20240909IPC to Staff . 96(d) _ Attachment 1_ Water Quality Certification.pdf

��IQAHO
POWER.
An IOACORP Company
Evaluation of Upstream Andrew Knight
Phosphorus Reductions Biologist
Brian Hoelscher
Riverside Operational Water-Quality Senior Biologist
Improvement Project Reasonable Assurance
Hells Canyon Complex, FERC Project No. 1971 February 2018
2018 Idaho Power

Idaho Power Company Phosphorus Reduction Reasonable Assurance
TABLE OF CONTENTS
Tableof Contents............................................................................................................................. i
Listof Tables ................................................................................................................................... i
Listof Figures................................................................................................................................. ii
1. Introduction................................................................................................................................1
2. Evaluation of Upstream Phosphorus Reductions.......................................................................2
2.1. Grand View Sediment Reduction Program.......................................................................2
2.1.1. Drain and Tributary Phosphorus Loading................................................................2
2.1.2. Surface Irrigation Soil Loss Model Development, Verification, and Use
for Evaluating Phosphorus Reductions....................................................................3
2.1.2.1. Total Suspended Solids...................................................................................3
2.1.2.2. Total Phosphorus.............................................................................................4
2.2. Aquatic Vegetation and Debris Removal..........................................................................5
3. Downstream Transport of Phosphorus.......................................................................................5
4. Translating Phosphorus to Oxygen............................................................................................8
5. Additional Benefits of Upstream Phosphorus Reductions.........................................................8
6. Conclusions................................................................................................................................9
7. Literature Cited..........................................................................................................................9
LIST OF TABLES
Table 1
2013 drain and tributary load summary. Summary limited to drains and tributaries
located on the south-side of the Snake River identified for inclusion in the Grand View
Sediment Reduction Program. Loads were calculated using data collected from April
17, 2013, to October 17, 2013, and represent daily and seasonal loads for a typical 183-
daygrowing season.....................................................................................................................12
Table 2
Summary of sediment annual load estimates derived from measured data and produced
by the SISL model from full implementation of the Grand View Sediment Reduction
Program.......................................................................................................................................13
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Table 3
Number of truckloads of aquatic vegetation and debris removed at the Swan Falls
project annually between April 15 and October 15 and the resulting TP removed from
theSnake River...........................................................................................................................13
Table 4
Snake River TP samples collected, mean, standard deviation, and median concentration
from 2003 to 2006 at Swan Falls Reservoir inflow (Inflow), Swan Falls Reservoir
outflow (Outflow), Celebration Park. .........................................................................................14
Table 5
TP, DO, and organic matter(OM) stoichiometric ratios. ...........................................................14
Table 6
IPC DO load allocation per SR—HC TMDL, with conversion to TP equivalent using
stoichiometric ratios proposed by IPC. TP load reduction with OM and DO equivalents
resulting from the Grand View Sediment Reduction Program and Swan Falls project. ............15
LIST OF FIGURES
Figure 1
Grand View Sediment Reduction Program area map.................................................................16
Figure 2
TP and TSS regression analysis for south-side drains and tributaries. Analysis indicates
there are 1.56 lbs of phosphorus per ton of TSS.........................................................................17
Figure 3
Sampling location map. From left to right, sampling locations are at Celebration Park
(river mile [RM] 447.6), Swan Falls Reservoir outflow (RM 457.6), and Swan Falls
Reservoir inflow(RM 472.0)......................................................................................................18
Figure 4
Snake River TP concentrations at Swan Falls Reservoir inflow (river mile [RM] 472.0),
Swan Falls Reservoir outflow(RM 457.6), and Celebration Park(RM 447.6). ........................19
Figure 5
Monthly 2005 total, orthophosphorus, and particulate phosphorus loads. Note:
Estimated phosphorus loads from drains and tributaries are not included in plots
(Naymik and Hoovestol 2008)....................................................................................................20
Figure 6
Monthly 2006 total, orthophosphorus, and particulate phosphorus loads. Note:
Estimated annual TP loads from drains and tributaries are not included in these plots
(Naymik and Hoovestol 2008)....................................................................................................21
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Idaho Power Company Phosphorus Reduction Reasonable Assurance
Figure 7
2005 and 2006 streamflow below C.J. Strike Reservoir.............................................................22
Figure 8
1912 through 2017 Snake River near Murphy, Idaho, period of record(POR) average
annual flow exceedance curve. Streamflow percent exceedance for 2003 through 2006
averageannual flows...................................................................................................................23
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Idaho Power Company Phosphorus Reduction Reasonable Assurance
1 . INTRODUCTION
The Snake River—Hells Canyon total maximum daily load(SR—HC TMDL) assigned Idaho
Power Company(IPC) a dissolved oxygen (DO) load allocation of 1,125 tons per year to the
transition zone and metalimnion of Brownlee Reservoir(IDEQ and ODEQ 2004). The Brownlee
Reservoir annual DO load allocation, as stated in the SR—HC TMDL is as follows:
The dissolved oxygen allocation requires the addition of 1,125 tons of oxygen
(1.02 x 106 kg) into the metalimnion and transition zone of Brownlee Reservoir
(approximately 17.3 tons/day(15,727 kg/day)).
