
334 percent,and the most recent(last five years)five-year rolling bands show a range from negative
40 percent to negative 102 percent. The previously approved net salvage percentage was negative
12 percent,and a review of peer gas distribution utilities indicates a range from negative five percent
to negative 10 percent. Although the historical rolling average has been below the approved net
salvage percent since the time of the last study, IGC staff indicated that there have been no material
changes in the cost of removal practices since the last study. As the historical rolling average has
Concentric Energy Advisors Page 1 3-34

Intermountain Gas Company
1@ 2025 Depreciation Study
continued to climb over the last five years,albeit slowly, Concentric believes continuing the use of a
negative 12 percent net salvage rate to be a fair expectation for the future of this account. If by the
next depreciation study the historical rolling average has continued to stay below the currently
approved negative 12 percent, Concentric will reassess what a reasonable expectation should be at
that point.
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Intermountain Gas Company
1@ 2025 Depreciation Study
ACCOUNT 390—STRUCTURES & IMPROVEMENTS
Previously Concentric Previously Concentric
Investment$ Investment Approved Recommended Approved Net Recommended
+ Curve Curve Salvage Net Salvage
$24,862,703 2.66% 50-R2 45-R2 5% 10%
The investment in Structures & Improvements is approximately $24.9 million, representing 2.66
percent of the total depreciable plant studied. This account contains all office buildings, structures,
and shops, as well as their components, in the IGC system. Retirements, additions, and other plant
transactions for the period 1959 through 2024 were analyzed by the retirement rate method. This
account did not utilize a T-Cut and retirements of$6,955,120 were recorded for the period 2016
through 2024.
■ Actual —Iowa 50-R2(RM 1.2733) —Iowa 45-R2(RM 1.2313)
100
80
on
c
> 60
N
C
aJ 40
U
QJ
d
20
0
0 10 20 30 40 50 60 70 80 90 100
Age(Years)
The currently approved life parameter for this account is an Iowa 50-R2 with a related Residual
Measure of 1.2733.The proposed life parameter is an Iowa 45-R4 that produces a better visual fit to
the data with a related Residual Measure of 1.2313 as seen in the graph above and on page 6-69.As
this account contains not just the physical office buildings and structures themselves, but
components that may need to be changed once or twice over the life of the building, Concentric
believes that shortening the average service life recommendation by five years better captures the
interim retirement experience. Both curves fit well to the data at the beginning, but due to
retirements at age 13 where 27 percent of beginning exposures were retired,neither curve produces
a great fit after that.However,Concentric is aware that this retirement is primarily related to the sale
of a building in 2023, which the magnitude of which is not expected to occur again within the next
five years. As such, Concentric has analyzed this account through the lens that these retirements
Concentric Energy Advisors Page 1 3-36

Intermountain Gas Company
1@ 2025 Depreciation Study
should not unduly affect the future retirement experience. As such, Concentric believes the subtle
and gradual decrease in the average service life is a fair recommendation within this study, and
recommends the use of the Iowa 45-R2 curve for this account.
A peer comparison of gas distribution utilities produced a range from 40 to 75 years with a mean
average service life recommendation of 52 years. Conversations with IGC operations and
management staff indicated that the recommended 45-year life for this account is a good
representation of the historical life and future expectations, taking into consideration the expected
interim retirements of the components within these structures.
Net Salvage Trend
—HistoricalPercent-Rolling Average —Concentric Recommendation
— — —Historical Net Salvage Percent Trendline
Year
O ci N M It Ln 1,0 r` 00 a) O ci N M � Ln W r` 00 a) O c-I N M �
O O O O O O O O O O O O O O O O O O O O O O O O O
N N N N N N N N N N N N N N N N N N N N N N N N N
0
20 r4—14 14� 13 12
20 20 20 20 20 19 19 18 _
40
V
a 42 40— — _
60 51 50 47 38
V
L
O
Y 80
100
103 101
120
As shown in the graph above,the historical net salvage activity for this account shows a range from
positive 103 percent to positive nine percent. The full depth band shows positive 101 percent. As
there is data dating back to 1975 within this account, Concentric has only displayed the most recent
and relevant 25 years in the graph above for conciseness.As shown on page 7-12 of this report,the
most recent (last three years) three-year rolling bands show a range from positive 133 percent to
negative 47 percent, and the most recent (last five years) five-year rolling bands show a range from
positive 164 percent to negative 43 percent. The previously approved net salvage percentage was
Concentric Energy Advisors Page 1 3-37

Intermountain Gas Company
1@ 2025 Depreciation Study
positive five percent,and a review of peer gas transmission and distribution utilities indicates a range
from negative four percent to negative 15 percent.Although the historical rolling average has been
below the approved net salvage percent since the time of the last study,IGC staff indicated that there
have been no material changes in the cost of removal or gross salvage practices since the last study.
As indicated above on page 3-36,the large increase in the positive net salvage rolling average occurs
due to large retirements that occurred in 2023. Alongside these retirements, there was over $6
million dollars in gross salvage proceeds.Concentric has discussed this sale with IGC operations and
management staff, and the determination was made that, although there will likely be sales of
structures and buildings in the future,a sale of this magnitude should not be expected over the next
five years.As can be seen in the backup data for the graph above on page 7-12,since 1996,there have
only been two years that have recorded any gross salvage proceeds - 2016 where $850,000 was
recorded, and the amount in 2023. As such, Concentric has moderately increased the net salvage
percentage to positive 10 percent for this account at this time to reflect the proceeds gained from this
sale,while being cognizant that any further increases would cause this account to increasingly stray
from the range of peer utilities.
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Intermountain Gas Company
1@ 2025 Depreciation Study
ACCOUNT 392.1 -TRANSPORTATION EQUIPMENT
Previously Concentric Previously Concentric
Investment$ Investment Approved Recommended Approved Net Recommended
i Curve Curve Salvage Net Salvage
$13,719,078 1.47% 10-1_2 10-1_2 16% 16%
The investment in Transportation Equipment is approximately $13.7 million, representing 1.47
percent of the total depreciable plant studied. This account contains vehicles such as light duty
trucks, and anything deemed Class 2600 and under. Retirements, additions, and other plant
transactions for the period 1986 through 2024 were analyzed by the retirement rate method. This
account did not utilize a T-Cut and retirements of$17,633,969 were recorded for the period 2016
through 2024.
■ Actual —Iowa 10-1_2(RM 0.1439) —Iowa 10-1_2(RM 0.1439)
100
■
80 ■
■
ao
c
60 ■
V)
c •
ai
i 40 ■
W
a
■
0
0 10 20 30 40
Age(Years)
The currently approved and proposed life parameter for this account is an Iowa 10-L2,with a related
Residual Measure of 0.1439 as seen in the graph above and on page 6-73. Both the visual and
mathematical fits to the retirement experience are robust, and Concentric finds no need based on
actuarial analysis to change either the approved Iowa curve or approved average service life
parameter at this time.
A peer comparison of gas transmission and distribution utilities produced a range from 7 to 16 years
with a mean average service life recommendation of 10 years. However, for an account such as
transportation equipment, some peer comparators have a different asset mix within the account,
leading to comparisons that need to be evaluated appropriately. Concentric placed more weight on
the peer accounts that have the most comparable group of vehicles within them. Conversations with
IGC operations and management staff indicated that the recommended 10-year life for this account
Concentric Energy Advisors Page 1 3-39

Intermountain Gas Company
1@ 2025 Depreciation Study
is still a good representation of the historical life and future expectations. As the fit to data is still
robust and it's not forecasted to change in the foreseeable future,Concentric recommends continuing
the use of the Iowa 10-L2 for this account.
Net Salvage Trend
Historical Percent-Rolling Average —Concentric Recommendation
— — —Historical Net Salvage Percent Trendline
Year
O 1_� rq m v in LO r` oo m O r-i C14 m a in tD r` a m O -1 N m `T
O O O O O O O O O O -1 -1 -1 -1 -1 -1 ­1 ­1 ­1 j N rV rV N N
O O O O O O O O O O O O O O O O O O O O O O O O O
N N N N N N N N N N N N N N N N N N N N N rV rV rV N
0
2
4
a
6
V
a 8
10 12 12 12 12 11 12 12 13
0 12 14 13 14
0 14 18 16 15 15 15 15 16 17 18 18
16 1 — — —
18 18 19
20
As shown in the graph above,the historical net salvage activity for this account shows a range from
positive 11 percent to positive 19 percent.The full depth band shows positive 19 percent.As there is
data dating back to 1975 within this account, Concentric has only displayed the most recent and
relevant 25 years in the graph above for conciseness.As shown on page 7-13 of this report,the most
recent(last three years)three-year rolling bands all produce positive 30 percent,and the most recent
(last five years) five-year rolling bands show a range from positive 29 percent to positive 30 percent.
The previously approved net salvage percentage was positive 16 percent, and a review of peer gas
transmission and distribution utilities indicates a range from positive 15 percent to positive 20
percent. With the above in mind, Concentric proposes to continue using a positive 16 percent net
salvage rate for this account.
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Intermountain Gas Company
1@ 2025 Depreciation Study
OTHER ACCOUNTS
The above analysis provides consideration relating to over 95 percent of the investment in
depreciable plant. Some of the accounts related to the remaining depreciable plant studied, as of
December 31, 2024, are subjected to amortization accounting. This is proposed for a number of
accounts that represent numerous units of property,but very small portions of depreciable gas plant
in service.
Concentric Energy Advisors Page 1 3-41

Intermountain Gas Company
16 2025 Depreciation Study
SECTION 4
4 CALCULATION OF ANNUAL AND ACCRUED DEPRECIATION
4.1 Calculation of Annual and Accrued Amortization
Amortization is the gradual extinguishment of an amount in an account by distributing such amount
over a fixed period,over the life of the asset or liability to which it applies,or over the period during
which it is anticipated the benefit will be realized. Normally,the distribution of the amount is in equal
amounts to each year of the amortization period.
The calculation of annual and accrued amortization requires the selection of an amortization period.
The amortization periods used in this report were based on judgment, which incorporated a
consideration of the period during which the assets will render most of their service,the amortization
period and service lives used by other utilities,and the service life estimates previously used for the
asset under depreciation accounting.
Amortization accounting is proposed for a number of IGC's accounts. The accounts and their
amortization periods are as follows:
Investment Previously Recommended
rcco�untTriitle]WInvestment percentage Approved Amortization
Period in Years
391.00 Office Furniture and $6,120,397 0.66% 10-SQ 15
Equipment
393.00 Stores Equipment $99,370 0.01% 30-SQ 30
394.00 Tools,Shop, &Garage $9,765,588 1.05% 15-SQ 20
Equipment
397.00 Communication Equipment $5,599,478 0.60% 10-SQ 15
398.00 Miscellaneous Equipment $85,946 0.01% - 25
For the purpose of calculating annual amortization amounts, as of December 31, 2024, the book
depreciation reserve for each plant account or subaccount is assigned or allocated to vintages. The
book reserve assigned to vintages with an age greater than the amortization period is equal to the
vintage's original cost. The remaining book reserve is allocated among vintages with an age less than
the amortization period in proportion to the calculated accrued amortization. The calculated accrued
amortization is equal to the original cost multiplied by the ratio of the vintage's age to its amortization
period. The annual amortization amount is determined by dividing the future amortizations(original
cost less allocated book reserve) by the remaining period of amortization for the vintage.
Concentric Energy Advisors Page 1 4-1

Intermountain Gas Company
1@ 2025 Depreciation Study
4.2 Monitoring of Book Accumulated Depreciation
The calculated accrued depreciation or amortization represents that portion of the depreciable cost
which will not be allocated to expense through future depreciation accruals, if current forecasts of
service life characteristics materialize and are used as a basis for depreciation accounting. Thus,the
calculated accrued depreciation provides a measure of the book accumulated depreciation. The use
of this measure is recommended in the amortization of book accumulated depreciation variances to
insure complete recovery of capital over the life of the property.
The recommended amortization of the variance between the book accumulated depreciation and the
calculated accrued depreciation is based on an amortization period equal to the composite remaining
life for each property group where the variance exceeds five percent of the calculated accrued
depreciation.
The composite remaining life for use in the calculation of accumulated depreciation variances is
derived by developing the composite sum of the individual remaining lives in accordance with the
following equation:
Book Cost
Life x Remaining Life)
Composite Remaining Life = ( 1 )
Book Cost
Z
Life
The book costs and lives of the several vintages, which are summed in the foregoing equation, are
defined by the estimated future survivor curve. In as much as book cost divided by life equals the
Whole Life annual accrual,the foregoing equation reduces to the following form:
Whole Life Future Accruals
Composite Remaining Life = (2)
ZWhole Life Annual Accrual
or
�BookCost—Calc,Reserve
Composite Remaining Life = (3)
ZWhole Life Annual Accrual
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Intermountain Gas Company
1@ 2025 Depreciation Study
SECTION 5
5 RESULTS OF THE STUDY
5.1 Qualification of Results
The calculated annual and accrued depreciation are the principal results of the study and are shown
in Tables 1, 1A, and 1B. Continued surveillance and periodic revisions are normally required to
maintain continued use of appropriate annual depreciation accrual rates. An assumption that accrual
rates can remain unchanged over a long period of time implies a disregard for the inherent variability
in service lives and salvage,and for the change of the composition of property in service. The annual
accrual rates and the accrued depreciation in Tables 1,1A,and 1B were calculated in accordance with
the Straight-line method, using the ALG procedure based on estimates which reflect considerations
of current historical evidence and expected future conditions.
5.2 Description of Detailed Tabulations
The following tables provide summaries by account of the original cost of investment,calculated and
booked accumulated depreciation amounts,the required amount of annual depreciation expense,the
required depreciation rate to be applied against the original cost of the account and the estimated
composite remaining life of the surviving plant in service.
The detailed calculations of annual depreciation applicable to depreciable assets,as of December 31,
2024, are presented in account sequence starting in Section 8 - Page 8-2. The tables indicate the
estimated Iowa survivor curves used in the calculations. The tables set forth (for each installation
year) the original cost, calculated accrued depreciation, booked accumulated depreciation, and the
calculated annual accrual.
Concentric Energy Advisors Page 1 5-1

INTERMOUNTAIN GAS COMPANY
TABLE 1. SUMMARY OF SERVICE LIFE AND NET SALVAGE ESTIMATES AND CALCULATED ANNUAL AND
ACCRUED DEPRECIATION RELATED TO THE RECOVERY OF AVERAGE ORIGINAL COST IN GAS PLANT AS OF DECEMBER 31, 2024
-
TOTAL -
ESTIMATED NET SURVIVING CALCULATED
SURVIVOR SALVAGE ORIGINAL COST ACCRUED BOOK ANNUAL ACCRUAL REMAINING
ACCOUNT DESCRIPTION CURVE PERCENT AS OF 12/31/2024 DEPRECIATION RESERVE AMOUNT RATE LIFE
361 STRUCTURES & IMPROVEMENTS - NAMPA 40-S5 -10 * 9,568,070 2,146,553 2,291 ,526 253,609 2.65 31 .8
361 .1 STRUCTURES AND IMPROVEMENTS - REXBURG 25-R3 -15 1 ,967,519 1 ,115,976 1 ,692,211 38,436 1 .95 12.7
362 GAS HOLDERS - NAMPA 40-R4 -15 * 10,132,429 2,822,657 3,1 18,494 230,563 2.28 30.3
362.1 GAS HOLDERS - REXBURG 25-R4 -15 1 ,578,228 1 ,136,530 1 ,429,694 41 ,219 2.61 9.3
363 MEASURE & REG EQUIPMENT - NAMPA 40-R2.5 -10 270,146 61,827 83,126 6,169 2.28 31 .7
363.1 MEASURE & REG EQUIPMENT - REXBURG 25-R3 -10 26,194 5,037 3,845 1 ,210 4.62 20.6
363.4 COMPRESSOR EQUIPMENT- NAMPA 40-R2.5 -10 9,418,365 3,081 ,864 3,703,334 216,128 2.29 28.1
363.5 LIQUEFACTION EQUIPMENT - NAMPA 40-R2.5 -10 4,108,052 1 ,624,255 2,636,198 60,403 1 .47 25.7
363.7 PURIFICATION EQUIPMENT - NAMPA 40-R2.5 -10 2,313,026 580,998 884,100 44,766 1 .94 30.9
363.16 PURIFICATION EQUIPMENT - REXBURG 25-R3 -10 655,656 424,223 621 ,301 9,703 1 .48 10.3
363.8 VAPORIZATION EQUIPMENT - NAMPA 40-R2.5 -10 2,278,225 1 ,044,723 1 ,239,384 38,061 1 .67 23.4
363.17 VAPORIZATION EQUIPMENT - REXBURG 25-R3 -10 1 ,091 ,437 701 ,406 942,091 24,713 2.26 10.4
TOTAL GAS OTHER STORAGE 43,407,348 14,746,047 18,645,303 964,980 2.22
TRANSMISSION PLANT
365 RIGHTS OF WAY 55-R5 0 782,865 360,705 492,368 8,939 1 .14 29.7
366 STRUCTURES AND IMPROVEMENTS 35-R5 -5 77,152 61,547 66,285 1 ,172 1 .52 8.4
367 MAINS 63-R4 -35 * 72,446,841 39,364,146 51 ,386,753 973,146 1 .34 37.6
368 COMPRESSOR STATION 20-L1 .5 5 9,199,933 1 ,227,884 1 ,175,688 441 ,335 4.80 17.2
370 COMMUNICATION EQUIPMENT - - 714,440 - 751 ,405 - - -
TOTAL TRANSMISSION PLANT 83,221,231 41,014,283 53,872,499 1,424,592 1.71
DISTRIBUTION PLANT
374 LAND RIGHTS 65-R5 0 1 ,484,249 347,560 553,456 16,105 1 .09 49.8
375 STRUCTURES AND IMPROVEMENTS 55-R4 -5 312,350 26,683 24,364 6,218 1 .99 50.5
376 MAINS 70-R4 -50 * 331 ,142,799 110,724,439 128,117,262 6,476,317 1 .96 54.4
378 MEASURE & REG STATION EQUIPMENT- GENERAL 45-SO -30 * 14,581 ,059 3,653,633 3,748,610 417,739 2.86 36.3
379 MEASURE & REG STATION EQUIPMENT - CITY GATE 45-SO -5 1 ,701 ,211 55,242 43,614 39,973 2.35 43.6
380 SERVICES 58-R3 -75 * 256,371 ,253 117,464,437 129,430,204 7,262,446 2.83 42.8
381 METERS 40-R3 0 * 74,759,880 20,553,480 21 ,070,218 1,812,618 2.42 29.0
381 .2 ERT UNITS 15-R3 0 28,898,085 13,806,999 14,362,691 1 ,834,750 6.35 7.8
383 REGULATORS 50-R3 0 20,442,204 6,384,585 7,435,968 359,419 1 .76 34.4
385 INDUSTRIAL MEASURE & REG. STATION EQUIPMENT 40-Rl -12 * 12,763,496 5,242,634 7,990,964 218,155 1 .71 25.3
387 OTHER DISTRIBUTION EQUIPMENT 30-R3 0 112,980 19,332 54,642 2,241 1 .98 24.9
TOTAL DISTRIBUTION PLANT 742,569,566 278,279,025 312,831,993 18,445,981 2.48
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 1 5-2

INTERMOUNTAIN GAS COMPANY
TABLE 1. SUMMARY OF SERVICE LIFE AND NET SALVAGE ESTIMATES AND CALCULATED ANNUAL AND
ACCRUED DEPRECIATION RELATED TO THE RECOVERY OF AVERAGE ORIGINAL COST IN GAS PLANT AS OF DECEMBER 31, 2024
-
TOTAL -
ESTIMATED NET SURVIVING CALCULATED
SURVIVOR SALVAGE ORIGINAL COST ACCRUED BOOK ANNUAL ACCRUAL REMAINING
ACCOUNT DESCRIPTION CURVE PERCENT AS OF 12/31/2024 DEPRECIATION RESERVE AMOUNT RATE LIFE
GENERAL PLANT
390 STRUCTURES & IMPROVEMENTS 45-R2 10 * 24,862,703 6,607,526 10,138,963 332,408 1 .34 31 .7
391 OFFICE FURNITURE & EQUIPMENT 15-SQ 0 6,120,397 2,174,939 2,555,956 358,292 5.85 9.7
392.1 TRANSPORTATION EQUIPMENT 10-L2 16 * 13,719,078 5,097,838 6,060,801 935,792 6.82 5.6
392.2 TRANSPORTATION EQUIPMENT - TRAILERS 20-R2 15 568,498 216,293 290,251 14,652 2.58 11 .1
393 STORES EQUIPMENT 30-SQ 0 99,370 9,116 13,992 3,116 3.14 27.2
394 TOOLS, SHOP, & GARAGE EQUIPMENT 20-SQ 0 9,765,588 3,480,892 4,639,927 363,394 3.72 12.9
396 POWER OPERATED EQUIPMENT 10-LO 30 3,779,184 364,127 874,562 191 ,832 5.08 8.6
397 COMMUNICATION EQUIPMENT 15-SQ 0 5,599,478 1 ,567,227 2,775,697 234,637 4.19 10.8
398 MISCELLANEOUS EQUIPMENT 25-SQ 0 85,946 7,373 85,850 4 0.00 22.9
TOTAL GENERAL PLANT 64,600,241 19,525,331 27,435,999 2,434,127 3.77
TOTAL GAS PLANT STUDIED 933,798,386 353,564,686 412,785,793 23,269,680 2.49
PLANT NOT STUDIED
301 ORGANIZATION 2,506 2,506
302 FRANCHISES 429,487 429,487
303 MISCELLANEOUS 74,089,963 38,940,956
360 LAND & LAND RIGHTS 292,588 -
365 LAND 3,070,327 -
374 LAND 11 ,970 -
389 LAND & LAND RIGHTS (GENERAL) 1 ,397,475 -
397 CAPITAL LEASE 379,348 -
TOTAL PLANT 1,013,472,048 452,158,742
* Any account denoted with an asterisk is written in detail within section 3.3 of the Concentric Depreciation Report
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 1 5-3

INTERMOUNTAIN GAS COMPANY
TABLE 1. SUMMARY OF SERVICE LIFE AND NET SALVAGE ESTIMATES AND CALCULATED ANNUAL AND
ACCRUED DEPRECIATION RELATED TO THE RECOVERY OF AVERAGE ORIGINAL COST IN GAS PLANT AS OF DECEMBER 31, 2024
- LIFE -
ESTIMATED NET SURVIVING CALCULATED
SURVIVOR SALVAGE ORIGINAL COST ACCRUED BOOK ANNUAL ACCRUAL REMAINING
ACCOUNT DESCRIPTION CURVE PERCENT AS OF 12/31/2024 DEPRECIATION RESERVE AMOUNT RATE LIFE
361 STRUCTURES & IMPROVEMENTS - NAMPA 40-S5 0 9,568,070 1 ,951 ,411 1,81 1 ,138 249,246 2.60 31 .8
361 .1 STRUCTURES AND IMPROVEMENTS - REXBURG 25-R3 0 1,967,519 970,414 1 ,357,836 43,689 2.22 12.7
362 GAS HOLDERS - NAMPA 40-R4 0 10,132,429 2,454,484 2,123,974 357,913 3.53 30.3
362.1 GAS HOLDERS - REXBURG 25-R4 0 1,578,228 988,287 1 ,170,666 43,604 2.76 9.3
363 MEASURE & REG EQUIPMENT - NAMPA 40-R2.5 0 270,146 56,207 65,117 5,974 2.21 31 .7
363.1 MEASURE & REG EQUIPMENT - REXBURG 25-R3 0 26,194 4,579 3,164 1 ,116 4.26 20.6
363.4 COMPRESSOR EQUIPMENT - NAMPA 40-R2.5 0 9,418,365 2,801,694 2,836,239 232,173 2.47 28.1
363.5 LIQUEFACTION EQUIPMENT - NAMPA 40-R2.5 0 4,108,052 1 ,476,595 2,263,323 59,584 1 .45 25.7
363.7 PURIFICATION EQUIPMENT - NAMPA 40-R2.5 0 2,313,026 528,180 750,695 42,298 1 .83 30.9
363.16 PURIFICATION EQUIPMENT - REXBURG 25-R3 0 655,656 385,657 515,855 13,575 2.07 10.3
363.8 VAPORIZATION EQUIPMENT - NAMPA 40-R2.5 0 2,278,225 949,748 1,046,164 43,143 1 .89 23.4
363.17 VAPORIZATION EQUIPMENT - REXBURG 25-R3 0 1,091,437 637,642 766,560 31 ,166 2.86 10.4
TOTAL GAS OTHER STORAGE 43,407,348 13,204,898 14,710,730 1,123,481 2.59
TRANSMISSION PLANT
365 RIGHTS OF WAY 55-R5 0 782,865 360,705 492,368 8,939 1 .14 29.7
366 STRUCTURES AND IMPROVEMENTS 35-R5 0 77,152 58,616 61 ,492 1 ,251 1 .62 8.4
367 MAINS 63-R4 0 72,446,841 29,158,627 36,325,455 769,853 1 .06 37.6
368 COMPRESSOR STATION 20-1-1 .5 0 9,199,933 1 ,292,510 1 ,173,724 469,505 5.10 17.2
370 COMMUNICATION EQUIPMENT - - 714,440 - 737,725 - - -
TOTAL TRANSMISSION PLANT 83,221,231 30,870,458 38,790,765 1,249,548 1.50
DISTRIBUTION PLANT
374 LAND RIGHTS 65-R5 0 1,484,249 347,560 553,456 16,105 1 .09 49.8
375 STRUCTURES AND IMPROVEMENTS 55-R4 0 312,350 25,413 28,215 5,377 1 .72 50.5
376 MAINS 70-R4 0 331,142,799 73,816,292 85,265,234 4,322,753 1 .31 54.4
378 MEASURE & REG STATION EQUIPMENT - GENERAL 45-SO 0 14,581,059 2,810,487 3,648,368 293,624 2.01 36.3
379 MEASURE & REG STATION EQUIPMENT - CITY GATE 45-SO 0 1,701,211 52,612 36,109 38,195 2.25 43.6
380 SERVICES 58-R3 0 256,371,253 67,122,535 85,201 ,779 3,738,012 1 .46 42.8
381 METERS 40-R3 0 74,759,880 20,553,480 21 ,602,952 1 ,766,614 2.36 29.0
381 .2 ERT UNITS 15-R3 0 28,898,085 13,806,999 14,642,184 1,789,188 6.19 7.8
383 REGULATORS 50-R3 0 20,442,204 6,384,585 7,535,587 355,494 1 .74 34.4
385 INDUSTRIAL MEASURE & REG. STATION EQUIPMENT 40-R1 0 12,763,496 4,680,923 8,010,687 157,476 1 .23 25.3
387 OTHER DISTRIBUTION EQUIPMENT 30-R3 0 112,980 19,332 54,195 2,261 2.00 24.9
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 5-4

INTERMOUNTAIN GAS COMPANY
TABLE 1. SUMMARY OF SERVICE LIFE AND NET SALVAGE ESTIMATES AND CALCULATED ANNUAL AND
ACCRUED DEPRECIATION RELATED TO THE RECOVERY OF AVERAGE ORIGINAL COST IN GAS PLANT AS OF DECEMBER 31, 2024
- LIFE -
ESTIMATED NET SURVIVING CALCULATED
SURVIVOR SALVAGE ORIGINAL COST ACCRUED BOOK ANNUAL ACCRUAL REMAINING
ACCOUNT DESCRIPTION CURVE PERCENT AS OF 12/31/2024 DEPRECIATION RESERVE AMOUNT RATE LIFE
TOTAL DISTRIBUTION PLANT 742,569,566 189,620,219 226,578,768 12,485,099 1.68
GENERAL PLANT
390 STRUCTURES & IMPROVEMENTS 45-R2 0 24,862,703 7,341 ,696 10,545,119 393,348 1 .58 31 .7
391 OFFICE FURNITURE & EQUIPMENT 15-SQ 0 6,120,397 2,174,939 2,564,566 357,167 5.84 9.7
392.1 TRANSPORTATION EQUIPMENT 1012 0 13,719,078 6,068,855 6,083,750 1 ,365,537 9.95 5.6
392.2 TRANSPORTATION EQUIPMENT - TRAILERS 20-R2 0 568,498 254,462 290,251 23,289 4.10 11 .1
393 STORES EQUIPMENT 30-SQ 0 99,370 9,116 13,992 3,116 3.14 27.2
394 TOOLS, SHOP, & GARAGE EQUIPMENT 20-SQ 0 9,765,588 3,480,892 4,641 ,332 363,242 3.72 12.9
396 POWER OPERATED EQUIPMENT 10-1-0 0 3,779,184 520,181 874,562 321 ,005 8.49 8.6
397 COMMUNICATION EQUIPMENT 15-SQ 0 5,599,478 1 ,567,227 2,777,752 234,419 4.19 10.8
398 MISCELLANEOUS EQUIPMENT 25-SQ 0 85,946 7,373 85,980 - - 22.9
TOTAL GENERAL PLANT 64,600,241 21,424,741 27,877,305 3,061,123 4.74
TOTAL GAS PLANT STUDIED 933,798,386 255,120,316 307,957,568 17,919,251 1.92
PLANT NOT STUDIED
301 ORGANIZATION 2,506 2,506
302 FRANCHISES 429,487 429,487
303 MISCELLANEOUS 74,089,963 38,940,956
360 LAND & LAND RIGHTS 292,588 -
365 LAND 3,070,327 -
374 LAND 11,970 -
389 LAND & LAND RIGHTS (GENERAL) 1,397,475 -
397 CAPITAL LEASE 379,348 -
TOTAL PLANT 1,013,472,048 347,330,517
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Page 1 5-5

INTERMOUNTAIN GAS COMPANY
TABLE 1. SUMMARY OF SERVICE LIFE AND NET SALVAGE ESTIMATES AND CALCULATED ANNUAL AND
ACCRUED DEPRECIATION RELATED TO THE RECOVERY OF AVERAGE ORIGINAL COST IN GAS PLANT AS OF DECEMBER 31, 2024
- NET SALVAGE -
ESTIMATED NET SURVIVING CALCULATED
SURVIVOR SALVAGE ORIGINAL COST ACCRUED BOOK ANNUAL ACCRUAL
ACCOUNT DESCRIPTION CURVE PERCENT AS OF 12/31/2024 DEPRECIATION RESERVE AMOUNT RATE
361 STRUCTURES & IMPROVEMENTS - NAMPA 40-S5 -10 9,568,070 195,141 480,389 4,363 0.05
361 .1 STRUCTURES AND IMPROVEMENTS - REXBURG 25-R3 -15 1 ,967,519 145,562 334,375 (5,253) (0.27)
362 GAS HOLDERS - NAMPA 40-R4 -15 10,132,429 368,173 994,520 (127,350) (1 .26)
362.1 GAS HOLDERS - REXBURG 25-R4 -15 1 ,578,228 148,243 259,029 (2,385) (0.15)
363 MEASURE & REG EQUIPMENT - NAMPA 40-R2.5 -10 270,146 5,621 18,009 195 0.07
363.1 MEASURE & REG EQUIPMENT - REXBURG 25-R3 -10 26,194 458 681 94 0.36
363.4 COMPRESSOR EQUIPMENT - NAMPA 40-R2.5 -10 9,418,365 280,169 867,094 (16,045) (0.17)
363.5 LIQUEFACTION EQUIPMENT - NAMPA 40-R2.5 -10 4,108,052 147,660 372,875 819 0.02
363.7 PURIFICATION EQUIPMENT - NAMPA 40-R2.5 -10 2,313,026 52,818 133,405 2,468 0.11
363.16 PURIFICATION EQUIPMENT - REXBURG 25-R3 -10 655,656 38,566 105,446 (3,872) (0.59)
363.8 VAPORIZATION EQUIPMENT - NAMPA 40-R2.5 -10 2,278,225 94,975 193,220 (5,082) (0.22)
363.17 VAPORIZATION EQUIPMENT - REXBURG 25-R3 -10 1 ,091 ,437 63,764 175,531 (6,453) (0.59)
TOTAL GAS OTHER STORAGE 43,407,348 1,541,149 3,934,572 (158,501) (0.37)
TRANSMISSION PLANT
365 RIGHTS OF WAY 55-R5 0 782,865 - - - -
366 STRUCTURES AND IMPROVEMENTS 35-R5 -5 77,152 2,931 4,793 (79) (0.10)
367 MAINS 63-R4 -35 72,446,841 10,205,519 15,061 ,297 203,293 0.28
368 COMPRESSOR STATION 20-L1 .5 5 9,199,933 (64,626) 1 ,964 (28,170) (0.31 )
370 COMMUNICATION EQUIPMENT - - 714,440 - 13,680 - -
TOTAL TRANSMISSION PLANT 83,221,231 10,143,825 15,081,734 175,044 0.21
DISTRIBUTION PLANT
374 LAND RIGHTS 65-R5 0 1 ,484,249 - - - -
375 STRUCTURES AND IMPROVEMENTS 55-R4 -5 312,350 1,271 (3,851) 841 0.27
376 MAINS 70-R4 -50 331 ,142,799 36,908,146 42,852,027 2,153,564 0.65
378 MEASURE & REG STATION EQUIPMENT - GENERAL 45-SO -30 14,581 ,059 843,146 100,242 124,1 15 0.85
379 MEASURE & REG STATION EQUIPMENT - CITY GATE 45-SO -5 1 ,701 ,211 2,631 7,505 1 ,778 0.10
380 SERVICES 58-R3 -75 256,371 ,253 50,341,901 44,228,425 3,524,434 1 .37
381 METERS 40-R3 0 74,759,880 - (532,735) 46,004 0.06
381 .2 ERT UNITS 15-R3 0 28,898,085 - (279,494) 45,562 0.16
383 REGULATORS 50-R3 0 20,442,204 - (99,619) 3,925 0.02
385 INDUSTRIAL MEASURE & REG. STATION EQUIPMENT 40-R1 -12 12,763,496 561,711 (19,722) 60,679 0.48
387 OTHER DISTRIBUTION EQUIPMENT 30-R3 0 112,980 - 447 (20) (0.02)
TOTAL DISTRIBUTION PLANT 742,569,566 88,658,806 86,253,225 5,960,882 0.80
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 5-6

INTERMOUNTAIN GAS COMPANY
TABLE 1. SUMMARY OF SERVICE LIFE AND NET SALVAGE ESTIMATES AND CALCULATED ANNUAL AND
ACCRUED DEPRECIATION RELATED TO THE RECOVERY OF AVERAGE ORIGINAL COST IN GAS PLANT AS OF DECEMBER 31, 2024
- NET SALVAGE -
ESTIMATED NET SURVIVING CALCULATED
SURVIVOR SALVAGE ORIGINAL COST ACCRUED BOOK ANNUAL ACCRUAL
ACCOUNT DESCRIPTION CURVE PERCENT AS OF 12/31/2024 DEPRECIATION RESERVE AMOUNT RATE
GENERAL PLANT
390 STRUCTURES & IMPROVEMENTS 45-R2 10 24,862,703 (734,170) (406,156) (60,940) (0.25)
391 OFFICE FURNITURE & EQUIPMENT 15-SQ 0 6,120,397 - (8,610) 1 ,125 0.02
392.1 TRANSPORTATION EQUIPMENT 10-1-2 16 13,719,078 (971,017) (22,950) (429,745) (3.13)
392.2 TRANSPORTATION EQUIPMENT - TRAILERS 20-R2 15 568,498 (38,169) 0 (8,637) (1 .52)
393 STORES EQUIPMENT 30-SQ 0 99,370 - - - -
394 TOOLS, SHOP, & GARAGE EQUIPMENT 20-SQ 0 9,765,588 - (1 ,406) 152 0.00
396 POWER OPERATED EQUIPMENT 10-1-0 30 3,779,184 (156,054) - (129,173) (3.42)
397 COMMUNICATION EQUIPMENT 15-SQ 0 5,599,478 - (2,055) 218 0.00
398 MISCELLANEOUS EQUIPMENT 25-SQ 0 85,946 - (129) 4 0.00
TOTAL GENERAL PLANT 64,600,241 (1,899,410) (441,306) (626,996) (0.97)
TOTAL GAS PLANT STUDIED 933,798,386 98,444,369 104,828,225 5,350,429 0.57
PLANT NOT STUDIED
301 ORGANIZATION 2,506 -
302 FRANCHISES 429,487 -
303 MISCELLANEOUS 74,089,963 -
360 LAND & LAND RIGHTS 292,588 -
365 LAND 3,070,327 -
374 LAND 11 ,970 -
389 LAND & LAND RIGHTS (GENERAL) 1 ,397,475 -
397 CAPITAL LEASE 379,348 -
TOTAL PLANT 1,013,472,048 104,828,225
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Page 1 5-7

Intermountain Gas Company
1@ 2025 Depreciation Study
SECTION 6
6 RETIREMENT RATE ANALYSIS
Concentric Energy Advisors Page 1 6-1

Intermountain Gas Company
Account 361.00 - Structures & Improvements - Nampa
Placement Band - 1974- 2024 Experience Band - 2016- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 38-S5 (RM 0.8918) Iowa 40-S5 (RM 0.5513)
100 ■■■■■■■ ■■■■■■■■■ ■■
MEMO
80
a,o
> 60
c
U 40
■
v
■
20 ■
0
0 10 20 30 40 50 60 70
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-2

Intermountain Gas Company
Account 361.00 - Structures & Improvements - Nampa
Placement Band - 1974- 2024 Experience Band - 2016- 2024
RETIREMENT RATE ANALYSIS
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 11,087,387 0 0.000001 1.00000 100.00
0.5 10,490,476 27,465 0.00262 0.99738 100.00
1.5 10,414,072 0 0.00000 1.00000 99.74
2.5 9,489,636 0 0.00000 1.00000 99.74
3.5 8,990,452 0 0.00000 1.00000 99.74
4.5 8,630,599 2,960 0.00034 0.99966 99.74
5.5 7,520,312 6,159 0.00082 0.99918 99.71
6.5 5,267,027 0 0.00000 1.00000 99.63
7.5 4,737,519 19,431 0.00410 0.99590 99.63
8.5 3,894,968 0 0.00000 1.00000 99.22
9.5 3,650,465 11,862 0.00325 0.99675 99.22
10.5 3,516,629 0 0.00000 1.00000 98.90
11.5 3,464,653 40,080 0.01157 0.98843 98.90
12.5 3,367,756 12 0.00000 1.00000 97.76
13.5 1,947,835 2,187 0.00112 0.99888 97.76
14.5 1,945,648 13,355 0.00686 0.99314 97.65
15.5 1,882,651 4 0.00000 1.00000 96.98
16.5 1,882,647 1,140 0.00061 0.99939 96.98
17.5 1,877,288 1,308 0.00070 0.99930 96.92
18.5 1,875,980 0 0.00000 1.00000 96.85
19.5 1,797,342 0 0.00000 1.00000 96.85
20.5 1,797,342 0 0.00000 1.00000 96.85
21.5 1,797,342 7 0.00000 1.00000 96.85
22.5 1,780,533 0 0.00000 1.00000 96.85
23.5 1,777,083 21 0.00001 0.99999 96.85
24.5 1,777,062 38 0.00002 0.99998 96.85
25.5 1,777,024 194 0.00011 0.99989 96.85
26.5 1,774,823 109 0.00006 0.99994 96.84
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-3

