20240828Compliance Filing with Distribution Risk Tree Program Report.pdf

RECEIVED
Wednesday, August 28, 2024
IDAHO PUBLIC
UTILITIES COMMISSION
11
Avista Corp.
1411 East Mission P.O. Box 3727
Spokane. Washington 99220-0500
Telephone [phone]
Toll Free 800-727-9170
Via Electronic Mail
August 27, 2024
Commission Secretary
State of Idaho
Idaho Public Utilities Commission
11331 W. Chinden Blvd. Building 8, Suite 201-A
Boise, Idaho 83702-5983
RE: Case No. AVU-E-23-01, Avista Wildfire -Distribution Risk Tree Program Report
Avista Corporation, dba Avista Utilities (Avista or the Company), hereby submits its third-party
Avista Wildfire - Distribution Risk Tree Program Report, per Commission Order 35909 in Case No.
AVU-E-23-01, at page 15,paragraph 14:
14. Wildfire Resiliency Plan. The Settling Parties agree to the following
Wildfire Resiliency Plan ("WRP") changes:
(a) For the Distribution Risk Tree program, the Company will have a
third party conduct a study, within a year of Commission Order, to see what the most
efficient vegetation management cycle should be in their service area (i.e., 2- or 3-
year cycles).
If you have any questions regarding this filing, please call me at [phone] or by email at
[e-mail].
Sincerely,
/s/Elizabeth Andrews
Elizabeth Andrews
Senior Manager, Revenue Requirements
Enclosures

AVU-E-23-01 -Avista Wildfire-Distribution Risk Tree Program Report
Avista Statement of Approval
In the 2023 Idaho Public Utilities Commission Case No. AVU-E-23-01 parties agreed to the following:
For the Distribution Risk Tree program, the Company will have a third party conduct
a study, within a year of Commission Order, to see what the most efficient
vegetation management cycle should be in their service area (i.e., 2- or 3-year
cycles).
In accordance with this directive, the Company hired an external vegetation management evaluation
service, Iapetus Infrastructure Services, to look at the key points of Avista's risk tree program, assess
the optimum frequency of maintenance across the service area, examine our fire risk profile, compare
our existing program to industry best practices, and to evaluate our strategies and their effectiveness.
Their report is attached. In summary, Iapetus found that Avista's approach to managing the risk
associated with utility-caused wildfires as an annual cycle is a reasonable and responsible approach
and that Avista is using best-in-class practices in this area. They sited, as partial evidence of this, a
reduction in actual tree fall-ins since the risk tree program began in 2020 of 62%. A summary of their
investigations is shown below:
Observation Comments
Considering the impact that drought and tree mortality has had on forests in the Western United States,
Risk Tree Avista has implemented an effective strategy to reduce the potential for utility-caused wildfires.As the
Cycle Risk Tree Program matures,the inventory of risk trees identified and removed should continue to reduce
in numbers as long as the goals and objectives remain in line with current standards.An annual cycle is
consistent with best-in-class programs at other major utilities in the West.
Avista has taken a comprehensive approach to identify and mitigate risk trees that pose a hazard to the
Risk Tree overhead distribution system.This approach has a two-fold benefit of reducing the volume of trees that
Strategy can potentially result in a utility-caused wildfire,as well as reduce the types of tree-related events that
cause interruption of electrical service.
Identifying By leveraging the industry-accepted UAA/ISA guide, Best Management Practices-Utility Risk Tree
Risk Trees Assessment,Avista is utilizing the most current protocols in use today by North American Utilities to
identify off-ROW risk trees that pose a hazard to the electrical grid and potentially pose a wildfire risk.
Outage Avista should commit to studying the root causes of tree-related outages through accurate reporting and
Investigations thorough post-outage investigations.A commitment to post-incident investigations does not mean every
outage needs to be investigated;however,the more data,the better the analysis.
We fully support their findings and have committed to the only recommendation they had for
improvement, to perform a more thorough investigation and documentation of root causes for tree-
related outages.