The SR—HC TMDL specifically allows IPC to use total phosphorus (TP) and organic matter
reductions to satisfy the DO load allocation. As stated in the SR—HC TMDL, the use of
equivalent reductions for meeting the DO load allocation is described as follows:
This load allocation does not require direct oxygenation of the metalimnetic and
transition zone waters. It can be accomplished through equivalent reductions in
total phosphorus or organic matter upstream, or other appropriate mechanism that
can be shown to result in the required improvement of dissolved oxygen in the
metalimnion and transition zones to the extent required.
The Riverside Operational Water-Quality Improvement Project(ROWQIP), as described in
Section 7.2.1. of the Hells Canyon Complex (HCC) Clean Water Act of 1972 (CWA) § 401
certification application(IPC 2017), hereafter referred to as the HCC § 401 application, is the
mechanism proposed to meet IPC's 1,125 tons per year DO load allocation assigned to the
transition zone and metalimnion of Brownlee Reservoir. Early implementation of the ROWQIP
began in 2010, and the project has since demonstrated the ability to meet IPC's DO load
allocation annually through a proposed phosphorus-reduction equivalency of 15,000 pounds
(lbs). IPC is proposing the Grand View Sediment Reduction Program and removal of aquatic
vegetation and debris at the Swan Falls hydroelectric project(Swan Falls project) as reasonable
assurance for the ROWQIP.
Sediment caused by the erosion of Idaho's croplands is the greatest nonpoint source pollutant to
Idaho's surface waters (Mahler et al. 2003). Erosion of sediments ftom cropland and deposition
of these sediments in the Snake River is a root cause of degradation. Sediment deposition in
Snake River substrate prevents oxygen exchange between the water column and the interstitial
substrate environment, provides a medium for macrophyte establishment, and reduces hyporheic
exchange (Groves and Chandler 2005). Channel aggradation is exacerbated by sediment.
Cropland erosion also results in phosphorus loading to the Snake River. Furrow-irrigated
agriculture is known to cause considerable amounts of cropland erosion. The Grand View
Sediment Reduction Program is an IPC incentive program offered to growers near Grand View,
Idaho, to convert from furrow to pressurized irrigation. The benefit is improved upland soil
retention and, therefore, less sediment erosion to the Snake River.
IPC removes aquatic vegetation and debris from the Snake River at the Swan Falls project.
Material is disposed of in a location where it cannot return to the river. Removal of this material
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results in downstream decreases in floating or submerged organic matter, excess nutrients, and
oxygen-demanding material.
The Grand View Sediment Reduction Program is not proposed in the HCC § 401 application
(IPC 2017) as a measure to address a SR-HC TMDL load allocation nor is removal of aquatic
vegetation and debris at the Swan Falls project a compliance measure for certification. Further,
these activities were initiated after EPA approval of the SR HC TMDL, therefore, associated
phosphorus reductions represents improvements toward SR-HC TMDL targets. This allows IPC
to use their benefits toward reasonable assurance of measures proposed in the HCC § 401
application. Specifically, phosphorus and organic matter reductions resulting from the Grand
View Sediment Reduction Program and aquatic vegetation and debris removal will be used to
provide reasonable assurance for meeting IPC's SR-HC TMDL DO load allocation.
2. EVALUATION OF UPSTREAM PHOSPHORUS REDUCTIONS
2.1 . Grand View Sediment Reduction Program
The Grand View Sediment Reduction Program targets furrow-irrigated lands located within the
Grand View Irrigation District (Figure 1). Research projects were initiated in 2015 and have
been completed on 14 projects totaling over 1,700 acres. Full implementation is expected to
occur within 10 years of HCC license issuance.
2.1.1. Drain and Tributary Phosphorus Loading
In 2013, IPC conducted a study to quantify pollutant loads contributed by drains and tributaries
to the Snake River in southwest Idaho near Grand View (Knight 2014). The study documented
and sampled 27 drains and tributaries between the C.J. Strike Reservoir outflow and near the
inflow to Swan Falls Reservoir.
The Grand View Sediment Reduction Program has specifically identified furrow-irrigated lands
located on the south side of the Snake River for program inclusion. For this evaluation, drain and
tributary data obtained from the 2013 study were limited to the program area. The study was
conducted between March 27 and October 30, 2013. For purposes of this analysis, data were
limited to those collected between April 17 and October 17, 2013. This period is analogous to the
April 15 to October 15, 183-day typical growing season as described in the ROWQIP.
Pollutant load estimates indicated drains and tributaries targeted for inclusion in the Grand View
Sediment Reduction Program cumulatively contributed average TP and total suspended solids
(TSS) loads of 95 and 70,946 lbs per day, respectively(Table 1). When extrapolated over a 183-
day typical growing season, the resulting TP and TSS loads contributed 17,374 and 12,983,101
lbs per year, respectively.