Intermountain Gas Company
Account 361.00 - Structures & Improvements - Nampa
Placement Band - 1974- 2024 Experience Band - 2016- 2024
27.5 1,774,714 20,721 0.01168 0.98832 96.83
28.5 1,753,993 230 0.00013 0.99987 95.70
29.5 1,753,763 1,461 0.00083 0.99917 95.69
30.5 1,752,302 380 0.00022 0.99978 95.61
31.5 1,751,922 1,487 0.00085 0.99915 95.59
32.5 1,750,435 2,401 0.00137 0.99863 95.51
33.5 1,748,035 7,514 0.00430 0.99570 95.38
34.5 1,740,038 101,807 0.05851 0.94149 94.97
35.5 1,531,319 1,279 0.00084 0.99916 89.41
36.5 1,325,254 5,919 0.00447 0.99553 89.33
37.5 1,319,335 5,398 0.00409 0.99591 88.93
38.5 1,313,937 24,175 0.01840 0.98160 88.57
39.5 1,285,682 764,503 0.59463 0.40537 86.94
40.5 521,179 109,642 0.21037 0.78963 35.24
41.5 411,537 91,844 0.22317 0.77683 27.83
42.5 318,517 0 0.00000 1.00000 21.62
43.5 316,627 50,200 0.15855 0.84145 21.62
44.5 263,013 0 0.00000 1.00000 18.19
45.5 263,013 72,300 0.27489 0.72511 18.19
46.5 189,890 2,944 0.015501 0.98450 13.19
47.5 186,947 128,782 0.68887 0.31113 12.99
48.51 51,553 0 0.00000 1.00000 4.04
49.5 29,531 0 0.00000 1.00000 4.04
Totals: 1,519,319
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 64

Intermountain Gas Company
Account 361.10 - Structures & Improvements - Rexburg
Placement Band - 2008- 2024 Experience Band - 2016- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 22-133 (RM 0.1085) Iowa 25-R3 (RM 0.055)
100
■
80
a,o
> 60
c
U 40
v
20
0
0 10 20 30 40 50
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-5

Intermountain Gas Company
Account 361.10 - Structures & Improvements - Rexburg
Placement Band - 2008- 2024 Experience Band - 2016- 2024
RETIREMENT RATE ANALYSIS'
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 2,099,797 0 0.000001 1.00000 100.00
0.5 2,076,355 3 0.00000 1.00000 100.00
1.5 2,053,518 0 0.00000 1.00000 100.00
2.5 2,005,952 0 0.00000 1.00000 100.00
3.5 1,996,791 0 0.000001 1.00000 100.00
4.5 1,988,367 0 0.00000 1.00000 100.00
5.5 1,911,148 830 0.00043 0.99957 100.00
6.5 1,732,473 30,463 0.01758 0.98242 99.96
7.5 1,698,034 1,000 0.00059 0.99941 98.20
8.5 1,678,439 5,300 0.00316 0.99684 98.14
9.5 1,673,139 0 0.00000 1.00000 97.83
10.5 1,609,079 88,310 0.05488 0.94512 97.83
11.5 1,520,769 0 0.00000 1.00000 92.46
12.5 1,520,769 0 0.00000 1.00000 92.46
13.5 1,337,083 2,000 0.00150 0.99850 92.46
14.5 1,335,083 0 0.00000 1.00000 92.32
15.5 1,1461,668 4,372 0.00381 0.99619 92.32
Totals: 132,278
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-6

Intermountain Gas Company
Account 362.00 - Gas Holders - Nampa
Placement Band - 1974- 2024 Experience Band - 2020- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 35-133.5 (RM 3.1484) Iowa 40-R4 (RM 2.3545)
100
80
a,o
> 60
c
U 40
v
20
0
0 10 20 30 40 50 60 70
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-7

Intermountain Gas Company
Account 362.00 - Gas Holders - Nampa
Placement Band - 1974- 2024 Experience Band - 2020- 2024
RETIREMENT RATE ANALYSIS
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 10,289,818 0 0.00000 1.00000 100.00
0.5 10,241,863 0 0.00000 1.00000 100.00
1.5 9,936,141 0 0.00000 1.00000 100.00
2.5 3,979,922 0 0.00000 1.00000 100.00
3.5 3,679,016 0 0.00000 1.00000 100.00
4.5 3,179,441 0 0.00000 1.00000 100.00
5.5 2,139,285 0 0.00000 1.00000 100.00
6.5 2,120,279 0 0.000001 1.00000 100.00
7.5 2,120,279 0 0.00000 1.00000 100.00
8.5 2,120,279 0 0.00000 1.00000 100.00
9.5 2,120,279 0 0.00000 1.00000 100.00
10.5 2,120,279 6,945 0.00328 0.99672 100.00
11.5 2,113,334 0 0.00000 1.00000 99.67
12.5 2,113,334 0 0.00000 1.00000 99.67
13.5 2,113,334 0 0.00000 1.00000 99.67
14.5 2,113,334 0 0.00000 1.00000 99.67
15.5 2,113,334 0 0.00000 1.00000 99.67
16.5 2,113,334 0 0.00000 1.00000 99.67
17.5 2,113,334 0 0.00000 1.00000 99.67
18.5 2,113,334 0 0.000001 1.00000 99.67
19.5 2,113,334 0 0.00000 1.00000 99.67
20.5 2,113,334 0 0.00000 1.00000 99.67
21.5 2,113,334 0 0.00000 1.00000 99.67
22.5 2,113,334 0 0.00000 1.00000 99.67
23.5 2,113,334 0 0.00000 1.00000 99.67
24.5 2,113,334 0 0.00000 1.00000 99.67
25.5 2,113,334 0 0.00000 1.00000 99.67
26.5 2,113,334 0 0.00000 1.00000 99.67
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-8

Intermountain Gas Company
Account 362.00 - Gas Holders - Nampa
Placement Band - 1974- 2024 Experience Band - 2020- 2024
27.5 2,113,334 0 0.00000 1.00000 99.67
28.5 2,113,334 0 0.00000 1.00000 99.67
29.5 2,113,334 0 0.00000 1.00000 99.67
30.5 2,113,334 0 0.00000 1.00000 99.67
31.5 2,113,334 0 0.00000 1.00000 99.67
32.5 2,113,334 0 0.00000 1.00000 99.67
33.5 2,113,334 0 0.00000 1.00000 99.67
34.5 2,113,334 0 0.000001 1.00000 99.67
35.5 2,113,334 0 0.000001 1.00000 99.67
36.5 2,113,334 0 0.00000 1.00000 99.67
37.5 2,113,334 0 0.00000 1.00000 99.67
38.5 2,113,334 0 0.000001 1.00000 99.67
39.5 2,113,334 0 0.00000 1.00000 99.67
40.5 2,113,334 0 0.00000 1.00000 99.67
41.5 2,113,334 0 0.00000 1.00000 99.67
42.5 2,113,334 0 0.00000 1.00000 99.67
43.5 2,113,334 0 0.00000 1.00000 99.67
44.5 2,113,334 0 0.00000 1.00000 99.67
45.5 2,113,334 1,800 0.00085 0.99915 99.67
46.5 2,111,534 43,976 0.02083 0.97917 99.59
47.5 2,067,558 99,818 0.04828 0.95172 97.52
48.5 1,967,739 0 0.00000 1.00000 92.81
49.5 1,967,739 4,849 0.00246 0.99754 92.81
Totals: 157,388
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-9

Intermountain Gas Company
Account 362.10 - Gas Holders - Rexburg
Placement Band - 2008- 2024 Experience Band - 2024- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 22-S5 (RM 0.0176) Iowa 25-R4 (RM 0.0821)
100100 ago
80
a,o
> 60
c
U 40
v
20
0
0 10 20 30 40 50
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-10

Intermountain Gas Company
Account 362.10 - Gas Holders - Rexburg
Placement Band - 2008- 2024 Experience Band - 2024- 2024
RETIREMENT RATE ANALYSIS'
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 1,578,228 0 0.000001 1.00000 100.00
0.5 1,578,228 0 0.00000 1.00000 100.00
1.5 1,578,228 0 0.00000 1.00000 100.00
2.5 1,578,228 0 0.00000 1.00000 100.00
3.5 1,578,228 0 0.000001 1.00000 100.00
4.5 1,578,228 0 0.00000 1.00000 100.00
5.5 1,578,228 0 0.00000 1.00000 100.00
6.5 1,578,228 0 0.00000 1.00000 100.00
7.5 1,578,228 0 0.00000 1.00000 100.00
8.5 1,578,228 0 0.00000 1.00000 100.00
9.5 1,578,228 0 0.00000 1.00000 100.00
10.5 1,578,228 0 0.00000 1.00000 100.00
11.5 1,578,228 0 0.00000 1.00000 100.00
12.5 1,578,228 0 0.00000 1.00000 100.00
13.5 1,578,228 0 0.00000 1.00000 100.00
14.5 1,578,228 0 0.00000 1.00000 100.00
15.5 1,578,228 0 0.00000 1.00000 100.00
Totals: 0
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-11

Intermountain Gas Company
Account 363.00 - Measure & Reg Equipment - Nampa
Placement Band - 1974- 2024 Experience Band - 2016- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 47-S4 (RM 1.1559) - Iowa 40-R2.5 (RM 1.9241)
100
■■■■Woom ■■■■ ■■■■■■� ■■■ ■■ ■■■■�■■
■
80
a,o
> 60
+.j
c
U 40
v
20
0
0 10 20 30 40 50 60 70 80 90
Age (Years)
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-12

Intermountain Gas Company
Account 363.00 - Measure & Reg Equipment - Nampa
Placement Band - 1974- 2024 Experience Band - 2016- 2024
RETIREMENT RATE ANALYSIS
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 19,863,276 92,968 0.004681 0.99532 100.00
0.5 18,879,107 110,000 0.00583 0.99417 99.53
1.5 18,754,749 788,000 0.04202 0.95798 98.95
2.5 17,232,317 18,000 0.00104 0.99896 94.79
3.5 15,793,743 0 0.00000 1.00000 94.69
4.5 15,414,006 13,869 0.00090 0.99910 94.69
5.5 15,263,650 0 0.00000 1.00000 94.60
6.5 14,820,377 0 0.00000 1.00000 94.60
7.5 14,689,330 4,000 0.00027 0.99973 94.60
8.5 11,589,751 7,614 0.00066 0.99934 94.57
9.5 10,307,947 0 0.00000 1.00000 94.51
10.5 6,525,119 0 0.00000 1.00000 94.51
11.5 6,054,400 51,595 0.00852 0.99148 94.51
12.5 5,806,400 0 0.00000 1.00000 93.70
13.5 5,621,744 0 0.00000 1.00000 93.70
14.5 5,569,758 0 0.00000 1.00000 93.70
15.5 4,330,688 0 0.00000 1.00000 93.70
16.5 4,294,608 15,000 0.003491 0.99651 93.70
17.5 4,267,064 0 0.00000 1.00000 93.37
18.5 4,191,168 0 0.00000 1.00000 93.37
19.5 3,927,626 0 0.00000 1.00000 93.37
20.5 3,905,990 0 0.00000 1.00000 93.37
21.5 3,905,990 0 0.00000 1.00000 93.37
22.5 3,863,971 0 0.00000 1.00000 93.37
23.5 3,413,730 0 0.00000 1.00000 93.37
24.5 3,413,730 0 0.00000 1.00000 93.37
25.51 3,413,730 0 0.00000 1.000001 93.37
26.5 3,413,730 0 0.00000 1.00000 93.37
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-13

Intermountain Gas Company
Account 363.00 - Measure & Reg Equipment - Nampa
Placement Band - 1974- 2024 Experience Band - 2016- 2024
27.5 3,413,730 0 0.00000 1.00000 93.37
28.5 3,413,730 0 0.00000 1.00000 93.37
29.5 3,413,730 0 0.00000 1.00000 93.37
30.5 3,413,730 0 0.00000 1.00000 93.37
31.5 3,413,730 0 0.00000 1.00000 93.37
32.5 3,413,730 0 0.00000 1.00000 93.37
33.5 3,413,730 0 0.00000 1.00000 93.37
34.5 3,413,730 0 0.000001 1.00000 93.37
35.5 3,409,765 0 0.000001 1.00000 93.37
36.5 3,409,765 0 0.00000 1.00000 93.37
37.5 3,409,765 0 0.00000 1.00000 93.37
38.5 3,409,765 0 0.000001 1.00000 93.37
39.5 3,409,765 0 0.00000 1.00000 93.37
40.5 3,409,765 0 0.00000 1.00000 93.37
41.5 3,409,765 0 0.00000 1.00000 93.37
42.5 3,378,965 0 0.00000 1.00000 93.37
43.5 3,378,104 2,500 0.00074 0.99926 93.37
44.5 3,160,511 0 0.00000 1.00000 93.30
45.5 3,160,511 11,000 0.00348 0.99652 93.30
46.5 3,135,826 0 0.00000 1.00000 92.98
47.5 3,057,041 234,394 0.07667 0.92333 92.98
48.51 2,772,641 36,225 0.01307 0.98693 85.85
49.5 2,702,473 90,297 0.03341 0.96659 84.73
Totals: 1,475,462
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-14

Intermountain Gas Company
Account 363.10 - Measure & Reg Equipment - Rexburg
Placement Band - 2008- 2024 Experience Band - 2024- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 22-R4 (RM 0.146) Iowa 25-R3 (RM 0.1801)
100
80
a,o
> 60
c
U 40
v
20
0
0 10 20 30 40 50
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-15

Intermountain Gas Company
Account 363.10 - Measure & Reg Equipment - Rexburg
Placement Band - 2008- 2024 Experience Band - 2024- 2024
RETIREMENT RATE ANALYSIS'
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 1,773,288 0 0.000001 1.00000 100.00
0.5 1,773,288 0 0.00000 1.00000 100.00
1.5 1,773,288 0 0.00000 1.00000 100.00
2.5 1,773,288 0 0.00000 1.00000 100.00
3.5 1,773,288 0 0.000001 1.00000 100.00
4.5 1,747,094 0 0.00000 1.00000 100.00
5.5 1,747,094 0 0.00000 1.00000 100.00
6.5 1,747,094 0 0.00000 1.00000 100.00
7.5 1,747,094 0 0.00000 1.00000 100.00
8.5 1,730,699 0 0.00000 1.00000 100.00
9.5 1,730,699 0 0.00000 1.00000 100.00
10.5 1,730,699 0 0.00000 1.00000 100.00
11.5 1,730,699 0 0.00000 1.00000 100.00
12.5 1,730,699 0 0.00000 1.00000 100.00
13.5 1,730,699 0 0.00000 1.00000 100.00
14.5 1,730,699 0 0.00000 1.00000 100.00
15.5 1,730,699 0 0.00000 1.00000 100.00
Totals: 0
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-16

Intermountain Gas Company
Account 365.00 - Rights of Way
Placement Band - 1973 - 2024 Experience Band - 2024- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 45-R5 (RM 1.8347) — Iowa 55-R5 (RM 0.4775)
100
80
a,o
> 60
c
U 40
v
20
0
0 10 20 30 40 50 60 70 80 90
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-17

Intermountain Gas Company
Account 365.00 - Rights of Way
Placement Band - 1973 - 2024 Experience Band - 2024- 2024
RETIREMENT RATE ANALYSIS'
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 782,865 0 0.00000 1.00000 100.00
0.5 782,865 0 0.00000 1.00000 100.00
1.5 782,865 0 0.00000 1.00000 100.00
2.5 782,865 0 0.00000 1.00000 100.00
3.5 782,865 0 0.00000 1.00000 100.00
4.5 782,865 0 0.00000 1.00000 100.00
5.5 782,865 0 0.00000 1.00000 100.00
6.5 782,865 0 0.000001 1.00000 100.00
7.5 782,865 0 0.00000 1.00000 100.00
8.5 782,865 0 0.00000 1.00000 100.00
9.5 773,903 0 0.00000 1.00000 100.00
10.5 773,903 0 0.00000 1.00000 100.00
11.5 770,527 0 0.00000 1.00000 100.00
12.5 744,571 0 0.00000 1.00000 100.00
13.5 678,620 0 0.00000 1.00000 100.00
14.5 623,714 0 0.00000 1.00000 100.00
15.5 623,714 0 0.00000 1.00000 100.00
16.5 623,714 0 0.00000 1.00000 100.00
17.5 608,268 0 0.00000 1.00000 100.00
18.5 600,059 0 0.000001 1.00000 100.00
19.5 600,059 0 0.00000 1.00000 100.00
20.5 600,059 0 0.00000 1.00000 100.00
21.5 600,059 0 0.00000 1.00000 100.00
22.5 600,059 0 0.00000 1.00000 100.00
23.5 447,046 0 0.00000 1.00000 100.00
24.5 445,621 0 0.00000 1.00000 100.00
25.5 406,053 0 0.00000 1.00000 100.00
26.5 287,672 0 0.00000 1.00000 100.00
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-18

Intermountain Gas Company
Account 365.00 - Rights of Way
Placement Band - 1973 - 2024 Experience Band - 2024- 2024
27.5 287,672 0 0.00000 1.00000 100.00
28.5 287,672 0 0.00000 1.00000 100.00
29.5 64,672 0 0.00000 1.00000 100.00
30.5 64,672 0 0.00000 1.00000 100.00
31.5 64,672 0 0.00000 1.00000 100.00
32.5 64,672 0 0.00000 1.00000 100.00
33.5 64,672 0 0.00000 1.00000 100.00
34.5 64,672 0 0.00000 1.00000 100.00
35.5 64,672 0 0.00000 1.00000 100.00
36.5 64,672 0 0.00000 1.00000 100.00
37.5 58,585 0 0.00000 1.00000 100.00
38.5 58,585 0 0.000001 1.00000 100.00
39.5 58,585 0 0.00000 1.00000 100.00
40.5 58,585 0 0.00000 1.00000 100.00
41.5 58,585 0 0.00000 1.00000 100.00
42.5 58,585 0 0.00000 1.00000 100.00
43.5 52,148 0 0.00000 1.00000 100.00
44.5 50,648 0 0.00000 1.00000 100.00
45.5 50,648 0 0.00000 1.00000 100.00
46.5 46,966 0 0.000001 1.00000 100.00
47.5 46,966 0 0.00000 1.00000 100.00
48.5 46,466 0 0.00000 1.00000 100.00
49.5 44,275 0 0.00000 1.00000 100.00
50.5 755 0 0.00000 1.00000 100.00
Totals: 0
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-19

Intermountain Gas Company
Account 366.00 - Transmission - Structures & Improvements
Placement Band - 1965 - 2024 Experience Band - 2024- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 35-R5 (RM 4.6164) — Iowa 35-R5 (RM 4.6164)
10010999999999999
80
a,o
> 60
c
U 40
v
20
0
0 10 20 30 40 50 60 70
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-20

Intermountain Gas Company
Account 366.00 - Transmission - Structures & Improvements
Placement Band - 1965 - 2024 Experience Band - 2024- 2024
RETIREMENT RATE ANALYSIS'
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 77,152 0 0.000001 1.00000 100.00
0.5 77,152 0 0.00000 1.00000 100.00
1.5 77,152 0 0.00000 1.00000 100.00
2.5 77,152 0 0.00000 1.00000 100.00
3.5 77,152 0 0.000001 1.00000 100.00
4.5 77,152 0 0.00000 1.00000 100.00
5.5 77,152 0 0.00000 1.00000 100.00
6.5 77,152 0 0.00000 1.00000 100.00
7.5 77,152 0 0.00000 1.00000 100.00
8.5 77,152 0 0.00000 1.00000 100.00
9.5 77,152 0 0.00000 1.00000 100.00
10.5 77,152 0 0.00000 1.00000 100.00
11.5 77,152 0 0.00000 1.00000 100.00
12.5 77,152 0 0.00000 1.00000 100.00
13.5 77,152 0 0.00000 1.00000 100.00
14.5 77,152 0 0.00000 1.00000 100.00
15.5 77,152 0 0.00000 1.00000 100.00
16.5 77,152 0 0.00000 1.00000 100.00
17.5 77,152 0 0.00000 1.00000 100.00
18.5 77,152 0 0.00000 1.00000 100.00
19.5 77,152 0 0.00000 1.00000 100.00
20.5 77,152 0 0.00000 1.00000 100.00
21.5 77,152 0 0.00000 1.00000 100.00
22.5 30,820 0 0.00000 1.00000 100.00
23.5 25,784 0 0.00000 1.00000 100.00
24.5 25,784 0 0.00000 1.00000 100.00
25.5 25,784 0 0.00000 1.00000 100.00
26.5 25,784 0 0.00000 1.00000 100.00
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-21

Intermountain Gas Company
Account 366.00 - Transmission - Structures & Improvements
Placement Band - 1965 - 2024 Experience Band - 2024- 2024
27.5 25,784 0 0.00000 1.00000 100.00
28.5 25,784 0 0.00000 1.00000 100.00
29.5 25,784 0 0.00000 1.00000 100.00
30.5 25,784 0 0.00000 1.00000 100.00
31.5 25,784 0 0.00000 1.00000 100.00
32.5 25,784 0 0.00000 1.00000 100.00
33.5 25,784 0 0.00000 1.00000 100.00
34.5 25,048 0 0.000001 1.00000 100.00
35.5 25,048 0 0.00000 1.00000 100.00
36.5 25,048 0 0.00000 1.00000 100.00
37.5 25,048 0 0.00000 1.00000 100.00
38.5 25,048 0 0.000001 1.00000 100.00
39.5 25,048 0 0.00000 1.00000 100.00
40.5 25,048 0 0.00000 1.00000 100.00
41.5 25,048 0 0.00000 1.00000 100.00
42.5 25,048 0 0.00000 1.00000 100.00
43.5 25,048 0 0.00000 1.00000 100.00
44.5 24,637 0 0.00000 1.00000 100.00
45.5 24,637 0 0.00000 1.00000 100.00
46.5 24,637 0 0.00000 1.00000 100.00
47.5 22,137 0 0.00000 1.00000 100.00
48.5 11,261 0 0.00000 1.00000 100.00
49.5 11,261 0 0.00000 1.00000 100.00
50.5 11,261 0 0.00000 1.00000 100.00
51.5 11,261 0 0.00000 1.00000 100.00
52.5 11,261 0 0.00000 1.00000 100.00
53.5 11,261 0 0.00000 1.00000 100.00
54.5 10,808 0 0.00000 1.00000 100.00
55.5 10,808 0 0.00000 1.00000 100.00
56.5 10,808 0 0.00000 1.000001 100.00
57.5 10,808 0 0.00000 1.00000 100.00
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-22

Intermountain Gas Company
Account 366.00 - Transmission - Structures & Improvements
Placement Band - 1965 - 2024 Experience Band - 2024- 2024
C 58.5 10,808 0 0.00000 1.00000. 100.00
Totals: 0
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-23

Intermountain Gas Company
Account 367.00 - Transmission - Mains
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 63-134 (RM 1.066) Iowa 63-R4 (RM 1.066)
100
80
a,o
> 60
c
U 40
v
20
0
0 20 40 60 80 100
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-24

Intermountain Gas Company
Account 367.00 - Transmission - Mains
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
RETIREMENT RATE ANALYSIS'
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 74,182,637 0 0.00000 1.00000 100.00
0.5 73,668,155 0 0.00000 1.00000 100.00
1.5 72,286,491 0 0.00000 1.00000 100.00
2.5 71,783,014 0 0.00000 1.00000 100.00
3.5 71,171,892 0 0.00000 1.00000 100.00
4.5 71,171,892 0 0.00000 1.00000 100.00
5.5 71,171,892 0 0.00000 1.00000 100.00
6.5 71,171,892 0 0.000001 1.00000 100.00
7.5 71,13 2,107 0 0.00000 1.00000 100.00
8.5 71,132,107 1 0.00000 1.00000 100.00
9.5 71,132,106 96 0.00000 1.00000 100.00
10.5 70,405,180 4,181 0.00006 0.99994 100.00
11.5 64,913,966 3,344 0.00005 0.99995 99.99
12.5 44,486,723 880 0.00002 0.99998 99.99
13.5 43,470,351 24,883 0.00057 0.99943 99.99
14.5 43,228,032 16,549 0.00038 0.99962 99.93
15.5 43,007,982 381,411 0.00887 0.99113 99.89
16.5 42,218,738 2,026 0.00005 0.99995 99.00
17.5 42,086,646 11,355 0.00027 0.99973 99.00
18.5 34,596,757 212,079 0.006131 0.99387 98.97
19.5 32,529,520 402,855 0.01238 0.98762 98.36
20.5 31,997,627 4,168 0.00013 0.99987 97.14
21.5 31,038,495 91 0.00000 1.00000 97.13
22.5 30,340,333 15,321 0.00050 0.99950 97.13
23.5 30,221,931 17,069 0.00056 0.99944 97.08
24.5 27,807,184 18,653 0.00067 0.99933 97.03
25.5 24,481,526 604 0.00002 0.99998 96.96
26.5 22,572,835 2,187 0.00010 0.99990 96.96
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-25

Intermountain Gas Company
Account 367.00 - Transmission - Mains
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
27.5 22,558,582 253 0.00001 0.99999 96.95
28.5 22,558,329 186 0.00001 0.99999 96.95
29.5 20,165,234 333 0.00002 0.99998 96.95
30.5 20,151,814 16,563 0.00082 0.99918 96.95
31.5 20,135,251 16,247 0.00081 0.99919 96.87
32.5 20,119,004 11,654 0.00058 0.99942 96.79
33.5 20,107,350 638 0.00003 0.99997 96.73
34.5 20,024,530 380 0.00002 0.99998 96.73
35.5 20,024,150 10,611 0.00053 0.99947 96.73
36.5 20,013,539 1,175 0.00006 0.99994 96.68
37.5 20,008,683 1,697 0.00008 0.99992 96.67
38.5 20,006,986 7,368 0.000371 0.99963 96.66
39.5 19,982,110 14,996 0.00075 0.99925 96.62
40.5 19,962,101 3,674 0.00018 0.99982 96.55
41.5 19,953,634 10,720 0.00054 0.99946 96.53
42.5 19,929,035 19,633 0.00099 0.99901 96.48
43.5 19,909,402 19,921 0.00100 0.99900 96.38
44.5 19,236,603 10,415 0.00054 0.99946 96.28
45.5 19,226,188 6,230 0.00032 0.99968 96.23
46.5 19,074,501 22,914 0.00120 0.99880 96.20
47.5 19,051,587 65,922 0.00346 0.99654 96.08
48.5 18,756,128 48,552 0.00259 0.99741 95.75
49.5 17,947,085 16,162 0.00090 0.99910 95.50
50.5 15,240,905 5,415 0.00036 0.99964 95.41
51.5 15,225,534 14,672 0.000961 0.99904 95.38
52.5 14,783,398 10,150 0.00069 0.99931 95.29
53.5 14,773,248 221,609 0.01500 0.98500 95.22
54.5 14,362,648 24,550 0.00171 0.99829 93.79
55.5 14,263,640 37 0.00000 1.00000 93.63
56.5 14,231,082 19 0.00000 1.00000 93.63
57.5 14,215,679 0 0.00000 1.00000 93.63
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-26

Intermountain Gas Company
Account 367.00 - Transmission - Mains
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
58.5 13,763,525 0 0.00000 1.00000 93.63
59.5 9,652,549 0 0.00000 1.00000 93.63
60.5 8,034,905 0 0.00000 1.00000 93.63
61.5 7,433,510 0 0.00000 1.00000 93.63
62.5 6,710,863 0 0.00000 1.00000 93.63
63.5 6,649,666 35,348 0.00532 0.99468 93.63
64.5 6,614,318 0 0.00000 1.00000 93.13
Totals: 1,735,797
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-27

Intermountain Gas Company
Account 368.00 - Transmission - Compressor Station
Placement Band - 1974- 2024 Experience Band - 2016- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 20-1-1.5 (RM 0.7506) — Iowa 20-1-1.5 (RM 0.7506)
100 ■ ■
■ ■
80 ■■
a,o
> 60
c
U 40
v
■■■■■■■■■■ ■■■
20
gas■■
0
0 10 20 30 40 50 60 70
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-28

Intermountain Gas Company
Account 368.00 - Transmission - Compressor Station
Placement Band - 1974- 2024 Experience Band - 2016- 2024
RETIREMENT RATE ANALYSIS
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 11,283,534 348 0.000031 0.99997 100.00
0.5 11,203,534 6 0.00000 1.00000 100.00
1.5 3,699,922 9 0.00000 1.00000 100.00
2.5 3,699,913 102 0.00003 0.99997 100.00
3.5 3,688,785 0 0.00000 1.00000 100.00
4.5 3,680,941 43,993 0.01195 0.98805 100.00
5.5 3,636,948 17 0.00000 1.00000 98.80
6.5 3,636,931 45,895 0.01262 0.98738 98.80
7.5 3,591,036 523,826 0.14587 0.85413 97.55
8.5 3,067,210 328 0.00011 0.99989 83.32
9.5 3,066,882 32,337 0.01054 0.98946 83.31
10.5 3,034,545 2,881 0.00095 0.99905 82.43
11.5 3,031,664 20,369 0.00672 0.99328 82.35
12.5 3,007,679 107,700 0.03581 0.96419 81.80
13.5 1,305,790 11,210 0.00858 0.99142 78.87
14.5 1,294,580 1,025 0.00079 0.99921 78.19
15.5 1,293,555 888,354 0.68675 0.31325 78.13
16.5 405,201 21,141 0.05217 0.94783 24.47
17.5 384,060 445 0.00116 0.99884 23.19
18.5 383,615 0 0.00000 1.00000 23.16
19.5 383,615 0 0.000001 1.00000 23.16
20.5 383,615 0 0.00000 1.00000 23.16
21.5 383,615 12 0.00003 0.99997 23.16
22.5 383,603 0 0.00000 1.00000 23.16
23.5 383,603 45 0.00012 0.99988 23.16
24.5 383,558 202 0.00053 0.99947 23.16
25.5 383,356 1,964 0.00512 0.99488 23.15
26.5 381,392 6,281 0.01647 0.98353 23.03
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-29

Intermountain Gas Company
Account 368.00 - Transmission - Compressor Station
Placement Band - 1974- 2024 Experience Band - 2016- 2024
27.5 375,111 0 0.00000 1.00000 22.65
28.5 375,111 1,082 0.00288 0.99712 22.65
29.5 374,029 4,068 0.01088 0.98912 22.58
30.5 369,961 32,411 0.08761 0.91239 22.33
31.5 337,550 78,051 0.23123 0.76877 20.37
32.5 259,499 379 0.00146 0.99854 15.66
33.5 259,120 3,143 0.01213 0.98787 15.64
34.5 255,977 9,030 0.035281 0.96472 15.45
35.5 246,947 0 0.000001 1.00000 14.90
36.5 246,947 68,038 0.27552 0.72448 14.90
37.5 178,909 1,495 0.008361 0.99164 10.79
38.5 177,414 10,618 0.05985 0.94015 10.70
39.5 166,796 26,224 0.15722 0.84278 10.06
40.5 140,572 0 0.00000 1.00000 8.48
41.51 140,572 140,572 1.00000 8.48
Totals: 2,083,601
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-30

Intermountain Gas Company
Account 374.00 - Distribution - Land Rights
Placement Band - 1959 - 2024 Experience Band - 2019- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 56-R5 (RM 2.2531) Iowa 65-R5 (RM 0.9003)
100
80
a10
> 60
c
U 40
v
20
0
0 10 20 30 40 50 60 70 80 90 100
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-31

Intermountain Gas Company
Account 374.00 - Distribution - Land Rights
Placement Band - 1959 - 2024 Experience Band - 2019- 2024
RETIREMENT RATE ANALYSIF
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 1,488,663 0 0.000001 1.00000 100.00
0.5 1,483,665 0 0.00000 1.00000 100.00
1.5 1,346,934 0 0.00000 1.00000 100.00
2.5 1,281,646 0 0.00000 1.00000 100.00
3.5 1,281,646 0 0.000001 1.00000 100.00
4.5 1,248,251 0 0.00000 1.00000 100.00
5.5 1,217,128 0 0.00000 1.00000 100.00
6.5 658,112 0 0.00000 1.00000 100.00
7.5 646,118 0 0.00000 1.00000 100.00
8.5 627,445 0 0.00000 1.00000 100.00
9.5 436,345 0 0.00000 1.00000 100.00
10.5 427,359 0 0.00000 1.00000 100.00
11.5 417,277 0 0.00000 1.00000 100.00
12.5 407,749 0 0.00000 1.00000 100.00
13.5 407,749 0 0.00000 1.00000 100.00
14.5 387,889 0 0.00000 1.00000 100.00
15.5 383,678 0 0.00000 1.00000 100.00
16.5 376,467 0 0.00000 1.00000 100.00
17.5 346,440 0 0.00000 1.00000 100.00
18.5 346,092 0 0.00000 1.00000 100.00
19.5 331,793 0 0.00000 1.00000 100.00
20.5 329,568 0 0.00000 1.00000 100.00
21.5 295,280 0 0.00000 1.00000 100.00
22.5 278,045 0 0.00000 1.00000 100.00
23.5 274,228 0 0.00000 1.00000 100.00
24.5 272,955 0 0.00000 1.00000 100.00
25.5 266,762 0 0.00000 1.00000 100.00
26.5 255,597 0 0.00000 1.00000 100.00
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-32

Intermountain Gas Company
Account 374.00 - Distribution - Land Rights
Placement Band - 1959 - 2024 Experience Band - 2019- 2024
27.5 245,074 0 0.00000 1.00000 100.00
28.5 242,042 0 0.00000 1.00000 100.00
29.5 224,911 0 0.00000 1.00000 100.00
30.5 222,399 0 0.00000 1.00000 100.00
31.5 214,897 0 0.00000 1.00000 100.00
32.5 210,361 0 0.00000 1.00000 100.00
33.5 208,745 0 0.00000 1.00000 100.00
34.5 206,245 0 0.000001 1.00000 100.00
35.5 206,245 0 0.00000 1.00000 100.00
36.5 206,245 0 0.00000 1.00000 100.00
37.5 206,245 0 0.00000 1.00000 100.00
38.5 206,245 0 0.000001 1.00000 100.00
39.5 204,282 0 0.00000 1.00000 100.00
40.5 204,282 0 0.00000 1.00000 100.00
41.5 204,282 0 0.00000 1.00000 100.00
42.5 204,282 0 0.00000 1.00000 100.00
43.5 199,010 0 0.00000 1.00000 100.00
44.5 197,596 0 0.00000 1.00000 100.00
45.5 195,340 0 0.00000 1.00000 100.00
46.5 192,990 0 0.00000 1.00000 100.00
47.5 192,990 0 0.00000 1.00000 100.00
48.5 191,490 0 0.00000 1.00000 100.00
49.5 191,490 0 0.00000 1.00000 100.00
50.5 183,760 0 0.00000 1.00000 100.00
51.5 182,275 0 0.00000 1.00000 100.00
52.5 179,165 0 0.00000 1.00000 100.00
53.5 177,298 0 0.00000 1.00000 100.00
54.5 176,661 0 0.00000 1.00000 100.00
55.5 176,201 0 0.00000 1.00000 100.00
56.5 176,051 25 0.00014 0.99986 100.00
57.5 175,626 0 0.00000 1.00000 99.99
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-33

Intermountain Gas Company
Account 374.00 - Distribution - Land Rights
Placement Band - 1959 - 2024 Experience Band - 2019- 2024
58.5 174,129 0 0.00000 1.00000 99.99
59.5 142,937 4,390 0.03071 0.96929 99.99
60.5 131,000 0 0.00000 1.00000 96.92
61.5 126,905 0 0.00000 1.00000 96.92
62.5 122,062 0 0.00000 1.00000 96.92
63.5 119,896 0 0.00000 1.00000 96.92
64.5 115,055 0 0.00000 1.00000 96.92
Totals: 4,415
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-34

Intermountain Gas Company
Account 375.00 - Distribution - Structures & Improvements
Placement Band - 1962 - 2024 Experience Band - 2024- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 53-R5 (RM 2.3264) — Iowa 55-R4 (RM 1.8759)
100
80
a,o
> 60
c
U 40
v
20
0
0 10 20 30 40 50 60 70 80 90
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-35

Intermountain Gas Company
Account 375.00 - Distribution - Structures & Improvements
Placement Band - 1962 - 2024 Experience Band - 2024- 2024
RETIREMENT RATE ANALYSIS'
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 312,350 0 0.000001 1.00000 100.00
0.5 189,959 0 0.00000 1.00000 100.00
1.5 189,959 0 0.00000 1.00000 100.00
2.5 18,864 0 0.00000 1.00000 100.00
3.5 18,864 0 0.000001 1.00000 100.00
4.5 18,864 0 0.00000 1.00000 100.00
5.5 18,864 0 0.00000 1.00000 100.00
6.5 18,864 0 0.00000 1.00000 100.00
7.5 18,864 0 0.00000 1.00000 100.00
8.5 18,864 0 0.00000 1.00000 100.00
9.5 18,864 0 0.00000 1.00000 100.00
10.5 18,864 0 0.00000 1.00000 100.00
11.5 18,864 0 0.00000 1.00000 100.00
12.5 18,864 0 0.00000 1.00000 100.00
13.5 18,864 0 0.00000 1.00000 100.00
14.5 18,864 0 0.00000 1.00000 100.00
15.5 18,864 0 0.00000 1.00000 100.00
16.5 18,864 0 0.00000 1.00000 100.00
17.5 18,864 0 0.00000 1.00000 100.00
18.5 18,864 0 0.00000 1.00000 100.00
19.5 18,864 0 0.00000 1.00000 100.00
20.5 18,864 0 0.00000 1.00000 100.00
21.5 18,864 0 0.00000 1.00000 100.00
22.5 18,864 0 0.00000 1.00000 100.00
23.5 18,864 0 0.00000 1.00000 100.00
24.5 18,864 0 0.00000 1.00000 100.00
25.5 18,864 0 0.00000 1.00000 100.00
26.5 18,864 0 0.00000 1.00000 100.00
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-36