Vern Malensky, Director Electrical Engineering
Date: August 26, 2024

AVU-E-23-01 -Avista Wildfire-Distribution Risk Tree Program Report
/II/�iiFVIMSTA
Distribution Risk Tree Program
MAY 2024
PROGRAM
ASSESSMENT
t
Iapetus
infrastructure services
PREPARED BY:
Adam Warf
Dr. Philip Charlton
Steve Hallmark
Iapetus Infrastructure Services, LLC
3900 Essex Lane, Suite 775
Houston, TX 77027
LEGAL DISCLAIMER:Recommendations made in this report are for Avista's internal use only.IIS is not responsible for Avista's action(s)or
inaction in response to these recommendations.Assumptions made by IIS in the composition of this report were made based upon information
collected by and from Avista. Gaps in information are noted,but numbers may be skewed as a result of missing or inaccurate data provided.

AVU-E-23-01 -Avista Wildfire-Distribution Risk Tree Program Report
iapetus
infrastructure services
Distribution Risk Tree Program Assessment for Avista Utilities
Executive Summary
Introduction
In 2020, Avista Utilities (Avista) began a risk tree inspection program on the distribution
system. Trees meeting predetermined risk criteria are scheduled for tree maintenance
within six months of identification. Its first full annual system assessment was completed
in 2022.
In June 2023, Avista agreed to the following terms with the Idaho Public Utilities
Commission (PUC):
For the Distribution Risk Tree program, the Company will have a
third party conduct a study, within a year of Commission Order,
to see what the most efficient vegetation management cycle
should be in their service area (i.e., 2- or 3-year cycles).
In response to the Commission Order (the "Order") above, Avista contracted Iapetus
Infrastructure Services ("IIS") to evaluate its current Distribution Risk Tree Program and
provide recommendations for enhancing its approach to timing of inspections and
subsequent mitigation measures.
Assessment Process
As directed by Avista, IIS performed a detailed review of Avista's Distribution Risk Tree
Program to assess the optimum frequency of maintenance per service area (i.e., one-,
two- or three-year cycles). All areas of review were made within the context of Avista's
Wildfire Resiliency Plan.
The team utilized the following process for this assessment:
1. Review Avista's Enhanced Vegetation Management and Wildfire Resiliency
Plans.
2. Assess Avista's tree-specific performance including tree-related outage data and
work completion records.
3. Interview Avista's Vegetation Management team.
4. Develop and document recommendations.
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Key Observations
Avista has developed a Risk Tree Program leveraging their internal experience and
history of tree outages and program performance, as well as collaboration with leading
wildfire mitigation programs at electric utilities with more mature and robust programs.
Based upon this review, the IIS team finds that Avista's approach to managing the risk
associated with utility-caused wildfires as an annual cycle is a reasonable and
responsible approach. IIS has identified the following major areas of focus to enhance
the foundation of Avista's Risk Tree Program and become a more progressive, best-in-
class program.
Observation Comments
Risk Tree Considering the impact that drought and tree mortality has had on
Cycle forests in the Western United States, Avista has implemented an
effective strategy to reduce the potential for utility-caused wildfires.
As the Risk Tree Program matures, the inventory of risk trees
identified and removed should continue to reduce in numbers as long
as the goals and objectives remain in line with current standards. An
annual cycle is consistent with best-in-class programs at other major
utilities in the West.
Risk Tree Avista has taken a comprehensive approach to identify and mitigate
Strategy risk trees that pose a hazard to the overhead distribution system.
This approach has a two-fold benefit of reducing the volume of trees
that can potentially result in a utility-caused wildfire, as well as
reduce the types of tree-related events that cause interruption of
electrical service.
Identifying By leveraging the industry-accepted UAA/ISA guide, Best
Risk Trees Management Practices— Utility Risk Tree Assessment, Avista is
utilizing the most current protocols in use today by North American
Utilities to identify off-ROW risk trees that pose a hazard to the
electrical grid and potentially pose a wildfire risk.
Outage Avista should commit to studying the root causes of tree-related
Investigations outages through accurate reporting and thorough post-outage
investigations. A commitment to post-incident investigations does not
mean every outage needs to be investigated; however, the more
data, the better the analysis.