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Idaho Power Company Phosphorus Reduction Reasonable Assurance
2.1.2. Surface Irrigation Soil Loss Model Development, Verification,
and Use for Evaluating Phosphorus Reductions
The Surface Irrigation Soil Loss (SISL)model, a version of the Universal Soil Loss Equation,
was developed by the Idaho National Resources Conservation Service (MRCS) to estimate
irrigation-induced soil loss (i.e., sediment) from furrow-irrigated fields. The model was
developed using data from southern Idaho and is used by Idaho NRCS to assess benefits of
conservation practices (MRCS 2003). Bjorneberg et al. (2007) evaluated the performance of the
SISL model and reported the model predicted the relative effects of conservation practices
reasonably well; however, the absolute differences between measured and predicted soil loss
were sometimes large and biased toward underprediction of measured soil loss. This suggests
that any error in modeled loads would likely result in conservative load reduction estimates.
With reasonable performance demonstrated in southern Idaho, IPC, in consultation with The
Freshwater Trust, selected the SISL model to evaluate sediment reductions to the Snake River
resulting from the Grand View Sediment Reduction Program. Modeling included only furrow-
irrigated acres, as observed from satellite imagery, for potential conversion to pressurized
irrigation. All furrow-irrigated fields were mapped and delineated with publicly available data on
soils, slope, crop data, and irrigation practices. Crop data from 2005 to 2014 (excluding 2006)
were used to populate the SISL model. IPC believes the 9 years of crop data represents typical
rotations and, therefore, represents average annual sediment loss. The SISL model does not
represent a growing season duration, however, represents a defined number of crop
category-specific flood irrigation events that occur in a growing season. Further, it was unknown
whether specific fields were siphon or gated-pipe irrigated; therefore,both irrigation methods
were modeled, and the average of the 2 was considered to represent the average annual sediment
loss.
Cumulative drain and tributary load estimates derived from measured data collected during the
2103 study were compared to program-wide SISL model sediment loss estimates to assess the
feasibility of using model predictions to evaluate sediment reduction as implementation occurs.
SISL is a soil-loss model. Data indicate TSS measured in south-side drains and tributaries is
dominated by the inorganic (i.e., sediment) component. As such, TSS and sediment are
considered analogous for purposes of this analysis.
2.1.2.1. Total Suspended Solids
Measured TSS data and SISL model sediment loss resulted in annual sediment loads of
12,983,101 and 21,474,000 lbs per year,respectively, for all south-side drains and tributaries
combined(Table 2). The between-estimate discrepancy is expected, and much of the difference
can likely be explained when the following factors are considered.
• Not all drains and tributaries were sampled. Sampling was limited due to 1)the timing of
sample events, 2) inaccessibility, and 3)private ownership. This resulted in a
conservative estimate of TSS loads delivered to the river.
• Measured-data load estimates were developed using samples collected at the point of
inflow to the river; whereas the SISL model estimates sediment loss at the edge of the
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field. Therefore, sediment stored between the edge of the field and the river was not
captured in measured data.
• Measured data represent finer-particle suspended sediment only. Therefore, larger-
particle unsuspended sediment is not represented in measured data.
Considering the factors above, it was determined the sediment loss estimate produced by the
SISL model is a reasonable approximation of the sediment load delivered to the Snake River by
drains and tributaries. The coarse validation of the modeled sediment load estimate supports the
use of the SISL model for estimating load reductions resulting from the Grand View Sediment
Reduction Program.
Many factors (e.g., wetted radius, application rate, uniformity of application, sprinkler pressure,
localized differences in field slope, application of erosion controls, such as polyacrylamide)
contribute to determining if, or how much,runoff might occur under sprinkler irrigation
(Klocke et al. 1996; Aase et al. 1998). Many of these are accounted for in the SISL model and
sediment loss should be reduced to almost zero and be negligible when pressurized irrigation
systems are used properly. Nevertheless, IPC applied an additional margin of safety to the model
results. SISL model sediment loss estimates were reduced to 90%to address any concerns
regarding the effectiveness of pressurized irrigation in reducing sediment loss (i.e., pressurized
irrigation will reduce sediment loss by 90%). The resulting annual sediment load reduction
estimate produced by the SISL model and adjusted to 90% is 19,326,600 lbs per year(Table 2).
The goal of the Grand View Sediment Reduction Program is 80% conversion of furrow-irrigated
acres to pressurized irrigation. This further reduces the annual sediment load reduction estimate
produced by the SISL model to 15,461,280 lbs per year.
2.1.2.2. Total Phosphorus
Following an evaluation of SISL model sediment loss, results were converted to a TP load.
Regression results for all south-side drains and tributaries combined indicated there are 1.56 lbs
of TP associated with each ton of TSS (Figure 2). This calculated TP:TSS ratio (1.56 lbs:1 ton)
falls within reported literature values that generally range from 0.8 lbs:I ton to 2.8 lbs:1 ton
(NRCS 2015; Mullins 2009; Mahler et al. 1996). SISL model sediment loss was then converted
to TP using the ratio described above.
Measured data for all south-side drains and tributaries combined and SISL model predictions
resulted in annual TP load estimates of 17,374 and 16,750 lbs per year, respectively. TP load
estimates were very similar compared to the TSS estimates. Two factors that likely contribute to
the relative difference between TSS and TP load estimates produced with measured data and the
SISL model include the following:
• The regression analysis indicates the TP:TSS ratio is considerably higher than
1.56 lbs TP:1 ton TSS, and that a few data points with considerably lower ratios skewed
the regression equation to a lower ratio than what was observed in most of drains and
tributaries (Figure 2).