Intermountain Gas Company
Account 375.00 - Distribution - Structures & Improvements
Placement Band - 1962 - 2024 Experience Band - 2024- 2024
27.5 18,864 0 0.00000 1.00000 100.00
28.5 18,864 0 0.00000 1.00000 100.00
29.5 18,864 0 0.00000 1.00000 100.00
30.5 18,864 0 0.00000 1.00000 100.00
31.5 18,864 0 0.00000 1.00000 100.00
32.5 18,864 0 0.00000 1.00000 100.00
33.5 18,864 0 0.00000 1.00000 100.00
34.5 18,864 0 0.000001 1.00000 100.00
35.5 18,864 0 0.000001 1.00000 100.00
36.5 18,864 0 0.00000 1.00000 100.00
37.5 18,864 0 0.00000 1.00000 100.00
38.5 18,864 0 0.000001 1.00000 100.00
39.5 18,864 0 0.00000 1.00000 100.00
40.5 18,864 0 0.00000 1.00000 100.00
41.5 18,864 0 0.00000 1.00000 100.00
42.5 18,864 0 0.00000 1.00000 100.00
43.5 18,864 0 0.00000 1.00000 100.00
44.5 18,864 0 0.00000 1.00000 100.00
45.5 18,864 0 0.00000 1.00000 100.00
46.5 18,864 0 0.00000 1.00000 100.00
47.5 18,864 0 0.00000 1.00000 100.00
48.5 18,864 0 0.00000 1.00000 100.00
49.5 18,864 0 0.00000 1.00000 100.00
50.5 18,864 0 0.00000 1.00000 100.00
51.5 18,864 0 0.00000 1.00000 100.00
52.5 18,864 0 0.00000 1.00000 100.00
53.5 18,864 0 0.00000 1.00000 100.00
54.5 18,864 0 0.00000 1.00000 100.00
55.5 18,017 0 0.00000 1.00000 100.00
56.5 12,094 0 0.00000 1.00000 100.00
57.5 6,581 0 0.00000 1.00000 100.00
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-37

Intermountain Gas Company
Account 375.00 - Distribution - Structures & Improvements
Placement Band - 1962 - 2024 Experience Band - 2024- 2024
58.5 6,581 0 0.00000 1.00000 100.00
59.5 6,581 0 0.00000 1.00000 100.00
60.5 6,581 0 0.00000 1.00000 100.00
61.5 6,581 0 0.00000 1.00000 100.00
Totals: 0
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-38

Intermountain Gas Company
Account 376.00 - Distribution - Mains
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 70-133.5 (RM 0.1833) Iowa 70-R4 (RM 0.1483)
100
80
a,o
> 60
c
U 40
v
20
0
0 20 40 60 80 100 120
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-39

Intermountain Gas Company
Account 376.00 - Distribution - Mains
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
RETIREMENT RATE ANALYSIS'
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 341,138,991 12,678 0.000041 0.99996 100.00
0.5 313,751,738 210,674 0.00067 0.99933 100.00
1.5 282,299,378 118,271 0.00042 0.99958 99.93
2.5 255,678,362 237,999 0.00093 0.99907 99.89
3.5 239,083,897 224,999 0.00094 0.99906 99.80
4.5 218,063,185 91,418 0.00042 0.99958 99.71
5.5 199,290,089 114,678 0.00058 0.99942 99.67
6.5 186,195,759 93,490 0.00050 0.99950 99.61
7.5 175,602,983 20,435 0.00012 0.99988 99.56
8.5 165,753,145 34,673 0.000211 0.99979 99.55
9.5 157,348,410 43,796 0.00028 0.99972 99.53
10.5 151,208,962 55,547 0.00037 0.99963 99.50
11.5 146,775,382 72,319 0.00049 0.99951 99.46
12.5 143,134,157 63,277 0.00044 0.99956 99.41
13.5 140,800,771 103,013 0.00073 0.99927 99.37
14.5 139,944,872 87,123 0.00062 0.99938 99.30
15.5 137,919,253 84,710 0.00061 0.99939 99.24
16.5 132,196,832 72,361 0.000551 0.99945 99.18
17.5 124,017,613 81,419 0.00066 0.99934 99.13
18.5 117,909,493 82,682 0.00070 0.99930 99.06
19.5 113,095,348 74,505 0.00066 0.99934 98.99
20.5 109,189,797 112,790 0.00103 0.99897 98.92
21.5 105,157,061 73,934 0.00070 0.99930 98.82
22.5 101,696,223 101,518 0.00100 0.99900 98.75
23.5 98,448,265 85,381 0.00087 0.99913 98.65
24.5 93,997,487 142,265 0.00151 0.99849 98.56
25.5 86,551,799 114,385 0.00132 0.99868 98.41
26.5 82,952,213 169,479 0.00204 0.99796 98.28
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-40

Intermountain Gas Company
Account 376.00 - Distribution - Mains
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
27.5 77,073,690 112,948 0.00147 0.99853 98.08
28.5 72,525,562 177,803 0.00245 0.99755 97.94
29.5 68,252,261 149,966 0.00220 0.99780 97.70
30.5 63,777,570 137,520 0.00216 0.99784 97.49
31.5 59,893,908 116,004 0.00194 0.99806 97.28
32.5 55,925,482 124,420 0.00222 0.99778 97.09
33.5 53,459,309 109,244 0.00204 0.99796 96.87
34.5 50,811,246 162,393 0.003201 0.99680 96.67
35.5 49,456,188 160,608 0.003251 0.99675 96.36
36.5 48,391,007 163,214 0.00337 0.99663 96.05
37.5 47,095,339 141,539 0.00301 0.99699 95.73
38.5 45,782,034 166,311 0.003631 0.99637 95.44
39.5 44,265,117 180,646 0.00408 0.99592 95.09
40.5 42,849,791 215,490 0.00503 0.99497 94.70
41.5 41,726,534 222,336 0.00533 0.99467 94.22
42.5 40,555,701 196,752 0.00485 0.99515 93.72
43.5 38,897,294 202,656 0.00521 0.99479 93.27
44.5 37,425,189 205,718 0.00550 0.99450 92.78
45.5 35,935,329 250,691 0.00698 0.99302 92.27
46.5 33,989,885 257,376 0.007571 0.99243 91.63
47.5 32,487,715 299,311 0.00921 0.99079 90.94
48.5 31,265,758 236,098 0.00755 0.99245 90.10
49.5 30,059,337 233,162 0.00776 0.99224 89.42
50.5 28,601,697 242,120 0.00847 0.99153 88.73
51.5 26,778,819 264,421 0.00987 0.99013 87.98
52.5 24,812,246 341,190 0.01375 0.98625 87.11
53.5 23,629,886 477,280 0.02020 0.97980 85.91
54.5 22,583,617 504,467 0.022341 0.97766 84.17
55.5 21,595,466 275,200 0.01274 0.98726 82.29
56.5 21,060,392 245,695 0.01167 0.98833 81.24
57.5 20,499,222 170,648 0.00832 0.99168 80.29
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-41

Intermountain Gas Company
Account 376.00 - Distribution - Mains
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
58.5 19,329,365 155,943 0.00807 0.99193 79.62
59.5 16,339,186 53,050 0.00325 0.99675 78.98
60.5 14,861,181 108,342 0.00729 0.99271 78.72
61.5 13,338,192 38,930 0.00292 0.99708 78.15
62.5 11,863,051 33,249 0.00280 0.99720 77.92
63.5 10,602,545 65,702 0.00620 0.99380 77.70
64.5 9,212,706 17,932 0.00195 0.99805 77.22
Totals: 9,996,194
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-42

Intermountain Gas Company
Account 378.00 - Distribution - Measure & Reg Station Equip. - General
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 43-131.5 (RM 0.5595) Iowa 45-SO (RM 0.5615)
100
IL
80
a,o
> 60
+j Nc
U 40
v
20
0
0 10 20 30 40 50 60 70 80 90 100
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-43

Intermountain Gas Company
Account 378.00 - Distribution - Measure & Reg Station Equip. - General
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
RETIREMENT RATE ANALYSIS'
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 17,291,580 14,582 0.000841 0.99916 100.00
0.5 16,405,756 82,798 0.00505 0.99495 99.92
1.5 15,709,462 31,688 0.00202 0.99798 99.42
2.5 15,307,677 24,165 0.00158 0.99842 99.22
3.5 14,704,576 30,033 0.00204 0.99796 99.06
4.5 14,108,181 40,470 0.00287 0.99713 98.86
5.5 13,040,016 65,282 0.00501 0.99499 98.58
6.5 11,809,156 54,193 0.00459 0.99541 98.09
7.5 10,651,265 72,766 0.00683 0.99317 97.64
8.5 9,524,476 21,627 0.002271 0.99773 96.97
9.5 9,026,298 20,376 0.00226 0.99774 96.75
10.5 7,819,214 21,798 0.00279 0.99721 96.53
11.5 7,162,300 37,393 0.00522 0.99478 96.26
12.5 5,273,413 39,528 0.00750 0.99250 95.76
13.5 5,066,515 47,752 0.00943 0.99057 95.04
14.5 4,987,007 165,725 0.03323 0.96677 94.14
15.5 4,409,191 103,445 0.02346 0.97654 91.01
16.5 3,900,260 124,888 0.032021 0.96798 88.87
17.5 3,645,413 181,388 0.04976 0.95024 86.02
18.5 3,464,026 81,398 0.02350 0.97650 81.74
19.5 3,194,431 35,178 0.01101 0.98899 79.82
20.5 3,159,253 52,715 0.01669 0.98331 78.94
21.5 3,075,758 27,211 0.00885 0.99115 77.62
22.5 3,001,635 46,409 0.01546 0.98454 76.93
23.5 2,955,226 60,269 0.02039 0.97961 75.74
24.5 2,838,702 72,844 0.02566 0.97434 74.20
25.5 2,480,432 39,834 0.01606 0.98394 72.30
26.5 2,189,250 105,734 0.04830 0.95170 71.14
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-44

Intermountain Gas Company
Account 378.00 - Distribution - Measure & Reg Station Equip. - General
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
27.5 1,948,705 27,194 0.01395 0.98605 67.70
28.5 1,902,994 42,805 0.02249 0.97751 66.76
29.5 1,808,666 22,979 0.01270 0.98730 65.26
30.5 1,784,808 26,604 0.01491 0.98509 64.43
31.5 1,698,435 51,062 0.03006 0.96994 63.47
32.5 1,645,955 61,721 0.03750 0.96250 61.56
33.5 1,543,672 51,205 0.03317 0.96683 59.25
34.5 1,444,174 36,637 0.025371 0.97463 57.28
35.5 1,370,883 29,969 0.02186 0.97814 55.83
36.5 1,307,242 31,566 0.02415 0.97585 54.61
37.5 1,275,675 27,816 0.02180 0.97820 53.29
38.5 1,214,674 30,531 0.02514 0.97486 52.13
39.5 1,184,143 26,490 0.02237 0.97763 50.82
40.5 1,144,710 60,938 0.05323 0.94677 49.68
41.5 1,066,565 31,625 0.02965 0.97035 47.04
42.5 1,007,600 29,510 0.02929 0.97071 45.65
43.5 861,860 24,393 0.02830 0.97170 44.31
44.5 814,287 46,150 0.05668 0.94332 43.06
45.5 762,920 23,446 0.03073 0.96927 40.62
46.5 734,523 27,481 0.03741 0.96259 39.37
47.5 688,443 50,489 0.07334 0.92666 37.90
48.5 637,954 30,861 0.04837 0.95163 35.12
49.5 544,227 63,212 0.11615 0.88385 33.42
50.5 467,332 22,233 0.04757 0.95243 29.54
51.5 417,144 15,310 0.03670 0.96330 28.13
52.5 365,333 25,644 0.07019 0.92981 27.10
53.5 339,689 7,462 0.02197 0.97803 25.20
54.5 323,814 10,444 0.03225 0.96775 24.65
55.5 313,370 27,642 0.08821 0.91179 23.86
56.5 285,595 2,446 0.00856 0.99144 21.76
57.5 283,149 5,506 0.01945 0.98055 21.57
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-45

Intermountain Gas Company
Account 378.00 - Distribution - Measure & Reg Station Equip. - General
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
58.5 219,841 6,470 0.02943 0.97057 21.15
59.5 173,675 6,935 0.03993 0.96007 20.53
60.5 166,739 2,773 0.01663 0.98337 19.71
61.5 163,966 9,882 0.06027 0.93973 19.38
62.5 154,085 0 0.00000 1.00000 18.21
63.5 142,629 6,637 0.04653 0.95347 18.21
64.5 132,695 4,964 0.03741 0.96259 17.36
Totals: 2,710,521
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-46

Intermountain Gas Company
Account 379.00 - Distribution - Measure & Reg Station Equip. - City Gate
Placement Band - 2023 - 2024 Experience Band - 2024- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 45-SO (RM 0.0017)
100
80
a,o
> 60
c
U 40
v
20
0
0 10 20 30 40 50 60 70 80 90 100
Age (Years)
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Page 1 6-47

Intermountain Gas Company
Account 379.00 - Distribution - Measure & Reg Station Equip. - City Gate
Placement Band - 2023 - 2024 Experience Band - 2024- 2024
RETIREMENT RATE ANALYSIS'
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 1,701,211 0 0.00000 1.000001 100.00
0.5 1,667,816 0 0.00000 1.00000 100.00
Totals: 0
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-48

Intermountain Gas Company
Account 380.00 - Distribution - Services
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 58-R3 (RM 0.6102) Iowa 58-R3 (RM 0.6102)
100
80
a,o
> 60
c
U 40
v
20
0
0 20 40 60 80 100
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-49

Intermountain Gas Company
Account 380.00 - Distribution - Services
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
RETIREMENT RATE ANALYSIF
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 268,774,349 11,954 0.000041 0.99996 100.00
0.5 250,470,809 31,779 0.00013 0.99987 100.00
1.5 234,361,131 63,132 0.00027 0.99973 99.99
2.5 218,989,655 67,953 0.00031 0.99969 99.96
3.5 205,190,614 88,352 0.00043 0.99957 99.93
4.5 192,087,085 64,848 0.00034 0.99966 99.89
5.5 180,810,817 75,578 0.00042 0.99958 99.86
6.5 170,925,319 83,277 0.00049 0.99951 99.82
7.5 162,660,145 51,017 0.00031 0.99969 99.77
8.5 154,836,159 97,083 0.000631 0.99937 99.74
9.5 149,011,340 126,892 0.00085 0.99915 99.68
10.5 141,664,769 141,975 0.00100 0.99900 99.60
11.5 138,503,038 163,960 0.00118 0.99882 99.50
12.5 135,392,054 193,270 0.001431 0.99857 99.38
13.5 132,991,795 198,478 0.00149 0.99851 99.24
14.5 130,879,897 217,666 0.00166 0.99834 99.09
15.5 128,476,489 223,532 0.00174 0.99826 98.93
16.5 123,272,002 250,920 0.002041 0.99796 98.76
17.5 116,846,952 279,349 0.00239 0.99761 98.56
18.5 110,342,362 285,895 0.00259 0.99741 98.32
19.5 104,118,945 263,903 0.00253 0.99747 98.07
20.5 98,662,714 266,893 0.00271 0.99729 97.82
21.5 93,285,386 291,266 0.00312 0.99688 97.55
22.5 88,564,829 311,126 0.00351 0.99649 97.25
23.5 83,697,766 336,332 0.00402 0.99598 96.91
24.5 78,051,640 365,185 0.00468 0.99532 96.52
25.5 72,235,875 399,469 0.00553 0.99447 96.07
26.5 66,685,003 346,029 0.00519 0.99481 95.54
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-50

Intermountain Gas Company
Account 380.00 - Distribution - Services
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
27.5 61,591,715 337,825 0.00548 0.99452 95.04
28.5 56,613,572 300,341 0.00531 0.99469 94.52
29.5 52,119,834 280,773 0.00539 0.99461 94.02
30.5 47,101,529 266,909 0.00567 0.99433 93.51
31.5 42,189,036 250,689 0.00594 0.99406 92.98
32.5 38,374,478 256,686 0.00669 0.99331 92.43
33.5 34,999,035 250,703 0.00716 0.99284 91.81
34.5 32,332,954 266,159 0.008231 0.99177 91.15
35.5 30,196,594 263,538 0.00873 0.99127 90.40
36.5 28,464,893 250,398 0.00880 0.99120 89.61
37.5 26,805,765 256,441 0.00957 0.99043 88.82
38.5 25,082,985 245,873 0.009801 0.99020 87.97
39.5 23,385,316 263,029 0.01125 0.98875 87.11
40.5 21,860,154 269,287 0.01232 0.98768 86.13
41.5 20,522,227 255,959 0.01247 0.98753 85.07
42.5 19,451,171 255,383 0.01313 0.98687 84.01
43.5 18,497,507 263,468 0.01424 0.98576 82.91
44.5 17,496,609 253,322 0.01448 0.98552 81.73
45.5 16,514,189 258,231 0.01564 0.98436 80.55
46.5 15,786,775 236,350 0.014971 0.98503 79.29
47.5 15,207,469 250,188 0.01645 0.98355 78.10
48.5 14,564,114 202,515 0.01391 0.98609 76.82
49.5 13,757,417 166,902 0.01213 0.98787 75.75
50.5 12,928,846 146,394 0.01132 0.98868 74.83
51.5 12,005,741 137,355 0.01144 0.98856 73.98
52.5 11,066,635 127,757 0.01154 0.98846 73.13
53.5 10,233,670 105,797 0.01034 0.98966 72.29
54.5 9,535,400 113,399 0.011891 0.98811 71.54
55.5 8,958,546 112,724 0.01258 0.98742 70.69
56.5 8,540,280 111,885 0.01310 0.98690 69.80
57.5 7,744,267 70,039 0.00904 0.99096 68.89
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-51

Intermountain Gas Company
Account 380.00 - Distribution - Services
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
58.5 6,829,286 110,201 0.01614 0.98386 68.27
59.5 5,830,469 59,348 0.01018 0.98982 67.17
60.5 5,037,508 31,341 0.00622 0.99378 66.49
61.5 4,334,678 37,255 0.00859 0.99141 66.08
62.5 3,685,081 21,188 0.00575 0.99425 65.51
63.5 3,179,806 14,579 0.00458 0.99542 65.13
64.5 2,746,062 5,754 0.00210 0.99790 64.83
Totals: 12,403,098
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-52

Intermountain Gas Company
Account 381.00 - Distribution - Meters
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 48-R3 (RM 1.2291) — Iowa 40-R3 (RM 2.4904)
100
■ammas,
80
■
a,o �
■
> 60
c
U 40
v ■
■
20
0
0 10 20 30 40 50 60 70 80 90
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-53

Intermountain Gas Company
Account 381.00 - Distribution - Meters
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
RETIREMENT RATE ANALYSIS'
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 79,014,648 5,072 0.000061 0.99994 100.00
0.5 70,770,884 113,856 0.00161 0.99839 99.99
1.5 61,547,449 92,257 0.00150 0.99850 99.83
2.5 53,639,473 61,274 0.00114 0.99886 99.68
3.5 47,772,054 26,334 0.00055 0.99945 99.57
4.5 42,173,389 3,476 0.00008 0.99992 99.52
5.5 42,169,914 4,579 0.00011 0.99989 99.51
6.5 39,664,637 5,011 0.00013 0.99987 99.50
7.5 38,372,594 9,740 0.00025 0.99975 99.49
8.5 36,825,128 10,668 0.000291 0.99971 99.47
9.5 34,879,715 13,723 0.00039 0.99961 99.44
10.5 33,852,472 18,630 0.00055 0.99945 99.40
11.5 31,040,835 22,025 0.00071 0.99929 99.35
12.5 30,572,879 27,848 0.00091 0.99909 99.28
13.5 30,234,139 28,818 0.00095 0.99905 99.19
14.5 29,544,956 48,906 0.00166 0.99834 99.10
15.5 29,208,194 47,534 0.00163 0.99837 98.94
16.5 28,120,027 48,215 0.001711 0.99829 98.78
17.5 26,591,572 58,348 0.00219 0.99781 98.61
18.5 24,863,793 77,999 0.00314 0.99686 98.39
19.5 23,257,949 66,457 0.00286 0.99714 98.08
20.5 22,167,689 69,177 0.00312 0.99688 97.80
21.5 21,211,588 121,451 0.00573 0.99427 97.49
22.5 20,250,939 124,565 0.00615 0.99385 96.93
23.5 19,272,394 76,464 0.00397 0.99603 96.33
24.5 18,320,938 67,297 0.00367 0.99633 95.95
25.5 16,956,341 81,453 0.00480 0.99520 95.60
26.5 15,640,597 64,617 0.00413 0.99587 95.14
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-54

Intermountain Gas Company
Account 381.00 - Distribution - Meters
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
27.5 14,259,570 62,309 0.00437 0.99563 94.75
28.5 13,001,199 53,419 0.00411 0.99589 94.34
29.5 11,676,768 50,855 0.00436 0.99564 93.95
30.5 10,293,267 62,400 0.00606 0.99394 93.54
31.5 9,307,963 39,773 0.00427 0.99573 92.97
32.5 8,442,275 34,782 0.00412 0.99588 92.57
33.5 7,700,971 38,621 0.00502 0.99498 92.19
34.5 7,198,982 28,831 0.004001 0.99600 91.73
35.5 7,040,402 43,532 0.006181 0.99382 91.36
36.5 6,740,402 41,337 0.00613 0.99387 90.80
37.5 6,487,530 41,978 0.00647 0.99353 90.24
38.5 6,191,203 39,175 0.006331 0.99367 89.66
39.5 5,963,557 40,150 0.00673 0.99327 89.09
40.5 5,801,083 54,430 0.00938 0.99062 88.49
41.5 5,695,705 49,439 0.00868 0.99132 87.66
42.5 5,355,527 51,930 0.009701 0.99030 86.90
43.5 5,133,297 70,031 0.01364 0.98636 86.06
44.5 4,905,245 74,732 0.01524 0.98476 84.89
45.5 4,749,264 79,675 0.01678 0.98322 83.60
46.5 4,593,118 91,343 0.01989 0.98011 82.20
47.5 4,461,618 94,792 0.02125 0.97875 80.57
48.5 4,320,567 111,674 0.02585 0.97415 78.86
49.5 4,062,927 114,162 0.02810 0.97190 76.82
50.5 3,709,099 139,264 0.03755 0.96245 74.66
51.5 3,305,827 152,647 0.04618 0.95382 71.86
52.5 2,893,696 121,918 0.04213 0.95787 68.54
53.5 2,561,645 139,302 0.05438 0.94562 65.65
54.5 2,267,845 103,117 0.04547 0.95453 62.08
55.5 2,082,321 115,234 0.05534 0.94466 59.26
56.5 1,924,614 117,189 0.06089 0.93911 55.98
57.5 1,674,674 77,247 0.04613 0.95387 52.57
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-55

Intermountain Gas Company
Account 381.00 - Distribution - Meters
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
58.5 1,398,243 198,049 0.14164 0.85836 50.14
59.5 1,035,327 83,661 0.08081 0.91919 43.04
60.5 825,960 41,483 0.05022 0.94978 39.56
61.5 680,564 56,454 0.08295 0.91705 37.57
62.5 504,271 59,504 0.11800 0.88200 34.45
63.5 387,489 46,578 0.12020 0.87980 30.38
64.5 320,882 37,963 0.11831 0.88169 26.73
Totals: 4,254,774
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-56

Intermountain Gas Company
Account 381.20 - Distribution - ERT Units
Placement Band - 2002 - 2024 Experience Band - 2016- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 15-R3 (RM 1.1442) — Iowa 15-R3 (RM 1.1442)
100110
80
■
a,o
> 60
c
U 40
v
■
20
■ ■ ■ ■ ■
0
0 10 20 30 40
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-57

Intermountain Gas Company
Account 381.20 - Distribution - ERT Units
Placement Band - 2002 - 2024 Experience Band - 2016- 2024
RETIREMENT RATE ANALYSIS'
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 50,374,167 139 0.000001 1.00000 100.00
0.5 48,732,490 5,513 0.00011 0.99989 100.00
1.5 47,468,360 132,775 0.00280 0.99720 99.99
2.5 46,167,450 270,578 0.00586 0.99414 99.71
3.5 45,507,266 1,126,035 0.02474 0.97526 99.13
4.5 43,285,304 304,968 0.00705 0.99295 96.68
5.5 42,980,337 341,762 0.00795 0.99205 96.00
6.5 40,279,479 465,547 0.01156 0.98844 95.24
7.5 39,483,955 465,658 0.011791 0.98821 94.14
8.5 32,782,546 944,566 0.02881 0.97119 93.03
9.5 24,449,538 1,117,275 0.04570 0.95430 90.35
10.5 17,008,588 2,055,518 0.12085 0.87915 86.22
11.5 14,953,070 9,301,990 0.62208 0.37792 75.80
12.5 5,651,081 4,671,769 0.82670 0.17330 28.65
13.5 979,312 246,637 0.25185 0.74815 4.97
14.5 732,674 9,566 0.01306 0.98694 3.72
15.5 723,108 4,095 0.00566 0.99434 3.67
16.5 623,027 11,690 0.01876 0.98124 3.65
17.5 0 0 0.00000 0.00000 3.58
Totals: 21,476,081
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-58

Intermountain Gas Company
Account 383.00 - Distribution - Regulators
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 50-R3 (RM 1.9379) — Iowa 50-R3 (RM 1.9379)
100 Imommoom
80 mamma
■
> 60
c
U 40
v
20
0
0 10 20 30 40 50 60 70 80 90
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-59

Intermountain Gas Company
Account 383.00 - Distribution - Regulators
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
RETIREMENT RATE ANALYSIF
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 21,272,051 1,230 0.000061 0.99994 100.00
0.5 20,470,998 158,412 0.00774 0.99226 99.99
1.5 19,728,130 135,827 0.00688 0.99312 99.22
2.5 19,132,781 24,860 0.00130 0.99870 98.54
3.5 18,806,554 1,839 0.00010 0.99990 98.41
4.5 18,307,705 2,135 0.00012 0.99988 98.40
5.5 18,305,570 1,934 0.00011 0.99989 98.39
6.5 16,190,499 2,234 0.00014 0.99986 98.38
7.5 16,105,491 3,104 0.00019 0.99981 98.37
8.5 15,027,051 3,056 0.000201 0.99980 98.35
9.5 14,205,324 3,624 0.00026 0.99974 98.33
10.5 13,452,380 4,553 0.00034 0.99966 98.30
11.5 11,437,955 4,971 0.00043 0.99957 98.27
12.5 10,941,775 6,351 0.00058 0.99942 98.23
13.5 10,630,939 6,112 0.00057 0.99943 98.17
14.5 10,309,061 7,097 0.00069 0.99931 98.11
15.5 10,089,843 8,723 0.00086 0.99914 98.04
16.5 9,735,193 11,147 0.001151 0.99885 97.96
17.5 9,205,949 10,367 0.00113 0.99887 97.85
18.5 8,339,057 24,424 0.00293 0.99707 97.74
19.5 7,459,859 11,013 0.00148 0.99852 97.45
20.5 6,884,511 13,086 0.00190 0.99810 97.31
21.5 6,273,166 18,938 0.00302 0.99698 97.13
22.5 5,759,612 14,021 0.00243 0.99757 96.84
23.5 5,288,950 24,349 0.00460 0.99540 96.60
24.5 4,747,742 24,765 0.00522 0.99478 96.16
25.5 4,310,480 13,627 0.00316 0.99684 95.66
26.5 3,849,042 10,622 0.00276 0.99724 95.36
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-60

Intermountain Gas Company
Account 383.00 - Distribution - Regulators
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
27.5 3,496,131 9,801 0.00280 0.99720 95.10
28.5 3,156,876 7,170 0.00227 0.99773 94.83
29.5 2,898,369 6,548 0.00226 0.99774 94.61
30.5 2,578,011 6,623 0.00257 0.99743 94.40
31.5 2,308,534 6,073 0.00263 0.99737 94.16
32.5 2,065,418 5,753 0.00279 0.99721 93.91
33.5 1,910,441 6,959 0.00364 0.99636 93.65
34.5 1,727,703 4,670 0.002701 0.99730 93.31
35.5 1,627,952 7,360 0.004521 0.99548 93.06
36.5 1,574,945 4,865 0.00309 0.99691 92.64
37.5 1,479,188 6,562 0.00444 0.99556 92.35
38.5 1,391,485 6,613 0.004751 0.99525 91.94
39.5 1,332,041 5,890 0.00442 0.99558 91.50
40.5 1,263,438 7,278 0.00576 0.99424 91.10
41.5 1,217,690 6,268 0.00515 0.99485 90.58
42.5 1,165,925 6,312 0.00541 0.99459 90.11
43.5 1,096,540 8,579 0.00782 0.99218 89.62
44.5 1,077,037 6,165 0.00572 0.99428 88.92
45.5 1,070,872 8,095 0.00756 0.99244 88.41
46.5 1,052,435 7,180 0.006821 0.99318 87.74
47.5 1,016,327 5,670 0.00558 0.99442 87.14
48.5 989,247 10,241 0.01035 0.98965 86.65
49.5 954,179 7,858 0.00824 0.99176 85.75
50.5 888,870 9,805 0.01103 0.98897 85.04
51.5 811,210 6,936 0.00855 0.99145 84.10
52.5 727,152 5,749 0.00791 0.99209 83.38
53.5 668,202 9,449 0.01414 0.98586 82.72
54.5 611,763 4,645 0.007591 0.99241 81.55
55.5 595,883 4,314 0.00724 0.99276 80.93
56.5 581,993 8,820 0.01515 0.98485 80.34
57.5 548,395 4,155 0.00758 0.99242 79.12
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-61

Intermountain Gas Company
Account 383.00 - Distribution - Regulators
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
58.5 508,315 5,651 0.01112 0.98888 78.52
59.5 485,299 8,253 0.01701 0.98299 77.65
60.5 429,096 7,500 0.01748 0.98252 76.33
61.5 378,596 15,181 0.04010 0.95990 75.00
62.5 300,028 11,335 0.03778 0.96222 71.99
63.5 250,596 10,177 0.04061 0.95939 69.27
64.5 221,451 6,924 0.03127 0.96873 66.46
Totals: 829,848
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-62

Intermountain Gas Company
Account 385.00 - Distribution - Measure & Reg Station Equip. - Industrial
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 40-R1 (RM 0.7962) — Iowa 40-R1 (RM 0.7962)
100
■AMA
UM
SAMMOOM
80
> 60
AN
cn
}' ego
c
U 40
20
0
0 10 20 30 40 50 60 70 80 90
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-63

Intermountain Gas Company
Account 385.00 - Distribution - Measure & Reg Station Equip. - Industrial
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
RETIREMENT RATE ANALYSIS'
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 16,361,528 23,526 0.001441 0.99856 100.00
0.5 16,208,416 85,951 0.00530 0.99470 99.86
1.5 16,122,466 73,122 0.00454 0.99546 99.33
2.5 16,049,344 68,327 0.00426 0.99574 98.88
3.5 15,909,541 81,432 0.00512 0.99488 98.46
4.5 15,777,471 82,521 0.00523 0.99477 97.96
5.5 15,627,882 80,559 0.00515 0.99485 97.45
6.5 14,764,907 87,915 0.00595 0.99405 96.95
7.5 14,548,143 81,640 0.00561 0.99439 96.37
8.5 13,817,808 78,825 0.005701 0.99430 95.83
9.5 13,305,191 93,010 0.00699 0.99301 95.28
10.5 12,634,804 88,354 0.00699 0.99301 94.61
11.5 11,567,066 88,932 0.00769 0.99231 93.95
12.5 11,106,976 87,926 0.00792 0.99208 93.23
13.5 10,698,825 90,651 0.00847 0.99153 92.49
14.5 10,464,219 97,351 0.00930 0.99070 91.71
15.5 10,098,904 91,576 0.00907 0.99093 90.86
16.5 9,598,672 89,250 0.009301 0.99070 90.04
17.5 9,207,753 96,181 0.01045 0.98955 89.20
18.5 8,850,634 95,332 0.01077 0.98923 88.27
19.5 8,404,015 90,989 0.01083 0.98917 87.32
20.5 8,009,156 85,274 0.01065 0.98935 86.37
21.5 7,590,893 93,436 0.01231 0.98769 85.45
22.5 7,227,281 95,446 0.01321 0.98679 84.40
23.5 6,813,797 106,613 0.01565 0.98435 83.29
24.5 6,201,619 100,017 0.01613 0.98387 81.99
25.5 5,821,486 78,087 0.01341 0.98659 80.67
26.5 5,413,104 70,825 0.01308 0.98692 79.59
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-64

Intermountain Gas Company
Account 385.00 - Distribution - Measure & Reg Station Equip. - Industrial
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
27.5 4,944,640 66,589 0.01347 0.98653 78.55
28.5 4,573,278 84,759 0.01853 0.98147 77.49
29.5 4,273,694 56,928 0.01332 0.98668 76.05
30.5 3,900,226 62,340 0.01598 0.98402 75.04
31.5 3,518,717 55,996 0.01591 0.98409 73.84
32.5 3,105,146 61,756 0.01989 0.98011 72.67
33.5 2,889,311 74,393 0.02575 0.97425 71.22
34.5 2,543,037 66,528 0.026161 0.97384 69.39
35.5 2,291,314 65,558 0.02861 0.97139 67.57
36.5 2,080,549 65,837 0.03164 0.96836 65.64
37.5 1,930,544 64,315 0.03331 0.96669 63.56
38.5 1,787,267 46,784 0.02618 0.97382 61.44
39.5 1,740,483 49,367 0.02836 0.97164 59.83
40.5 1,611,570 45,721 0.02837 0.97163 58.13
41.5 1,475,264 49,021 0.03323 0.96677 56.48
42.5 1,363,742 37,619 0.02759 0.97241 54.60
43.5 1,219,216 42,373 0.03475 0.96525 53.09
44.5 1,100,225 35,307 0.03209 0.96791 51.25
45.5 986,171 28,128 0.02852 0.97148 49.61
46.5 916,098 28,112 0.03069 0.96931 48.20
47.5 788,991 18,197 0.02306 0.97694 46.72
48.5 720,150 38,624 0.05363 0.94637 45.64
49.5 627,448 17,166 0.02736 0.97264 43.19
50.5 531,615 18,127 0.03410 0.96590 42.01
51.5 414,893 4,346 0.01047 0.98953 40.58
52.5 410,547 4,261 0.01038 0.98962 40.16
53.5 363,516 4,372 0.012031 0.98797 39.74
54.5 317,557 5,228 0.01646 0.98354 39.26
55.5 243,942 6,291 0.02579 0.97421 38.61
56.5 215,886 10,338 0.04789 0.95211 37.61
57.5 205,549 0 0.00000 1.00000 35.81
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-65

Intermountain Gas Company
Account 385.00 - Distribution - Measure & Reg Station Equip. - Industrial
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
58.5 205,549 584 0.00284 0.99716 35.81
59.5 204,965 0 0.00000 1.00000 35.71
60.5 204,965 0 0.00000 1.00000 35.71
61.5 204,183 0 0.00000 1.00000 35.71
62.5 166,864 0 0.00000 1.00000 35.71
63.5 146,716 0 0.00000 1.00000 35.71
64.5 137,843 0 0.00000 1.00000 35.71
Totals: 3,598,033
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-66

Intermountain Gas Company
Account 387.00 - Distribution - Other Distribution Equip
Placement Band - 2011 - 2024 Experience Band - 2024- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 30-133 (RM 0.0596)
100109
80
a,o
> 60
c
U 40
v
20
0
0 10 20 30 40 50 60
Age (Years)
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Page 1 6-67

Intermountain Gas Company
Account 387.00 - Distribution - Other Distribution Equip
Placement Band - 2011 - 2024 Experience Band - 2024- 2024
RETIREMENT RATE ANALYSIS
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 112,980 0 0.00000 1.00000 100.00
0.5 112,980 0 0.00000 1.00000 100.00
1.5 86,054 0 0.00000 1.00000 100.00
2.5 86,054 0 0.00000 1.00000 100.00
3.5 62,767 0 0.00000 1.00000 100.00
4.5 62,767 0 0.00000 1.00000 100.00
5.5 62,767 0 0.00000 1.00000 100.00
6.5 39,669 0 0.000001 1.00000 100.00
7.5 6,400 0 0.00000 1.00000 100.00
8.5 6,400 0 0.00000 1.00000 100.00
9.5 6,400 0 0.00000 1.00000 100.00
10.5 6,400 0 0.00000 1.00000 100.00
11.5 2,995 0 0.00000 1.00000 100.00
12.5 2,995 0 0.00000 1.00000 100.00
Totals: 0
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Pagel 6-68

Intermountain Gas Company
Account 390.00 - General - Structures & Improvements
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 50-R2 (RM 1.2733) Iowa 45-R2 (RM 1.2313)
100
80
a,o
> 60
c
U 40
v
20
0
0 10 20 30 40 50 60 70 80 90 100
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-69

Intermountain Gas Company
Account 390.00 - General - Structures & Improvements
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
RETIREMENT RATE ANALYSIS'
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 31,817,822 15,500 0.000491 0.99951 100.00
0.5 31,090,830 44,430 0.00143 0.99857 99.95
1.5 30,887,314 64,729 0.00210 0.99790 99.81
2.5 30,556,445 35,902 0.00117 0.99883 99.60
3.5 29,528,418 65,080 0.00220 0.99780 99.48
4.5 28,745,532 69,144 0.00241 0.99759 99.26
5.5 28,296,674 41,240 0.00146 0.99854 99.02
6.5 22,367,014 19,442 0.00087 0.99913 98.88
7.5 21,487,846 137,635 0.00641 0.99359 98.79
8.5 20,868,041 105,394 0.005051 0.99495 98.16
9.5 20,365,604 130,274 0.00640 0.99360 97.66
10.5 17,323,141 111,583 0.00644 0.99356 97.03
11.5 16,488,816 98,541 0.00598 0.99402 96.41
12.5 15,615,404 4,213,936 0.26986 0.73014 95.83
13.5 10,339,155 75,976 0.00735 0.99265 69.97
14.5 10,236,098 40,874 0.00399 0.99601 69.46
15.5 10,131,581 43,070 0.00425 0.99575 69.18
16.5 9,869,392 52,569 0.00533 0.99467 68.89
17.5 8,684,416 105,509 0.01215 0.98785 68.52
18.5 8,517,476 50,575 0.00594 0.99406 67.69
19.5 8,430,916 55,268 0.006561 0.99344 67.29
20.5 8,022,449 25,116 0.00313 0.99687 66.85
21.5 7,987,178 15,830 0.00198 0.99802 66.64
22.5 7,917,434 51,895 0.00655 0.99345 66.51
23.5 7,815,794 20,638 0.00264 0.99736 66.07
24.5 7,393,497 66,565 0.00900 0.99100 65.90
25.5 6,006,112 118,508 0.01973 0.98027 65.31
26.5 5,747,277 78,945 0.01374 0.98626 64.02
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-70