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Distribution Risk Tree Program Assessment for Avista Utilities
Table of Contents
ExecutiveSummary ........................................................................................................2
Introduction .................................................................................................................. 2
AssessmentProcess....................................................................................................2
KeyObservations......................................................................................................... 3
Avista Distribution Risk Tree Program............................................................................. 5
Wildfire Resiliency Plan................................................................................................ 5
FireRisk Profile............................................................................................................ 6
Risk Assessment Strategy........................................................................................... 8
Risk Tree Workload, Cost, and Tree Failure.............................................................. 10
IdentifyingRisk Trees............................................................................................. 10
Post-outage Investigations ..................................................................................... 12
Tree-related Outages................................................................................................. 13
Cycle Length and Objectives.................................................................................. 15
Historical Risk Tree Workload ................................................................................ 16
IISConsulting Team...................................................................................................... 18
AdamWarf................................................................................................................. 18
SteveHallmark........................................................................................................... 18
Dr. Phil Charlton......................................................................................................... 18
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Distribution Risk Tree Program Assessment for Avista Utilities
Avista Distribution Risk Tree Program
Wildfire Resiliency Plan
Wildfires are generally defined as "unplanned, uncontrolled fires fueled by an area of
combustible vegetation" and, like all fires, require three fundamental elements to exist:
fuel, oxygen, and heat. The fuel supply across North America has increased over the
past few decades due to political policies around fire suppression and forest
management, the introduction of non-native grasses, and dryer climates and droughts
that left forests damaged by insects and disease. Oxygen often comes in the form of
high winds that can spread the fires quickly. Sparks that initiate the fires are primarily
generated by human activities and weather, but about 10% of wildfire ignitions are
sparked by faults in electrical infrastructure or electric equipment failure.' In recent
years, wildfires have emerged as a significant risk to public safety and to the bulk power
system (BPS) assets that serve the Western Interconnection of North America.
Wildfires initiated by electric utility infrastructure prompted the state of California to
enact legislation in 2018 that required each electrical corporation, local publicly owned
electric utility, and electrical cooperative to do two things: 1) construct, maintain, and
operate its electrical lines and equipment in a manner that will minimize the risk of
catastrophic wildfire posed by those electrical lines and equipment and 2) prepare and
submit wildfire mitigation plans (WMPs) on an annual basis for review and approval by
the California Public Utility Commission (CPUC).
Recognizing the value of WMPs, a significant number of electric utilities outside of
California in the Western US have voluntarily developed their own WMPs to identify and
reduce their wildfire risk exposure. Both investor-owned and publicly owned utilities
(e.g., municipal, cooperative, REA, and federal utilities) have developed WMPs as
guiding documents to codify their risk reduction efforts as they relate to wildfires.
Electric Utilities in the Western US with WMPs include:
• Bonneville Power
• Idaho Power
• Northwestern Energy
• PacifiCorp
• Puget Sound Energy
A WMP details a utility's initiatives and activities for reducing the risks of its lines and
equipment igniting wildfires in the high fire risk areas of its service territory. The risks
associated with the equipment vary depending upon several factors: age and condition,
population density (ingress and egress), surrounding climate, terrain and vegetation,
"Wildfire Mitigation Webinar Series." U.S. Department of Energy, Office of Electricity.April 2021.
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voltage class and type of construction, and policies and regulations around land/forest
management. New technologies and increasing data capture have enabled companies
to perform risk analyses at the asset level, allowing them to prioritize activities and
develop initiatives for specific lines and equipment. This granularity provides for more
effective and efficient mitigations.
While each utility's risks are unique, general metrics for various aspects of the plan
enable a utility to assess the outcomes and measure the performance of individual
initiatives. Identifying plan successes and deficiencies ensures that the iterative
development process is one of continuous improvement.
In general, WMPs describe how the utilities' electric systems are designed, constructed,
operated, inspected, and maintained to promote wildfire safety, prevention, mitigation,
and recovery.
Fire Risk Profile
As identified in the Wildfire Resiliency Plan, Avista has committed to reducing fire risk to
its communities, customers, and the company. Like other utility wildfire plans, Avista is
making investments in four key areas:
1. Grid Hardening — to invest in electric line infrastructure to reduce spark-ignition
outage events and protect critical assets from the impact of wildfires.