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Idaho Power Company Phosphorus Reduction Reasonable Assurance
• The TP:TSS ratio was likely higher in suspended sediments represented in the measured
data relative to unsuspended sediment. The suspended fraction of the sediment load is
generally represented by finer clays and silts with increased TP absorptive capacity
relative to larger particles not represented in the measured data.
The close agreement between measured data and modeled TP load estimates supports using the
SISL model to evaluate TP load reductions resulting from the Grand View Sediment Reduction
Program. Further, TP load estimates produced by the SISL model are less than those produced
using measured data, which did not include data from all drains and tributaries in the modeled
area, suggesting the SISL model may yield conservative estimates of load reductions resulting
from the Grand View Sediment Reduction Program. The Grand View Sediment Reduction
Program assumes a 90% efficiency and targets 80% of the furrow-irrigated lands for conversion
to sprinklers. The potential Grand View Sediment Reduction Program annual TP load reduction
is 12,060 lbs per year.
2.2. Aquatic Vegetation and Debris Removal
IPC has been removing aquatic vegetation and debris that accumulates on the trash rake over the
intake turbines at the Swan Falls project since October 2011. IPC proposed continued operation
as part of the project final license application. Idaho Department of Environmental Quality
(IDEA) acknowledged the proposed action in the CWA § 401 certification for the project but did
not make it a condition of the certification necessary to ensure compliance with Idaho water
quality standards. Since IPC proposed continued operation as part of the license application,
Federal Energy Regulatory Commission included the action in the license issued September 28,
2012. Article 404 requires IPC remove aquatic vegetation and debris that accumulates on the
trash rake and dispose of the material in a location where it cannot return to the Snake River.
IPC has removed 56-417 truckloads of material from the Snake River annually between April 15
and October 15 and disposed of the material in a location where it cannot return to the river
(Table 3). IPC weighed 8 truckloads from June through September 2014 to estimate a wet weight
of material removed from the river. The average truckload of material weighed 14,019 lbs. This
material was then converted to TP using a value of 489.2 milligrams TP per kilogram of wet
weight. This value is based on 2002-2003 laboratory results of TP concentrations measured in
wet material collected upstream at IPC's Upper Salmon Falls `B"hydroelectric project. IPC
estimates that annually 1,547 lbs TP is removed from the Snake River through aquatic vegetation
and debris removal at the Swan Falls project.
3. DOWNSTREAM TRANSPORT OF PHOSPHORUS
Snake River phosphorus data were reviewed to evaluate trends in TP transport through the river.
The data were collected between 2003 and 2006 and describe conditions in the Snake River at
Swan Falls Reservoir inflow, Swan Falls Reservoir outflow, and at Celebration Park(Figure 3).
This river reach and locations were used to evaluate TP transport due to the following:
• minimal sources of phosphorus to the reach;
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• best available data applicable to the evaluation; and
• represents TP transport in both Swan Falls Reservoir(14.5 miles) and a free-flowing
section downstream (10 miles).
Concentration data were analyzed to evaluate between-location differences. Mean TP
concentrations from 2003 to 2006 varied between locations within a year(Table 4), however,
median concentrations were not statistically different (P>0.050)when using a Kruskal-Wallis
one-way analysis of variance on ranks. This test was used due to the non-normal distribution of
data. The lack of statistical difference in median TP concentrations between upstream and
downstream locations indicates TP is not being appreciably retained within a year either in Swan
Falls Reservoir or in a riverine reach of the Snake River. The between location variability may
be attributable to the following:
• the timing and duration of sample collection, which may have been biased toward
conditions of export;
• sample collection at Swan Falls Reservoir inflow occurring in an unmixed location
relative to upstream contributions;
• in-reservoir load contributions from 2 minor tributary sources (Castle Creek and
Sinker Creek); and
• processes related to TP uptake and release by macrophytes and algae.
USGS (2016) identifies 3 approaches to estimate reach-scale nutrient attenuation. Mass—balance
is the preferred method when there are minimal surface and groundwater contributions within the
evaluated reach. The mass—balance method of estimating nutrient attenuation does not consider
adsorption,uptake, and remineralization processes. However,phosphorus is a conservative
constituent that remains in the system regardless of phase. As such, results obtained using the
mass—balance method can be used to describe TP transport within the evaluated reach. The intent
of this evaluation is to generally describe TP attenuation, and how it is transported downstream
to Brownlee Reservoir. Given that Snake River hydraulics are similar between the evaluated
reach and Brownlee Reservoir, it is reasonable to suggest transport dynamics are similar as well.
While load data indicate minimal, if any, long-term storage of TP occurs, some level of
short-term storage and subsequent export is likely dictated by streamflow conditions.