Intermountain Gas Company
Account 390.00 - General - Structures & Improvements
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
27.5 4,829,054 102,105 0.02114 0.97886 63.14
28.5 4,675,275 38,769 0.00829 0.99171 61.81
29.5 4,625,441 44,320 0.00958 0.99042 61.30
30.5 4,553,398 22,718 0.00499 0.99501 60.71
31.5 4,494,375 50,983 0.01134 0.98866 60.41
32.5 4,435,118 45,002 0.01015 0.98985 59.72
33.5 4,368,331 23,060 0.00528 0.99472 59.11
34.5 4,333,167 46,005 0.01062 0.98938 58.80
35.5 4,143,068 27,498 0.00664 0.99336 58.18
36.5 4,082,088 37,164 0.00910 0.99090 57.79
37.5 4,037,485 23,274 0.00576 0.99424 57.26
38.5 3,742,051 29,292 0.007831 0.99217 56.93
39.5 3,682,620 9,750 0.00265 0.99735 56.48
40.5 3,654,412 21,727 0.00595 0.99405 56.33
41.5 3,599,209 60,691 0.01686 0.98314 55.99
42.5 3,471,678 43,793 0.012611 0.98739 55.05
43.5 3,373,853 84,196 0.02496 0.97504 54.36
44.5 3,227,661 5,168 0.00160 0.99840 53.00
45.5 3,209,387 5,613 0.00175 0.99825 52.92
46.5 2,822,976 2,078 0.00074 0.99926 52.83
47.5 2,717,839 14,276 0.00525 0.99475 52.79
48.5 2,504,016 7,315 0.00292 0.99708 52.51
49.5 2,493,075 12,026 0.00482 0.99518 52.36
50.5 2,410,926 106,454 0.04415 0.95585 52.11
51.5 1,448,115 26,558 0.01834 0.98166 49.81
52.5 1,420,232 4,215 0.00297 0.99703 48.90
53.5 1,410,850 1,713 0.00121 0.99879 48.75
54.5 1,407,225 129 0.00009 0.99991 48.69
55.5 1,406,054 2,642 0.00188 0.99812 48.69
56.5 1,403,412 54,543 0.03886 0.96114 48.60
57.5 1,346,279 115 0.00009 0.99991 46.71
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-71

Intermountain Gas Company
Account 390.00 - General - Structures & Improvements
Placement Band - 1959 - 2024 Experience Band - 2016- 2024
58.5 1,346,165 47,760 0.03548 0.96452 46.71
59.5 0 0 0.00000 0.00000 45.05
Totals: 6,955,120
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-72

Intermountain Gas Company
Account 392.10 - General - Transportation Equipment
Placement Band - 1986- 2024 Experience Band - 2016- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 10-1-2 (RM 0.1439) Iowa 10-1-2 (RM 0.1439)
100
■
■
80
■
a,o
> 60
+j ■
c
U 40
■
v
■
20
0
0 10 20 30 40
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-73

Intermountain Gas Company
Account 392.10 - General - Transportation Equipment
Placement Band - 1986- 2024 Experience Band - 2016- 2024
RETIREMENT RATE ANALYSIS'
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 31,353,047 69,064 0.002201 0.99780 100.00
0.5 30,453,627 184,348 0.00605 0.99395 99.78
1.5 29,621,166 391,203 0.01321 0.98679 99.18
2.5 28,189,103 478,418 0.01697 0.98303 97.87
3.5 26,511,166 776,606 0.02929 0.97071 96.21
4.5 23,782,983 1,049,117 0.04411 0.95589 93.39
5.5 20,903,418 1,493,609 0.07145 0.92855 89.27
6.5 18,584,762 1,923,341 0.10349 0.89651 82.89
7.5 15,098,638 2,204,392 0.14600 0.85400 74.31
8.5 11,883,512 1,948,637 0.163981 0.83602 63.46
9.5 8,732,608 1,244,444 0.14251 0.85749 53.05
10.5 7,112,390 1,410,057 0.19825 0.80175 45.49
11.5 5,600,735 1,072,923 0.19157 0.80843 36.47
12.5 4,120,561 695,864 0.16888 0.83112 29.48
13.5 3,063,287 645,195 0.21062 0.78938 24.50
14.5 2,315,805 571,159 0.24664 0.75336 19.34
15.5 1,719,311 414,027 0.24081 0.75919 14.57
16.5 1,171,409 357,572 0.30525 0.69475 11.06
17.5 789,222 206,384 0.26150 0.73850 7.68
18.5 556,883 154,409 0.27727 0.72273 5.67
19.5 361,683 97,733 0.270221 0.72978 4.10
20.5 263,950 54,920 0.20807 0.79193 2.99
21.5 209,030 149,672 0.71603 0.28397 2.37
22.5 40,875 22,474 0.54982 0.45018 0.67
23.5 18,401 10,171 0.55274 0.44726 0.30
24.5 8,230 4,018 0.48821 0.51179 0.13
25.5 4,212 2,565 0.60897 0.39103 0.07
26.5 1,647 1,076 0.65331 0.34669 0.03
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-74

Intermountain Gas Company
Account 392.10 - General - Transportation Equipment
Placement Band - 1986- 2024 Experience Band -2016- 2024
27.5 571 406 0.71103F 0.28897 0.01
28.5 165 123 0.74545 0.25455 0.00
29.5 42 42 1.00000 0.00
Totals: 17,633,969
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-75

Intermountain Gas Company
Account 392.20 - General - Transportation Equipment- Trailers
Placement Band - 1983 - 2024 Experience Band - 2017- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 20-132 (RM 0.7394) — Iowa 20-R2 (RM 0.7394)
100
■
Suwon ■ �
80
> 60
c
U 40
v
20
0
0 10 20 30 40 50
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-76

Intermountain Gas Company
Account 392.20 - General - Transportation Equipment- Trailers
Placement Band - 1983 - 2024 Experience Band - 2017- 2024
RETIREMENT RATE ANALYSIS'
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 738,873 0 0.000001 1.00000 100.00
0.5 733,813 0 0.00000 1.00000 100.00
1.5 722,055 0 0.00000 1.00000 100.00
2.5 640,130 0 0.00000 1.00000 100.00
3.5 640,130 0 0.000001 1.00000 100.00
4.5 640,130 46,966 0.07337 0.92663 100.00
5.5 593,163 42,197 0.07114 0.92886 92.66
6.5 528,731 0 0.00000 1.00000 86.07
7.5 501,833 0 0.00000 1.00000 86.07
8.5 426,008 0 0.00000 1.00000 86.07
9.5 356,549 0 0.00000 1.00000 86.07
10.5 340,608 0 0.00000 1.00000 86.07
11.5 324,026 0 0.00000 1.00000 86.07
12.5 324,026 10,190 0.03145 0.96855 86.07
13.5 243,643 44,756 0.18369 0.81631 83.36
14.5 197,259 0 0.00000 1.00000 68.05
15.5 173,265 0 0.00000 1.00000 68.05
16.5 173,265 0 0.00000 1.00000 68.05
17.5 115,861 15,598 0.13463 0.86537 68.05
18.5 100,262 0 0.00000 1.00000 58.89
19.5 48,359 0 0.00000 1.00000 58.89
20.5 48,359 0 0.00000 1.00000 58.89
21.5 48,359 10,668 0.22060 0.77940 58.89
22.5 33,045 0 0.00000 1.00000 45.90
23.5 33,045 0 0.00000 1.00000 45.90
24.5 33,045 0 0.00000 1.00000 45.90
25.5 16,838 0 0.00000 1.00000 45.90
26.5 14,583 0 0.00000 1.00000 45.90
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-77

Intermountain Gas Company
Account 392.20 - General - Transportation Equipment- Trailers
Placement Band - 1983 - 2024 Experience Band - 2017- 2024
27.5 14,583 0 0.00000 1.00000 45.90
28.5 10,859 0 0.00000 1.00000 45.90
29.5 10,859 0 0.00000 1.00000 45.90
Totals: 170,375
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-78

Intermountain Gas Company
Account 396.00 - General - Power Operated Equipment
Placement Band - 1983 - 2024 Experience Band - 2016- 2024
Actual and Smooth Survivor Curves
■ Actual Iowa 10-LO (RM 1.4227) Iowa 10-LO (RM 1.4227)
100
80
a,o
> 60
c
U 40
■
20 ■ ■ ■ ■
Boom
0 SUN
0 10 20 30 40 50
Age (Years)
Concentric Energy Advisors Intennounta in Gas Company 2025 Depreciation Study Page 1 6-79

Intermountain Gas Company
Account 396.00 - General - Power Operated Equipment
Placement Band - 1983 - 2024 Experience Band - 2016- 2024
RETIREMENT RATE ANALYSIS'
Age at Begin of Exposures at Beginning Retirements During Retmt
Interval of Age Interval Age Interval Ratio Survivor Ratio %Surviving
0 13,829,132 197,685 0.014291 0.98571 100.00
0.5 12,059,935 4,404,186 0.36519 0.63481 98.57
1.5 6,334,858 3,098,892 0.48918 0.51082 62.57
2.5 3,178,441 468,685 0.14746 0.85254 31.96
3.5 2,482,179 209,463 0.08439 0.91561 27.25
4.5 2,186,493 104,773 0.04792 0.95208 24.95
5.5 2,048,374 84,777 0.04139 0.95861 23.75
6.5 1,919,076 185,440 0.09663 0.90337 22.77
7.5 1,616,903 142,615 0.08820 0.91180 20.57
8.5 1,466,605 87,924 0.059951 0.94005 18.76
9.5 1,257,044 131,627 0.10471 0.89529 17.64
10.5 1,125,417 73,271 0.06511 0.93489 15.79
11.5 1,040,813 79,287 0.07618 0.92382 14.76
12.5 961,526 86,248 0.08970 0.91030 13.64
13.5 875,278 113,246 0.12938 0.87062 12.42
14.5 762,032 119,751 0.15715 0.84285 10.81
15.5 642,281 94,799 0.14760 0.85240 9.11
16.5 547,482 55,300 0.10101 0.89899 7.77
17.5 492,182 112,282 0.22813 0.77187 6.99
18.5 379,900 33,684 0.08867 0.91133 5.40
19.5 273,953 28,649 0.104581 0.89542 4.92
20.5 245,304 32,613 0.13295 0.86705 4.41
21.5 198,664 16,538 0.08325 0.91675 3.82
22.5 182,126 12,356 0.06784 0.93216 3.50
23.5 107,736 11,479 0.10655 0.89345 3.26
24.5 96,257 17,979 0.18678 0.81322 2.91
25.5 78,278 12,291 0.15702 0.84298 2.37
26.5 65,987 11,976 0.18149 0.81851 2.00
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Pagel 6-80

Intermountain Gas Company
Account 396.00 - General - Power Operated Equipment
Placement Band - 1983 - 2024 Experience Band - 2016- 2024
27.5 54,010 9,552 0.17685 0.82315 1.64
28.5 44,458 1,702 0.03828 0.96172 1.35
29.5 30,041 966 0.03216 0.96784 1.30
30.5 21,400 105 0.00491 0.99509 1.26
31.5 9,808 198 0.02019 0.97981 1.25
32.5 9,610 4 0.00042 0.99958 1.22
33.5 9,606 0 0.00000 1.00000 1.22
34.5 9,606 0 0.000001 1.00000 1.22
35.5 9,606 0 0.000001 1.00000 1.22
36.5 9,606 0 0.00000 1.00000 1.22
37.5 9,606 9,606 1.00000 1.22
Totals: 10,049,949
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Paged 6-81

Intermountain Gas Company
1@ 2025 Depreciation Study
SECTION 7
7 NET SALVAGE
Concentric Energy Advisors Page 1 7-1

Intermountaion Gas Company
ACCOUNT 361 - Structures & Improvements - Nampa
SUMMARY OF BOOK SALVAGE
Cost of Cost of Gross Gross Net Net
Regular Removal Removal Salvage Salvage Salvage Salvage 3-Year 3-Year 5-Year 5-Year Historical Historical Concentric
Year Retirements Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Recommendation
2015 1,500 218 15 0 -218 -15 -218 - 10.00
2016 1,188,138 9,072 1 0 -9,072 -1 -4,645 -1 - 10.00
2017 43 0 0 -43 0 -3,1 1 1 -1 -3,1 1 1 -1 - 10.00
2018 50,200 9,230 18 -500 -1 -8,730 -17 -5,948 -1 -4,516 -1 - 10.00
2019 1,743 0 0 -1,743 0 -3,505 -21 -3,961 -2 -3,961 -2 - 10.00
2020 74,125 5,410 7 0 -5,410 -7 -5,294 -13 -5,000 -2 -4,203 -2 - 10.00
2021 44,679 2,963 7 0 -2,963 -7 -3,372 -9 -3,778 -11 -4,026 -2 - 10.00
2022 135,182 13,456 10 0 -13,456 -10 -7,276 -9 -6,460 -11 -5,204 -3 - 10.00
2023 1,500 569 38 0 -569 -38 -5,663 -9 -4,828 -9 -4,689 -3 - 10.00
2024 25,494 432 2 0 -432 -2 -4,819 -9 -4,566 -8 -4,264 -3 - 10.00
TOTAL 1,520,817 43,136 2.84 -500 (0.03) -42,636 (2.80)
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Page 1 7-2

Intermountaion Gas Company
ACCOUNT 361 - Structures & Improvements - Rexburg
SUMMARY OF BOOK SALVAGE
Cost of Cost of Gross Gross Net Net
Regular Removal Removal Salvage Salvage Salvage Salvage 3-Year 3-Year 5-Year 5-Year Historical Historical Concentric
Year Retirements Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Recommendation
2015 3,158 0 0 -3,158 0 -3,158 - 15.00
2016 31,296 1 0 0 -1 0 -1,580 -10 - 15.00
2017 1,000 0 0 0 0 0 -1,053 -10 -1,580 -10 - 15.00
2018 5,300 6,306 119 0 -6,306 -1 19 -2,102 -17 -3,155 -25 - 15.00
2019 86,310 1,297 2 0 -1,297 -2 -2,534 -8 -2,152 -9 -2,691 -9 - 15.00
2020 2,000 0 0 0 0 -2,534 -8 -1,521 -6 -2,691 -9 - 15.00
2021 0 0 0 0 -432 -1 -1,521 -8 -2,691 -9 - 15.00
2022 0 0 0 0 0 0 -1,521 -8 -2,691 -9 - 15.00
2023 2,000 560 28 0 -560 -28 -187 -28 -371 -2 -2,264 -9 - 15.00
2024 4,372 178 4 0 -178 -4 -246 -12 -148 -9 -1,917 -9 - 15.00
TOTAL 132,278 11,500 8.69 0 0.00 -11,500 (8.69)
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Page 1 7-3

Intermountaion Gas Company
ACCOUNT 362 - Gas Holders - Nampa
SUMMARY OF BOOK SALVAGE
Cost of Cost of Gross Gross Net Net
Regular Removal Removal Salvage Salvage Salvage Salvage 3-Year 3-Year 5-Year 5-Year Historical Historical Concentric
Year Retirements Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Recommendation
2015 0 0 0 0 - 15.00
2016 0 0 0 0 0 - 15.00
2017 0 0 0 0 0 0 0 - 15.00
2018 0 0 0 0 0 0 0 - 15.00
2019 0 0 0 0 0 0 0 0 0 - 15.00
2020 1,800 519 29 0 -519 -29 -173 -29 -104 -29 -519 -29 - 15.00
2021 43,976 5,818 13 0 -5,818 -13 -2,1 12 -14 -1,267 -14 -3,168 -14 - 15.00
2022 99,818 15,324 15 0 -15,324 -15 -7,220 -15 -4,332 -15 -7,220 -15 - 15.00
2023 -149 0 0 149 0 -6,998 -15 -4,302 -15 -5,378 -15 - 15.00
2024 11,795 603 5 0 -603 -5 -5,259 -14 -4,423 -14 -4,423 -14 - 15.00
TOTAL 157,389 22,115 14.05 0 0.00 -22,115 (14.05)
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Page 1 7-4

Intermountaion Gas Company
ACCOUNT 363 - Measurement and Regulating Equipment - Nampa
SUMMARY OF BOOK SALVAGE
Cost of Cost of Gross Gross Net Net
Regular Removal Removal Salvage Salvage Salvage Salvage 3-Year 3-Year 5-Year 5-Year Historical Historical Concentric
Year Retirements Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Recommendation
2015 1,509 0 0 -1,509 0 -1,509 - 10.00
2016 1,008,968 10,002 1 0 -10,002 -1 -5,756 -1 - 10.00
2017 15 0 0 -15 0 -3,842 -1 -3,842 -1 - 10.00
2018 17,500 62,236 356 0 -62,236 -356 -24,085 -7 -18,441 -7 - 10.00
2019 0 0 0 0 -20,751 -356 -14,753 -7 -18,441 -7 - 10.00
2020 24,869 1,524 6 0 -1,524 -6 -21,254 -150 -14,756 -7 -15,057 -7 - 10.00
2021 55,595 0 0 0 0 -508 -2 -12,755 -65 -15,057 -7 - 10.00
2022 234,394 6,583 3 0 -6,583 -3 -2,703 -3 -14,069 -21 -13,645 -6 - 10.00
2023 36,225 3,974 11 0 -3,974 -11 -3,519 -3 -2,416 -3 -12,263 -6 - 10.00
2024 97,911 964 1 0 -964 -1 -3,841 -3 -2,609 -3 -10,851 -6 - 10.00
TOTAL 1,475,463 86,809 5.88 0 0.00 -86,809 (5.88)
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Page 1 7-5

Intermountain Gas Company
ACCOUNT 367 - Transmission Mains
SUMMARY OF BOOK SALVAGE
Cost of Cost of Gross Gross Net Net
Regular Removal Removal Salvage Salvage Salvage Salvage 3-Year 3-Year 5-Year 5-Year Historical Historical Concentric
Year Retirements Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Recommendation
1975 203,777 4,496 2 -2,421 -1 -2,075 -1 -2,075 -1 - 35.00
1976 42,416 1,233 3 0 0 -1,233 -3 -1,654 -1 - 35.00
1977 51,619 410 1 -1,081 -2 671 1 -879 -1 -879 -1 - 35.00
1978 221,791 1,107 0 -68,136 -31 67,029 30 22,156 21 16,098 12 - 35.00
1979 11,423 265 2 0 0 -265 -2 22,478 24 12,825 12 12,825 12 - 35.00
1980 5,055 7,806 154 -56 -1 -7,750 -153 19,671 25 11,690 18 9,396 11 - 35.00
1981 0 0 0 0 0 0 0 -2,672 -49 11,937 21 9,396 11 - 35.00
1982 3,772 444 12 0 0 -444 -12 -2,731 -93 11,714 24 7,990 10 - 35.00
1983 0 0 0 0 0 0 0 -148 -12 -1,692 -42 7,990 10 - 35.00
1984 18,972 380 2 -80 0 -300 -2 -248 -3 -1,699 -31 6,954 10 - 35.00
1985 227 261 115 0 0 -261 -1 15 -187 -3 -201 -4 6,152 10 - 35.00
1986 1,847 579 31 0 0 -579 -31 -380 -5 -317 -6 5,479 10 - 35.00
1987 0 0 0 0 0 0 0 -280 -41 -228 -5 5,479 10 - 35.00
1988 0 0 0 0 0 0 0 -193 -31 -228 -5 5,479 10 - 35.00
1989 -16,666 0 0 0 0 0 0 0 0 -168 6 5,479 10 - 35.00
1990 17,161 2,589 15 -1,281 -7 -1,308 -8 -436 -264 -377 -81 4,862 10 - 35.00
1991 17,041 -1,748 -10 0 0 1,748 10 147 3 88 3 4,603 10 - 35.00
1992 12,040 459 4 0 0 -459 -4 -6 0 -4 0 4,213 9 - 35.00
1993 0 0 0 0 0 0 0 430 4 -4 0 4,213 9 - 35.00
1994 0 0 0 0 0 0 0 18,258 9 10,955 9 4,213 9 - 35.00
1995 10,775 2,018 19 0 0 -2,018 -19 17,585 9 10,551 9 3,768 9 - 35.00
1996 0 73 0 0 0 -73 0 -697 -19 10,537 9 3,512 9 - 35.00
1997 0 30,547 0 0 0 -30,547 0 -10,879 -303 4,427 4 1,384 4 - 35.00
1998 5,264 8,866 168 0 0 -8,866 -168 -13,162 -750 -8,301 -259 781 2 - 35.00
1999 15,548 28,772 185 -904 -6 -27,868 -179 -22,427 -323 -13,874 -220 -811 -2 - 35.00
2000 1,734 0 0 0 0 0 0 -12,245 -163 -13,471 -299 -81 1 -2 - 35.00
2001 8,905 30,505 343 0 0 -30,505 -343 -19,458 -223 -19,557 -311 -2,374 -7 - 35.00
2002 17,625 6,197 35 0 0 -6,197 -35 -12,234 -130 -14,687 -150 -2,565 -8 - 35.00
2003 20,042 11,993 60 0 0 -1 1,993 -60 -16,232 -105 -15,313 -120 -3,014 -9 - 35.00
2004 10,295 4,294 42 0 0 -4,294 -42 -7,495 -47 -10,598 -90 -3,072 -10 - 35.00
2005 499 12,994 2,604 0 0 -12,994 -2,604 -9,760 -95 -13,197 -115 -3,504 -12 - 35.00
2006 21,056 100 0 0 0 -100 0 -5,796 -55 -7,116 -51 -3,362 -11 - 35.00
2007 24,716 46,757 189 0 0 -46,757 -189 -19,950 -129 -15,227 -99 -5,098 -18 - 35.00
2008 30,895 39,566 128 -25,029 -81 -14,537 -47 -20,465 -80 -15,736 -90 -5,461 -19 - 35.00
2009 1,187 2,871 242 0 0 -2,871 -242 -21,388 -113 -15,452 -99 -5,365 -19 - 35.00
2010 1,388 11,169 805 0 0 -1 1,169 -805 -9,525 -85 -15,087 -95 -5,572 -21 - 35.00
2011 14,767 23,107 156 0 0 -23,107 -156 -12,382 -214 -19,688 -135 -6,177 -23 - 35.00
2012 11,529 1,866 16 0 0 -1,866 -16 -12,047 -131 -10,710 -90 -6,033 -23 - 35.00
2013 299,568 0 0 0 0 0 0 -8,324 -8 -7,802 -12 -6,033 -17 - 35.00
2014 29,790 7,293 24 0 0 -7,293 -24 -3,053 -3 -8,687 -12 -6,074 -17 - 35.00
2015 0 17,289 0 0 0 -17,289 0 -8,194 -7 -9,911 -14 -6,424 -18 - 35.00
2016 0 12,761 0 0 0 -12,761 0 -12,448 -125 -7,842 -12 -6,616 -20 - 35.00
2017 0 1,081 0 0 0 -1,081 0 -10,377 0 -7,685 -12 -6,453 -20 - 35.00
2018 0 0 0 0 0 0 0 -4,614 0 -7,685 -129 -6,453 -20 - 35.00
2019 0 0 0 0 0 0 0 -360 0 -6,226 0 -6,453 -20 - 35.00
2020 4,028 0 0 0 0 0 0 0 0 -2,768 -344 -6,453 -20 - 35.00
2021 15,275 27,431 180 0 0 -27,431 -180 -9,144 -142 -5,702 -148 -7,053 -22 - 35.00
2022 142 0 0 0 -142 0 -9,191 -143 -5,515 -143 -6,861 -22 - 35.00
2023 35,348 66,855 189 0 0 -66,855 -189 -31,476 -187 -18,886 -173 -8,482 -27 - 35.00
2024 9,786 3,018 31 0 0 -3,018 -31 -23,338 -155 -19,489 -151 -8,338 -27 - 35.00
TOTAL 1,180,495 415,845 35.23 -98,988 (8.39) -316,857 (26.84)
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Page 1 7-6

Intermountain Gas Company
ACCOUNT 368 - Compressor Station Equipment
SUMMARY OF BOOK SALVAGE
Cost of Cost of Gross Gross Net Net
Regular Removal Removal Salvage Salvage Salvage Salvage 3-Year 3-Year 5-Year 5-Year Historical Historical Concentric
Year Retirements Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Recommendation
2002 94,165 0 0 0 0 0 5.00
2003 0 0 0 0 0 5.00
2004 0 0 0 0 0 0 0 5.00
2005 0 0 0 0 0 0 0 5.00
2006 0 0 0 0 0 0 0 0 0 5.00
2007 1,845,621 0 -5,500 0 5,500 0 1,833 0 1,100 0 5,500 0 5.00
2008 682 0 0 -682 0 1,606 0 964 0 2,409 0 5.00
2009 0 0 0 0 1,606 0 964 0 2,409 0 5.00
2010 0 0 0 0 -227 0 964 0 2,409 0 5.00
2011 0 0 0 0 0 0 964 0 2,409 0 5.00
2012 0 0 0 0 0 0 -136 0 2,409 0 5.00
2013 0 0 0 0 0 0 0 0 2,409 0 5.00
2014 0 0 0 0 0 0 0 0 2,409 0 5.00
2015 0 0 0 0 0 0 0 0 2,409 0 5.00
2016 0 0 0 0 0 0 0 0 2,409 0 5.00
2017 0 0 0 0 0 0 0 0 2,409 0 5.00
2018 0 0 0 0 0 0 0 0 2,409 0 5.00
2019 0 0 0 0 0 0 0 0 2,409 0 5.00
2020 0 0 0 0 0 0 0 0 2,409 0 5.00
2021 15,180 188 1 0 -188 -1 -63 -1 -38 -1 1,543 0 5.00
2022 0 0 0 0 -63 -1 -38 -1 1,543 0 5.00
2023 12,662 0 0 0 0 -63 -1 -38 -1 1,543 0 5.00
2024 104,712 1,388 1 0 -1,388 -1 -463 -1 -315 -1 811 0 5.00
TOTAL 2,072,340 2,257 0.11 -5,500 (0.27) 3,243 0.16
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Page 1 7-7

Intermountain Gas Company
ACCOUNT 376 - Distribution Mains
SUMMARY OF BOOK SALVAGE
Cost of Cost of Gross Gross Net Net
Regular Removal Removal Salvage Salvage Salvage Salvage 3-Year 3-Year 5-Year 5-Year Historical Historical Concentric
Year Retirements Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Recommendation
1975 48,981 11,300 23 -123 0 -1 1,177 -23 -1 1,177 -23 - 50.00
1976 24,718 9,701 39 -3,507 -14 -6,194 -25 -8,686 -24 - 50.00
1977 36,204 5,292 15 0 0 -5,292 -15 -7,554 -21 -7,554 -21 - 50.00
1978 45,387 4,433 10 -7,162 -16 2,729 6 -2,919 -8 -4,984 -13 - 50.00
1979 23,475 9,508 41 -166 -1 -9,342 -40 -3,968 -1 1 -5,855 -16 -5,855 -16 - 50.00
1980 28,312 20,601 73 -3,938 -14 -16,663 -59 -7,759 -24 -6,952 -22 -7,657 -22 - 50.00
1981 16,869 8,656 51 -725 -4 -7,931 -47 -1 1,312 -49 -7,300 -24 -7,696 -24 - 50.00
1982 23,277 5,350 23 -1,349 -6 -4,001 -17 -9,532 -42 -7,042 -26 -7,234 -23 - 50.00
1983 26,092 5,580 21 -5,496 -21 -84 0 -4,005 -18 -7,604 -32 -6,439 -21 - 50.00
1984 31,158 18,822 60 -290 -1 -18,532 -59 -7,539 -28 -9,442 -38 -7,649 -25 - 50.00
1985 22,421 8,499 38 -348 -2 -8,151 -36 -8,922 -34 -7,740 -32 -7,694 -26 - 50.00
1986 40,885 12,022 29 -249 -1 -11,773 -29 -12,819 -41 -8,508 -30 -8,034 -26 - 50.00
1987 34,078 18,590 55 -4,680 -14 -13,910 -41 -1 1,278 -35 -10,490 -34 -8,486 -27 - 50.00
1988 107,515 19,542 18 -28 0 -19,514 -18 -15,066 -25 -14,376 -30 -9,274 -25 - 50.00
1989 106,179 31,074 29 -1,093 -1 -29,981 -28 -21,135 -26 -16,666 -27 -10,654 -26 - 50.00
1990 75,204 25,021 33 -4,583 -6 -20,438 -27 -23,311 -24 -19,123 -26 -11,266 -26 - 50.00
1991 60,577 20,310 34 -337 -1 -19,973 -33 -23,464 -29 -20,763 -27 -11,778 -27 - 50.00
1992 50,022 29,416 59 -3,736 -7 -25,680 -51 -22,030 -36 -23,117 -29 -12,550 -28 - 50.00
1993 18,578 6,420 35 0 0 -6,420 -35 -17,358 -40 -20,498 -33 -12,228 -28 - 50.00
1994 50,001 31,058 62 -28 0 -31,030 -62 -87,786 -30 -52,671 -30 -13,168 -30 - 50.00
1995 96,581 27,423 28 -2,742 -3 -24,681 -26 -96,013 -30 -57,608 -30 -13,716 -30 - 50.00
1996 91,501 29,078 32 -1,133 -1 -27,945 -31 -27,885 -35 -63,197 -30 -14,363 -30 - 50.00
1997 42,756 25,729 60 -280 -1 -25,449 -60 -26,025 -34 -68,286 -31 -14,845 -31 - 50.00
1998 76,658 68,172 89 -124 0 -68,048 -89 -40,481 -58 -35,431 -50 -17,062 -35 - 50.00
1999 70,746 68,322 97 0 0 -68,322 -97 -53,940 -85 -42,889 -57 -19,112 -38 - 50.00
2000 95,495 51,726 54 0 0 -51,726 -54 -62,699 -77 -48,298 -64 -20,366 -39 - 50.00
2001 105,726 63,582 60 -68 0 -63,514 -60 -61,187 -67 -55,412 -71 -21,965 -41 - 50.00
2002 102,579 69,554 68 -60 0 -69,494 -68 -61,578 -61 -64,221 -71 -23,662 -43 - 50.00
2003 1 1 1,741 58,285 52 -7,481 -7 -50,804 -45 -61,271 -57 -60,772 -62 -24,598 -43 - 50.00
2004 106,681 47,700 45 0 0 -47,700 -45 -55,999 -52 -56,647 -54 -25,368 -43 - 50.00
2005 141,827 55,553 39 0 0 -55,553 -39 -51,352 -43 -57,413 -50 -26,342 -43 - 50.00
2006 184,680 111,061 60 -750 0 -110,311 -60 -71,188 -49 -66,772 -52 -28,966 -44 - 50.00
2007 276,879 253,459 92 -1,322 0 -252,137 -91 -139,334 -69 -103,301 -63 -35,728 -50 - 50.00
2008 103,461 140,227 136 -21,525 -21 -1 18,702 -1 15 -160,383 -85 -1 16,880 -72 -38,169 -52 - 50.00
2009 117,340 67,971 58 -640 -1 -67,331 -57 -146,057 -88 -120,807 -73 -39,002 -53 - 50.00
2010 133,117 62,930 47 0 0 -62,930 -47 -82,988 -70 -122,282 -75 -39,667 -52 - 50.00
2011 212,504 163,262 77 0 0 -163,262 -77 -97,841 -63 -132,872 -79 -43,007 -54 - 50.00
2012 490,721 167,567 34 -3,012 -1 -164,555 -34 -130,249 -47 -1 15,356 -55 -46,206 -51 - 50.00
2013 846,699 118,554 14 -1,781 0 -116,773 -14 -148,197 -29 -114,970 -32 -48,015 -44 - 50.00
2014 922,927 174,698 19 -656 0 -174,042 -19 -151,790 -20 -136,312 -26 -51,166 -39 - 50.00
2015 553,581 262,332 47 0 0 -262,332 -47 -184,382 -24 -176,193 -29 -56,316 -40 - 50.00
2016 548,457 249,885 46 0 0 -249,885 -46 -228,753 -34 -193,517 -29 -60,925 -41 - 50.00
2017 312,758 296,844 95 0 0 -296,844 -95 -269,687 -57 -219,975 -35 -66,412 -43 - 50.00
2018 551,463 496,471 90 0 0 -496,471 -90 -347,733 -74 -295,915 -51 -76,186 -47 - 50.00
2019 307,524 703,706 229 0 0 -703,706 -229 -499,007 -128 -401,848 -88 -90,131 -54 - 50.00
2020 505,115 568,036 112 0 0 -568,036 -112 -589,405 -130 -462,989 -104 -100,520 -58 - 50.00
2021 464,230 79,113 17 0 0 -79,1 13 -17 -450,285 -106 -428,834 -100 -100,064 -56 - 50.00
2022 385,684 507,811 132 0 0 -507,811 -132 -384,987 -85 -471,028 -106 -108,559 -59 - 50.00
2023 479,096 313,635 65 0 0 -313,635 -65 -300,186 -68 -434,460 -101 -112,744 -59 - 50.00
2024 208,859 376,080 180 0 0 -376,080 -180 -399,176 -1 12 -368,935 -90 -1 18,01 1 -62 - 50.00
TOTAL 9,517,319 5,979,961 62.83 -79,412 (0.83) -5,900,549 (62.00)
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Page 1 7-8

Intermountain Gas Company
ACCOUNT 378 - Measuring and Regulating Station Equipment - General
SUMMARY OF BOOK SALVAGE
Cost of Cost of Gross Gross Net Net
Regular Removal Removal Salvage Salvage Salvage Salvage 3-Year 3-Year 5-Year 5-Year Historical Historical Concentric
Year Retirements Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Recommendation
1975 30,219 8,336 28 0 0 -8,336 -28 -8,336 -28 - 30.00
1976 18,757 1,307 7 -5,933 -32 4,626 25 -1,855 -8 - 30.00
1977 2,794 514 18 -1,344 -48 830 30 -960 -6 -960 -6 - 30.00
1978 609 482 79 -1,585 -260 1,103 181 2,186 30 -444 -3 - 30.00
1979 578 51 9 -1,687 -292 1,636 283 1,190 90 -28 0 -28 0 - 30.00
1980 10,570 1,938 18 0 0 -1,938 -18 267 7 1,251 19 -347 -3 - 30.00
1981 8,679 3,741 43 -803 -9 -2,938 -34 -1,080 -16 -261 -6 -717 -7 - 30.00
1982 5,885 3,032 52 -2,933 -50 -99 -2 -1,658 -20 -447 -8 -640 -7 - 30.00
1983 8,681 3,427 39 -782 -9 -2,645 -30 -1,894 -24 -1,197 -17 -862 -9 - 30.00
1984 6,101 8,025 132 -1,836 -30 -6,189 -101 -2,978 -43 -2,762 -35 -1,395 -15 - 30.00
1985 11,105 2,540 23 -1,860 -17 -680 -6 -3,171 -37 -2,510 -31 -1,330 -14 - 30.00
1986 5,264 3,530 67 -726 -14 -2,804 -53 -3,224 -43 -2,483 -34 -1,453 -16 - 30.00
1987 22,075 3,029 14 -1,470 -7 -1,559 -7 -1,681 -13 -2,775 -26 -1,461 -14 - 30.00
1988 18,378 6,069 33 -4,157 -23 -1,912 -10 -2,092 -14 -2,629 -21 -1,493 -14 - 30.00
1989 14,691 1,867 13 -5,509 -37 3,642 25 57 0 -663 -5 -1,151 -11 - 30.00
1990 19,426 5,095 26 -1,221 -6 -3,874 -20 -715 -4 -1,301 -8 -1,321 -11 - 30.00
1991 6,131 2,520 41 -550 -9 -1,970 -32 -734 -5 -1,135 -7 -1,359 -12 - 30.00
1992 8,715 3,684 42 -1,456 -17 -2,228 -26 -2,691 -24 -1,268 -9 -1,408 -13 - 30.00
1993 8,508 534 6 -5,703 -67 5,169 61 324 4 148 1 -1,061 -10 - 30.00
1994 28,558 5,542 19 0 0 -5,542 -19 -8,569 -11 -5,142 -11 -1,285 -11 - 30.00
1995 1,746 137 8 -18 -1 -119 -7 -8,609 -11 -5,165 -11 -1,230 -11 - 30.00
1996 13,108 1,116 9 0 0 -1,1 16 -9 -2,259 -16 -5,389 -11 -1,225 -11 - 30.00
1997 21,795 186 1 0 0 -186 -1 -474 -4 -5,426 -10 -1,180 -10 - 30.00
1998 8,551 1,314 15 -3,608 -42 2,294 27 331 2 -934 -6 -1,035 -9 - 30.00
1999 7,164 1,041 15 -67 -1 -974 -14 378 3 -20 0 -1,032 -9 - 30.00
2000 46,629 1,746 4 0 0 -1,746 -4 -142 -1 -346 -2 -1,060 -8 - 30.00
2001 2,204 1,533 70 0 0 -1,533 -70 -1,418 -8 -429 -2 -1,077 -9 - 30.00
2002 27,958 2,313 8 0 0 -2,313 -8 -1,864 -7 -854 -5 -1,121 -9 - 30.00
2003 19,078 2,436 13 -326 -2 -2,1 10 -11 -1,985 -12 -1,735 -8 -1,156 -9 - 30.00
2004 36,256 1,944 5 0 0 -1,944 -5 -2,122 -8 -1,929 -7 -1,182 -8 - 30.00
2005 44,763 9,719 22 0 0 -9,719 -22 -4,591 -14 -3,524 -14 -1,457 -10 - 30.00
2006 45,652 11,192 25 0 0 -1 1,192 -25 -7,618 -18 -5,456 -16 -1,761 -11 - 30.00
2007 135,420 8,577 6 0 0 -8,577 -6 -9,829 -13 -6,708 -12 -1,968 -10 - 30.00
2008 107,907 26,795 25 0 0 -26,795 -25 -15,521 -16 -11,645 -16 -2,698 -12 - 30.00
2009 66,933 19,336 29 -876 -1 -18,460 -28 -17,944 -17 -14,949 -19 -3,149 -13 - 30.00
2010 85,203 10,063 12 -500 -1 -9,563 -11 -18,273 -21 -14,918 -17 -3,327 -13 - 30.00
2011 42,179 12,197 29 0 0 -12,197 -29 -13,407 -21 -15,1 19 -17 -3,566 -14 - 30.00
2012 60,065 5,833 10 0 0 -5,833 -10 -9,198 -15 -14,570 -20 -3,626 -14 - 30.00
2013 27,104 9,965 37 -7,000 -26 -2,965 -11 -6,998 -16 -9,804 -17 -3,609 -14 - 30.00
2014 84,826 13,205 16 0 0 -13,205 -16 -7,334 -13 -8,753 -15 -3,849 -14 - 30.00
2015 95,099 33,372 35 0 0 -33,372 -35 -16,514 -24 -13,514 -22 -4,569 -15 - 30.00
2016 49,738 94,284 190 0 0 -94,284 -190 -46,953 -61 -29,932 -47 -6,705 -22 - 30.00
2017 11,000 18,016 164 0 0 -18,016 -164 -48,557 -93 -32,368 -60 -6,968 -23 - 30.00
2018 137,994 254,595 184 0 0 -254,595 -184 -122,298 -185 -82,694 -109 -12,596 -39 - 30.00
2019 270,120 58,334 22 0 0 -58,334 -22 -110,315 -79 -91,720 -81 -13,612 -36 - 30.00
2020 196,033 103,320 53 0 0 -103,320 -53 -138,750 -69 -105,710 -79 -15,563 -38 - 30.00
2021 202,740 81,104 40 0 0 -81,104 -40 -80,919 -36 -103,074 -63 -16,957 -38 - 30.00
2022 166,418 6,391 4 -489 0 -5,901 -4 -63,442 -34 -100,651 -52 -16,727 -36 - 30.00
2023 42,673 7,506 18 0 0 -7,506 -18 -31,504 -23 -51,233 -29 -16,539 -35 - 30.00
2024 316,157 45,256 14 0 0 -45,256 -14 -19,555 -11 -48,618 -26 -17,113 -33 - 30.00
TOTAL 2,608,236 908,089 34.82 -52,439 (2.01) -855,650 (32.81)
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Page 1 7-9