This has become a key focus of utilities that are exposed to the highest
probability of utility-caused wildfire ignitions, as well as protecting assets from
any wildfire that encroaches on the utility's assets. Some examples include
undergrounding, fire-resistant overhead construction materials (e.g. composite
poles, or fire-retardant wrapped material on poles), as well as the use of tree wire
and construction standards that reduce the failure potential of overhead lines.
2. Enhanced Vegetation Management — to inspect 100% of distribution line
assets annually and combine remote sensing technologies such as LiDAR and
satellite imagery to aid in overall vegetation management decision-making.
Annual inspections of overhead electrical facilities in high fire risk (or high fire
threat) areas of a utility's footprint are becoming commonplace, and in certain
states a regulatory requirement. Such inspections take place for infrastructure
(typically poles and hardware), as well as to identify hazardous trees.
3. Situational Awareness — to automate Avista's non-reclosing protection strategy
and align short-term, weather-related fire risk with system protection levels.
This is a basic tenet of a utility wildfire risk reduction effort. Seasonal adjustments
to reclosure settings are an accepted standard for many utilities in high fire risk
areas. Increasingly, remote switching at the sub-circuit level is being deployed to
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isolate electrical facilities damaged by wildfire, as well as proactive de-energizing
of line segments during high fire threat periods. It should be noted that proactive
de-energizing is a very complex process for any utility to deploy, and requires
significant buy-in among the utility, regulators, and customers.
As documented in Avista's Wildfire Resiliency Report:
"Avista has developed a computer algorithm to monitor, forecast, and adapt to
fire-weather events. Avista's Fire Weather Dashboard combines the National
Weather Service's 7-day forecast with Avista infrastructure data to quantify the
daily fire risk on 350 distribution circuits. This allows system operators to align
circuit protection settings with fire-weather conditions and minimize the potential
for spark-ignition on a circuit-by-circuit basis. This monitoring system is similar to
those used in California. In fact, Avista worked closely with San Diego Gas &
Electric to calibrate the system to achieve a balance between electric service
reliability and fire ignition potential. This monitoring system supports Avista's fire
season circuit protection program known internally as Dry Land Mode."
Observation: San Diego Gas & Electric (SDG&E) has been at the forefront of
managing wildfire risk and developed one of the most
comprehensive utility wildfire management programs in the United
States. Leveraging SDG&E's experience and knowledge is
commendable.
4. Emergency Response & Operation — to help customers be better prepared for
wildfires and partner with emergency first responders before, during, and after
fire events.
Emergency Response Plans are core to a utility's ability to effectively manage
the complexities of any emergency, including wildfire. By actively engaging local
and state agencies in the development and execution of a utility emergency
response plan, all parties involved can perform at their highest level. In turn, the
customers are best served with reliable information that keeps them informed
and able to make informed decisions.
These are core principles of a proactive Wildfire Mitigation Plan (WMP), which is the
term typically used by most electric utilities in the Western United States. These
principles provide focus for the utility on design and maintenance practices that can best
reduce the risk of utility-caused wildfires, as well as establish clear operating
procedures during periods of elevated wildfire potential. Avista has established a
framework for a plan to identify and reduce risk from wildfire on their system.
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Distribution Risk Tree Program Assessment for Avista Utilities
Risk Assessment Strategy
For this report, IIS will focus specifically on the Risk Assessment Strategy as it relates to
the Distribution Risk Tree Program.
In 2019, Avista developed the initial wildland urban interface (WUI) map that combined
data from the Wildfire Hazard Potential with the location of Avista electric lines in areas
of low, medium, and high population. This analysis indicated that 3,240 miles of Avista's
7,725-mile distribution system were located in high fire threat districts (42% of the
system). Avista's 2020 Wildfire Plan focused on grid hardening and vegetation
programs in these elevated risk areas.
In 2023, Avista's WUI map was updated and now includes additional data which
measures the impact of fire on human development. The USDA's Housing Unit Impact
dataset14 combined with the Wildfire Hazard Potential data mentioned previously, was
used to refine the Avista WUI map. Areas shown on the 2023 WUI map with either an
orange or pink highlight indicate these high fire risk zones. Communities like Chewelah
and Colville border national forest lands, as do many other areas including Sandpoint,
St. Maries, Grangeville, and portions of the Lewiston/Clarkston Valley, placing them
more at risk. In total, 2,746 miles of electric distribution lines are in high fire risk areas or
about 36% of the system. This analysis indicates slightly lower risk values as compared
to 2019.