Naymik and Hoovestol (2008) reported that when Swan Falls Reservoir inflow and outflow
loads were evaluated on an annual basis, TP was slightly retained in 2003 and 2004 (4% and 2%,
respectively) with low streamflow. A small amount of export occurred in 2005 (6%)under
conditions of slightly higher flows. Export was highest in 2006 (27%) and was associated with
the highest annual flows among evaluated years. The export observed in 2006 may have been
related to unaccounted for in-reservoir tributary loading resulting from rain and snowmelt events.
Seasonal trends are discernible in plots of the data(Figure 4). These findings are generally
consistent with those reported in the literature. Wetzel (2001) reported that in a stream
dominated by particulate phosphorus, no annual net retention of phosphorus occurred,
but transport dynamics included short periods of storage with export occurring during pulses in
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Idaho Power Company Phosphorus Reduction Reasonable Assurance
streamflow. Similar findings representing differing stream types have been reported by others
(Nyenje et al. 2014; Ensign et al. 2006).
Naymik and Hoovestol (2008) evaluated monthly loads at both the Swan Falls Reservoir inflow
and outflow locations using FLUX, a water-quality analysis software developed by the U.S.
Army Corps of Engineers. FLUX Method 2 was used to generate interpolated daily phosphorus
concentrations, and the average daily streamflow was applied to generate daily loads. Daily loads
were summed to generate monthly phosphorus loads for 2005 (Figure 5) and 2006 (Figure 6).
Seasonal pulses of export are evident in both years,with most of the export occurring between
April and May. This period of export is associated with marked increases in streamflow(Figure
7). An additional description of seasonal phosphorus storage and export trends within Swan Falls
Reservoir is provided by Naymik and Hoovestol (2008) as reported in the Swan Falls project
license application (IPC 2008).
Naymik and Hoovestol (2008) determined that pulses in streamflow were the primary
mechanism by which phosphorus was transported from Swan Falls Reservoir. These findings,
along with an independent analysis of data and a literature review, suggest the primary factor
affecting Snake River TP transport dynamics is streamflow,where particulate phosphorus is
deposited during low-flow conditions and exported during streamflow pulses. Myers et al. (1998)
reported similar phosphorus transport dynamics in a free-flowing section of the Snake River
between Swan Falls Dam and Brownlee Reservoir in 1995. They concluded that increased flows
preceded by low-flow conditions resulted in mobilization and transport of sediments and
associated phosphorus. Based on the period of record,Naymik and Hoovestol (2008)reported
that flows measured below Swan Falls Reservoir(USGS gage#13172500) during their 2003-
2006 study were generally biased toward low flows, representing conditions when storage would
be more likely to occur.
Swan Falls Reservoir inflow and outflow loads reported by Naymik and Hoovestol (2008)were
compared to 1912 through 2017 Snake River flows near Murphy, Idaho, to determine the
occurrence frequency of flows that facilitate downstream transport of TP (Figure 8). In 2003 and
2004, when minimal storage occurred, average annual flows were in the 991h percentile of
historically low flows, indicating that flows equal or greater to these occur 99% of the time. The
small amount of downstream export that was observed in 2005 was associated with an average
annual flow that is exceeded 93% of the time. This indicates that flows of required magnitude to
facilitate downstream transport of TP are likely to occur in approximately 14 out 15 years. These
findings support the concept that TP is functionally transported through the evaluated reach at
about a 1:1 ratio on an annual basis even during low water years, when storage might otherwise
be expected.
Based on this analysis, and in the absence of water storage reservoirs between Swan Falls
Reservoir and Brownlee Reservoir, it is reasonable to suggest similar transport dynamics exist
within the extent of river between C. J. Strike Reservoir and the inflow to Brownlee Reservoir.
Therefore, reductions in TP loading to the Snake River resulting from the Grand View Sediment
Reduction Program and Swan Falls project aquatic vegetation and debris removal translate to
reduced TP loading to, and reduced oxygen demand within, Brownlee Reservoir.
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The growth, transport, and subsequent deposition and decay of organic material in Brownlee
Reservoir are not limited to temporal periods identified in the SR-HC TMDL. If phosphorus
reductions equivalent to 1,125 tons of DO occur within the May to September SR-HC TMDL
critical period, the oxygen benefits would likely not be fully realized due to the deposition of
organic material in the transition zone that occurs during periods outside the critical period.
Therefore, it is logical that upstream nutrient reductions occurring outside this period would
contribute to improved DO conditions within Brownlee Reservoir for the May to September
critical period.
4. TRANSLATING PHOSPHORUS TO OXYGEN
Phosphorus, oxygen, and organic matter can be related by inorganic stoichiometry, which varies
in response to environmental conditions (Sterner and Elser 2002). IPC has proposed the use of
stoichiometric ratios based on those reported in the literature and with consideration for what
might typically apply within the Snake River and Brownlee Reservoir environments (Table 5).
The proposed stoichiometry, as used to establish a TP-DO equivalency for the ROWQIP by
Harrison et al. (2014), indicates a phosphorus reduction of approximately 15,000 lbs annually is
needed for IPC to satisfy the assigned DO load allocation of 1,125 tons (Table 6). Additional
support for the stoichiometric logic used to derive the TP-DO equivalent is provided in Exhibit
7.2-2 of the HCC §401 application(Harrison et al. 2014).