Intermountain Gas Company
ACCOUNT 380 - Services
SUMMARY OF BOOK SALVAGE
Cost of Cost of Gross Gross Net Net
Regular Removal Removal Salvage Salvage Salvage Salvage 3-Year 3-Year 5-Year 5-Year Historical Historical Concentric
Year Retirements Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Recommendation
1975 108,632 40,535 37 -416 0 -40,1 19 -37 -40,1 19 -37 - 75.00
1976 145,694 66,384 46 -367 0 -66,017 -45 -53,068 -42 - 75.00
1977 194,451 87,382 45 -26,778 -14 -60,604 -31 -55,580 -37 -55,580 -37 - 75.00
1978 205,286 76,471 37 -107,046 -52 30,575 15 -32,015 -18 -34,041 -21 - 75.00
1979 142,776 70,195 49 -13,314 -9 -56,881 -40 -28,970 -16 -38,609 -24 -38,609 -24 - 75.00
1980 137,537 68,053 49 -19,008 -14 -49,045 -36 -25,117 -16 -40,394 -24 -40,349 -26 - 75.00
1981 114,984 71,353 62 -3,471 -3 -67,882 -59 -57,936 -44 -40,767 -26 -44,282 -30 - 75.00
1982 107,451 65,256 61 -2,087 -2 -63,169 -59 -60,032 -50 -41,280 -29 -46,643 -32 - 75.00
1983 112,025 80,391 72 -4,709 -4 -75,682 -68 -68,911 -62 -62,532 -51 -49,869 -35 - 75.00
1984 131,665 105,190 80 -4,229 -3 -100,961 -77 -79,937 -68 -71,348 -59 -54,979 -39 - 75.00
1985 190,612 123,383 65 -2,1 10 -1 -121,273 -64 -99,305 -69 -85,793 -65 -61,005 -42 - 75.00
1986 119,182 93,339 78 -3,262 -3 -90,077 -76 -104,104 -71 -90,232 -68 -63,428 -45 - 75.00
1987 166,800 108,037 65 -4,792 -3 -103,245 -62 -104,865 -66 -98,248 -68 -66,491 -46 - 75.00
1988 155,024 117,220 76 -2,539 -2 -114,681 -74 -102,668 -70 -106,047 -69 -69,933 -48 - 75.00
1989 164,620 94,183 57 -787 0 -93,396 -57 -103,774 -64 -104,534 -66 -71,497 -49 - 75.00
1990 177,319 110,387 62 -1,172 -1 -109,215 -62 -105,764 -64 -102,123 -65 -73,855 -50 - 75.00
1991 140,351 85,397 61 -395 0 -85,002 -61 -95,871 -60 -101,108 -63 -74,510 -50 - 75.00
1992 134,329 80,219 60 -207 0 -80,012 -60 -91,410 -61 -96,461 -63 -74,816 -51 - 75.00
1993 124,949 70,648 57 -465 0 -70,183 -56 -78,399 -59 -87,562 -59 -74,572 -51 - 75.00
1994 181,592 96,245 53 0 0 -96,245 -53 -504,371 -51 -302,623 -51 -75,656 -51 - 75.00
1995 193,173 104,634 54 0 0 -104,634 -54 -539,249 -51 -323,550 -51 -77,036 -51 - 75.00
1996 149,402 103,675 69 0 0 -103,675 -69 -101,518 -58 -344,285 -52 -78,247 -52 - 75.00
1997 170,886 99,347 58 0 0 -99,347 -58 -102,552 -60 -364,154 -52 -79,164 -52 - 75.00
1998 158,011 111,459 71 -125 0 -111,334 -70 -104,785 -66 -103,047 -60 -80,504 -53 - 75.00
1999 212,878 133,528 63 -143 0 -133,385 -63 -114,689 -64 -110,475 -62 -82,620 -54 - 75.00
2000 215,773 118,625 55 0 0 -118,625 -55 -121,115 -62 -113,273 -62 -84,004 -54 - 75.00
2001 184,916 97,642 53 -103 0 -97,539 -53 -116,516 -57 -112,046 -59 -84,506 -54 - 75.00
2002 224,198 98,519 44 -1 14 0 -98,405 -44 -104,856 -50 -1 1 1,858 -56 -85,002 -53 - 75.00
2003 261,360 138,741 53 0 0 -138,741 -53 -1 1 1,562 -50 -1 17,339 -53 -86,855 -53 - 75.00
2004 293,696 142,427 48 0 0 -142,427 -48 -126,524 -49 -119,147 -50 -88,708 -53 - 75.00
2005 323,114 164,968 51 0 0 -164,968 -51 -148,712 -51 -128,416 -50 -91,168 -53 - 75.00
2006 329,162 141,023 43 0 0 -141,023 -43 -149,473 -47 -137,1 13 -48 -92,726 -52 - 75.00
2007 476,169 238,230 50 -5,790 -1 -232,440 -49 -179,477 -48 -163,920 -49 -96,959 -52 - 75.00
2008 339,000 162,274 48 -3,887 -1 -158,387 -47 -177,283 -46 -167,849 -48 -98,766 -52 - 75.00
2009 290,156 151,575 52 -3,560 -1 -148,015 -51 -179,614 -49 -168,967 -48 -100,173 -52 - 75.00
2010 248,275 137,384 55 -250 0 -137,134 -55 -147,845 -51 -163,400 -49 -101,200 -52 - 75.00
2011 234,360 115,683 49 0 0 -1 15,683 -49 -133,61 1 -52 -158,332 -50 -101,591 -52 - 75.00
2012 289,642 145,917 50 0 0 -145,917 -50 -132,911 -52 -141,027 -50 -102,758 -52 - 75.00
2013 228,334 116,797 51 -574 0 -116,223 -51 -125,941 -50 -132,594 -51 -103,103 -52 - 75.00
2014 302,875 354,613 117 0 0 -354,613 -117 -205,584 -75 -173,914 -67 -109,391 -54 - 75.00
2015 379,504 430,619 113 0 0 -430,619 -113 -300,485 -99 -232,611 -81 -117,226 -57 - 75.00
2016 395,893 525,226 133 0 0 -525,226 -133 -436,819 -122 -314,519 -99 -126,940 -60 - 75.00
2017 287,886 15,681 5 0 0 -15,681 -5 -323,842 -91 -288,472 -90 -124,352 -58 - 75.00
2018 379,038 1,424,072 376 0 0 -1,424,072 -376 -654,993 -185 -550,042 -158 -153,892 -71 - 75.00
2019 534,133 653,063 122 0 0 -653,063 -122 -697,605 -174 -609,732 -154 -164,984 -74 - 75.00
2020 333,452 478,143 143 0 0 -478,143 -143 -851,759 -205 -619,237 -160 -171,792 -76 - 75.00
2021 258,775 640,559 248 0 0 -640,559 -248 -590,588 -157 -642,303 -179 -181,766 -80 - 75.00
2022 421,105 732,837 174 0 0 -732,837 -174 -617,179 -183 -785,735 -204 -193,246 -84 - 75.00
2023 404,667 600,998 149 0 0 -600,998 -149 -658,131 -182 -621,120 -159 -201,568 -86 - 75.00
2024 61,012 754,956 1,237 0 0 -754,956 -1,237 -696,264 -236 -641,499 -217 -212,636 -92 - 75.00
TOTAL 11,536,125 10,843,483 94.00 -211,700 (1.84) -10,631,783 (92.16)
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Page 1 7-10

Intermountain Gas Company
ACCOUNT 385 - Measuring and Regulating Station Equipment - Industrial
SUMMARY OF BOOK SALVAGE
Cost of Cost of Gross Gross Net Net
Regular Removal Removal Salvage Salvage Salvage Salvage 3-Year 3-Year 5-Year 5-Year Historical Historical Concentric
Year Retirements Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Recommendation
1975 34,029 3,124 9 -2,462 -7 -662 -2 -662 -2 - 12.00
1976 31,834 2,368 7 -4,666 -15 2,298 7 818 2 - 12.00
1977 38,301 2,112 6 -2,520 -7 408 1 681 2 681 2 - 12.00
1978 31,435 1,726 5 -4,452 -14 2,726 9 1,811 5 1,193 4 - 12.00
1979 30,806 2,284 7 -5,948 -19 3,664 12 2,266 7 1,687 5 1,687 5 - 12.00
1980 33,372 2,274 7 -6,467 -19 4,193 13 3,528 11 2,658 8 2,105 6 - 12.00
1981 35,890 7,808 22 -6,014 -17 -1,794 -5 2,021 6 1,839 5 1,548 5 - 12.00
1982 77,126 8,012 10 -16,503 -21 8,491 11 3,630 7 3,456 8 2,416 6 - 12.00
1983 105,667 13,835 13 -18,803 -18 4,968 5 3,888 5 3,904 7 2,699 6 - 12.00
1984 118,951 3,568 3 -10,475 -9 6,907 6 6,789 7 4,553 6 3,120 6 - 12.00
1985 84,429 3,253 4 -5,030 -6 1,777 2 4,551 4 4,070 5 2,998 5 - 12.00
1986 53,715 4,059 8 -2,451 -5 -1,608 -3 2,359 3 4,107 5 2,614 5 - 12.00
1987 38,700 5,418 14 -2,578 -7 -2,840 -7 -890 -2 1,841 2 2,194 4 - 12.00
1988 82,159 3,355 4 -4,790 -6 1,435 2 -1,004 -2 1,134 2 2,140 4 - 12.00
1989 10,881 1,771 16 -245 -2 -1,526 -14 -977 -2 -552 -1 1,896 4 - 12.00
1990 29,083 4,457 15 -5,751 -20 1,294 4 401 1 -649 -2 1,858 4 - 12.00
1991 9,066 1,934 21 -1,220 -13 -714 -8 -315 -2 -470 -1 1,707 3 - 12.00
1992 11,138 3,789 34 -3,589 -32 -200 -2 127 1 58 0 1,601 3 - 12.00
1993 103,041 8,446 8 -981 -1 -7,465 -7 -2,793 -7 -1,722 -5 1,124 2 - 12.00
1994 52,598 2,098 4 -5,231 -10 3,133 6 8,162 2 4,897 2 1,224 2 - 12.00
1995 96,483 3,480 4 -15 0 -3,465 -4 7,007 2 4,204 2 1,001 2 - 12.00
1996 44,854 2,866 6 0 0 -2,866 -6 -1,066 -2 3,631 2 825 2 - 12.00
1997 116,312 2,293 2 -7,307 -6 5,014 4 -439 -1 4,634 2 1,007 2 - 12.00
1998 27,530 2,287 8 -1,225 -4 -1,062 -4 362 1 151 0 921 2 - 12.00
1999 34,986 0 0 0 0 0 0 1,317 2 -476 -1 921 2 - 12.00
2000 77,066 1,496 2 -1,171 -2 -325 0 -462 -1 152 0 871 2 - 12.00
2001 99,103 289 0 0 0 -289 0 -205 0 668 1 827 1 - 12.00
2002 51,187 2,949 6 -1,416 -3 -1,533 -3 -716 -1 -642 -1 739 1 - 12.00
2003 93,736 3,078 3 0 0 -3,078 -3 -1,633 -2 -1,045 -1 603 1 - 12.00
2004 80,995 528 1 0 0 -528 -1 -1,713 -2 -1,151 -1 564 1 - 12.00
2005 49,637 1,136 2 0 0 -1,136 -2 -1,581 -2 -1,313 -2 507 1 - 12.00
2006 126,810 3,004 2 0 0 -3,004 -2 -1,556 -2 -1,856 -2 394 1 - 12.00
2007 31,247 2,614 8 0 0 -2,614 -8 -2,251 -3 -2,072 -3 300 0 - 12.00
2008 278,819 13,836 5 -51 0 -13,785 -5 -6,468 -4 -4,213 -4 -127 0 - 12.00
2009 157,239 7,425 5 -330 0 -7,095 -5 -7,831 -5 -5,527 -4 -332 0 - 12.00
2010 201,847 11,983 6 0 0 -11,983 -6 -10,954 -5 -7,696 -5 -665 -1 - 12.00
2011 61,397 1,499 2 0 0 -1,499 -2 -6,859 -5 -7,395 -5 -688 -1 - 12.00
2012 80,480 8,698 11 0 0 -8,698 -11 -7,393 -6 -8,612 -6 -904 -1 - 12.00
2013 51,563 7,069 14 0 0 -7,069 -14 -5,755 -9 -7,269 -7 -1,067 -1 - 12.00
2014 152,898 7,684 5 0 0 -7,684 -5 -7,817 -8 -7,387 -7 -1,236 -2 - 12.00
2015 44,599 21,409 48 0 0 -21,409 -48 -12,054 -15 -9,272 -12 -1,741 -2 - 12.00
2016 75,095 17,059 23 0 0 -17,059 -23 -15,384 -17 -12,384 -15 -2,1 14 -3 - 12.00
2017 14,981 8,963 60 0 0 -8,963 -60 -15,811 -35 -12,437 -18 -2,277 -3 - 12.00
2018 75,911 26,048 34 0 0 -26,048 -34 -17,357 -31 -16,233 -22 -2,830 -4 - 12.00
2019 32,633 26,051 80 0 0 -26,051 -80 -20,354 -49 -19,906 -41 -3,358 -5 - 12.00
2020 24,157 10,458 43 0 0 -10,458 -43 -20,852 -47 -17,716 -40 -3,516 -5 - 12.00
2021 1,690 1,860 110 0 0 -1,860 -1 10 -12,790 -66 -14,676 -49 -3,480 -5 - 12.00
2022 6,086 3,059 50 0 0 -3,059 -50 -5,126 -48 -13,495 -48 -3,471 -5 - 12.00
2023 0 0 0 0 0 0 0 -1,640 -63 -8,286 -64 -3,471 -5 - 12.00
2024 0 17,277 0 0 0 -17,277 0 -6,779 -334 -6,531 -102 -3,758 -6 - 12.00
TOTAL 3,201,561 302,089 9.44 -121,691 (3.80) -180,398 (5.63)
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Page 1 7-11

Intermountain Gas Company
ACCOUNT 390 - General Structures and Improvements
SUMMARY OF BOOK SALVAGE
Cost of Cost of Gross Gross Net Net
Regular Removal Removal Salvage Salvage Salvage Salvage 3-Year 3-Year 5-Year 5-Year Historical Historical Concentric
Year Retirements Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Recommendation
1975 16,675 0 0 -485 -3 485 3 485 3 10.00
1976 59,022 0 0 -425 -1 425 1 455 1 10.00
1977 3,409 0 0 -881 -26 881 26 597 2 597 2 10.00
1978 15,780 0 0 -3,108 -20 3,108 20 1,471 6 1,225 5 10.00
1979 9,777 0 0 -1,534 -16 1,534 16 1,841 19 1,287 6 1,287 6 10.00
1980 181 0 0 0 0 0 0 1,547 18 1,190 7 1,287 6 10.00
1981 5,996 0 0 0 0 0 0 511 10 1,105 16 1,287 6 10.00
1982 19,383 0 0 0 0 0 0 0 0 928 9 1,287 5 10.00
1983 12,868 0 0 0 0 0 0 0 0 307 3 1,287 4 10.00
1984 28,705 0 0 0 0 0 0 0 0 0 0 1,287 4 10.00
1985 2,025 0 0 0 0 0 0 0 0 0 0 1,287 4 10.00
1986 13,588 0 0 0 0 0 0 0 0 0 0 1,287 3 10.00
1987 8,901 0 0 -8,030 -90 8,030 90 2,677 33 1,606 12 2,411 7 10.00
1988 1,894 0 0 0 0 0 0 2,677 33 1,606 15 2,411 7 10.00
1989 59,737 0 0 0 0 0 0 2,677 11 1,606 9 2,411 6 10.00
1990 227,768 3,941 2 -82,225 -36 78,284 34 26,095 27 17,263 28 13,250 19 10.00
1991 1,758 0 0 0 0 0 0 26,095 27 17,263 29 13,250 19 10.00
1992 198,320 0 0 0 0 0 0 26,095 18 15,657 16 13,250 14 10.00
1993 4,400 501 11 0 0 -501 -11 -167 0 15,557 16 11,531 13 10.00
1994 578 0 0 -53 -9 53 9 30,766 13 18,460 13 10,255 13 10.00
1995 2,000 0 0 0 0 0 0 30,766 13 18,460 13 10,255 13 10.00
1996 98,261 2,120 2 -70,998 -72 68,878 70 22,977 68 32,235 20 16,118 20 10.00
1997 26,554 0 0 0 0 0 0 22,959 54 32,235 20 16,118 20 10.00
1998 0 0 0 0 0 0 0 22,959 55 13,786 54 16,118 20 10.00
1999 0 0 0 0 0 0 0 0 0 13,776 54 16,118 20 10.00
2000 0 0 0 0 0 0 0 0 0 13,776 55 16,118 20 10.00
2001 0 0 0 0 0 0 0 0 0 0 0 16,118 20 10.00
2002 946 0 0 0 0 0 0 0 0 0 0 16,118 20 10.00
2003 0 0 0 0 0 0 0 0 0 0 0 16,118 20 10.00
2004 0 0 0 0 0 0 0 0 0 0 0 16,118 20 10.00
2005 34,281 0 0 0 0 0 0 0 0 0 0 16,118 19 10.00
2006 568 0 0 0 0 0 0 0 0 0 0 16,118 19 10.00
2007 30,857 0 0 0 0 0 0 0 0 0 0 16,118 18 10.00
2008 257,582 0 0 0 0 0 0 0 0 0 0 16,118 14 10.00
2009 5,000 0 0 0 0 0 0 0 0 0 0 16,118 14 10.00
2010 16,965 0 0 0 0 0 0 0 0 0 0 16,118 14 10.00
2011 3,000 0 0 0 0 0 0 0 0 0 0 16,118 14 10.00
2012 74,354 0 0 -1 0 1 0 0 0 0 0 14,653 13 10.00
2013 28,531 0 0 0 0 0 0 0 0 0 0 14,653 13 10.00
2014 3,200 6,905 216 0 0 -6,905 -216 -2,301 -7 -1,381 -5 12,856 12 10.00
2015 405,861 750 0 0 0 -750 0 -2,552 -2 -1,531 -1 11,809 9 10.00
2016 152,577 69,604 46 -850,000 -557 780,396 511 257,580 138 154,548 116 66,709 51 10.00
2017 6,728 15,977 237 0 0 -15,977 -237 254,556 135 151,353 127 61,196 50 10.00
2018 81,519 22,214 27 0 0 -22,214 -27 247,402 308 146,910 113 55,983 47 10.00
2019 113,190 49,220 43 0 0 -49,220 -43 -29,137 -43 138,447 91 49,795 42 10.00
2020 61,993 10,950 18 0 0 -10,950 -18 -27,461 -32 136,407 164 46,420 40 10.00
2021 60,063 11,678 19 0 0 -1 1,678 -19 -23,949 -31 -22,008 -34 43,362 38 10.00
2022 155,288 107,360 69 0 0 -107,360 -69 -43,329 -47 -40,284 -43 35,826 31 10.00
2023 4,270,621 18,347 0 -6,100,523 -143 6,082,176 142 1,987,713 133 1,180,594 127 323,747 103 10.00
2024 87,170 96,227 110 0 0 -96,227 -1 10 1,959,530 130 1,171,192 126 304,658 101 10.00
TOTAL 6,667,874 415,795 6.24 -7,118,263 (106.75) 6,702,468 100.52
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Page 1 7-12

Intermountain Gas Company
ACCOUNT 392.1 - Transportation Equipment
SUMMARY OF BOOK SALVAGE
Cost of Cost of Gross Gross Net Net
Regular Removal Removal Salvage Salvage Salvage Salvage 3-Year 3-Year 5-Year 5-Year Historical Historical Concentric
Year Retirements Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Recommendation
1975 25,054 0 0 -7,681 -31 7,681 31 7,681 31 16.00
1976 16,152 0 0 -6,997 -43 6,997 43 7,339 36 16.00
1977 33,327 0 0 -1 1,525 -35 11,525 35 8,734 35 8,734 35 16.00
1978 118,966 0 0 -32,307 -27 32,307 27 16,943 30 14,628 30 16.00
1979 73,557 0 0 -18,836 -26 18,836 26 20,889 28 15,469 29 15,469 29 16.00
1980 69,116 0 0 -17,358 -25 17,358 25 22,834 26 17,405 28 15,784 28 16.00
1981 108,889 0 0 -28,567 -26 28,567 26 21,587 26 21,719 27 17,610 28 16.00
1982 33,355 0 0 -8,065 -24 8,065 24 17,997 26 21,027 26 16,417 27 16.00
1983 52,019 0 0 -12,535 -24 12,535 24 16,389 25 17,072 25 15,986 27 16.00
1984 68,174 0 0 -13,468 -20 13,468 20 11,356 22 15,999 24 15,734 26 16.00
1985 105,607 0 0 -19,939 -19 19,939 19 15,314 20 16,515 22 16,116 25 16.00
1986 303,286 0 0 -51,677 -17 51,677 17 28,361 18 21,137 19 19,080 23 16.00
1987 407,732 0 0 -67,162 -16 67,162 16 46,259 17 32,956 18 22,778 21 16.00
1988 124,972 0 0 -23,417 -19 23,417 19 47,419 17 35,133 17 22,824 21 16.00
1989 138,390 0 0 -27,082 -20 27,082 20 39,220 18 37,855 18 23,108 21 16.00
1990 155,897 0 0 -25,775 -17 25,775 17 25,425 18 39,023 17 23,274 20 16.00
1991 214,357 0 0 -32,202 -15 32,202 15 28,353 17 35,128 17 23,800 20 16.00
1992 35,430 0 0 -7,000 -20 7,000 20 21,659 16 23,095 17 22,866 20 16.00
1993 362,160 0 0 -71,807 -20 71,807 20 37,003 18 32,773 18 25,442 20 16.00
1994 168,651 0 0 -43,014 -26 43,014 26 175,471 20 105,283 20 26,321 20 16.00
1995 218,614 0 0 -44,160 -20 44,160 20 190,191 20 1 14,1 15 20 27,170 20 16.00
1996 343,112 0 0 -64,946 -19 64,946 19 50,707 21 127,104 20 28,887 20 16.00
1997 113,910 0 0 -19,512 -17 19,512 17 42,873 19 131,006 20 28,480 20 16.00
1998 182,103 0 0 -36,396 -20 36,396 20 40,285 19 41,606 20 28,810 20 16.00
1999 394,554 0 0 -50,504 -13 50,504 13 35,471 15 43,104 17 29,677 19 16.00
2000 185,586 0 0 -19,050 -10 19,050 10 35,317 14 38,082 16 29,269 19 16.00
2001 393,451 0 0 -48,850 -12 48,850 12 39,468 12 34,862 14 29,994 18 16.00
2002 181,752 0 0 -7,000 -4 7,000 4 24,967 10 32,360 12 29,173 18 16.00
2003 662,532 0 0 -35,399 -5 35,399 5 30,416 7 32,161 9 29,387 16 16.00
2004 521,347 0 0 -27,748 -5 27,748 5 23,382 5 27,609 7 29,333 15 16.00
2005 146,667 0 0 -12,261 -8 12,261 8 25,136 6 26,252 7 28,782 15 16.00
2006 250,914 0 0 -12,413 -5 12,413 5 17,474 6 18,964 5 28,270 15 16.00
2007 481,723 0 0 -24,461 -5 24,461 5 16,378 6 22,456 5 28,155 14 16.00
2008 1,495,559 0 0 -49,162 -3 49,162 3 28,679 4 25,209 4 28,773 12 16.00
2009 0 0 0 -20 0 20 0 24,548 4 19,663 4 27,951 12 16.00
2010 631,257 0 0 -64,578 -10 64,578 10 37,920 5 30,127 5 28,969 12 16.00
2011 418,459 0 0 -42,747 -10 42,747 10 35,782 10 36,194 6 29,341 12 16.00
2012 907,227 0 0 -71,955 -8 71,955 8 59,760 9 45,692 7 30,463 11 16.00
2013 635,853 20,301 3 -1 19,1 14 -19 98,813 16 71,172 11 55,623 11 32,215 12 16.00
2014 279,498 0 0 -59,446 -21 59,446 21 76,738 13 67,508 12 32,896 12 16.00
2015 841,443 0 0 -199,132 -24 199,132 24 119,130 20 94,419 15 36,950 13 16.00
2016 281,433 1,200 0 -99,352 -35 98,152 35 118,910 25 105,500 18 38,408 13 16.00
2017 458,737 700 0 -175,260 -38 174,560 38 157,281 30 126,021 25 41,574 14 16.00
2018 562,136 750 0 -180,151 -32 179,401 32 150,704 35 142,138 29 44,706 15 16.00
2019 931,549 0 0 -243,668 -26 243,668 26 199,210 31 178,983 29 49,128 16 16.00
2020 1,182,865 0 0 -343,301 -29 343,301 29 255,457 29 207,816 30 55,523 17 16.00
2021 718,824 0 0 -230,637 -32 230,637 32 272,535 29 234,313 30 59,249 17 16.00
2022 421,395 0 0 -130,672 -31 130,672 31 234,870 30 225,536 30 60,737 18 16.00
2023 817,285 0 0 -224,826 -28 224,826 28 195,378 30 234,621 29 64,085 18 16.00
2024 322,606 0 0 -119,569 -37 119,569 37 158,355 30 209,801 30 65,195 19 16.00
TOTAL 17,597,480 22,951 0.13 -3,282,703 (18.65) 3,259,752 18.52
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Page 1 7-13

Intermountain Gas Company
ACCOUNT 392.2 - Transportation Equipment - Trailers
SUMMARY OF BOOK SALVAGE
Cost of Cost of Gross Gross Net Net
Regular Removal Removal Salvage Salvage Salvage Salvage 3-Year 3-Year 5-Year 5-Year Historical Historical Concentric
Year Retirements Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Recommendation
2017 31,724 0 0 -3,500 -1 1 3,500 11 3,500 11 15.00
2018 57,634 0 0 -32,338 -56 32,338 56 17,919 40 15.00
2019 10,191 0 0 -8,100 -79 8,100 79 14,646 44 14,646 44 15.00
2020 42,197 0 0 -5,357 -13 5,357 13 15,265 42 12,324 35 15.00
2021 28,630 0 0 0 0 0 0 4,486 17 9,859 29 12,324 29 15.00
2022 0 0 0 0 0 0 0 1,786 8 9,159 33 12,324 29 15.00
2023 0 0 0 0 0 0 0 0 0 2,691 17 12,324 29 15.00
2024 0 0 0 0 0 0 0 0 0 1,071 8 12,324 29 15.00
TOTAL 170,376 0 0.00 -49,295 (28.93) 49,295 28.93
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Page 1 7-14

Intermountain Gas Company
ACCOUNT 396 - Power Operated Equipment
SUMMARY OF BOOK SALVAGE
Cost of Cost of Gross Gross Net Net
Regular Removal Removal Salvage Salvage Salvage Salvage 3-Year 3-Year 5-Year 5-Year Historical Historical Concentric
Year Retirements Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Amount Percent Recommendation
1975 0 0 0 0 0 30.00
1976 0 0 0 0 0 30.00
1977 0 0 0 0 0 0 0 30.00
1978 9,485 0 0 -7,702 -81 7,702 81 2,567 81 7,702 81 30.00
1979 1,208 0 0 -60 -5 60 5 2,587 73 1,552 73 3,881 73 30.00
1980 8,873 0 0 -10,525 -119 10,525 119 6,096 93 3,657 93 6,096 93 30.00
1981 2,282 0 0 0 0 0 0 3,528 86 3,657 84 6,096 84 30.00
1982 601 0 0 -2,840 -473 2,840 473 4,455 114 4,225 94 5,282 94 30.00
1983 18,105 0 0 -17,139 -95 17,139 95 6,660 95 6,113 98 7,653 94 30.00
1984 27,436 0 0 -1 1,627 -42 11,627 42 10,535 68 8,426 74 8,316 73 30.00
1985 9,228 0 0 0 0 0 0 9,589 53 6,321 55 8,316 65 30.00
1986 16,682 0 0 -2,047 -12 2,047 12 4,558 26 6,731 47 7,420 55 30.00
1987 846 0 0 -46 -5 46 5 698 8 6,172 43 6,498 55 30.00
1988 1,442 0 0 -100 -7 100 7 731 12 2,764 25 5,787 54 30.00
1989 31,348 0 0 0 0 0 0 49 0 439 4 5,787 41 30.00
1990 2,524 0 0 0 0 0 0 33 0 439 4 5,787 40 30.00
1991 10,182 0 0 0 0 0 0 0 0 29 0 5,787 37 30.00
1992 2,924 1,313 45 0 0 -1,313 -45 -438 -8 -243 -3 5,077 35 30.00
1993 5,427 0 0 -1,000 -18 1,000 18 -104 -2 -63 -1 4,707 35 30.00
1994 6,118 0 0 -525 -9 525 9 17,433 34 10,460 34 4,358 34 30.00
1995 42,263 0 -1,575 -4 1,575 4 17,958 27 10,775 27 4,144 27 30.00
1996 150,420 0 0 -128,142 -85 128,142 85 43,414 66 36,403 52 13,001 52 30.00
1997 24,791 0 0 -12,500 -50 12,500 50 47,406 65 38,903 52 12,968 52 30.00
1998 1,460 0 0 0 0 0 0 46,881 80 28,548 63 12,968 52 30.00
1999 16,019 1,000 6 -2,000 -12 1,000 6 4,500 32 28,643 61 12,220 50 30.00
2000 0 0 0 0 0 0 0 333 6 28,328 74 12,220 50 30.00
2001 0 0 0 0 0 0 0 333 6 2,700 32 12,220 50 30.00
2002 71,141 0 0 -26,519 -37 26,519 37 8,840 37 5,504 31 13,061 48 30.00
2003 58,087 0 0 0 0 0 0 8,840 21 5,504 19 13,061 43 30.00
2004 26,751 0 0 -7,100 -27 7,100 27 11,206 22 6,724 22 12,730 42 30.00
2005 6,898 0 0 -1,590 -23 1,590 23 2,897 9 7,042 22 12,143 42 30.00
2006 6,578 0 0 -815 -12 815 12 3,168 24 7,205 21 11,577 41 30.00
2007 80,454 0 0 -849 -1 849 1 1,085 3 2,071 6 11,066 36 30.00
2008 12,177 0 0 -15,900 -131 15,900 131 5,855 18 5,251 20 11,286 38 30.00
2009 136,995 15,900 12 -102,368 -75 86,468 63 34,406 45 21,124 43 14,555 42 30.00
2010 384,278 0 0 -153,518 -40 153,518 40 85,295 48 51,510 42 20,345 42 30.00
2011 204,071 0 0 -172,780 -85 172,780 85 137,589 57 85,903 53 26,442 48 30.00
2012 407,742 0 0 -300,904 -74 300,904 74 209,067 63 145,914 64 36,998 54 30.00
2013 274,088 0 0 -316,910 -116 316,910 116 263,531 89 206,116 73 47,365 62 30.00
2014 851,975 0 0 -742,318 -87 742,318 87 453,377 89 337,286 79 72,185 69 30.00
2015 530,191 0 0 -601,850 -1 14 601,850 114 553,693 100 426,952 94 90,450 76 30.00
2016 674,528 0 0 -650,284 -96 650,284 96 664,817 97 522,453 95 109,1 1 1 80 30.00
2017 0 0 0 -28,917 0 28,917 0 427,017 106 468,056 100 106,524 80 30.00
2018 798,310 0 0 -705,960 -88 705,960 88 461,720 94 545,866 96 125,256 82 30.00
2019 1,462,398 0 0 -1,500,758 -103 1,500,758 103 745,212 99 697,554 101 166,938 86 30.00
2020 956,924 0 0 -784,260 -82 784,260 82 996,993 93 734,036 94 185,095 86 30.00
2021 740,547 0 0 -725,833 -98 725,833 98 1,003,617 95 749,146 95 200,544 87 30.00
2022 518,769 0 0 -496,513 -96 496,513 96 668,869 91 842,665 94 208,766 87 30.00
2023 448,066 0 0 -570,318 -127 570,318 127 597,555 105 815,536 99 218,537 89 30.00
2024 1,223,427 0 0 -1,172,360 -96 1,172,360 96 746,397 102 749,857 96 243,638 90 30.00
TOTAL 10,264,059 18,213 0.18 -9,276,452 (90.38) 9,258,239 90.20
Concentric Energy Advisors Intermountain Gas Company 2025 Depreciation Study Page 1 7-15

Intermountain Gas Company
1@ 2025 Depreciation Study
SECTION 8
8 DETAILED DEPRECIATION CALCULATIONS
Concentric Energy Advisors Page 1 8-1

Intermountain Gas Company ALG - Remaining Life
S5
Account #: 361.00 - Structures and Improvements - Nampa Survivor Curve:e: 40
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -10%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1974 29,530.98 31,270 32,484 0.9626 0 1.54 0 50.5
1975 22,021.53 23,243 24,224 0.9595 0 1.66 0 49.5
1976 61612.08 6,952 7,273 0.9558 0 1.80 0 48.5
1978 823.18 858 905 0.9478 0 2.12 0 46.5
1980 31413.60 3,521 3,755 0.9376 0 2.52 0 44.5
1981 11890.00 1,937 2,069 0.9318 10 2.75 3 43.5
1982 11176.00 1,197 1,279 0.9251 15 3.01 5 42.5
1985 41080.28 4,042 4,318 0.9006 170 4.00 43 39.5
1988 204,785.98 194,872 208,188 0.8651 17,077 5.39 3,167 36.5
1989 106,911.98 100,101 106,941 0.8512 10,662 5.97 1,786 35.5
1990 482.46 443 473 0.8345 58 6.61 9 34.5
1998 21006.31 1,460 1,560 0.6615 647 13.52 48 26.5
2001 3,450.00 2,231 2,384 0.5879 1,411 16.50 86 23.5
2002 16,802.00 10,387 11,097 0.5620 7,385 17.50 422 22.5
2005 78,638.66 42,213 45,098 0.4880 41,405 20.50 2,020 19.5
2007 41218.80 2,033 2,172 0.4380 2,469 22.50 110 17.5
2009 49,641.40 21,187 22,635 0.3880 31,971 24.50 1,305 15.5
2011 1,4191909.67 527,922 563,996 0.3380 997,905 26.50 37,657 13.5
2012 56,816.45 19,499 20,832 0.3120 41,666 27.50 1,515 12.5
2013 511976.05 16,409 17,530 0.2870 39,644 28.50 1,391 11.5
2014 121,975.02 35,153 37,555 0.2620 96,617 29.50 3,275 10.5
2015 244,502.69 64,011 68,385 0.2380 200,568 30.50 6,576 9.5
2016 823,119.78 191,952 205,068 0.2120 700,364 31.50 22,234 8.5
2017 529,508.12 109,502 116,985 0.1880 465,474 32.50 14,322 7.5
2018 2,247,126.63 400,438 427,800 0.1620 2,044,039 33.50 61,016 6.5
2019 1,107,326.95 168,092 179,578 0.1380 1,038,482 34.50 30,101 5.5
2020 359,853.03 44,334 47,363 0.1120 348,475 35.50 9,816 4.5
2021 499,184.53 48,321 51,623 0.0880 497,480 36.50 13,630 3.5
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Pagel 8-2

Intermountain Gas Company ALG - Remaining Life
S5
Account #: 361.00 - Structures and Improvements - Nampa Survivor Curve:e: 40
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -10%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2022 924,435.45 63,046 67,355 0.0620 949,524 37.50 25,321 2.5
2023 48,939.26 2,046 2,185 0.0380 51,648 38.50 1,341 1.5
2024 596,911.28 7,879 8,418 0.0120 648,185 39.50 16,410 0.5
TOTAL 9,568,070.15 2,146,553 2,291,526 8,233,351 253,609
COMPOSITE ANNUAL ACCRUAL RATE 2.65%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.24
COMPOSITE AVERAGE AGE(YEARS) 8.29
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 31.84
Concentric Energy Advisors Intermountain GasCompany2025Depreciation Study Page 1 8-3

Intermountain Gas Company ALG - Remaining Life
R3
Account #: 361.10 - Structures and Improvements - Rexburg Survivor Curve:e: 25
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -15%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2008 1,142,296.01 772,683 1,171,658 0.5882 141,982 10.30 13,787 16.5
2009 1881414.65 120,884 183,302 0.5579 33,374 11.05 3,020 15.5
2011 183,686.36 104,542 158,523 0.4949 52,717 12.63 4,174 13.5
2014 64,059.96 29,040 44,035 0.3942 29,634 15.15 1,956 10.5
2016 18,595.15 6,916 10,487 0.3234 10,898 16.92 644 8.5
2017 3,975.88 1,313 1,991 0.2871 2,582 17.82 145 7.5
2018 177,844.87 51,151 77,563 0.2501 126,959 18.75 6,772 6.5
2019 771219.55 18,888 28,641 0.2127 60,161 19.68 3,057 5.5
2020 8,423.20 1,693 21568 0.1748 7,119 20.63 345 4.5
2021 9,161.50 1,438 2,181 0.1365 8,355 21.59 387 3.5
2022 47,566.10 5,350 8,112 0.0978 46,589 22.55 2,066 2.5
2023 22,833.94 1,547 2,345 0.0589 23,914 23.53 1,016 1.5
2024 23,441.46 531 805 0.0197 26,152 24.51 1,067 0.5
TOTAL 1,967,518.63 1,115,976 1,692,211 570,435 38,436
COMPOSITE ANNUAL ACCRUAL RATE 1.95%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.86
COMPOSITE AVERAGE AGE(YEARS) 13.68
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 12.67
Concentric Energy Advisors Intermountain GasCompany2025Depreciation Study Page 1 8-4

Intermountain Gas Company ALG - Remaining Life
Account #: 362.00 - Gas Holders - Nampa Survivor Curve: R4
ASL: 40
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -15%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1974 1,962,889.98 2,121,749 2,257,323 0.9399 0 2.42 0 50.5
2018 19,005.78 3,532 4,339 0.1616 17,518 33.52 523 6.5
2019 1,040,155.97 164,714 202,376 0.1377 993,804 34.51 28,796 5.5
2020 499,574.39 64,230 78,916 0.1118 495,594 35.51 13,957 4.5
2021 300,906.42 30,417 37,372 0.0879 308,670 36.51 8,455 3.5
2022 5,956,218.53 423,993 520,939 0.0619 6,328,712 37.50 168,751 2.5
2023 305,722.28 13,360 16,415 0.0380 335,166 38.50 8,705 1.5
2024 47,955.55 662 813 0.01201 54,336 39.501 1,376 0.5
TOTAL 10,132,428.90 2,822,657 3,118,494 8,533,800 230,563
COMPOSITE ANNUAL ACCRUAL RATE 2.28%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.31
COMPOSITE AVERAGE AGE (YEARS) 12.20
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 30.30
Concentric Energy Advisors Intermountain GasCompany2025Depreciation Study Page 1 8-5