The WUI map serves to identify and prioritize the areas of highest risk. The Avista WUI
identifies three wildfire risk levels: Gr, dF_,,*,
c
Tier 1: Moderate levels of fuel and low to
moderate housing densities (low) "C
Tier 2: Moderate to high levels of fuel 03
and moderate housing densities
(medium)
Tier 3: High fuel levels and moderate to e
high housing densities (high)
rP �
e
Kenne,wck
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By overlaying the vegetation management polygons with the WUI map, the percentages
of the polygon with a tier 3 (highest risk), tier 2, and tier 1 WUI designation were
calculated. These percentages were then used to generate a risk score for each
vegetation management polygon. A weight was applied to each of the WUI tier levels to
ensure that tier 3 areas are placed at higher priority levels than WUI tiers with lower risk.
The following table demonstrates how the overall risk weighting score for Avista is
calculated on each vegetation management polygon.
Table 1. Weighting calculation example for risk tree prioritization
WUI Tier Weight applied Sample calculation CDA R P4 (WUI %) x weight
3 10 0.229 x 10 = 2.29
2 5 0.655 x 5 = 3.275
1 1 0.009 x 1 = 0.009
Overall risk score 5.574
In 2017, the California Public Utilities Commission adopted the CPUC Fire-Threat Map
which describes the boundaries of a new High Fire Threat District (HFTD) where utility
infrastructure and operations will have stricter fire-safety regulations. The CPUC Fire-
Threat Map incorporates the fire hazards associated with past powerline wildfires and
ranks fire-threat areas based on the risks that utility-associated wildfires pose to people
and property.
The main team that handled the development of the CPUC Fire-Threat Map was a
group of utility mapping experts known as the Peer Development Panel (PDP), with
oversight from a team of independent experts known as the Independent Review Team
(IRT). The members of the IRT were selected by CAL FIRE and CAL FIRE served as
the Chair of the IRT. The development of CPUC Fire-Threat Map includes input from
many stakeholders, including investor-owned and publicly-owned electric utilities,
communications infrastructure providers, public interest groups, and local public safety
agencies. Additional intormation on C;alitornia's approach can be tound at the CCalitornia
PUC Fire Safety Rulemaking Background webpage.
The process that Avista has utilized to define Risk Tiers is comparable to the California
approach utilized to delineate the High Fire Threat Districts.
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Risk Tree Workload, Cost, and Tree Failure
Identifying Risk Trees
Industry research has shown that the vast majority (80% or more) of tree-caused
outages are a result of trees or tree parts falling from off the ROW.
• On TransAlta's distribution system, where all overhangs were removed, 90-98%
of tree-caused outages were due to tree failure 2
• Niagara Mohawk reported 86% of tree-caused outages result from trees outside
the right-of-way 3
• Puget Sound Energy found 66% of all outages were caused by trees greater than
15 feet from the nearest conductor 4
• A survey of 71 utilities by the University of Wisconsin found about 81% of
outages are due to off-ROW trees, broken branches, and whole tree failures
rather than on-ROW grow-ins 5
Risk is the combination of the likelihood of an event and severity of the potential
consequences. The Utility Arborist Association developed, and the International Society
of Arboriculture published, the Utility Risk Tree Assessment best management practices
which aid in the development of this tool.
The likelihood a tree will cause an outage, damage utility infrastructure, or cause a
wildfire is dependent on the likelihood that a) the tree will fail and b) the failed tree will
impact the electrical system.
Table 2. Likelihood matrix presented in the UAA//SA Utility Risk Tree Assessment
Likelihood Likelihood of Impact on the System
of Failure Very low Low Medium High
Imminent Unlikely Somewhat likely Likely Very likely
Probable Unlikely Unlikely Somewhat likely Likely
Possible Unlikely Unlikely Unlikely Somewhat likely
Improbable Unlikely Unlikely Unlikely Unlikely
2 Guggenmoos, S. 1996. "Outage statistics as a basis for determining line clearance program status."
UAA Q. 5(1).
3 Finch, K.E., and C.Allen. 2001. "Understanding Tree-Caused Outages." EEI Natural Resource
Conference.Apr. 2001. Palm Springs, CA.