As described in Section 2.1.2.2., the SISL model phosphorus load reduction estimate resulting
from full implementation of the Grand View Sediment Reduction Program is 12,060 lbs per year.
The phosphorus reduction from Swan Falls project aquatic vegetation and debris removal
(Section 2.2.) is 1,547 lbs per year. Stoichiometric relationships indicate this cumulative level of
TP reduction translates to an DO demand reduction of 1,021 tons per year within the transition
zone and metalimnion of Brownlee Reservoir(Table 6).
5. ADDITIONAL BENEFITS OF UPSTREAM
PHOSPHORUS REDUCTIONS
IPC believes reducing TP loading to the Snake River addresses a core issue underlying DO
demand and generally degraded water-quality conditions within the Snake River and Brownlee
Reservoir rather than using direct aeration, or a similar reservoir-specific measure, to meet IPC's
SR-HC TMDL DO load allocation within Brownlee Reservoir. Upstream TP reductions will not
only contribute to improving in-reservoir DO conditions but will also provide in-river benefits
that contribute to supporting beneficial uses. Improvements in water quality conditions are likely
to include, but are not limited to, the following:
• increased hyporheic exchange;
• reduction of habitat that contributes to mercury methylation;
• reduction of near-substrate anoxia;
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Idaho Power Company Phosphorus Reduction Reasonable Assurance
• dampening of diel DO swings; and
• reduced algal and aquatic plant growth.
6. CONCLUSIONS
• TP reductions resulting from the Grand View Sediment Reduction Program and the Swan
Falls project aquatic vegetation and debris removal would result in 13,607 lbs TP
reductions annually from April 15 through October 15.
• IPC has demonstrated minimal annual storage of TP within the Snake River indicating
about a 1:1 ratio of TP transport in most years. IPC concludes that upstream phosphorus
loads are functionally transported through the Snake River into Brownlee Reservoir.
• IPC concludes that upstream phosphorus reductions achieved through implementation of
the Grand View Sediment Reduction Program and the Swan Falls project aquatic
vegetation and debris removal translates to reduced loading to, and reduced oxygen
demand within Brownlee Reservoir.
• These reductions would be equivalent to 1,021 tons of DO within the transition zone and
metalimnion of Brownlee Reservoir. Therefore, the Grand View Sediment Reduction
Program and Swan Falls project aquatic vegetation and debris removal provide
reasonable assurance that IPC's DO load allocation within the transition zone and
metalimnion of Brownlee Reservoir will be met.
• Grand View Sediment Reduction Program research projects were initiated in 2015 and
have been completed on 14 projects totaling over 1,700 acres. Full implementation is
expected to occur within 10 years of HCC license issuance. IPC will continue to remove
aquatic vegetation and debris at the Swan Falls project at least through 2042.
7. LITERATURE CITED
Aase, J., D. Bjorneberg, and R. Sojka. 1998. Sprinkler irrigation runoff and erosion control with
polyacrylamide—laboratory tests. Soil Science Society of American Journal 62(6).
Madison, WI.
Bjorneberg, D. L., C. J. Prestwich, and R. G. Evans. 2007. Evaluating the Surface Irrigation Soil
Loss (SISL) model. Applied Engineering in Agriculture 23(4):485-491.
Cole, T. M. and S. A. Wells. 2002 CE-QUAL-W2: A Two-Dimensional, Laterally Averaged,
Hydrodynamic and Water Quality Model. Version 3.1. User Manual. Draft Instruction
Report EL-02-1. U.S. Army Corp of Engineers.
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Ensign, S. H., S. K. McMillan, S. P. Thompson, M. F. Piehler. 2006.Nitrogen and phosphorus
attenuation within the stream network of a coastal, agricultural watershed. Journal of
Environmental Quality 35:1237-1247.
Groves, P. and J. Chandler. 2005. Habitat Quality of Historic Snake River Fall Chinook Salmon
Spawning Locations and Implications for Incubation Survival. Part 2: Intra-Gravel Water
Quality. River Research and Applications 21:469-483.
Harrison, J., S. King, and S. Mooney. 2014. Technical memorandum—IPC equivalent seasonal
phosphorus load reduction. In: Technical Appendices for New License Application:
Hells Canyon Hydroelectric Complex. Technical Report E.7.2-2.
[IDEQ and ODEQ] Idaho Department of Environmental Quality and Oregon Department of
Environmental Quality. 2004. Snake River—Hells Canyon total maximum daily load
(TMDL). Boise, ID, and Pendleton, OR: IDEQ Boise Regional Office and ODEQ
Pendleton Office. 710 p., plus appendices.
[IPC] Idaho Power Company. 2008. Swan Falls Project FERC No. 503 license application.
Boise, ID: Idaho Power Company. 706 p. with exhibits.
[IPC] Idaho Power Company. 2017. CWA Section 401 water-quality certification application.
Hells Canyon Complex FERC No. 1971. Boise, ID: Idaho Power Company.
Klocke,N. L., W. L. Kranz, C. D. Yonts, and K. Wertz. 1996. G96-1305 water runoff from
sprinkler irrigation: A case study. Historical Materials from University of Nebraska—
Lincoln Extension. Paper 1208.