Intermountain Gas Company ALG - Remaining Life
Account #: 362.10 - Gas Holders - Rexburg Survivor Curve: R4
ASL: 25
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -15%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2008 F 1,578,228.35 1,136,530 1,429,694 0.6262 385,268 9.35 41,219 16.5
TOTAL 1,578,228.35 1,136,530 1,429,694 385,268 41,219
COMPOSITE ANNUAL ACCRUAL RATE 2.61%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.91
COMPOSITE AVERAGE AGE(YEARS) 16.50
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 9.35
Concentric Energy Advisors Intermountain GasCompany2025Depreciation Study Page 1 8-6

Intermountain Gas Company ALG - Remaining Life
R2.5
Account #: 363.00 - Measuring & Regulating Equipment - Nampa Survivor Curve:e: 40
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -10%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1974 24,223.76 22,930 26,646 0.8606 0 5.85 0 50.5
2008 36,079.81 14,605 21,206 0.3680 18,481 25.25 732 16.5
2013 46,857.55 13,503 19,607 0.2620 31,937 29.50 1,083 11.5
2014 1,761.40 465 675 0.2401 1,262 30.37 42 10.5
2022 160,898.47 10,320 14,985 0.0583 162,003 37.65 4,303 2.5
2024 324.92 4 6 0.0113 352 39.53 9 0.5
TOTAL 270,145.91 61,827 83,126 214,035 6,169
COMPOSITE ANNUAL ACCRUAL RATE 2.28%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.31
COMPOSITE AVERAGE AGE (YEARS) 10.28
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 31.68
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Pagel 8-7

Intermountain Gas Company ALG - Remaining Life
R3
Account #: 363.10 - Measuring & Regulating Equipment - Rexburg Survivor Curve:e: 25
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -10%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2020 F 26,194.41 5,037 3,845 0.1748 24,969 20.63 1,210 4.5
TOTAL 26,194.41 51037 3,845 24,969 1,210
COMPOSITE ANNUAL ACCRUAL RATE 4.62%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.15
COMPOSITE AVERAGE AGE(YEARS) 4.50
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 20.63
Concentric Energy Advisors Intermountain GasCompany2025Depreciation Study Page 1 8-8

Intermountain Gas Company ALG - Remaining Life
R3
Account #: 363.16 - Purifications Equipment - Rexburg Survivor Curve:e: 25
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -10%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2008 F 655,656.47 424,223 621,301 0.5882 99,922 10.30 9,703 16.5
TOTAL 655,656.47 424,223 621,301 99,922 9,703
COMPOSITE ANNUAL ACCRUAL RATE 1.48%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.95
COMPOSITE AVERAGE AGE(YEARS) 16.50
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 10.30
Concentric Energy Advisors Intermountain GasCompany2025Depreciation Study Page 1 8-9

Intermountain Gas Company ALG - Remaining Life
R3
Account #: 363.17 - Vaporization Equipment - Rexburg Survivor Curve:e: 25
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -10%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2008 1,075,042.50 695,574 934,257 0.5882 248,290 10.30 24,110 16.5
2016 16,394.82 5,832 7,834 0.3234 10,201 16.92 603 8.5
TOTAL 1,091,437.32 701,406 942,091 258,490 24,713
COMPOSITE ANNUAL ACCRUAL RATE 2.26%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.86
COMPOSITE AVERAGE AGE(YEARS) 16.38
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 10.40
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 1 8-10

Intermountain Gas Company ALG - Remaining Life
Survivor Curve: R2.5
Account #: 363.40 - Compressor Equipment - Nampa ASL: 40
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -10%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1974 605,814.26 573,467 666,396 0.8606 0 5.85 0 50.5
1975 33,943.22 31,851 37,338 0.8531 0 6.13 0 49.5
1976 411469.22 38,532 45,616 0.8447 0 6.41 0 48.5
1977 781784.53 72,507 86,663 0.8367 0 6.71 0 47.5
1978 121320.36 11,221 13,552 0.8280 0 7.03 0 46.5
1980 214,409.82 190,796 231,275 0.8090 4,575 7.72 593 44.5
1981 861.77 757 918 0.7990 30 8.09 4 43.5
19821 8,796.16 7,630 9,249 0.7886 427 8.48 50 42.5
2001 450,240.75 250,609 303,778 0.5060 191,487 19.74 9,701 23.5
2002 421018.76 22,489 27,260 0.4866 18,961 20.49 925 22.5
2004 21,636.34 10,667 12,930 0.4482 10,870 22.03 493 20.5
2005 263,541.52 124,470 150,877 0.4294 139,019 22.82 6,093 19.5
2007 12,544.93 5,371 6,511 0.3892 7,289 24.43 298 17.5
2009 4041287.68 154,797 187,638 0.3481 257,078 26.08 9,858 15.5
2014 3,615,285.56 954,674 1,157,217 0.2401 2,819,597 30.37 92,831 10.5
2015 451426.45 10,937 13,257 0.2189 36,712 31.26 1,174 9.5
2016 2,394,483.41 515,434 624,788 0.1957 2,009,144 32.15 62,490 8.5
2021 1,1581141.241 105,089 127,384 0.0825 1,146,571 36.72 31,226 3.5
2023 14,358.66 566 686 0.0358 15,109 38.59 392 1.5
TOTAL 9,418,364.64 3,081,864 3,703,334 6,656,867 216,128
COMPOSITE ANNUAL ACCRUAL RATE 2.29%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.39
COMPOSITE AVERAGE AGE (YEARS) 14.33
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 28.11
Concentric Energy Advisors lntermountainGasCompany2025 Depreciation Study Page 1 8-11

Intermountain Gas Company ALG - Remaining Life
R2.5
Account #: 363.50 - Liquefaction Equipment - Nampa Survivor Curve:e: 40
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -10%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1974 766,942.95 725,992 843,637 0.8606 0 5.85 0 50.5
1976 3,213.78 2,986 3,535 0.8447 0 6.41 0 48.5
1980 682.87 608 751 0.8090 0 7.72 0 44.5
1989 3,964.75 3,066 4,361 0.7030 0 11.84 0 35.5
2006 75,896.00 34,113 68,253 0.4086 15,232 23.62 645 18.5
2009 834,782.51 319,628 639,510 0.3481 278,751 26.08 10,689 15.5
2010 51,986.05 18,659 37,332 0.3263 19,852 26.92 737 14.5
20111 184,655.42 62,143 124,335 0.3059 78,786 27.77 2,837 13.5
2012 196,404.44 61,275 122,598 0.2836 93,447 28.63 3,264 12.5
2013 315,334.28 90,871 181,813 0.2620 165,054 29.50 5,596 11.5
2014 92,546.59 24,438 48,896 0.2401 52,905 30.37 1,742 10.5
2015 603,713.98 145,348 290,812 0.2189 373,273 31.26 11,941 9.5
2016 177,287.02 38,163 76,356 0.1957 118,660 32.15 3,691 8.5
2017 67,025.39 12,835 25,681 0.1741 48,047 33.05 1,454 7.5
2018 145,037.87 24,014 48,047 0.1505 111,494 33.96 3,283 6.5
2019 381614.83 5,463 10,931 0.1286 31,545 34.87 905 5.5
2020 379,737.81 43,734 87,503 0.1047 330,208 35.79 9,226 4.5
2022 170,218.78 10,918 21,845 0.0583 165,396 37.65 4,393 2.5
2024 6.39 0 0 0.0113 7 39.53 0 0.5
TOTAL 4,108,051.71 1,624,255 2,636,198 1,882,659 60,403
COMPOSITE ANNUAL ACCRUAL RATE 1.47%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.64
COMPOSITE AVERAGE AGE (YEARS) 18.19
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 25.67
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 8-12

Intermountain Gas Company ALG - Remaining Life
R2.5
Account #: 363.70 - Purifications Equipment - Nampa Survivor Curve:e: 40
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -10%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1974 421,248.92 398,756 463,374 0.8606 0 5.85 0 50.5
1976 3,206.71 2,980 3,527 0.8447 0 6.41 0 48.5
2014 731234.13 19,339 45,007 0.2401 35,550 30.37 1,170 10.5
2015 243,406.16 58,602 136,385 0.2189 131,362 31.26 4,202 9.5
2016 36,741.47 7,909 18,407 0.1957 22,009 32.15 685 8.5
2017 241754.64 4,740 11,033 0.1741 16,197 33.05 490 7.5
2018 2981234.89 49,379 114,921 0.1505 213,137 33.96 6,276 6.5
20191 97,871.44 13,847 32,226 0.1286 75,432 34.87 2,163 5.5
2022 223,458.52 14,333 33,357 0.0583 212,447 37.65 5,643 2.5
2024 890,869.31 11,113 25,863 0.0113 954,094 39.53 24,137 0.5
TOTAL 2,313,026.19 580,998 884,100 1,660,229 44,766
COMPOSITE ANNUAL ACCRUAL RATE 1.94%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.38
COMPOSITE AVERAGE AGE(YEARS) 12.32
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 30.91
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 8-13

Intermountain Gas Company ALG - Remaining Life
R2.5
Account #: 363.80 - Vaporization Equipment - Nampa Survivor Curve:e: 40
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -10%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1974 793,945.86 751,553 873,340 0.8606 0 5.85 0 50.5
1976 2,116.63 1,967 2,328 0.8447 0 6.41 0 48.5
1978 11364.93 1,243 1,501 0.8280 0 7.03 0 46.5
1982 22,003.74 19,087 23,844 0.7886 360 8.48 42 42.5
2013 1081527.83 31,275 39,068 0.2620 80,313 29.50 2,723 11.5
2015 381,643.37 91,883 114,780 0.2189 305,028 31.26 9,758 9.5
2016 487,067.48 104,846 130,972 0.1957 404,802 32.15 12,591 8.5
2017 39,266.84 7,520 9,393 0.1741 33,800 33.05 1,023 7.5
2021 262,431.83 23,813 29,747 0.0825 258,928 36.72 7,052 3.5
2022 179,856.43 11,536 14,411 0.0583 183,431 37.65 4,872 2.5
TOTAL 2,278,224.94 1,044,723 1,239,384 1,266,663 38,061
COMPOSITE ANNUAL ACCRUAL RATE 1.67%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.54
COMPOSITE AVERAGE AGE(YEARS) 22.77
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 23.42
Concentric Energy Advisors lntermountainGasCompany2025 Depreciation Study Page 8-14

Intermountain Gas Company ALG - Remaining Life
Account #: 365.00 - Transmission - Rights of Way Survivor Curve: R5
ASL: 55
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 0/
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1973 755.00 656 755 0.8684 0 7.23 0 51.5
1974 43,519.94 37,336 43,520 0.8579 0 7.81 0 50.5
1975 21191.15 1,856 2,191 0.8469 0 8.42 0 49.5
1976 500.00 418 500 0.8353 0 9.07 0 48.5
1978 31681.52 2,981 3,682 0.8097 0 10.45 0 46.5
1980 1,500.00 1,174 1,500 0.7826 0 11.95 0 44.5
1981 61437.75 4,947 6,438 0.7684 0 12.74 0 43.5
1987 61087.00 4,106 5,721 0.6746 366 17.91 20 37.5
1995 223,000.00 119,390 166,344 0.5354 56,656 25.54 2,219 29.5
19981 118,381.00 57,045 79,480 0.4819 38,901 28.51 1,365 26.5
1999 39,568.00 18,356 25,575 0.4639 13,993 29.50 474 25.5
2000 11425.00 634 884 0.4450 541 30.50 18 24.5
2001 153,012.29 65,336 91,032 0.4270 61,980 31.50 1,968 23.5
2006 8,209.00 2,758 3,843 0.3360 4,366 36.50 120 18.5
2007 15,446.00 4,912 6,844 0.3180 8,602 37.50 229 17.5
2010 541905.88 14,495 20,196 0.2640 34,710 40.50 857 14.5
2011 65,951.00 16,158 22,513 0.2450 43,438 41.50 1,047 13.5
2012 25,956.35 5,892 8,209 0.2270 17,747 42.50 418 12.5
2013 3,376.43 706 983 0.2090 2,393 43.50 55 11.5
2015 81961.84 1,550 21160 0.1730 6,802 45.50 149 9.5
TOTAL 782,865.15 360,705 492,368 290,497 8,939
COMPOSITE ANNUAL ACCRUAL RATE 1.14%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.63
COMPOSITE AVERAGE AGE (YEARS) 25.58
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 29.65
Concentric Energy Advisors lntermountainGasCompany2025 Depreciation Study Page 1 8-15

Intermountain Gas Company ALG - Remaining Life
R5
Account #: 366.00 - Transmisison - Structures and Improvements Survivor Curve:e: 35
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -5/0
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1965 10,807.91 11,348 11,348 1.0000 0 0 59.5
1970 452.72 475 475 1.0000 0 0 54.5
1976 101876.28 11,420 11,420 1.0000 0 0 48.5
1977 21499.81 2,611 2,625 0.9946 0 0.50 0 47.5
1980 411.08 421 432 0.9761 0 0.90 0 44.5
1990 735.75 691 773 0.8942 0 3.72 0 34.5
2001 51036.87 3,514 3,985 0.6645 1,304 11.73 111 23.5
20021 46,331.69 31,066 35,227 0.6386 13,421 12.66 1,061 22.5
TOTAL 771152.11 61,547 66,285 14,725 1,172
COMPOSITE ANNUAL ACCRUAL RATE 1.52%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.86
COMPOSITE AVERAGE AGE (YEARS) 32.64
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 8.42
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 1 8-16

Intermountain Gas Company ALG - Remaining Life
R4
Account #: 367.00 - Transmission - Mains Survivor Curve:e: 63
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -35%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1959 6,614,318.46 7,777,446 8,929,330 0.8710 0 8.14 0 65.5
1961 61,196.72 70,826 82,616 0.8573 0 9.00 0 63.5
1962 7221647.02 829,101 975,573 0.8499 0 9.46 0 62.5
1963 601,395.52 683,606 811,884 0.8420 0 9.95 0 61.5
1964 1,6171643.58 1,820,650 2,183,819 0.8337 0 10.47 0 60.5
1965 4,110,975.77 4,578,821 5,549,817 0.8250 0 11.01 0 59.5
1966 4521154.18 498,404 610,408 0.8165 0 11.58 0 58.5
1967 15,384.13 16,760 20,769 0.8070 0 12.17 0 57.5
1968 32,521.30 35,001 43,904 0.7972 0 12.79 0 56.5
1969 74,457.86 79,112 100,518 0.7870 0 13.42 0 55.5
1970 188,990.95 198,140 255,138 0.7766 0 14.07 0 54.5
1972 427,463.66 435,773 577,076 0.7551 0 15.41 0 52.5
1973 9,956.61 10,002 13,441 0.7441 0 16.10 0 51.5
1974 2,690,017.77 2,664,086 3,631,524 0.7336 0 16.80 0 50.5
1975 760,490.87 741,517 1,026,663 0.7223 0 17.51 0 49.5
1976 229,536.52 220,228 309,243 0.7107 631 18.23 35 48.5
1978 145,456.68 134,920 189,453 0.6871 6,913 19.71 351 46.5
1980 6521878.25 584,024 820,084 0.6626 61,302 21.24 2,886 44.5
1982 13,878.77 11,958 16,791 0.6382 1,946 22.81 85 42.5
1983 4,793.08 4,047 5,682 0.6254 788 23.62 33 41.5
1984 5,013.09 4,144 5,819 0.6123 949 24.43 39 40.5
1985 17,507.75 14,160 19,883 0.5991 3,753 25.26 149 39.5
1987 3,681.57 2,843 3,992 0.5720 978 26.95 36 37.5
1990 82,182.14 58,926 82,743 0.5311 28,203 29.56 954 34.5
1994 13,086.33 8,362 11,742 0.4733 5,924 33.17 179 30.5
1995 2,392,909.38 1,481,280 2,080,008 0.4585 1,150,419 34.10 33,740 29.5
1997 12,066.39 6,998 9,826 0.4296 6,463 35.96 180 27.5
1998 1,908,086.81 1,067,821 1,499,430 0.4145 1,076,487 36.91 29,168 26.5
Concentric Energy Advisors lntermountainGasCompany2025 Depreciation Study Page 1 8-17

Intermountain Gas Company ALG - Remaining Life
R4
Account #: 367.00 - Transmission - Mains Survivor Curve:e: 63
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -35%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1999 3,307,004.60 1,782,881 2,503,514 0.3994 1,960,942 37.86 51,801 25.5
2000 2,397,678.51 1,243,118 1,745,582 0.3841 1,491,284 38.81 38,426 24.5
2001 1031080.54 51,319 72,062 0.3688 67,097 39.77 1,687 23.5
2002 698,071.43 332,968 467,552 0.3533 474,845 40.73 11,658 22.5
2003 954,963.96 435,582 611,643 0.3379 677,558 41.70 16,248 21.5
2004 129,038.44 56,145 78,839 0.3223 95,363 42.67 2,235 20.5
2005 1,855,157.47 770,623 1,082,106 0.3077 1,422,356 43.65 32,588 19.5
2006 7,478,533.73 2,948,240 4,139,907 0.2920 5,956,113 44.62 133,471 18.5
2007 1301066.18 48,522 68,135 0.2763 107,454 45.61 2,356 17.5
2008 4071833.42 143,469 201,458 0.2606 349,117 46.59 7,494 16.5
2009 203,500.58 67,264 94,452 0.2448 180,274 47.57 3,789 15.5
2010 217,436.58 67,221 94,391 0.2290 199,149 48.56 4,101 14.5
2011 1,015,492.08 292,224 410,340 0.2132 960,574 49.55 19,385 13.5
2012 20,423,898.16 5,440,559 7,639,612 0.1973 19,932,650 50.54 394,373 12.5
2013 5,487,033.34 1,351,646 1,897,976 0.1825 5,509,519 51.53 106,908 11.5
2014 726,830.36 163,403 229,449 0.1665 751,771 52.53 14,312 10.5
2017 39,784.77 6,381 8,960 0.1188 44,750 55.51 806 7.5
2021 6111121.38 46,118 64,759 0.0559 760,255 59.50 12,776 3.5
2022 5031477.53 27,188 38,177 0.0400 641,518 60.50 10,603 2.5
2023 1,381,664.42 44,766 62,860 0.0240 1,802,387 61.50 29,306 1.5
2024 514,482.02 5,556 7,802 0.0080 686,748 62.50 10,988 0.5
Concentric Energy Advisors lntermountainGasCompany2025 Depreciation Study Page 1 8-18

Intermountain Gas Company ALG - Remaining Life
R4
Account #: 367.00 - Transmission - Mains Survivor Curve:e: 63
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -35%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
TOTAL 72,446,840.66 39,364,146 51,386,753 46,416,482 973,146
COMPOSITE ANNUAL ACCRUAL RATE 1.34%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.71
COMPOSITE AVERAGE AGE(YEARS) 27.54
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 37.64
Concentric Energy Advisors lntermountainGasCompany2025 Depreciation Study Page 1 8-19

Intermountain Gas Company ALG - Remaining Life
L1.5
Account #: 368.00 - Transmission - Compressor Station Survivor Curve:e: 20
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 5%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2011 1,594,189.11 709,837 679,662 0.4687 8341818 10.58 78,882 13.5
2012 3,616.39 1,542 1,476 0.4488 1,959 10.98 178 12.5
2020 7,844.36 1,517 1A53 0.2036 5,999 15.93 377 4.5
2021 11,025.84 1,695 1,622 0.1618 8,852 16.76 528 3.5
2023 7,503,606.23 511,465 489,722 0.0718 6,638,703 18.57 357,583 1.5
2024 79,651.36 1,829 1,752 0.0242 73,917 19.52 3,787 0.5
TOTAL 9,199,933.29 1,227,884 1,175,688 7,564,249 441,335
COMPOSITE ANNUAL ACCRUAL RATE 4.80%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.13
COMPOSITE AVERAGE AGE (YEARS) 3.58
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 17.18
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Pagel 8-20

Intermountain Gas Company ALG - Remaining Life
R5
Account #: 374.00 - Distribution - Land Rights Survivor Curve:e: 65
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 0/
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1959 115,054.57 104,035 115,055 0.9042 0 6.24 0 65.5
1960 4,841.80 4,343 4,842 0.8970 0 6.69 0 64.5
1961 21165.70 1,927 2,166 0.8899 0 7.16 0 63.5
1962 41842.48 4,273 4,842 0.8824 0 7.67 0 62.5
1963 4,095.30 3,579 4,095 0.8739 0 8.20 0 61.5
1964 7,547.22 6,533 7,547 0.8656 0 8.75 0 60.5
1965 31,191.89 26,703 31,192 0.8561 0 9.34 0 59.5
1966 11497.84 1,269 1,498 0.8469 0 9.951 0 58.5
1967 400.00 335 400 0.8373 0 10.60 0 57.5
1968 150.00 124 150 0.8266 0 11.27 0 56.5
1969 460.00 375 460 0.8161 0 11.96 0 55.5
1970 636.92 512 637 0.8045 0 12.68 0 54.5
1971 1,866.69 1,481 1,867 0.7934 0 13.43 0 53.5
1972 31110.00 2,432 3,110 0.7818 0 14.20 0 52.5
1973 11485.00 1,142 1,485 0.7692 0 14.99 0 51.5
1974 7,729.62 5,852 7,730 0.7570 0 15.80 0 50.5
1976 11500.00 1,097 1,500 0.7311 0 17.47 0 48.5
1978 2,350.00 1,655 2,350 0.7042 0 19.21 0 46.5
1979 2,256.04 1,559 21256 0.6909 0 20.09 0 45.5
1980 11414.00 958 1,414 0.6774 0 21.00 0 44.5
1981 5,272.14 3,494 5,272 0.6627 0 21.91 0 43.5
1985 1,963.50 1,189 1,964 0.6054 0 25.67 0 39.5
1990 2,500.00 1,326 21500 0.5305 0 30.54 0 34.5
1991 1,616.00 832 1,616 0.5147 0 31.53 0 33.5
1992 4,536.00 2,267 4,536 0.4997 0 32.52 0 32.5
1993 7,502.00 3,637 7,414 0.4849 88 33.51 3 31.5
1994 21512.00 11178 2,401 0.4689 111 34.51 3 30.5
1995 171131.00 7,777 15,851 0.4540 1,280 35.50 36 29.5
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 1 8-21

Intermountain Gas Company ALG - Remaining Life
R5
Account #: 374.00 - Distribution - Land Rights Survivor Curve:e: 65
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 0/
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1996 3,032.00 1,328 2,707 0.4380 325 36.50 9 28.5
1997 10,522.20 4,451 9,072 0.4230 11450 37.50 39 27.5
1998 111165.00 4,555 9,285 0.4080 1,880 38.50 49 26.5
1999 61193.00 2,428 4,948 0.3920 1,245 39.50 32 25.5
2000 1,273.91 480 979 0.3770 295 40.50 7 24.5
2001 31817.00 1,382 2,816 0.3620 1,001 41.50 24 23.5
2002 17,234.22 5,963 12,154 0.3460 5,080 42.50 120 22.5
2003 34,288.80 11,350 23,133 0.3310 11,156 43.501 256 21.5
2004 2,225.00 701 1,429 0.3150 796 44.50 18 20.5
2005 141299.00 4,290 8,743 0.3000 5,556 45.50 122 19.5
2006 347.50 99 202 0.2850 146 46.50 3 18.5
2007 30,027.00 8,077 16,463 0.2690 13,564 47.50 286 17.5
2008 7,211.00 1,832 3,733 0.2540 3,478 48.50 72 16.5
2009 41211.00 1,002 2,043 0.2380 2,168 49.50 44 15.5
2010 19,860.45 4,429 9,027 0.2230 10,833 50.50 215 14.5
2012 9,528.00 1,829 31729 0.1920 5,799 52.50 110 12.5
2013 10,081.62 1,784 3,637 0.1770 6,445 53.50 120 11.5
2014 8,986.15 1,456 2,967 0.1620 6,019 54.50 110 10.5
2015 191,099.93 27,901 56,868 0.1460 134,232 55.50 2,419 9.5
2016 18,673.03 2,446 4,986 0.1310 13,687 56.50 242 8.5
2017 11,994.28 1,379 2,811 0.1150 9,183 57.50 160 7.5
2018 559,015.81 55,902 113,940 0.1000 445,076 58.50 7,608 6.5
2019 311122.61 2,645 5,392 0.0850 25,731 59.501 432 5.5
2020 33,395.61 2,304 4,697 0.0690 28,699 60.50 474 4.5
2022 65,287.93 2,481 5,057 0.0380 60,231 62.50 964 2.5
2023 136,730.97 3,145 6,410 0.0230 130,321 63.50 2,052 1.5
2024 4,997.97 40 81 0.0080 4,916 64.50 76 0.5
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 1 8-22

Intermountain Gas Company ALG - Remaining Life
R5
Account #: 374.00 - Distribution - Land Rights Survivor Curve:e: 65
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 0/
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
TOTAL 1,484,248.70 347,560 553,456 930,792 16,105
COMPOSITE ANNUAL ACCRUAL RATE 1.09%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.37
COMPOSITE AVERAGE AGE(YEARS) 15.93
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 49.78
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 1 8-23

Intermountain Gas Company ALG - Remaining Life
R4
Account #: 375.00 - Distribution - Structures and Improvements Survivor Curve:e: 55
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -5/
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1962 6,580.69 6,252 5,708 0.9048 1,201 5.24 229 62.5
1967 5,513.17 5,054 4,614 0.8730 1,174 6.98 168 57.5
1968 5,922.78 5,383 4,915 0.8656 1,304 7.39 176 56.5
1969 847.26 763 697 0.8578 193 7.83 25 55.5
2022 171,095.141 8,075 7,373 0.0450 172,276 52.50 3,281 2.5
2024 122,391.13 1,157 11056 0.0090 127,455 54.50 2,339 0.5
TOTAL 312,350.17 26,683 24,364 303,603 6,218
COMPOSITE ANNUAL ACCRUAL RATE 1.99%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.08
COMPOSITE AVERAGE AGE (YEARS) 5.12
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 50.51
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Pagel 8-24

Intermountain Gas Company ALG - Remaining Life
Account #: 376.00 - Distribution - Mains Survivor Curve: R4
ASL: 70
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -50%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1959 9,194,773.67 11,316,744 13,094,401 0.8205 697,760 12.58 55,475 65.5
1960 1,324,136.63 1,612,381 1,865,657 0.8118 120,547 13.16 9,162 64.5
1961 1,227,257.43 1,478,913 1,711,223 0.8034 129,663 13.76 9,423 63.5
1962 1,436'211.47 1,712,014 1,980,941 0.7947 173,376 14.38 12,057 62.5
1963 1,414,647.17 1,667,339 1,929,247 0.7858 192,723 15.02 12,833 61.5
1964 1,424,955.35 1,658,520 1,919,043 0.7759 218,390 15.67 13,936 60.5
1965 2,834,235.86 3,259,513 3,771,524 0.7667 479,830 16.34 29,374 59.5
19661 999,208.84 1,134,871 1,313,139 0.7572 185,674 17.01 10,914 58.5
1967 315,474.72 353,437 408,956 0.7469 64,256 17.70 3,631 57.5
1968 2591874.28 287,330 332,464 0.7371 57,347 18.39 3,118 56.5
1969 483,684.08 527,624 610,505 0.7272 115,021 19.10 6,022 55.5
1970 568,989.33 612,178 708,341 0.7173 145,143 19.82 7,325 54.5
1971 841,170.28 891,203 1,031,195 0.7063 230,560 20.54 11,223 53.5
1972 1,7021151.69 1,777,046 2,056,188 0.6960 497,039 21.28 23,359 52.5
1973 1,580,757.70 1,625,556 1,880,902 0.6856 490,234 22.03 22,256 51.5
1974 1,224,477.57 1,238,241 1,432,746 0.6742 403,970 22.78 17,730 50.5
1975 970,323.40 965,554 1,117,226 0.6634 338,260 23.55 14,361 49.5
1976 922,645.82 902,998 1,044,843 0.6525 339,126 24.33 13,936 48.5
1977 1,244,793.04 1,197,615 1,385,739 0.6414 481,450 25.12 19,163 47.5
1978 1,694'753.61 1,600,017 1,851,351 0.6294 690,780 25.93 26,644 46.5
1979 1,284,141.86 1,190,592 1,377,613 0.6181 548,600 26.74 20,518 45.5
1980 1,269,449.52 1,154,920 1,336,337 0.6065 567,837 27.56 20,604 44.5
1981 1,461,654.60 1,302,422 1,507,009 0.5940 685,473 28.39 24,143 43.5
1982 948,496.65 828,393 958,519 0.5823 464,226 29.23 15,879 42.5
1983 907,766.99 776,522 898,500 0.5703 463,151 30.09 15,394 41.5
1984 1,234,680.03 1,033,853 1,196,253 0.5582 655,767 30.95 21,189 40.5
1985 1,350,606.35 1,104,485 1,277,980 0.5452 747,929 31.82 23,505 39.5
1986 1,171,766.74 936,652 1,083,783 0.5329 673,867 32.70 20,609 38.5
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 8-25

Intermountain Gas Company ALG - Remaining Life
Account #: 376.00 - Distribution - Mains Survivor Curve: R4
ASL: 70
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -50%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1987 1,132,453.58 884,061 1,022,931 0.5204 675,749 33.59 20,119 37.5
1988 9041572.50 687,927 795,988 0.5070 560,870 34.48 16,265 36.5
1989 1,192,665.30 884,427 1,023,355 0.4944 765,643 35.39 21,636 35.5
1990 2,538,817.87 1,833,890 2,121,961 0.4816 1,686,266 36.30 46,455 34.5
1991 2,341,753.19 1,646,615 1,905,269 0.4688 1,607,361 37.22 43,189 33.5
1992 3,852,422.07 2,628,238 3,041,087 0.4548 2,737,546 38.14 71,772 32.5
1993 3,746'143.01 2,482,569 2,872,536 0.4418 2,746,678 39.07 70,295 31.5
1994 4,3241724.12 2,780,625 3,217,411 0.4286 3,269,675 40.01 81,719 30.5
1995 4,095,498.60 2,546,622 2,946,651 0.4145 3,196,597 40.95 78,053 29.5
1996 4,435,180.45 2,669,424 3,088,743 0.4013 3,564,028 41.90 85,055 28.5
1997 5,709,042.95 3,321,635 3,843,405 0.3879 4,720,160 42.86 110,140 27.5
1998 3,485,201.81 1,958,021 2,265,591 0.3745 2,962,211 43.81 67,610 26.5
1999 7,303,422.91 3,944,725 4,564,370 0.3601 6,390,764 44.78 142,729 25.5
2000 4,365,397.46 2,269,570 2,626,079 0.3466 3,922,017 45.74 85,744 24.5
2001 3,146,439.60 1,571,741 1,818,633 0.3330 2,901,026 46.71 62,106 23.5
2002 3,386,904.43 1,617,484 1,871,562 0.3184 3,208,795 47.68 67,294 22.5
2003 3,919'945.81 1,791,964 2,073,449 0.3048 3,806,469 48.66 78,227 21.5
2004 3,831,045.67 1,672,481 1,935,198 0.2910 3,811,370 49.64 76,784 20.5
2005 4,731,463.39 1,968,194 2,277,362 0.2773 4,819,833 50.62 95,219 19.5
2006 6,026'700.42 2,373,556 2,746,399 0.2626 6,293,652 51.60 121,966 18.5
2007 8,106,857.74 3,025,479 3,500,728 0.2488 8,659,559 52.59 164,672 17.5
2008 5,637,711.31 1,986,786 2,298,874 0.2349 6,157,693 53.57 114,938 16.5
2009 1,938,496.42 639,966 740,493 0.2201 2,167,252 54.56 39,720 15.5
2010 7521885.52 232,901 269,486 0.2062 859,842 55.551 15,478 14.5
2011 2,270,109.64 655,051 757,948 0.1924 2,647,216 56.54 46,817 13.5
2012 3,568,906.44 955,575 1,105,678 0.1785 4,247,681 57.54 73,825 12.5
2013 4,378,033.18 1,074,107 1,242,830 0.1636 5,324,220 58.53 90,965 11.5
2014 6,095,651.40 1,367,864 1,582,731 0.1496 7,560,746 59.53 127,018 10.5
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Pagel 8-26

Intermountain Gas Company ALG - Remaining Life
Account #: 376.00 - Distribution - Mains Survivor Curve: R4
ASL: 70
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -50%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2015 8,370,062.39 1,703,726 1,971,351 0.1357 10,583,743 60.52 174,879 9.5
2016 9,829,403.48 1,780,940 2,060,694 0.1208 12,683,411 61.52 206,179 8.5
2017 10,499,286.02 1,681,986 1,946,195 0.1068 13,802,734 62.51 220,797 7.5
2018 12,979'652.06 1,808,130 2,092,155 0.0929 17,377,323 63.51 273,614 6.5
2019 18,681,677.64 2,210,977 2,558,281 0.0789 25,464,235 64.51 394,746 5.5
2020 20,795,713.83 1,993,269 2,306,376 0.0639 28,887,195 65.51 440,986 4.5
2021 16,356'465.14 1,224,281 1,416,594 0.0499 23,118,104 66.50 347,619 3.5
20221 26,502,745.03 1,431,148 1,655,956 0.0360 38,098,162 67.50 564,393 2.5
2023 31,241,686.82 984,113 1,138,700 0.0210 45,723,831 68.50 667,485 1.5
2024 27,374,574.91 287,433 332,584 0.0070 40,729,279 69.50 586,026 0.5
TOTAL 331,142,798.79 110,724,439 128,117,262 368,596,936 6,476,317
COMPOSITE ANNUAL ACCRUAL RATE 1.96%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.39
COMPOSITE AVERAGE AGE(YEARS) 16.30
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 54.39
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 8-27

Intermountain Gas Company ALG - Remaining Life
SO
Account #: 378.00 - Distribution - Measure and Reg Station Equip - General Survivor Curve:e: 45
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -30%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1959 127,730.97 131,811 135,237 0.7938 301813 9.29 3,316 65.5
1960 3,297.38 3,364 3,451 0.7847 835 9.69 86 64.5
1961 111455.38 11,555 11,855 0.7759 3,037 10.09 301 63.5
1965 39,696.88 38,179 39,172 0.7398 12,434 11.71 1,062 59.5
1966 57,801.59 54,914 56,341 0.7308 18,801 12.12 1,551 58.5
1968 133.27 123 127 0.7126 47 12.94 4 56.5
1970 8,412.58 7,588 7,785 0.6938 3,151 13.78 229 54.5
1972 36,501.96 32,040 32,873 0.6752 14,579 14.63 997 52.5
1973 27,954.76 24,181 24,809 0.6654 11,532 15.05 766 51.5
1974 13,683.48 11,669 11,972 0.6560 5,817 15.48 376 50.5
1975 621865.78 52,827 54,201 0.6464 27,525 15.91 1,730 49.5
1977 18,597.97 15,165 15,559 0.6272 8,618 16.79 513 47.5
1978 4,951.20 3,972 4,075 0.6171 2,361 17.23 137 46.5
1979 51216.91 4,119 4,226 0.6073 2,556 17.67 145 45.5
1980 23,179.54 18,003 18,471 0.5975 11,662 18.12 644 44.5
1981 116,230.09 88,778 91,086 0.5876 60,013 18.57 3,232 43.5
1982 27,339.94 20,513 21,046 0.5771 14,496 19.02 762 42.5
1983 17,207.71 12,684 13,014 0.5670 9,356 19.48 480 41.5
1984 12,942.94 9,370 9,614 0.5569 7,212 19.94 362 40.5
1986 33,185.23 23,140 23,741 0.5364 19,399 20.87 929 38.5
1988 33,672.12 22,543 23,129 0.5150 20,645 21.82 946 36.5
1989 36,654.20 24,035 24,660 0.5044 22,990 22.31 1,031 35.5
1990 48,293.03 30,997 31,803 0.4937 30,978 22.79 1,359 34.5
1991 401561.00 25,437 26,098 0.4824 26,631 23.28 1,144 33.5
1992 1,418.10 869 892 0.4715 952 23.78 40 32.5
1993 59,769.29 35,781 36,711 0.4605 40,989 24.28 1,688 31.5
1994 878.38 513 526 0.4494 615 24.79 25 30.5
1995 51,523.73 29,346 30,108 0.4381 36,872 25.30 1,458 29.5
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 1 8-28

Intermountain Gas Company ALG - Remaining Life
SO
Account #: 378.00 - Distribution - Measure and Reg Station Equip - General Survivor Curve:e: 45
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -30%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1996 18,516.37 10,258 10,525 0.4262 13,546 25.81 525 28.5
1997 1341811.74 72,682 74,571 0.4147 100,684 26.34 3,823 27.5
1998 251,347.64 131,701 135,124 0.4031 191,628 26.87 7,132 26.5
1999 285,425.48 145,186 148,960 0.3913 222,093 27.40 8,105 25.5
2000 56,254.94 27,699 28,419 0.3788 44,712 27.95 1,600 24.5
2002 461912.11 21,613 22,175 0.3544 38,811 29.05 1,336 22.5
2003 30,780.00 13,683 14,039 0.3420 25,975 29.62 877 21.5
2005 188,197.15 77,280 79,288 0.3159 165,368 30.78 5,373 19.5
2007 129,959.45 48,942 50,215 0.2897 118,733 31.97 3,714 17.5
2008 4051485.99 145,615 149,400 0.2762 377,732 32.58 11,594 16.5
2009 412,090.39 140,315 143,963 0.2619 391,755 33.20 11,799 15.5
2010 31,756.03 10,237 10,503 0.2480 30,779 33.84 910 14.5
2011 167,369.60 50,870 52,193 0.2338 165,388 34.48 4,796 13.5
2012 1,8511493.36 527,746 541,465 0.2193 1,865,477 35.14 53,086 12.5
2013 635,116.65 168,829 173,218 0.2045 652,434 35.81 18,218 11.5
2014 1,186,708.57 291,065 298,632 0.1887 1,244,090 36.50 34,085 10.5
2015 476,550.14 107,306 110,096 0.1732 509,420 37.20 13,693 9.5
2016 1,054,024.05 215,633 221,239 0.1574 1,148,993 37.92 30,300 8.5
2017 1,103,697.60 202,523 207,788 0.1412 1,227,019 38.66 31,740 7.5
2018 1,165'578.29 187,558 192,433 0.1238 1,322,818 39.42 33,561 6.5
2019 1,027,694.83 142,498 146,202 0.1067 1,189,801 40.19 29,601 5.5
2020 566,362.22 65,528 67,232 0.0890 669,039 41.00 16,319 4.5
2021 578,935.77 53,225 54,609 0.0707 698,008 41.83 16,688 3.5
2022 370,096.62 24,961 25,610 0.0519 455,516 42.68 10,672 2.5
2023 613,496.97 24,987 25,637 0.0313 771,909 43.58 17,714 1.5
2024 8711241.39 12,176 12,492 0.0108 1,120,122 44.51 25,165 0.5
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 8-29