4 Rogers, B.I. 2001. "Puget Sound Energy Tree Watch Program." EEI Natural Resource Conference,Apr.
2001, Palm Springs, CA
5 "Utility Vegetation Management in North America," College of Natural Resources, University of
Wisconsin—Stevens Point, and CNUC. March 22, 2021.
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Tree risk rating is based on the likelihood of failure and impact combined with the
severity of the consequence of impact. The severity of consequence will differ for 69kV
vs 7.2kV, single- vs multi-phase lines, sections with and without special equipment, and
so forth. Following is a risk rating matrix which combines these factors.
Table 3. Risk Tree Rating Matrix presented in the UAA11SA Utility Risk Tree Assessment
Likelihood of Consequence of Failure
Failure & Impact Negligible Minor Significant Severe
Imminent Low Moderate High Extreme
Probable Low Moderate High High
Possible Low Low Moderate Moderate
Improbable Low Low Low Low
The consequence assessment should reflect what portion of the system is involved
(e.g., 69kV, multi-phase, single-phase) and Wildfire Hazard Potential (WHP)
designation.
Observation: By leveraging the industry-accepted UAA/ISA guide, Best Management
Practices— Utility Risk Tree Assessment, Avista is utilizing the most
current protocol in use today by North American Utilities to identify off-
ROW risk trees that pose a hazard to the electrical grid and potentially
pose a wildfire risk.
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Post-outage Investigations
One of the greatest challenges facing UVM professionals is knowing which trees cause
outages and how. Utilities cannot effectively manage a problem they do not understand.
Not all tree species have the same failure rate. Not all portions of the system respond
the same to tree contact (1- vs 3-phase) and the consequence of failure varies widely
(e.g., 69kV vs 1-phase 7.2KV). Best Management Practices— Utility Risk Tree
Assessment provides general guidance regarding risk factors, but best practices utilities
collect utility-specific data through post-outage investigations. Utilities need to study the
root causes of their specific tree-related outages to replace intuition, anecdotal
evidence, and generalized industry data with reliable data.
The Avista VM team does not currently investigate tree-related interruptions. Utilities
that begin post-event investigation of tree-related outages initially find a 25-40% error
rate in unaudited reporting.
Observation: Avista should commit to studying the root causes of tree-related outages
through accurate reporting and thorough post-outage investigations. A
commitment to post-incident investigations does not mean every outage
needs to be investigated; however, the more data, the better the
analysis. Those selected for investigation should include incidents on all
voltages, construction types, and in both storm and non-storm situations.
They should also be timely—conducted close to the outage occurrence.
The objective of these investigations is to understand which trees fail, how they fail, and
how they impact the electrical system. These post-outage investigations should be
performed by an experienced arborist to:
• Give direct feedback on which trees are causing the majority of interruptions
• Provide learning opportunities for the arborist
• Refine assessment criteria
These investigations should go beyond simply indicating it was a "tree-related event" to
identifying distinct characteristics about the tree and the site surrounding it. The data
can then be used to drive the risk tree mitigation process. Data collected during post-
outage investigations often include:
• Voltage • Orientation to the line
• Line configuration (single-wire • Tree or tree part that failed
primary, 2-wire primary, etc.) . Nature of failure (trunk failure,
• Tree species branch failure, uprooted tree, etc.)
• Height • Condition of tree or tree part failure
• Diameter . Site conditions
• Distance to the line • Date of last maintenance
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Tree-related Outages
Since the full rollout of the Risk Tree Program, Avista has documented that more than
60% of the tree-related outages in Idaho from 2020 to 2023 occurred in Tiers 2 and 3.
Tree-related Outages by Tier
400
a
350
6 300
ca
250
0 200
150
= 100
z 50 ■
Tier 0 Tier 1 Tier 2 Tier 3
■2020 2021 2022 2023
Note: Although the WUI map identifies three wildfire risk levels, Avista also collects
outage data for Tier 0 (i.e., nominal risk with low levels of fuel).
Over the past ten years in Idaho, 92% of spark-related outage events fall into five basic
cause categories: animal, weather, public, tree, and equipment. Of these categories,
electric utilities can have the most influence over reducing equipment- and tree-related
events. Animal, weather, and public are much harder to predict and guard against.