Knight, A. 2014. Evaluation of drain and tributary pollutant sources to the C.J. Strike—Swan
Falls Reach, Snake River, Idaho. 2013 Study Summary. Boise, ID: Idaho Power
Company. 62 p.
Mahler, R., F. Bailery, S. Norris, and K. Loeffelman. 1996. BMP's for erosion control:
Brochure WQ-27. University of Idaho Cooperative Extension.
http://www.webpages.uidaho.edu/—karenl/wq/wgbr/wgbr27.html. Accessed on:
December 18, 2017.
Mahler, R., F. Bailery, S. Norris and K. Loeffelman. 2003. BMPs for Erosion Control: Brochure
WQ-27. hqp://www.uiweb.uidaho.edu/wq/wgbr/wgbr27.html. Accessed on: October 23,
2012.
Mullins, G. 2009. Phosphorus, agriculture and the environment. Virginia Cooperative Extension,
1-11.
Myers, R., Parkinson, S., and Harrison, J. 1998. Tributary Nutrient Loadings to the Snake River,
Swan Falls to Farewell Bend, March through October 1995. Idaho Power Company.
Boise, ID. Technical Report AQ-98-HCC-01. 27 p.
Page 10 FERC Project No. 1971

Idaho Power Company Phosphorus Reduction Reasonable Assurance
Naymik, J., and C. Hoovestol. 2008. Descriptive water quality of the Swan Falls Project.
Technical Report Appendix E.2.2-A. In: Swan Falls Project FERC No. 503 License
Application. Boise, ID: Idaho Power Company. 64 p. with appendices.
[NRCS] National Resources Conservation Service. 2003. Predicting irrigation induced soil loss
on surface-irrigation cropland using Surface Irrigation Soil Loss model (SISL). Idaho
NRCS Agronomy Technical Note No. 32 (Rev. 3).
[NRCS] National Resources Conservation Service. 2015. The REAL cost of soil erosion. NRCS
Newsroom.
https://www.nres.usda.gov/wps/portal/nres/detail/ne/newsroom/releases/?cid=NRC SEPR
D386010. Accessed on: December 18, 2017.
Nyenje, P.M., M. G. Meijer, J. W. Foppen, R. Kulabako, and S. Uhlenbrook. 2014.
Phosphorus transport and retention in a channel draining an urban, tropical catchment
with informal settlements. Hydrology and Earth System Sciences 18:1009-1025.
Copernicus Publications.
Sterner, R. and Elser, J. 2002. Ecological Stoichiometry. Princeton University Press. Princeton,
NJ.
[USGS] United States Geologic Survey. 2016. Nutrient attenuation in rivers and streams,
Puget Sound Basin, Washington. Scientific Investigations Report 2015-5074. Version
1.1. USGS Science Publishing Network, Tacoma Publishing Service Center. 80 p.
Wetzel, R.G. 2001. Limnology—lake and reservoir ecosystems. Third ed. San Diego, CA:
Academic Press. 1006 p.
FERC Project No. 1971 Page 11

Phosphorus Reduction Reasonable Assurance Idaho Power Company
Table 1
2013 drain and tributary load summary. Summary limited to drains and tributaries located on the south-
side of the Snake River identified for inclusion in the Grand View Sediment Reduction Program. Loads
were calculated using data collected from April 17, 2013, to October 17, 2013, and represent daily and
seasonal loads for a typical 183-day growing season.
Average Daily Loads (kg/day)
Drain RM* River Position Orthophosphorus TP TSS
476.3 Left Bank 1.17 2.25 657
476.8 Left Bank 0.11 0.29 156
477 Left Bank 0.20 7.67 11,633
477.5 Left Bank 0.13 1.78 1,239
477.55 Left Bank 0.09 2.29 1,519
477.7 Left Bank 0.01 0.14 563
478 Left Bank 0.10 , 1.61 1,043
478.1 Left Bank 0.49 2.38 1,312
478.9 Left Bank 1.5= 6.14 4,272
479.1 Left Bank 1.02 1.37 179
479.7 Left Bank 0.01 0.36 387
479.9 Left Bank 0.08 1.20 1,017
480.1 Left Bank 0.29 ■ 0.64 166
483.1 Left Bank 0.46 2.04 1,212
485.3 Left Bank 2.33 I 3.22 738
486.5 Left Bank 0.32 0.35 33
490.4 Left Bank 4.00 9.33 6,054
Cumulative Average Daily Load (kg/day) 12 43 32,181
Cumulative Average Daily Load (Ibs/day) 27 95 70,946
Total Seasonal Load (Ibs/day*183 days) 4,988 17,374 12,983,101
Site location described in Snake River miles at point of inflow to river
Page 12 FERC Project No. 1971

Idaho Power Company Phosphorus Reduction Reasonable Assurance
Table 2
Summary of sediment annual load estimates derived from measured data and produced by the SISL
model from full implementation of the Grand View Sediment Reduction Program.
Load Estimate(Ibs/year)
Measured Data SISL
Sediment 12,983,101 21,474,000
Load Reduction Efficiency(total*90%) 19,326,600*
Load Reduction at Program Buildout(90%adjusted load*80%) 15,461,280**
Reflects conservative assumption of 90%efficiency from pressurized irrigation.