Intermountain Gas Company ALG - Remaining Life
SO
Account #: 378.00 - Distribution - Measure and Reg Station Equip - General Survivor Curve:e: 45
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -30%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
TOTAL 14,581,058.76 3,653,633 3,748,610 15,206,767 417,739
COMPOSITE ANNUAL ACCRUAL RATE 2.86%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.26
COMPOSITE AVERAGE AGE(YEARS) 11.70
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 36.33
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 1 8-30

Intermountain Gas Company ALG - Remaining Life
SO
Account #: 379.00 - Distribution - Measure and Reg Station Equip - City Gate Survivor Curve:e: 45
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -5/
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2023 1,667,815.72 54,865 43,316 0.0313 1,707,890 43.58 39,192 1.5
2024 33,395.04 377 298 0.0108 34,767 44.51 781 0.5
TOTAL 1,701,210.76 55,242 43,614 1,742,658 39,973
COMPOSITE ANNUAL ACCRUAL RATE 2.35%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.03
COMPOSITE AVERAGE AGE(YEARS) 1.48
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 43.60
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 1 8-31

Intermountain Gas Company ALG - Remaining Life
R3
Account #: 380.00 - Distribution - Services Survivor Curve:e: 58
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -75%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1959 2,740,307.78 4,081,675 4,497,463 0.8511 298,075 8.63 34,529 65.5
1960 4191164.72 619,855 682,997 0.8450 50,541 8.99 5,620 64.5
1961 484,087.11 710,464 782,837 0.8387 64,315 9.37 6,866 63.5
1962 612,341.81 891,570 982,391 0.8320 89,207 9.76 9,143 62.5
1963 671,489.98 969,111 1,067,832 0.8247 107,276 10.16 10,557 61.5
1964 733,612.52 1,049,640 1,156,564 0.8176 127,258 10.58 12,025 60.5
1965 888,616.69 1,259,832 1,388,167 0.8101 166,912 11.02 15,146 59.5
19661 844,941.23 1,186,526 1,307,394 0.8024 171,254 11.47 14,927 58.5
1967 684,128.16 950,572 1,047,404 0.7940 149,820 11.94 12,545 57.5
1968 305,541.50 420,112 462,908 0.7857 71,790 12.43 5,776 56.5
1969 463,455.82 630,322 694,531 0.7772 116,517 12.93 9,011 55.5
1970 592,472.68 796,698 877,855 0.7684 158,972 13.45 11,820 54.5
1971 705,208.45 936,298 1,031,676 0.7587 202,439 13.98 14,476 53.5
1972 8011750.03 1,051,315 1,158,409 0.7493 244,653 14.54 16,831 52.5
1973 776,711.59 1,005,488 1,107,914 0.7397 251,331 15.10 16,642 51.5
1974 661,668.59 845,038 931,120 0.7298 226,800 15.68 14,461 50.5
1975 6041182.29 760,244 837,688 0.7190 219,631 16.28 13,489 49.5
1976 393,167.60 487,561 537,228 0.7086 150,816 16.89 8,927 48.5
1977 342,955.78 418,902 461,575 0.6980 138,598 17.52 7,911 47.5
1978 469,183.93 564,158 621,628 0.6871 199,444 18.16 10,983 46.5
1979 729,097.81 861,681 949,458 0.6753 326,464 18.81 17,353 45.5
1980 737,429.05 856,880 944,168 0.6640 346,333 19.48 17,780 44.5
1981 6981281.73 797,350 878,574 0.6525 343,419 20.16 17,037 43.5
1982 815,096.89 914,007 1,007,114 0.6408 419,305 20.85 20,112 42.5
19831 1,068,640.79 1,175,858 1,295,639 0.6288 574,483 21.55 26,657 41.5
1984 1,262,132.11 1,360,490 1,499,079 0.6160 709,652 22.26 31,874 40.5
1985 1,451,796.40 1,533,609 1,689,833 0.6036 850,811 22.99 37,009 39.5
1986 1,466,338.95 1,516,972 1,671,501 0.5912 894,592 23.73 37,706 38.5
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 8-32

Intermountain Gas Company ALG - Remaining Life
R3
Account #: 380.00 - Distribution - Services Survivor Curve:e: 58
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -75%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1987 1,408,729.52 1,426,039 1,571,306 0.5785 893,971 24.47 36,531 37.5
1988 1,468,163.47 1,451,210 1,599,040 0.5648 970,246 25.23 38,460 36.5
1989 1,870,201.10 1,806,025 1,990,000 0.5518 1,282,852 25.99 49,352 35.5
1990 2,415'377.64 2,276,614 2,508,526 0.5386 1,718,384 26.77 64,191 34.5
1991 3,118,756.33 2,866,558 3,158,566 0.5252 2,299,257 27.55 83,443 33.5
1992 3,563,868.91 3,186,990 3,511,639 0.5110 2,725,131 28.35 96,128 32.5
1993 4,645,584.02 4,042,936 4,454,778 0.4973 3,674,994 29.15 126,060 31.5
19941 4,737,532.24 4,008,213 4,416,518 0.4835 3,874,163 29.97 129,288 30.5
1995 4,193,396.71 3,445,913 3,796,939 0.4696 3,541,506 30.79 115,035 29.5
1996 4,640,317.57 3,691,848 4,067,926 0.4546 4,052,629 31.62 128,183 28.5
1997 4,747'258.72 3,658,380 4,031,049 0.4404 4,276,654 32.45 131,774 27.5
1998 5,151,403.03 3,839,920 4,231,082 0.4260 4,783,873 33.30 143,656 26.5
1999 5,450,580.30 3,924,145 4,323,887 0.4114 5,214,629 34.15 152,676 25.5
2000 5,3091793.91 3,678,944 4,053,707 0.3959 5,238,432 35.02 149,594 24.5
2001 4,555,936.98 3,038,468 3,347,988 0.3811 4,624,901 35.89 128,871 23.5
2002 4,429,291.36 2,838,046 3,127,150 0.3661 4,624,110 36.77 125,774 22.5
2003 5,110,434.70 3,140,694 3,460,628 0.3512 5,482,633 37.65 145,620 21.5
2004 5,192'328.62 3,044,639 3,354,787 0.3351 5,731,788 38.54 148,713 20.5
2005 5,937,522.36 3,322,934 3,661,432 0.3198 6,729,232 39.44 170,613 19.5
2006 6,225,239.65 3,316,076 3,653,875 0.3044 7,240,294 40.35 179,450 18.5
2007 6,174'131.30 3,121,703 3,439,701 0.2889 7,365,028 41.26 178,506 17.5
2008 4,980,954.88 2,374,247 2,616,105 0.2724 6,100,566 42.18 144,639 16.5
2009 2,185,741.82 981,546 1,081,533 0.2566 2,743,515 43.10 63,651 15.5
2010 1,913!420.49 806,315 888,452 0.2408 2,460,033 44.03 55,869 14.5
2011 2,206,989.07 868,693 957,184 0.2249 2,905,047 44.97 64,603 13.5
2012 2,9471023.80 1,077,565 1,187,333 0.2089 3,969,959 45.91 86,475 12.5
2013 3,019,756.17 1,014,110 1,117,414 0.1919 4,167,159 46.85 88,939 11.5
2014 7,219,679.06 2,220,503 2,446,699 0.1758 10,187,740 47.801 213,113 10.5
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Pagel 8-33

Intermountain Gas Company ALG - Remaining Life
R3
Account #: 380.00 - Distribution - Services Survivor Curve:e: 58
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -75%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2015 5,727,735.51 1,599,155 1,762,056 0.1595 8,261,481 48.76 169,435 9.5
2016 7,772,970.03 1,948,178 2,146,634 0.1432 11,456,064 49.72 230,421 8.5
2017 8,181,895.98 1,803,106 1,986,783 0.1259 12,331,535 50.68 243,319 7.5
2018 9,809'920.80 1,878,796 2,070,184 0.1094 15,097,178 51.65 292,315 6.5
2019 11,211,419.84 1,823,678 2,009,450 0.0930 17,610,534 52.62 334,694 5.5
2020 13,015,176.53 1,741,040 1,918,395 0.0764 20,858,164 53.59 389,220 4.5
2021 13,731'087.69 1,415,332 1,559,508 0.0589 22,469,896 54.57 411,798 3.5
20221 15,308,344.62 1,131,593 1,246,865 0.0422 25,542,738 55.54 459,867 2.5
2023 16,077,899.59 719,727 793,044 0.0256 27,343,281 56.52 483,741 1.5
2024 18,291,586.54 282,331 311,091 0.0088 31,699,186 57.51 551,216 0.5
TOTAL 256,371,252.85 117,464,437 129,430,204 319,219,488 7,262,446
COMPOSITE ANNUAL ACCRUAL RATE 2.83%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.50
COMPOSITE AVERAGE AGE(YEARS) 16.72
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 42.82
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 8-34

Intermountain Gas Company ALG - Remaining Life
Account #: 381.00 - Distribution - Meters Survivor Curve: R3
ASL: 40
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 0/
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1959 282,918.96 279,258 282,919 0.9871 0 0.64 0 65.5
1960 20,028.51 19,651 20,029 0.9812 0 0.83 0 64.5
1961 571277.92 55,881 57,278 0.9756 0 1.04 0 63.5
1962 119,838.99 116,172 119,113 0.9694 726 1.27 574 62.5
1963 103,912.67 100,130 102,665 0.9636 1,248 1.50 831 61.5
1964 1251705.67 120,313 123,358 0.9571 2,347 1.74 1,345 60.5
1965 1641867.88 156,803 160,772 0.9511 4,096 1.99 2,055 59.5
19661 199,183.41 188,113 192,875 0.9444 6,309 2.24 2,810 58.5
1967 132,751.05 124,558 127,711 0.9383 5,040 2.50 2,017 57.5
1968 421472.55 39,564 40,566 0.9315 1,907 2.75 692 56.5
1969 82,406.92 76,258 78,188 0.9254 4,219 3.01 1,402 55.5
1970 154,498.26 141,938 145,531 0.9187 8,968 3.27 2,746 54.5
1971 210,132.23 191,741 196,595 0.9125 13,537 3.52 3,843 53.5
1972 2591483.69 235,020 240,969 0.9057 18,515 3.78 4,896 52.5
1973 264,008.03 237,438 243,449 0.8994 20,559 4.04 5,083 51.5
1974 239,666.19 213,864 219,277 0.8923 20,389 4.31 4,725 50.5
1975 145,966.86 129,271 132,543 0.8856 13,423 4.59 2,922 49.5
1976 461259.09 40,619 41,647 0.8781 4,612 4.88 944 48.5
1977 401156.71 34,967 35,852 0.8708 4,305 5.19 830 47.5
1978 76,470.40 65,976 67,646 0.8628 8,825 5.51 1,603 46.5
1979 81,249.38 69,411 71,168 0.8543 10,081 5.84 1,725 45.5
1980 158,020.73 133,531 136,911 0.8450 21,110 6.20 3,405 44.5
1981 170,300.38 142,291 145,893 0.8355 24,407 6.58 3,711 43.5
1982 290,739.04 240,011 246,086 0.8255 44,653 6.98 6,400 42.5
1983 501949.09 41,545 42,597 0.8154 8,353 7.40 1,129 41.5
1984 1221324.68 98,327 100,816 0.8038 21,509 7.84 2,742 40.5
1985 188,471.15 149,371 153,152 0.7925 35,319 8.31 4,248 39.5
1986 254,348.74 198,316 203,336 0.7797 51,013 8.81 5,793 38.5
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 8-35

Intermountain Gas Company ALG - Remaining Life
Account #: 381.00 - Distribution - Meters Survivor Curve: R3
ASL: 40
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 0/
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1987 211,534.80 162,315 166,424 0.7673 45,111 9.32 4,838 37.5
1988 2561468.74 193,172 198,062 0.7532 58,407 9.86 5,921 36.5
1989 129,748.02 95,980 98,409 0.7397 31,339 10.43 3,005 35.5
1990 463,369.12 335,702 344,199 0.7245 119,170 11.01 10,821 34.5
1991 7061520.64 501,531 514,226 0.7099 192,294 11.62 161548 33.5
1992 8251915.32 572,822 587,322 0.6936 238,593 12.25 19,480 32.5
1993 922,904.24 625,711 641,550 0.6780 281,355 12.90 21,818 31.5
1994 1,332,645.78 880,399 902,685 0.6606 429,961 13.56 31,702 30.5
1995 1,271,011.83 818,811 839,538 0.6442 431,473 14.25 30,285 29.5
1996 1,196,063.27 748,640 767,591 0.6259 428,473 14.95 28,662 28.5
1997 1,316'410.11 801,351 821,637 0.6087 494,773 15.67 31,580 27.5
1998 1,2341290.83 727,837 746,261 0.5897 488,030 16.40 29,755 26.5
1999 1,297,299.45 740,654 759,403 0.5709 537,897 17.15 31,363 25.5
2000 8741992.20 483,503 495,742 0.5526 379,250 17.91 21,171 24.5
2001 853,980.71 455,274 466,799 0.5331 387,182 18.69 20,714 23.5
2002 8391198.34 430,156 441,045 0.5126 398,153 19.48 20,436 22.5
2003 886,924.27 437,484 448,559 0.4933 438,366 20.29 21,608 21.5
2004 1,023,803.06 483,276 495,509 0.4720 528,294 21.10 25,032 20.5
2005 1,527'845.44 690,769 708,255 0.4521 819,590 21.93 37,366 19.5
2006 1,669,430.76 718,189 736,369 0.4302 933,062 22.78 40,967 18.5
2007 1,480,240.49 606,425 621,776 0.4097 858,465 23.63 36,330 17.5
2008 1,040,632.74 402,975 413,175 0.3872 627,457 24.49 25,616 16.5
2009 287,856.51 105,396 108,064 0.3661 179,793 25.37 7,087 15.5
2010 660,364.97 226,571 232,307 0.3431 428,058 26.26 16,302 14.5
2011 310,891.78 99,983 102,514 0.3216 208,378 27.15 7,674 13.5
2012 445,931.22 132,896 136,261 0.2980 309,671 28.06 11,036 12.5
2013 2,793,007.441 768,468 787,921 0.2751 2,005,087 28.98 69,195 11.5
2014 1,013,520.41 255,367 261,831 0.2520 751,690 29.90 25,139 10.5
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 8-36

Intermountain Gas Company ALG - Remaining Life
Account #: 381.00 - Distribution - Meters Survivor Curve: R3
ASL: 40
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 0/
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2015 1,934,745.40 444,256 455,502 0.2296 1,479,243 30.83 47,974 9.5
2016 1,537,725.55 315,511 323,497 0.2052 1,214,228 31.77 38,213 8.5
2017 1,287,032.09 234,755 240,697 0.1824 1,046,335 32.72 31,976 7.5
2018 2,500'697.73 394,160 404,138 0.1576 2,096,560 33.68 62,256 6.5
2020 5,572,331.08 609,836 625,273 0.1094 4,947,058 35.60 138,955 4.5
2021 5,806,145.29 500,257 512,921 0.0862 5,293,224 36.57 144,733 3.5
2022 7,815,719.13 475,508 487,545 0.0608 7,328,174 37.55 195,173 2.5
120231 9,109,579.53 340,1521 348,762 0.03731 8,760,8171 38.531 227,4021 1.5
2024 8,238,692.13 97,052 99,509 0.0118 8,139,184 39.51 206,014 0.5
TOTAL 74,759,879.60 20,553,480 21,070,218 53,689,662 1,812,618
COMPOSITE ANNUAL ACCRUAL RATE 2.42%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.28
COMPOSITE AVERAGE AGE(YEARS) 12.74
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 29.00
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Pagel 8-37

Intermountain Gas Company ALG - Remaining Life
R3
Account #: 381.20 - Distribution - ERT Units Survivor Curve:e: 15
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 0%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2007 611,336.80 528,219 549,479 0.8640 61,858 2.07 29,910 17.5
2008 951986.08 80,686 83,933 0.8406 12,053 2.41 4,994 16.5
2014 6,323,674.69 3,904,237 4,061,371 0.6174 2,262,304 5.74 393,912 10.5
2015 7,388,441.93 4,195,748 4,364,615 0.5679 3,023,827 6.48 466,536 9.5
2016 6,235,751.05 3,220,952 3,350,587 0.5165 2,885,164 7.26 397,500 8.5
2017 329,976.49 152,482 158,619 0.4621 171,357 8.07 21,232 7.5
2018 2,359,095.69 956,330 994,820 0.4054 1,364,276 8.92 153,014 6.5
2020 1,095,926.38 314,640 327,304 0.2871 768,623 10.69 71,869 4.5
2021 389,606.66 87,630 91,157 0.2249 298,449 11.62 25,680 3.5
2022 1,168'134.67 189,728 197,364 0.1624 970,770 12.57 77,234 2.5
2023 1,258,616.34 123,093 128,047 0.0978 1,130,570 13.53 83,544 1.5
2024 1,641,538.64 53,252 55,395 0.0324 1,586,144 14.51 109,325 0.5
TOTAL 28,898,085.42 13,806,999 14,362,691 14,535,395 1,834,750
COMPOSITE ANNUAL ACCRUAL RATE 6.35%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.50
COMPOSITE AVERAGE AGE(YEARS) 8.01
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 7.84
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 8-38

Intermountain Gas Company ALG - Remaining Life
R3
Account #: 383.00 - Distribution - Regulators Survivor Curve:e: 50
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 0/
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1959 214,527.25 194,190 214,527 0.9052 0 4.75 0 65.5
1960 18,967.56 17,069 18,968 0.8999 0 5.01 0 64.5
1961 381097.41 34,078 38,097 0.8945 0 5.28 0 63.5
1962 631387.87 56,352 63,388 0.8890 0 5.56 0 62.5
1963 431000.14 37,982 43,000 0.8833 0 5.84 0 61.5
1964 47,949.94 42,076 47,950 0.8775 0 6.13 0 60.5
1965 17,364.67 15,132 17,365 0.8714 0 6.44 0 59.5
19661 35,925.59 31,076 35,926 0.8650 0 6.75 0 58.5
1967 24,778.34 21,270 24,778 0.8584 0 7.08 0 57.5
1968 9,575.15 8,153 9,522 0.8515 53 7.43 7 56.5
1969 11,235.54 9,486 11,079 0.8443 157 7.79 20 55.5
1970 46,989.27 39,316 45,917 0.8367 1,072 8.17 131 54.5
1971 53,201.47 44,093 51,497 0.8288 1,704 8.56 199 53.5
1972 77,121.83 63,286 73,913 0.8206 3,209 8.98 358 52.5
1973 67,854.68 55,091 64,342 0.8119 3,513 9.41 373 51.5
1974 571450.56 46,127 53,872 0.8029 3,578 9.86 363 50.5
1975 24,827.60 19,701 23,009 0.7935 1,819 10.33 176 49.5
1976 21,409.98 16,779 19,596 0.7837 1,814 10.82 168 48.5
1977 28,927.94 22,379 26,136 0.7736 2,792 11.32 247 47.5
1978 10,341.81 7,891 9,216 0.7630 1,126 11.85 95 46.5
1980 10,923.66 8,093 9,452 0.7409 1,471 12.96 114 44.5
1981 63,073.10 45,993 53,716 0.7292 9,358 13.54 691 43.5
1982 45,497.09 32,631 38,110 0.7172 7,388 14.14 522 42.5
1983 38,470.69 27,118 31,671 0.7049 6,799 14.76 461 41.5
1984 62,712.06 43,416 50,705 0.6923 12,007 15.39 780 40.5
1985 52,831.89 35,889 41,915 0.6793 10,917 16.04 681 39.5
1986 811140.22 54,039 63,113 0.6660 18,027 16.70 1,080 38.5
1987 90,892.82 59,308 69,266 0.6525 21,627 17.38 1,245 37.5
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 8-39

Intermountain Gas Company ALG - Remaining Life
R3
Account #: 383.00 - Distribution - Regulators Survivor Curve:e: 50
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 0/
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1988 45,646.74 29,155 34,050 0.6387 11,597 18.07 642 36.5
1989 951080.73 59,378 69,348 0.6245 25,733 18.77 1,371 35.5
1990 175,778.73 107,260 125,270 0.6102 50,508 19.49 2,591 34.5
1991 149,224.10 88,878 103,801 0.5956 45,423 20.22 2,246 33.5
1992 237,042.06 137,650 160,763 0.5807 76,279 20.97 3,638 32.5
1993 262,855.17 148,671 173,634 0.5656 89,221 21.72 4,108 31.5
1994 313,809.23 172,689 201,686 0.5503 112,124 22.49 4,986 30.5
1995 251,337.54 134,390 156,956 0.5347 94,382 23.27 4,057 29.5
1996 329,453.59 170,953 199,658 0.5189 129,795 24.05 5,396 28.5
1997 3421289.94 172,138 201,041 0.5029 141,249 24.85 5,683 27.5
1998 447,810.87 217,950 254,546 0.4867 193,265 25.66 7,531 26.5
1999 412,496.28 194,038 226,619 0.4704 185,877 26.48 7,019 25.5
2000 516,859.71 234,551 273,934 0.4538 242,925 27.31 8,894 24.5
2001 456,640.73 199,552 233,059 0.4370 223,582 28.15 7,942 23.5
2002 494,616.37 207,739 242,620 0.4200 251,996 29.00 8,689 22.5
2003 598,257.80 240,978 281,441 0.4028 316,817 29.86 10,610 21.5
2004 5641335.60 217,551 254,080 0.3855 310,255 30.73 10,097 20.5
2005 854,773.63 314,471 367,274 0.3679 487,499 31.60 15,426 19.5
2006 856,525.30 300,041 350,421 0.3503 506,105 32.49 15,578 18.5
2007 518,096.44 172,215 201,132 0.3324 316,964 33.38 9,495 17.5
2008 345,927.46 108,760 127,021 0.3144 218,906 34.28 6,386 16.5
2009 212,120.91 62,830 73,380 0.2962 138,741 35.19 3,943 15.5
2010 315,766.79 87,752 102,486 0.2779 213,281 36.11 5,907 14.5
2011 304,485.00 78,983 92,246 0.2594 212,239 37.03 5,732 13.5
2012 491,208.80 118,283 138,144 0.2408 353,065 37.96 9,301 12.5
2013 2,009,871.85 446,393 521,346 0.2221 1,488,525 38.89 38,271 11.5
2014 749,320.27 152,337 177,916 0.2033 571,405 39.84 14,344 10.5
2015 818,670.54 150,881 176,215 0.1843 642,455 40.78 15,753 9.5
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 840

Intermountain Gas Company ALG - Remaining Life
R3
Account #: 383.00 - Distribution - Regulators Survivor Curve:e: 50
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 0/
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2016 1,075,336.41 177,753 207,600 0.1653 867,737 41.74 20,791 8.5
2017 821774.66 12,093 14,124 0.1461 68,651 42.69 1,608 7.5
2018 2,113,137.37 268,157 313,183 0.1269 1,799,954 43.66 41,230 6.5
2020 497,010.05 43,787 51,139 0.0881 445,871 45.59 9,779 4.5
2021 301,367.06 20,674 24,145 0.0686 277,222 46.57 5,953 3.5
2022 459,521.93 22,563 26,351 0.0491 433,171 47.54 9,111 2.5
2023 584,455.16 17,241 20,136 0.0295 564,319 48.52 11,629 1.5
2024 799,823.43 7,838 9,154 0.0098 790,669 49.51 15,971 0.5
TOTAL 20,442,204.38 6,384,585 7,435,968 13,006,236 359,419
COMPOSITE ANNUAL ACCRUAL RATE 1.76%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.36
COMPOSITE AVERAGE AGE (YEARS) 17.29
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 34.38
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 1 8-41

Intermountain Gas Company ALG - Remaining Life
R1
Account #: 385.00 - Distribution - Measure & Reg. Station Equip - Industrial Survivor Curve:e: 40
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -12%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1959 137,842.97 136,241 154,384 0.8825 0 4.72 0 65.5
1960 8,873.19 8,689 9,938 0.8743 0 5.03 0 64.5
1961 201147.80 19,558 22,566 0.8667 0 5.35 0 63.5
1962 371318.59 35,873 41,797 0.8583 0 5.67 0 62.5
1963 782.45 745 876 0.8503 0 6.00 0 61.5
1968 211764.28 19,660 24,376 0.8065 0 7.74 0 56.5
1969 681387.06 61,103 76,594 0.7978 0 8.10 0 55.5
1970 411586.75 36,705 46,577 0.7880 0 8.48 0 54.5
1971 42,769.87 37,313 47,902 0.7789 0 8.86 0 53.5
1973 98,595.71 83,861 110,427 0.7594 0 9.64 0 51.5
1974 78,667.25 65,994 88,107 0.7490 0 10.04 0 50.5
1975 54,078.12 44,776 60,567 0.7393 0 10.44 0 49.5
1976 50,643.99 41,318 56,721 0.7284 0 10.86 0 48.5
1977 98,994.74 79,645 110,874 0.7183 0 11.28 0 47.5
1978 41,944.91 33,241 46,978 0.7076 0 11.71 0 46.5
1979 781747.60 61,447 88,197 0.6967 0 12.15 0 45.5
1980 76,617.88 58,790 85,812 0.6851 0 12.59 0 44.5
1981 106,907.04 80,672 119,736 0.6738 0 13.04 0 43.5
1982 62,501.10 46,356 70,001 0.6622 0 13.50 0 42.5
1983 90,585.75 66,044 101,456 0.6510 0 13.97 0 41.5
1984 79,545.90 56,890 89,091 0.6386 0 14.45 0 40.5
1986 78,962.85 54,301 85,183 0.6140 3,255 15.43 211 38.5
1987 84,168.25 56,748 89,021 0.6020 5,247 15.93 329 37.5
1988 145,206.57 95,731 150,176 0.5886 12,455 16.45 757 36.5
19891 185,194.32 119,502 187,465 0.5761 19,953 16.97 1,176 35.5
1990 271,881.51 171,249 268,642 0.5624 35,865 17.50 2,050 34.5
1991 1541078.38 94,826 148,756 0.5495 23,812 18.031 1,320 33.5
1992 3571575.39 214,379 336,302 0.5353 64,183 18.58 3,454 32.5
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 1 8-42

Intermountain Gas Company ALG - Remaining Life
R1
Account #: 385.00 - Distribution - Measure & Reg. Station Equip - Industrial Survivor Curve:e: 40
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -12%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1993 319,169.23 186,585 292,700 0.5220 64,770 19.14 3,385 31.5
1994 3161539.80 179,829 282,102 0.5072 72,423 19.70 3,676 30.5
1995 214,824.00 118,747 186,281 0.4935 54,322 20.27 2,680 29.5
1996 304,773.01 163,293 256,161 0.4784 85,184 20.85 4,085 28.5
1997 397,639.00 206,779 324,378 0.4643 120,977 21.44 5,642 27.5
1998 330,294.26 165,987 260,388 0.4487 109,541 22.04 4,970 26.5
1999 280,116.93 136,024 213,384 0.4336 100,347 22.65 4,431 25.5
2000 5051564.57 237,172 372,057 0.4189 194,175 23.26 8,348 24.5
2001 318,037.66 143,671 225,379 0.4033 130,823 23.88 5,478 23.5
2002 270,176.02 117,093 183,686 0.3870 118,911 24.51 4,852 22.5
2003 332,988.87 138,632 217,475 0.3717 155,472 25.14 6,183 21.5
2004 3031870.24 120,846 189,574 0.3551 150,761 25.79 5,847 20.5
2005 351,286.24 133,573 209,539 0.3395 183,901 26.43 6,957 19.5
2006 260,937.86 94,257 147,862 0.3225 144,388 27.09 5,330 18.5
2007 301,669.83 103,618 162,548 0.3067 175,322 27.75 6,319 17.5
2008 4081655.77 132,466 207,802 0.2894 249,892 28.41 8,796 16.5
2009 267,964.20 82,041 128,699 0.2734 171,421 29.08 5,895 15.5
2010 143,955.07 41,249 64,708 0.2558 96,521 29.75 3,244 14.5
2011 320,224.43 85,911 134,771 0.2395 223,880 30.43 7,357 13.5
2012 371,158.64 92,227 144,678 0.2219 271,020 31.11 8,711 12.5
2013 979,383.31 224,570 352,288 0.2047 744,621 31.80 23,417 11.5
2014 577,377.82 121,236 190,186 0.1875 456,477 32.49 14,051 10.5
2015 433,792.17 82,992 130,192 0.1708 355,655 33.18 10,719 9.5
2016 648,694.38 110,942 174,038 0.1527 552,500 33.88 16,308 8.5
2017 128,848.91 19,609 30,761 0.1359 113,550 34.58 3,284 7.5
2018 782,416.34 102,984 161,553 0.1175 714,754 35.29 20,256 6.5
2019 67,068.01 7,546 11,838 0.1005 63,278 36.00 1,758 5.5
2020 50,637.60 4,641 7,281 0.0818 49,433 36.71 1,346 4.5
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Pagel 843

Intermountain Gas Company ALG - Remaining Life
R1
Account #: 385.00 - Distribution - Measure & Reg. Station Equip - Industrial Survivor Curve:e: 40
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: -12%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2021 71,475.98 5,167 8,105 0.0645 71,948 37.43 1,922 3.5
2024 129,585.68 1,289 2,022 0.0089 143,114 39.63 3,611 0.5
TOTAL 12,763,496.05 5,242,634 7,990,964 6,304,151 218,155
COMPOSITE ANNUAL ACCRUAL RATE 1.71%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.63
COMPOSITE AVERAGE AGE(YEARS) 22.17
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 25.33
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 1 8-44

Intermountain Gas Company ALG - Remaining Life
R3
Account #: 387.00 - Distribution - Other Distribution Equipment Survivor Curve:e: 30
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 0%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2011 2,994.50 1,258 2,995 0.4200 0 17.40 0 13.5
2013 3,405.70 1,232 3,406 0.3617 0 19.14 0 11.5
2017 33,268.61 8,011 22,946 0.2408 10,323 22.78 453 7.5
2018 23,098.01 4,848 13,885 0.2099 9,213 23.71 388 6.5
2021 23,286.72 2,661 7,623 0.1143 15,664 26.58 589 3.5
2023 26,926.53 1,322 3,787 0.0491 23,140 28.53 811 1.5
TOTAL 112,980.07 19,332 54,642 58,339 2,241
COMPOSITE ANNUAL ACCRUAL RATE 1.98%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.48
COMPOSITE AVERAGE AGE (YEARS) 5.32
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 24.87
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Pagel 8-45

Intermountain Gas Company ALG - Remaining Life
R2
Account #: 390.00 - General - Structures and Improvements Survivor Curve:e: 45
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 10/
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1965 1,298,404.98 991,317 1,168,564 0.8483 0 6.83 0 59.5
1967 2,589.66 1,944 2,331 0.8340 0 7.48 0 57.5
1969 11041.60 768 937 0.8188 0 8.16 0 55.5
1970 1,912.25 1,396 11721 0.8110 0 8.51 0 54.5
1971 5,166.90 3,734 4,650 0.8029 0 8.87 0 53.5
1972 1,324.81 947 1,192 0.7947 0 9.25 0 52.5
1973 856,356.73 605,633 770,721 0.7858 0 9.64 0 51.5
1974 701123.17 49,038 63,111 0.7770 0 10.03 0 50.5
1975 3,625.46 2,506 3,263 0.7680 0 10.45 0 49.5
1976 199,547.05 136,246 179,592 0.7586 0 10.87 0 48.5
1977 103,058.71 69,476 92,753 0.7490 0 11.30 0 47.5
1978 3801797.76 253,183 342,718 0.7388 0 11.75 0 46.5
1979 13,105.93 8,594 11,795 0.7286 0 12.22 0 45.5
1980 61,996.33 40,068 55,797 0.7181 0 12.69 0 44.5
1981 54,031.29 34,396 48,628 0.7073 0 13.18 0 43.5
1982 661840.73 41,857 60,157 0.6958 0 13.68 0 42.5
1983 33,475.39 20,621 30,128 0.6844 0 14.20 0 41.5
1984 18,457.45 11,176 16,612 0.6728 0 14.73 0 40.5
1985 30,139.68 17,927 27,126 0.6609 0 15.27 0 39.5
1986 272,160.11 158,900 244,944 0.6487 0 15.82 0 38.5
1987 7,438.83 4,256 6,695 0.6356 0 16.39 0 37.5
1988 33,481.85 18,770 30,134 0.6229 0 16.97 0 36.5
1989 144,093.77 79,093 129,684 0.6099 0 17.56 0 35.5
1990 12,103.82 6,499 10,893 0.5966 0 18.17 0 34.5
1991 21,784.91 11,418 19,274 0.5824 333 18.78 18 33.5
1992 8,274.44 4,233 7,146 0.5685 301 19.41 16 32.5
1993 36,304.54 18,115 30,576 0.5544 2,098 20.05 105 31.5
1994 27,723.47 13,476 22,746 0.5401 2,205 20.70 106 30.5
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 1 846

Intermountain Gas Company ALG - Remaining Life
R2
Account #: 390.00 - General - Structures and Improvements Survivor Curve:e: 45
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 10/
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1995 11,065.67 5,234 8,834 0.5255 1,125 21.37 53 29.5
1996 511674.22 23,719 40,036 0.5100 6,470 22.04 294 28.5
1997 839,277.24 373,815 630,981 0.4949 124,369 22.73 5,472 27.5
1998 140,327.26 60,571 102,241 0.4796 24,054 23.42 1,027 26.5
1999 1,320,819.60 551,657 931,170 0.4641 257,568 24.13 10,675 25.5
2000 401,659.30 161,812 273,130 0.4476 88,363 24.84 3,557 24.5
2001 49,745.00 19,326 32,621 0.4317 12,150 25.57 475 23.5
20021 53,914.03 20,161 34,031 0.4155 14,492 26.30 551 22.5
2003 10,155.11 3,648 6,157 0.3991 2,983 27.05 110 21.5
2004 3531199.90 121,589 2051236 0.3825 112,644 27.80 4,051 20.5
2005 35,984.55 11,820 19,952 0.3650 12,434 28.57 435 19.5
2006 61,431.91 19,239 32,474 0.3480 22,815 29.34 778 18.5
2007 1,132,407.28 337,150 569,093 0.3308 450,074 30.12 14,943 17.5
2008 2191118.81 61,811 104,333 0.3134 92,874 30.91 3,005 16.5
2009 63,643.56 16,903 28,532 0.2951 28,748 31.71 907 15.5
2010 27,080.00 6,759 11,409 0.2773 12,963 32.51 399 14.5
2011 1,062,312.43 248,103 418,785 0.2595 537,296 33.32 16,123 13.5
2012 7741872.23 168,321 284,117 0.2414 413,268 34.15 12,103 12.5
2013 722,742.37 145,171 245,042 0.2232 405,426 34.98 11,592 11.5
2014 2,912'189.39 534,468 902,156 0.2039 1,718,815 35.81 47,996 10.5
2015 397,042.17 66,233 111,797 0.1854 245,541 36.66 6,699 9.5
2016 482,169.94 72,314 122,062 0.1666 311,891 37.51 8,316 8.5
2017 859,725.94 114,299 192,931 0.1477 580,823 38.36 15,140 7.5
2018 5,888!420.72 677,710 1,143,941 0.1279 4,155,638 39.23 105,933 6.5
2019 379,713.56 37,161 62,726 0.1087 279,016 40.10 6,958 5.5
2020 717,806.17 57,755 97,487 0.0894 548,539 40.98 13,386 4.5
2021 9921125.81 62,450 105,413 0.0699 787,500 41.86 18,812 3.5
2022 266,138.95 12,072 20,377 0.0504 219,148 42.75 5,126 2.5
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 1 847

Intermountain Gas Company ALG - Remaining Life
R2
Account #: 390.00 - General - Structures and Improvements Survivor Curve:e: 45
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 10%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2023 159,086.73 4,267 7,202 0.0298 135,976 43.65 3,115 1.5
2024 711,491.43 6,403 10,809 0.0100 629,534 44.55 14,132 0.5
TOTAL 24,862,702.90 6,607,526 10,138,963 12,237,470 332,408
COMPOSITE ANNUAL ACCRUAL RATE 1.34%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.41
COMPOSITE AVERAGE AGE(YEARS) 17.08
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 31.71
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 1 8-48

Intermountain Gas Company
ALG - Remaining Life
SQ
Account #: 391.00 - General - Office Furniture & Equipment Survivor Curve:e: 15
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 0%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2015 719,936.88 455,960 535,838 0.6333 184,099 5.50 33,473 9.5
2016 6831811.13 387,493 455,376 0.5667 228,435 6.50 35,144 8.5
2017 334,074.65 167,037 196,300 0.5000 137,775 7.50 18,370 7.5
2018 1,007,562.44 436,610 513,098 0.4333 494,464 8.50 58,172 6.5
2019 713,446.76 261,597 307,425 0.3667 406,022 9.50 42,739 5.5
2020 553,082.05 165,925 194,992 0.3000 358,090 10.50 34,104 4.5
2021 539,479.28 125,878 147,931 0.2333 391,549 11.50 34,048 3.5
2022 6051536.76 100,923 118,603 0.1667 486,934 12.50 38,955 2.5
2023 620,988.01 62,099 72,978 0.1000 548,010 13.50 40,593 1.5
2024 342,478.96 11,416 13,416 0.0333 329,063 14.50 22,694 0.5
TOTAL 6,120,396.92 2,174,939 2,555,956 3,564,441 358,292
COMPOSITE ANNUAL ACCRUAL RATE 5.85%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.42
COMPOSITE AVERAGE AGE(YEARS) 5.33
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 9.67
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 8-49

Intermountain Gas Company ALG - Remaining Life
Account #: 392.10 - Transportation Equipment Survivor Curve: L2
ASL: 10
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 16/
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2002 18,483.00 13,866 15,526 0.8931 0 1.13 0 22.5
2005 40,791.05 28,607 34,017 0.8349 248 1.69 147 19.5
2006 251955.60 17,750 21,106 0.8141 697 1.89 368 18.5
2007 24,614.61 16,386 19,484 0.7925 1,192 2.11 566 17.5
2008 133,874.28 86,590 102,963 0.7700 9,492 2.33 4,077 16.5
2009 25,335.94 15,885 18,889 0.7464 2,394 2.56 935 15.5
2010 102,286.69 62,035 73,765 0.7220 12,156 2.80 4,338 14.5
2011 361,410.05 211,568 251,572 0.6969 52,012 3.051 17,047 13.5
2012 407,250.03 229,782 273,230 0.6717 68,860 3.30 20,858 12.5
2013 101,598.67 55,217 65,658 0.6470 19,685 3.55 5,548 11.5
2014 375,773.28 196,587 233,758 0.6228 81,891 3.79 21,615 10.5
2015 1,202,267.67 604,630 718,956 0.5987 290,948 4.03 72,230 9.5
2016 1,010,733.64 486,741 578,776 0.5733 270,240 4.28 63,126 8.5
2017 1,5621783.68 714,130 849,161 0.5440 463,577 4.57 101,381 7.5
2018 825,047.24 351,579 418,057 0.5073 274,982 4.94 55,701 6.5
2019 1,830,447.69 706,670 840,291 0.4596 697,285 5.41 128,863 5.5
2020 1,951,577.42 652,287 775,625 0.3979 863,700 6.03 143,345 4.5
2021 1,1991518.89 324,748 386,153 0.3223 621,443 6.78 91,672 3.5
2022 1,0401859.55 208,001 247,331 0.2379 626,991 7.62 82,258 2.5
2023 648,112.90 79,975 95,097 0.1469 449,318 8.53 52,663 1.5
2024 830,356.14 34,805 41,386 0.0499 656,113 9.50 69,054 0.5
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 8-50