Spark-related Outage Events (2014-2023)
Public
18%
Weather
8%
■ Equipment
54%
Tree
8%
■ Other
■ Animal 8%
4%
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As covered previously under the Fire Risk Profile section of this report, Avista has
identified Grid Hardening and Enhanced Vegetation Management as two of the four
areas for reducing wildfire risk on the company's electrical grid.
Additionally, research and industry data has shown the following:
1. Unless the distribution lines are entirely enveloped by vegetation, a shorter cycle
seldom results in fewer tree-related interruptions.6
2. At distribution voltages (15kV and below), trees in incidental contact are unlikely
to result in an electrical fault (phase-to-ground) causing an interruption.
• Tree grow-ins represent only 2-14% of all tree-caused outages.',$
• At voltage gradients below 2kV per foot, the probability of a fault occurring is
almost zero.g
3. Due to the above, almost all tree-related outages are caused by whole trees or
limbs falling on the conductors and creating a phase-to-phase electrical fault or
physical damage rather than by tree growth resulting in incidental contact with
the lines.10
Observation: Avista has taken a comprehensive approach to identify and mitigate risk
trees that pose a hazard to the overhead distribution system. This
approach has a two-fold benefit by reducing the volume of trees that can
potentially result in a utility-caused wildfire, as well as reduce the types
of tree-related events that cause interruption of electrical service.
6 Guggenmoos, S. 1996. "Outage statistics as a basis for determining line clearance program status."
UAA Q. 5(1).
Rees, W.T., Jr., T.C. Birx, D.L. Neal, C.J. Summerson, F.L. Tiburzi, Jr., and J.A. Thurber. 1994. "Priority
Trimming to Improve Reliability." ISA conference presentation, Halifax, NS.
8 Finch, K.E., and C. Allen. 2001. "Understanding Tree-Caused Outages." EEI Natural Resource
Conference.Apr. 2001. Palm Springs, CA.
9 Russell, D. et. al. 2011. "Best Practices in Vegetation Management for Enhancing Electric Service in
Texas." PUCT Project 38257.
10 Guggenmoos, S. 2003. "Effects of Tree Mortality on Power Line Security." Arboriculture & Urban
Forestry, 181-196.
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Cycle Length and Objectives
As currently designed and implemented, Avista's Enhanced Vegetation Management
Program incorporates two primary components relative to management of vegetation on
the overhead distribution system: Routine and Risk Tree.
The Routine Maintenance Program emphasizes maintaining a five-year cycle for
addressing the vegetation on the entire distribution system and preventing grow-in
outages. To meet these objectives, the routine maintenance program prioritizes work
based on time since last trim and number of grow-in related outages.
The Risk Tree Program objective is to identify risk trees, with the potential of imminent
fall-in or grow-in hazard to the energized facilities, and ensure they are trimmed or
removed to eliminate potential for fire ignitions and outages. A risk tree is defined as
visibly dead, diseased, dying, or possessing obvious structural defects that could fall
into the conductor. The corresponding risk tree annual patrol identifies trees which are
deemed a threat to reliability and pose a fire risk.
The Routine Maintenance Program and Risk Tree Program are interrelated because
risk inspections and mitigation are performed as part of routine maintenance if a
polygon is on the routine plan for the year. This allows for planning and mitigation work
to happen using the same planners and crews. While the Risk Tree Program and
Routine Maintenance work planning and mitigation contracts are separate, this enables
Avista to move crews between programs as needed to meet work plan objectives and
gain efficiencies.
Observation: Implementing an extensive risk tree assessment and mitigation program
is a best practice today. This includes documenting the root cause of
outages (e.g., which trees/conditions result in failure) and aggressively
targeting higher risk, off-ROW trees (see previous reference).
Important to note: The optimum cycle for preventing tree growth into the conductors
may be different from the optimum cycle for off-ROW risk tree mitigation.
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Historical Risk Tree Workload
Beginning in 2020 when Avista implemented the system-wide patrol of the overhead
distribution system, the annual volume of risk trees abated has increased year-over-
year. Expenditures had initially shown an annual cost per tree increase for 2020-22, but
a reduction in cost per tree in 2023.
Idaho Risk Tree Expenditures
16000 $600
14000 $500
'0 12000
a) 10000 $400
fy
8000 $300
a� V)
6000 $200 v
n 4000
121� 2000 $100
0 $0
2020 2021 2022 2023
Total Risk Trees Completed Cost/Risk Tree
Contributing factors include:
• More than 90% of the U.S. West was in moderate drought or worse by late June
2021. More than a quarter was in exceptional drought, the highest level,
indicating widespread risk of crop loss, fire, and water shortages."
Moderate drought or worse Severe drought or worse —Extreme drought or worse —Exceptional drought
IuC'
80
60
40
20
0 A . , - AAL .A
2000 2002 2004 2006 2008 2010 2012 2014 2016 2018 2020
Data as of June 24,2021
Chart:The Conversation!r -BY-ND-C:_urcr r,n_=,hAcrito,-�,nt-r,dsta
11 "National Drought Highlights Report," U.S. Drought Monitor, June 24, 2001.
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• Trees in Western forests have been dying at an alarming rate over the past two
decades due to droughts, high temperatures, pests, and fires.12
• Labor cost and availability has had a significant impact on utilities. Based upon
Avista's experience in 2022, the increased volume of risk trees required
mobilization of crews from outside the region to accomplish the workload.
Conversely, by achieving a stabilized workforce in 2023, per unit costs
decreased by 17%.
To determine if a program is influencing system performance, one of the most valuable
measures for a risk tree program is to show a reduction in the occurrence of actual tree
fall-ins. For the evaluation period from 2020 to 2023, Avista has recognized a 62%
reduction in tree fall-ins.
Idaho Tree Events by Outage Type
350
300
v, 250
c
> 200
w
m 150
100
50
0
2020 2021 2022 2023
■Tree Fall-In ■Tree Grow-in
Observation: Considering the impact that drought and tree mortality has had on
forests in the western United States, Avista has implemented an
effective strategy to reduce the potential for utility caused wildfires. By
maintaining the current annual cycle of identifying and abatement of risk
trees, the inventory of risk trees identified and removed should continue
to reduce in numbers so long as the goals and objectives remain
consistent with current practices. By doing so, the annual cycle should
continue to reduce the overall risk exposure from hazard trees.
12 Daniel Johnson and Raquel Partelli Feltrin, "Trees are dying of thirst in the Western drought,"
The Conversation, June 29, 2021.
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IIS Consulting Team
Adam Warf
Mr. Wares experience includes leading business development strategies for a
Q r utility vegetation management consulting firm, vegetation management field
1 , operations at two major investor-owned utilities in the southeastern US,
project management at a variety of utilities in the mid-Atlantic and southeastern regions,
and vegetation management program development and assessments across the
country. His utility arboricultural experience provides a broad understanding of the many
different methods used to create a successful utility right-of-way vegetation
management program, including remote sensing, work management solutions, data
analytics, optimization, and the utilization of third-party consulting foresters for planning
and auditing duties.
Steve Hallmark
Mr. Hallmark serves in a senior leadership role to IIS' Chief Operating Officer,
driving strategic solutions, innovation, and an entrepreneurial vision to power
and energy companies. Mr. Hallmark has extensive experience managing
large-scale utility vegetation management programs, including budget, regulatory
compliance, and contract design and enforcement. Over the years, he has served in a
leadership capacity on vegetation management issues and acted as a government and
industry liaison. Most recently, he served as part of a team at the direction of the
California Governor's Office overseeing PG&E's Wildfire Mitigation Program. With over
40 years of utility vegetation management and line construction practices experience,
Mr. Hallmark is recognized as a highly qualified subject matter expert on a national
level.
Dr. Phil Charlton
,0 Dr. Charlton has worked with over 150 electric utilities in seven countries,
helping to develop long-term vegetation management programs for distribution
W line clearance and transmission rights-of-way maintenance. Most of these
studies required detailed evaluation of the vegetation conditions, work practices, and
operating procedures. Dr. Charlton has also been active in industry research since
1980. His research has encompassed cost and effectiveness issues related to rights-of-
way maintenance, environmental concerns with use of herbicides, wetlands protection,
reliability, and more.
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