Intermountain Gas Company ALG - Remaining Life
Account #: 392.10 - Transportation Equipment Survivor Curve: L2
ASL: 10
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 16/
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
TOTAL 13,719,078.02 5,097,838 6,060,801 5,463,225 935,792
COMPOSITE ANNUAL ACCRUAL RATE 6.82%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.44
COMPOSITE AVERAGE AGE(YEARS) 6.23
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 5.59
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 1 8-51

Intermountain Gas Company ALG - Remaining Life
R2
Account #: 392.20 - Transportation Equipment - Trailers Survivor Curve:e: 20
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 15/
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1983 234.00 199 199 1.0000 0 0 42.5
1991 835.38 676 710 0.9518 0 1.03 0 33.5
1993 920.75 723 783 0.9234 0 1.57 0 31.5
1994 8,868.59 6,851 7,538 0.9089 0 1.86 0 30.5
1996 3,724.34 2,785 3,166 0.8797 0 2.43 0 28.5
1998 2,255.40 1,628 1,917 0.8493 0 3.03 0 26.5
1999 161206.41 11,476 13,775 0.8331 0 3.36 0 25.5
20021 4,646.25 3,074 3,949 0.7783 0 4.451 0 22.5
2005 51,903.17 31,379 42,897 0.7113 1,221 5.78 211 19.5
2007 57,404.40 32,167 43,975 0.6593 4,819 6.82 707 17.5
2009 23,994.39 12,266 16,768 0.6014 3,627 7.98 455 15.5
2010 1,627.92 789 1,079 0.5704 305 8.60 35 14.5
2011 70,192.63 32,105 43,890 0.5381 15,774 9.24 1,707 13.5
2013 161582.35 6,621 9,051 0.4698 5,044 10.61 475 11.5
2014 15,940.47 5,878 8,036 0.4339 5,513 11.33 487 10.5
2015 69,458.75 23,430 32,030 0.3969 27,010 12.06 2,239 9.5
2016 75,825.39 23,125 31,614 0.3588 32,838 12.83 2,560 8.5
2017 26,897.82 7,310 9,994 0.3198 12,869 13.61 946 7.5
2018 22,235.85 5,287 7,228 0.2798 11,672 14.41 810 6.5
2022 81,925.62 7,754 10,600 0.1114 59,037 17.77 3,321 2.5
2023 111757.92 673 919 0.0673 9,075 18.65 486 1.5
2024 5,059.90 97 133 0.0226 4,168 19.55 213 0.5
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 1 8-52

Intermountain Gas Company ALG - Remaining Life
R2
Account #: 392.20 - Transportation Equipment - Trailers Survivor Curve:e: 20
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 15/
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
TOTAL 568,497.70 216,293 290,251 192,972 14,652
COMPOSITE ANNUAL ACCRUAL RATE 2.58%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.51
COMPOSITE AVERAGE AGE(YEARS) 11.64
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 11.05
Concentric Energy Advisors Intermountain GasCompany2025 Depreciation Study Page 1 8-53

Intermountain Gas Company ALG - Remaining Life
survivor curve: sQ
Account #: 393.00 - General - Stores Equipment Ae: 30
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net salvage: 0%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2018 5,267.15 1,141 1,752 0.2167 3,516 23.50 150 6.5
2019 34,851.38 6,389 9,807 0.1833 25,045 24.50 1,022 5.5
2020 2,826.59 424 651 0.1500 2,176 25.50 85 4.5
2022 3,320.54 277 425 0.0833 2,896 27.50 105 2.5
2024 53,104.40 885 1,358 0.0167 51,746 29.50 1,754 0.5
TOTAL 99,370.06 9,116 13,992 85,378 3,116
COMPOSITE ANNUAL ACCRUAL RATE 3.14%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.14
COMPOSITE AVERAGE AGE(YEARS) 2.75
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 27.25
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Intermountain Gas Company
ALG - Remaining Life
SQ
Account #: 394.00 - General - Tools, Shop & Garage Equipment Survivor Curve:e: 20
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 0%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2010 687,580.59 498,496 664,481 0.7250 23,100 5.50 4,200 14.5
2011 2421399.26 163,620 218,100 0.6750 24,299 6.50 3,738 13.5
2012 494,787.73 309,242 412,211 0.6250 82,577 7.50 11,010 12.5
2013 610,390.68 350,975 467,839 0.5750 142,552 8.50 16,771 11.5
2014 429,890.55 225,693 300,842 0.5250 129,049 9.50 13,584 10.5
2015 518,111.67 246,103 328,048 0.4750 190,064 10.50 18,101 9.5
2016 1,725,680.88 733,414 977,620 0.4250 748,061 11.50 65,049 8.5
20171 689,307.34 258,490 344,560 0.3750 344,747 12.50 27,580 7.5
2018 528,622.43 171,802 229,007 0.3250 299,615 13.50 22,194 6.5
2019 4651975.68 128,143 170,811 0.2750 295,164 14.50 20,356 5.5
2020 513,662.62 115,574 154,057 0.2250 359,606 15.50 23,200 4.5
2021 581,400.20 101,745 135,623 0.1750 445,777 16.50 27,017 3.5
2022 915,268.03 114,409 152,503 0.1250 762,765 17.50 43,587 2.5
2023 5821459.74 43,684 58,230 0.0750 524,230 18.50 28,337 1.5
2024 780,050.73 19,501 25,995 0.0250 754,056 19.50 38,670 0.5
TOTAL 9,765,588.13 3,480,892 4,639,927 5,125,661 363,394
COMPOSITE ANNUAL ACCRUAL RATE 3.72%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.48
COMPOSITE AVERAGE AGE(YEARS) 7.13
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 12.87
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Intermountain Gas Company ALG - Remaining Life
Account #: 396.00 - Power Operated Equipment Survivor Curve: LO
ASL: 10
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 30/
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
1993 11,487.00 6,819 8,041 0.8480 0 1.57 0 31.5
1994 7,674.71 4,482 5,372 0.8343 0 1.70 0 30.5
1995 121715.82 7,302 8,901 0.8204 0 1.84 0 29.5
2001 62,034.00 31,586 43,424 0.7274 0 2.75 0 23.5
2003 14,026.98 6,797 9,819 0.6922 0 3.10 0 21.5
2005 72,263.10 33,102 50,584 0.6544 0 3.48 0 19.5
2013 11,333.45 3,717 7,933 0.4685 0 5.33 0 11.5
2015 121,636.45 34,969 85,146 0.4107 0 5.90 0 9.5
2016 71683.60 2,042 5,379 0.3796 0 6.21 0 8.5
2017 116,732.90 28,354 78,991 0.3470 2,722 6.54 416 7.5
2018 44,520.53 9,745 27,148 0.3127 4,016 6.88 584 6.5
2019 331346.00 6,456 17,987 0.2766 5,356 7.24 740 5.5
2020 86,223.33 14,401 40,119 0.2386 20,238 7.62 2,655 4.5
2021 227,577.40 31,510 87,783 0.1978 71,522 8.03 8,909 3.5
2022 57,525.29 6,149 17,130 0.1527 23,138 8.48 2,729 2.5
2023 1,320,890.73 93,572 260,675 0.1012 663,948 8.99 73,838 1.5
2024 1,571,512.80 43,122 120,131 0.0392 979,928 9.61 101,961 0.5
TOTAL 3,779,184.09 364,127 874,562 1,770,867 191,832
COMPOSITE ANNUAL ACCRUAL RATE 5.08%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.23
COMPOSITE AVERAGE AGE(YEARS) 2.89
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 8.63
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Intermountain Gas Company
ALG - Remaining Life
SQ
Account #: 397.00 - General - Communication Equipment Survivor Curve:e: 15
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 0%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2015 270,139.22 171,088 270,139 0.6333 0 5.50 0 9.5
2016 1701674.85 96,716 170,675 0.5667 0 6.50 0 8.5
2017 286,411.61 143,206 257,321 0.5000 29,091 7.50 3,879 7.5
2018 1,309,043.02 567,252 1,019,273 0.4333 289,770 8.50 34,091 6.5
2019 329,836.59 120,940 217,313 0.3667 112,524 9.50 11,845 5.5
2020 343,445.46 103,034 185,137 0.3000 158,308 10.50 15,077 4.5
2021 411,793.66 96,085 172,652 0.2333 239,142 11.50 20,795 3.5
20221 526,739.78 87,790 157,746 0.1667 368,993 12.50 29,519 2.5
2023 1,741,047.46 174,105 312,842 0.1000 1,428,205 13.50 105,793 1.5
2024 210,345.90 7,012 12,599 0.0333 197,747 14.50 13,638 0.5
TOTAL 5,599,477.55 1,567,227 2,775,697 2,823,781 234,637
COMPOSITE ANNUAL ACCRUAL RATE 4.19%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 0.50
COMPOSITE AVERAGE AGE(YEARS) 4.20
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 10.80
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Intermountain Gas Company
ALG - Remaining Life
SQ
Account #: 398.00 - General - Miscellaneous Equipment Survivor Curve:e: 25
CALCULATED ANNUAL ACCRUAL AND ACCRUED DEPRECIATION Net Salvage: 0%
BASED ON ORIGINAL COST AS OF December 31, 2024 Truncation Year:
Accumulated ALG
Calculated Accumulated Allocated Actual Depreciation Net Book Remaining Annual Average
Year Original Cost Depreciation Booked Amount Factor Value Life Accrual Age
2020 15,955.63 2,872 15,956 0.1800 0 20.50 0 4.5
2021 2,122.06 297 2,122 0.1400 0 21.50 0 3.5
2022 21,073.29 2,107 21,073 0.1000 0 22.50 0 2.5
2023 29,021.77 1,741 29,022 0.0600 0 23.50 0 1.5
2024 17,773.24 355 17,677 0.0200 96 24.50 4 0.5
TOTAL 85,945.99 7,373 85,850 96 4
COMPOSITE ANNUAL ACCRUAL RATE 0.00%
THEORETICAL ACCUMULATED DEPRECIATION FACTOR 1.00
COMPOSITE AVERAGE AGE(YEARS) 2.14
DIRECTED WEIGHTED ALG COMPOSITE REMAINING LIFE(YEARS) 22.86
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Intermountain Gas Company
16 2025 Depreciation Study
SECTION 9
9 ESTIMATION OF SURVIVOR CURVES
9.1 Average Service Life
All assets have a service life, which is defined as "the period of time from its installation until it is
retired from service"3. All account groups of property are made up of various assets with differing
service lives and investment values. To calculate a depreciation rate, one must first calculate an
average life for all assets in a single account. This can be done by ascertaining the age at retirement
for every asset in an account and plotting it as a percentage of the units surviving at each age interval
(a"Survivor Curve"). From the average life for each account,remaining lives can then be found which
are then used to calculate the annual depreciation accruals and ultimately depreciation rate. A
discussion of the general concept of survivor curves is presented and the Iowa type survivor curves
are reviewed.
9.2 Survivor Curves
A survivor curve is defined as "a graph of the percent of units remaining in service expressed as a
function of age" 4. To calculate the average life of the group, the remaining life expectancy, the
probable life and the frequency curve,one must first create a survivor curve. Figure 1 shows a typical
40-R4 smoothed survivor curve as well as the accompanying derived curves. The type 40-R4 refers
to the Iowa type curve,whose designation will be explained in further detail in the next section
To calculate the average service life,one must calculate the area under the survivor curve and divide
by the percent surviving at age zero. The remaining life is equal to the area under the survivor curve
and to the right of the current age, divided by the percent surviving at the current age. In Figure 1,
for example, the hatched area to the right of age 45 divided by 28.9 percent surviving balance
represents the remaining life for an asset that has reached that age. The probable life is"the total life
expectancy of the property surviving at any age and is equal to the remaining life plus the current
age."5 If the probable life of the property is calculated for each year of age, the probable life curve
shown in the chart can be developed. The frequency curve is calculated by taking the difference
between the percent surviving on successive years on the survivor curve. Alternatively, frequency
can be empirically determined by finding the amount of retirements at any given age. Plotting
retirement frequency from the youngest to oldest ages and then taking the cumulative frequencies
will generate percent surviving versus age.
3 Wolf,Frank K.and W.Chester Fitch, Depreciation Systems (Iowa State University Press, 1994),21.
4 Ibid,23.
5 Ibid,29.
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Figure 1: Typical Survivor Curve (40-R4) and Derived Curves
100
90
80
Probable Life Curve
70 Survivor Curve
00 60
c
�+ 50 Service a aqua
c
R to average age
u
w 40
30 28.9%Surviving at 45 years
20
10 Frequency curve Mode
0
0 5 10 15 20 25 30 35 40 45 50 55 60 65
Age in Years
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9.3 Iowa Type Curves
In 1931, Robley Winfrey and Edwin Kurtz of the Engineering Research Institute at Iowa State
University published Bulletin 103,which laid the groundwork for what would eventually be known
as the Iowa Curves. "The 13 type curves can be used as valuable aids in forecasting the probable
future service lives of individual items and of groups of items of different kinds of physical
equipment"6. The 13 curves described in Bulletin 103 eventually became a series of 22 generalized
survivor curves which are used throughout the regulated utility industry. These 22 curves were
described in Bulletin 125,published in 1967 by Harold A. Cowles,which became known as the Iowa
curves.
The Iowa curves are organized with three variables: the average life of the plant; the location of the
mode; and the variation of the life. All Iowa curves have both a letter and a number to represent the
shape and height of the mode. The L curves, or left-moded curves, are used when the mode of the
curve should be to the left of the average life. There are six L curves which are presented in Figure 2.
The R curves, or right-moded, are used when the mode of the curve should be to the right of the
average life. There are five R curves,which are presented in Figure 3. The S curves,or symmetrically-
moded, are used when the mode is equal to the average life. There are seven S curves, which are
presented in Figure 4. The 0 curves,or origin curves,are used when the mode occurs at age 0. There
are four 0 curves,which are presented in Figure 5. There are some occasions where it is appropriate
to use a half curve. In these cases,the curve is assumed to be exactly halfway between the two curves.
In addition to Bulletin 125, Iowa curves have also been presented in subsequent Experiment Station
bulletins and in the text Engineering Valuation and Depreciation'. In 1957, Frank V. B. Couch,Jr.,an
Iowa State College graduate student, submitted a thesis$presenting his development of the fourth
family consisting of the four 0-type survivor curves.
6 Ibid,34
7 Marston, Anson, Robley Winfrey and Jean C. Hempstead, Engineering Valuation and Depreciation (The Iowa State
University Press, 1953)
8 Couch, Frank V. B., Jr.,Classification of Type O Retirement Characteristics of Industrial Property Unpublished M.S.Thesis
(Engineering Valuation,Library,Iowa State College,Ames,Iowa, 1957)
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Figure 2: Left Modal or "L" Iowa Type Survivor Curves
Iowa Survivor Curves - Left-Modal (L)
100% ` ` ` \ 30%
La` L1 L2 •L 4 L5 0
F-F-T I
%%
90% ` 25i
% d 2 0%
80% c
C',15%
70% % ` c
9 10%
60% ` 1 LL 5% �.
C
♦`�. ; ,
2 %
50%
0%
c 0 25 50 75 100 125 150 175 200 225 250 275 300
Age(Percent of Life)
d ———LO — —L1 — - L2 L3 L4 L5
a 40%
30%
20%
10%
0%
0 25 50 75 100 125 150 175 200 225 250 275 300
Age(Percent of Average Life)
———LO — —L1 — L2 L3 L4 L5
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Figure 3: Right Modal or "R" Iowa Type Survivor Curves
Iowa Survivor Curves - Right-Modal (R)
100% ` _ 1 ` 35% TT
Rim R ♦ R .R� 5• 30%
90°/a
``� ♦ ♦ . � 225%
m
80% -
� ♦ o l
`� \`' j*,-15% I
709/641
\\ v 10%
1.
60% 5% `
2 0%
3 0 0 25 50 75 100 125 150 175 200 225 250 275 300
50%
Age(Percent of Life)
\N ———R1 — —R2 — R3 — R4 — R5
d 40%
30% \
20%
10%
0%
0 25 50 75 100 125 150 175 200 225 250 275 300
Age(Percent of Average Life)
———R1 — —R2 R3 — R4 — R5
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Figure 4: Symmetrical or "S" Iowa Type Survivor Curves
Iowa Survivor Curves - Symmetrical Modal (S)
100% T
S0� �% S2 `S�. S4 5.S b
90% o%
♦ `.
50%
80% ♦ ;,, 1 1
♦♦` d40% 1 1
70% 2R 1 1
530%
bO 60% \ 1
4A 50% 10%
..
a 40%
�\ 0 25 50 75 100 125 150 175 200 225 250 275 300
\ Age(Percent of Life)
30%
——— S6 ——— SO S1— -S2— -S3 — S4— -S5
\
\
20%
10%
0%
0 25 50 75 100 125 150 175 200 225 250 275 300
Age(Percent of Average Life)
———SO — —S1 — S2 S3 S4 — S5 S6
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16 2025 Depreciation Study
Figure 5: Origin Modal or "O" Iowa Type Survivor Curves
Iowa Survivor Curves - Origin Modal (0)
100%
12%
90% ` 10%
80%
\ . 6% - -
\ � c4%
\ ` {�
c 60% L` 2% `
50% \ ` 0%
0 25 50 75 100 125 150 175 200 225 250 275 300
d 4\ , 03 O�♦Ol Age(Percent of Life)
o_ 40% \ % ---01 — —02 03 04
30%
`�
v
zo% Nb
10%
o% ` — —
0 25 50 75 100 125 150 175 200 225 250 275 300
Age(Percentof Average Life)
———OS — —02 03 04
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9.4 Retirement Rate Method of Analysis
The retirement rate method is a widely accepted actuarial method used to create survivor curves.
This method is also referred to as an original life table. These survivor curves can then be used to
determine the average service life of a plant account. The retirement rate method is thoroughly
explained in several publications,including Statistical Analyses of Industrial Property Retirements,9
Engineering Valuation and Depreciation 10 and Depreciation Systems. "
The retirement rate method is a subgroup of the placement and the experience band methods, as
described in "Depreciation Systems". The placement band method creates a survivor curve which
describes the life characteristics of assets placed into service during a selected timeframe. The
experience band method creates a survivor curve which describes the life characteristics of assets
removed from service during a selected time frame. The retirement rate method creates both
placement and experience bands to give the most complete or representative data. An example of
the calculations used in the development of a life table follows. The example includes schedules of
annual aged property transactions, a schedule of plant exposed to retirement, a life table and
illustrations of smoothing the stub survivor curve.
9.5 Schedules of Annual Transactions in Plant Records
The property group used to illustrate the retirement rate method is observed for the experience band
2015-2024 during which there were placements during the years 2010-2024. In order to illustrate
the summation of the aged data by age interval, the data was compiled in the manner presented in
Schedules 1 and 2. In Schedule 1 (page 9-10),the year of installation (year placed) and the year of
retirement are shown. The age interval during which a retirement occurred is determined from this
information. In the example which follows, $10,000 of the asset invested in 2010 were retired in
2015. The$10,000 retirement occurred during the age interval between 4 1/z and 5 1/a years (2015 -
2010) on the basis that approximately one-half of the amount of property was installed prior to and
after July 1 of each year. That is,on the average,property installed during a year is placed in service
at the midpoint of the year for the purpose of the analysis. All retirements also are stated as occurring
at the midpoint of a one-year age interval of time, except the first age interval which encompasses
only one-half year.
The total retirements occurring in each age interval in a band are determined by summing the
amounts for each transaction year-installation year combination for that age interval. For example,
the total of $143,000 retired for age interval 41/z-51/2 is the sum of the retirements entered on
Schedule 1 immediately above the stair step line drawn on the table beginning with the 2015
9 Winfrey,supra note 2
10 Anson,Winfrey&Hempstead,supra note 8
11 Wolf&Fitch,supra note 3
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retirements of 2010 installations and ending with the 2024 retirements of the 2019 installations.
Thus,the total amount of$143,000 for age interval 41/z-51/z equals the sum of:
$10 + $12 + $13 + $11 + $13 + $13 + $15 + $17 + $19 + $20= $143k
Other transactions which affect the group are recorded in a similar manner in Schedule 2 (page 6-
11). The entries illustrated include transfers and sales. The entries which are credits to the plant
account are shown in parentheses. The items recorded on this schedule are not totaled with the
retirements but are used in developing the exposures at the beginning of each age interval.
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SCHEDULE 1. RETIREMENTS FOR EACH YEAR 2015-2024—SUMMARIZED BY AGE INTERVAL
Experience Band 2015-2024 Placement Band 2010-2024
Retirements(Thousands of Dollars)
Annual Survivors at the Beginning of the Year
Year Total During Age
Placed 2017 2018 2019 2020 2021 2022 2023 2024 Age Interval Interval
T1) (2) (3) (4) (5) (6) (7) (8) (9)" (10) (11) (12) (13)
2010 10 11 12 13 14 16 23 24 25 26 26 131/2- 141/2
2011 11 12 13 15 16 18 20 21 22 19 44 121/2- 131/2
2012 11 12 13 14 16 17 19 21 22 18 64 111/2- 121/2
2013 8 9 10 11 11 13 14 15 16 17 83 101/2- 1 11/2
2014 9 10 11 12 13 14 16 17 19 20 93 91/2- 101/2
2015 4 9 10 11 12 13 14 15 16 20 105 81/2- 91/2
2016 5 11 12 13 14 15 16 18 20 113 71/2-81/2
2017 6 12 13 15 16 17 19 19 124 61/2- 71/2
2018 6 13 15 16 17 19 19 131 51/2- 61/2
2019 7 14 16 17 19 20 143 41/2- 51/2
2020 8 18 20 22 23 146 31/2-41/2
2021 9 20 22 25 150 21/2- 31/2
2022 11 23 25 151 11/2- 21/2
2023 11 24 153 1/2- 11/2
2024 13 80 '0- 1/2
Total 53 68 86 106 128 157 196 231 273 308 1,606
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SCHEDULE 2.OTHER TRANSACTIONS FOR EACH YEAR 2015-2024—SUMMARIZED BY AGE INTERVAL
Experience Band 2015-2024 Placement Band 2010-2024
Acquistions,Transfers and Sales(Thousands of Dollars)
Annual Survivors at the Beginning of the Year
Total
During Age Ag
rd 2015 terval �nterv) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) PF (13)
2010 0 131/2- 141/2
2011 0 121/2- 131/2
2012 0 111/2- 121/2
2013 (5)b 60 101/2- 111/2
2014 6° 0 91/2- 101/2
2015 (5) 81/2-91/2
2016 6 71/2-81/2
2017 0 61/2-71/2
2018 = (12)b 0 51/2-61/2
2019 22° 0 41/2-51/2
2020 (19)b 10 31/2-41/2
2021 0 21/2-31/2
2022 (102)c (121) 11/2-21/2
2023 0 1/2- 11/2
2024 0 '0- 1/2
Total 0 0 0 0 0 0 60 (30) 22 (102) (50)
a=Transfer Affecting Exposures at Beginning of Year
b=Transfer Affecting Exposures at End of Year
c=Sale With Continued Use
Parentheses denote Credit amount
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9.6 Schedule of Plant Exposed to Retirement
The development of the amount of plant exposed to retirement at the beginning of each age interval
is illustrated in Schedule 3 (page 9-13). The surviving plant at the beginning of each year from 2015
through 2024 is recorded by year in the portion of the table titled"Annual Survivors at the Beginning
of the Year." The last amount entered in each column is the amount of new plant added to the group
during the year. The amounts entered in Schedule 3 for each successive year following the beginning
balance or addition,are obtained by adding or subtracting the net entries shown on Schedules 1 and
2. For the purpose of determining the plant exposed to retirement, transfers-in are considered as
being exposed to retirement in this group at the beginning of the year in which they occurred, and
the sales and transfers-out are considered to be removed from the plant exposed to retirement at
the beginning of the following year. Thus,the amounts of plant shown at the beginning of each year
are the amounts of plant from each placement year considered to be exposed to retirement at the
beginning of each successive transaction year. For example,the exposures for the installation year
2020 are calculated in the following manner:
Exposures at age 0 = amount of addition = $750,000
Exposures at age '/2 = $750,000- $ 8,000 = $742,000
Exposures at age 1'/2 = $742,000- $18,000 = $724,000
Exposures at age 2'/2 = $724,000- $20,000- $19,000 = $685,000
Exposures at age 3'/2 = $685,000- $22,000 = $663,000
For the entire experience band 2015-2024,the total exposures at the beginning of an age interval are
obtained by summing diagonally in a manner similar to the summing of the retirements during an
age interval (Schedule 1). For example, the figure of 3,789, shown as the total exposures at the
beginning of age interval 41/2-51/2,is obtained by summing:
$255 + $268 + $ 284 + $31 1 + $334 + $374 + $405 + $448 + $501 $ $609 = $3,789k
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SCHEDULE 3- PLANT EXPOSED TO RETIREMENT AT THE BEGINNING OF EACH YEAR, 2015-2024-SUMMARIZED BY AGE INTERVAL
Experience Band 2015-2024 Placement Band 2010-2024
Exposures(Thousands of Dollars)
Annual Survivors at the Beginning of the Year
Total at
Year Beginning of Age
Placed 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 Age Interval Intel
11) (2) (3) (4) (5) (6) (7) (8) (9)Ir (10)- (11) (12) (13)
2010 255 245 234 222 209 195 239 216 192 167 167 131/2- 141/2
2011 279 268 256 243 228 212 194 174 153 131 323 121/2- 131/2
2012 307 296 284 271 257 241 224 205 184 162 531 111/2- 121/2
2013 338 330 321 311 300 289 276 262 242 226 823 101/2- 111/2
2014 376 367 357 346 334 321 307 297 280 261 1,097 91/2- 101/2
2015 420 416 407 397 386 374 361 347 332 316 1,503 81/2-91/2
2016 460 455 444 432 419 405 390 374 356 1,952 71/2-81/2
2017 510 504 492 479 464 448 431 412 2,463 61/2- 71/2
2018 580 574 561 546 530 501 482 3,057 51/2-61/2
2019 660 653 639 623 628 609 3,789 41/2-51/2
2020 750 742 724 685 663 4,332 31/2-41/2
2021 850 841 821 799 4,955 21/2-31/2
2022 960 949 926 5,719 11/2-21/2
2023 1,080 1,069 6,579 1/2- 11/2
2024 1,220 7,490 '0- 1/2
Total 1,975 2,382 2,824 3,318 3,872 4,494 5,247 6,017 6,852 7,799 44,780
Additions during the year are denoted by bold red font.
r 1,555 F 1,922 Pr 2,314 r 2,738 F 3,212 r 3,744 F 4,397 Pr 5,057 F 5,772 rr 6,579 44,780
420 460 510 580 660 750 850 960 1,080 1,220 0
1,975 2,382 2,824 3,318 3,872 4,494 5,247 6,017 6,852 7,799 44,780
Concentric Energy Advisors Page 1 9-13

Intermountain Gas Company
1@ 2025 Depreciation Study
9.7 Original Life Tables
The original life table, illustrated in Schedule 4 (page 9-15) is developed from the totals shown on
the schedules of retirements and exposures, Schedules 1 and 3, respectively. The exposures at the
beginning of the age interval are obtained from the corresponding age interval of the exposure
schedule, and the retirements during the age interval are obtained from the corresponding age
interval of the retirement schedule. The retirement ratio is the result of dividing the retirements
during the age interval by the exposures at the beginning of the age interval. The percent surviving
at the beginning of each age interval is derived from survivor ratios,each of which equals one minus
the retirement ratio. The percent surviving is developed by starting with 100 percent at age zero and
successively multiplying the percent surviving at the beginning of each interval by the survivor ratio,
i.e.,one minus the retirement ratio for that age interval. The calculations necessary to determine the
percent surviving at age 51/2 are as follows:
Percent surviving at age 4'/2 = 88.15
Exposures at age 4'/2 = $3,789,000
Retirements from age 4'/2 to 5'/2 = $143,000
Retirement Ratio = $143,000-$3,789,000 = 0.0377
Survivor Ratio = 1.000- 0.0377 = 0.9623
Percent surviving at age 5'/2 = (88.15) x (0.9623) = 84.83
The totals of the exposures and retirements (columns 2 and 3)are shown for the purpose of checking
with the respective totals in Schedules 1 and 3. The ratio of the total retirements to the total
exposures, other than for each age interval, is meaningless. The original survivor curve is plotted
from the original life table(column 6,Schedule 4). When the curve terminates at a percent surviving
greater than zero,it is called a stub survivor curve. Survivor curves developed from retirement rate
studies generally are stub curves.
Concentric Energy Advisors Page 1 9-14

Intermountain Gas Company
1@ 2025 Depreciation Study
SCHEDULE 4: ORIGINAL LIFE TABLE-CALCULATED BY THE RETIREMENT RATE METHOD
Experience Band 2015-2024 Placement Band 2010-2024
Age at Exposures at Retirements %Surviving at
Beginning of Beginning of Age During Age Beginning of Age
Interval Interval Interval Retirement Ratio Survivor Ratio Interval
(�) (2) (3) (4) (5) (6)
0 7,490 80 0.0107 0.9893 100.00
0.5 6,579 153 0.0233 0.9767 98.93
1.5 5,719 151 0.0264 0.9736 96.63
2.5 4,955 150 0.0303 0.9697 94.08
3.5 4,332 146 0.0337 0.9663 91.23
4.5 3,789 143 0.0377 0.9623 88.16
5.5 3,057 131 0.0429 0.9571 84.83
6.5 2,463 124 0.0503 0.9497 81.19
7.5 1,952 113 0.0579 0.9421 77.11
8.5 1,503 105 0.0699 0.9301 72.64
9.5 1,097 93 0.0848 0.9152 67.57
10.5 823 83 0.1009 0.8991 61.84
11.5 531 64 0.1205 0.8795 55.60
12.5 323 44 0.1362 0.8638 48.90
13.5 167 26 0.1557 0.8443 42.24
35.66
Total 44,780 1,606
Exposure and Retirement Amounts are in Thousands of Dollars.
Column 2 from Schedule 3,Column 12,Plant Exposed to Retirement.
Column 3 from Schedule 1,Column 12,Retirements for Each Year.
Column 4=Column 3 divided by Column 2.
Column 5= 1.0000 minus Column 4.
Column 6=Column 5 multiplied by Column 6 as of the Preceding Age Interval.
Concentric Energy Advisors Page 1 9-15

Intermountain Gas Company
1@ 2025 Depreciation Study
9.8 Smoothing the Original Survivor Curve
The smoothing of the original survivor curve eliminates any irregularities and serves as the basis for
the preliminary extrapolation to zero percent surviving of the original stub curve. Even if the original
survivor curve is complete from 100 percent to zero percent, it is desirable to eliminate any
irregularities,as there is still an extrapolation for the vintages which have not yet lived to the age at
which the curve reaches zero percent. In this study, the smoothing of the original curve with
established type curves was used to eliminate irregularities in the original curve.
The Iowa type curves are used in this study to smooth those original stub curves which are expressed
as percentages surviving at ages in years. Each original survivor curve was compared to the Iowa
curves using visual and mathematical matching in order to determine the better fitting smooth
curves. In Figures 6, 7, and 8,the original curve developed in Schedule 4 is compared with the L, S,
and R Iowa type curves which most nearly fit the original survivor curve. In Figure 6, the L1 curve
with an average life between 12 and 13 years appears to be the best fit. In Figure 7,the SO type curve
with a 12-year average life appears to be the best fit and appears to be better than the L1 fitting. In
Figure 8,the R1 type curve with a 12-year average life appears to be the best fit and appears to be
better than either the L1 or the SO.
In Figure 9, the three fittings, 12-L1, 12-SO and 12-R1 are drawn for comparison purposes. It is
probable that the 12-111 Iowa curve would be selected as the most representative of the plotted
survivor characteristics of the group.
Concentric Energy Advisors Page 1 9-16

Intermountain Gas Company
1@ 2025 Depreciation Study
Figure 6: Illustration of the Matching of an Original Survivor Curve with a L1 Iowa Type Curve Original and Smooth Survivor Curves
100
■ ORIGINAL CURVE■ 2006-2016 EXPERIENCE:
■ 2002-2016 PLACEMENTS
90
80
IOW 13-L1
70 IO A 12-L1
z 60
> ■
D
Z 50 IOW 11-L1
W ■
U
w 40
a
30
20
10
0
0 5 10 15 20 25 30 35 40 45
AGE IN YEARS
Concentric Energy Advisors Page 1 9-17

Intermountain Gas Company
1@ 2025 Depreciation Study
Figure 7: Illustration of the Matching of an Original Survivor Curve with a SO Iowa Type Curve Original and Smooth Survivor Curves
100
ORIGINAL CURVE■ 2006-2016 EXPERIENCE:
2002-2016 PLACEMENTS
90
80
IOW 13-SO
70
IOWA 11-SO
c9
z 60
rr
D
(n 50
H
z
W
U
W 40
a
30
20
10
0
0 5 10 15 20 25 30 35 40 45
AGE IN YEARS
Concentric Energy Advisors Page 9-18

Intermountain Gas Company
1@ 2025 Depreciation Study
Figure 8: Illustration of the Matching of an Original Survivor Curve with a R1 Iowa Type Curve Original and Smooth Survivor Curves
100
ORIGINAL CURVE■ 2006-2016 EXPERIENCE:
2002-2016 PLACEMENTS
90
ao IO A 12-R1
IOW 13-Rl
70
z 60
' IO A 11-Rl
50
Z
W
U
W 40
a
30
20
10
0
0 5 10 15 20 25 30 35 40 45
AGE IN YEARS
Concentric Energy Advisors Page 1 9-19

Intermountain Gas Company
1@ 2025 Depreciation Study
Figure 9: Illustration of the Matching of an Original Survivor Curve with a L1, R 1, and SO Iowa Type Curve Original and Smooth
100
ORIGINAL CURVE ■ 2006-2016 EXPERIENCE:
2002-2016 PLACEMENTS
90
80 ■ �
70
IO A 12-R1
z 60
IOWA 2-L1
(n 50
H
Z
W
U
w 40
a
30
20
10
0
0 5 10 15 20 25 30 35 40 45
AGE IN YEARS
Survivor Curve
Concentric Energy Advisors Page 1 9-20

Intermountain Gas Company
1@ 2025 Depreciation Study
SECTION 10
10 ESTIMATION OF NET SALVAGE
The estimates of net salvage were based primarily on the professional judgment of Concentric,based
in part on historical data, and in part through a comparison to North American natural gas
transmission and distribution peer companies. The analysis of historic net salvage activity
considered gross salvage and cost of removal as recorded to the depreciation reserve account. Net
salvages as a percentage of the cost of plant retired are calculated for each plant component on rolling
annual and three-year and five-year moving average bands.
When a utility retires plant,the plant may be: (1) sold to a third party; (2) reused by the utility for
additional service; (3) abandoned in place; or (4) physically removed. In the circumstances where
the plant is sold or re-used,salvage proceeds (or positive salvage amount) are normally recognized.
In circumstances where the plant is abandoned in place or physically removed, a cost of removal
expenditure (or negative salvage) is incurred. The net of these gross salvage proceeds and the costs
of removal are expressed as a percentage of the account's original cost of plant retired to determine
a net salvage percentage. In the circumstances where the salvage proceeds exceed the costs of
retirement,a net positive salvage percentage exists. In the circumstances where the costs of removal
exceed the salvage proceeds,a net negative salvage as a percentage of the original cost is the result.
The net salvage percentages estimated is usually determined using the "Traditional Approach" for
net salvage estimation.The estimation of the net salvage as a percentage of original cost,as developed
using the traditional approach,includes the following five steps.
1. The annual retirement,gross salvage and cost of removal transactions for the period of analysis
is extracted from the plant accounting systems.
2. A net salvage amount (gross salvage proceeds less cost of retirement) is calculated for each
historic year. Additionally, a net salvage amount is also calculated for each historic three-year
rolling band and the most recent five-year rolling band.
3. The net salvage amount determined above is compared to the original booked costs retired for
each period in the manner described,which results in a net salvage percentage of original costs
retired for each year,in addition to three-year rolling bands and the most recent five-year rolling
band. The annual, the three-year rolling average, and the most recent five-year rolling average
net salvage percentages are analyzed to determine a reasonable estimated net salvage
percentage. At this point the net salvage percentage is based purely upon statistical analysis.
4. Each account is then compared to the net salvage percentage currently approved, compared to
North American natural gas transmission and distribution peer companies, and discussed with
company engineering staff. Based on the statistical analysis, the review of current and peer
company net salvage percentages, and with the professional judgment of Concentric, a net
salvage percentage is determined for each account.
Concentric Energy Advisors Page 1 10-1

Intermountain Gas Company
1@ 2025 Depreciation Study
5. The net salvage percentage is then used in the depreciation rate calculations in the technical
update or report.
Concentric Energy Advisors Page 1 10-2

EXHIBIT NO. 3
CASE NO. INT-G-26-01
INTERMOUNTAIN GAS COMPANY
General Plant Amortization Account Detail
(1 page)

Exhibit No.3
Case No. INT-G-26-01
Intermountain Gas Company
Page 1 of 1
Intermountain Gas Company
General Plant Amortization Account Detail
As of December 31, 2024
Line Lives Investment
Number Account Equipment Proposed Approved 12/31/2024
(a) (b) (c) (d) (e)
1 Account 391: Furniture and Office Equipment
2 391 Computers 15 10 $ 4,747,043
3 391 Desks, Chairs,Tables 15 10 495,666
4 391 Office Equipment 15 10 877,688
5 Total Account $ 6,120,397
6 Account 394:Tools, Shop, and Garage Equipment
7 394 Detectors 20 15 $ 715,159
8 394 Mains Construction 20 15 291,551
9 394 Power Tools 20 15 610,145
10 394 Racks, Shelving 20 15 26,861
11 394 Miscellaneous Tools 20 15 398,888
12 394 Tools 20 15 7,722,984
13 Total Account $ 9,765,588
14 Account 397: Communications Equipment
15 396 Bridges/Routers/Gateways 15 10 $ 23,814
16 397 Communication 15 10 5,067,380
17 397 Radio 15 10 96,660
18 397 SCADA 15 10 411,624
19 Total Account $ 5,599,478