**Reflects program load reduction potential at full implementation based on 80%conversion of furrow-irrigated acres in the
program area.
Table 3
Number of truckloads of aquatic vegetation and debris removed at the Swan Falls project annually
between April 15 and October 15 and the resulting TP removed from the Snake River.
Number of Truckloads TP(Ibs)
2012 56 384
2013 227 1,557
2014 417 2,860
2015 308 2,112
2016 209 1,433
2017 136 933
Average 1,547
FERC Project No. 1971 Page 13

Phosphorus Reduction Reasonable Assurance Idaho Power Company
Table 4
Snake River TP samples collected, mean, standard deviation, and median concentration from 2003 to
2006 at Swan Falls Reservoir inflow (Inflow), Swan Falls Reservoir outflow(Outflow), Celebration Park.
Count Mean Standard Deviation Median
2003
Inflow 17 0.081 0.063 0.067
Outflow 17 0.080 0.017 0.076
Celebration Park 17 0.074 0.015 0.071
2004
Inflow 23 0.078 0.021 0.076
Outflow 23 0.083 0.020 0.078
Celebration Park 23 0.088 0.020 0.081
2005
Inflow 25 0.072 0.015 0.070
Outflow 25 0.079 0.025 0.074
Celebration Park 25 0.080 0.032 0.068
2006
Inflow 20 0.077 0.022 0.070
Outflow 20 0.093 0.038 0.076
Celebration Park 20 0.089 0.026 0.082
Table 5
TP, DO, and organic matter(OM)stoichiometric ratios.
Stoichiometry or Load W2 Brwn'02 Brwn'95 SR'95 Proposed
TP/OM 0.005 0.01 0.01 0.02 0.01
DO/OM 1.4 1.7 1.4 1.4 1.5
TP/DO 0.36% 0.59% 0.71% 1.43% 0.67%
*Notes: Ratios obtained from Harrison et al.,2014
W2:Stoichiometry are modeled default values per Cole and Wells 2002.
Brwn'95:Stoichiometry are optimized model values used in the 1995 Brownlee model application.
SR'95:Stoichiometry are optimized model values used in the 1995 Snake River model application.
Brwn'02: Based on data collected in upper end of reservoir.
Proposed: Recommended for conversion of DO allocation to TP reduction.
Page 14 FERC Project No. 1971

Idaho Power Company Phosphorus Reduction Reasonable Assurance
Table 6
IPC DO load allocation per SR—HC TMDL, with conversion to TP equivalent using stoichiometric ratios
proposed by IPC. TP load reduction with OM and DO equivalents resulting from the Grand View
Sediment Reduction Program and Swan Falls project.
TMDL Annual Load
DO Load Allocation per SR-HC TMDL (tons/yr) 1,125
OM Load Allocation Equivalent(tons/yr) 750
TP Load Allocation Equivalent(tons/yr) 7.5
TP Load Allocation Equivalent(Ibs/yr) 15,000
Grand View Sediment Reduction Program Annual Load
TP Reduction via SISL(Ibs/yr) 12,060
TP Reduction via SISL(tons/yr) 6.03
OM Reduction Equivalent(tons/yr) 603
DO Demand Reduction Equivalent(tons/yr) 905
Swan Falls project aquatic vegetation and debris removal Annual Load
TP Reduction (Ibs/yr) 1,547
TP Reduction (tons/yr) 0.77
OM Reduction Equivalent(tons/yr) 77
DO Demand Reduction Equivalent(tons/yr) 116
Example TP to DO equivalent calculation method:
• TP Ibs to tons: 12,060 Ibs TP/(2,000 Ibs/1 ton)=6.03 tons TP/yr
• TP tons to OM tons:6.03 tons TP/0.01 TP:OM ratio=603 tons OM/yr
• OM tons to DO tons:603 tons OM/1.5 DO:OM ratio=905 tons DO/yr
FERC Project No. 1971 Page 15

Phosphorus Reduction Reasonable Assurance Idaho Power Company
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Figure 1
Grand View Sediment Reduction Program area map
Page 16 FERC Project No. 1971

Idaho Power Company Phosphorus Reduction Reasonable Assurance
120
•
100
80
V) 60 y=1.5614x
RZ=0.5625
40
zo �r ..i •
0
0 10 20 30 40 5o 60
TSS(tons/day)
Figure 2
TP and TSS regression analysis for south-side drains and tributaries. Analysis indicates there are 1.56
Ibs of phosphorus per ton of TSS.
FERC Project No. 1971 Page 17

Phosphorus Reduction Reasonable Assurance Idaho Power Company
RM 447.6
• Celebration Park
RM 457.6
Swan Falls Outflow
1
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f
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z SINKER CREEK
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Figure 3
Sampling location map. From left to right, sampling locations are at Celebration Park (river mile [RM]
447.6), Swan Falls Reservoir outflow (RM 457.6), and Swan Falls Reservoir inflow (RM 472.0).
Page 18 FERC Project No. 1971

Idaho Power Company Phosphorus Reduction Reasonable Assurance
0.35
• RM 447.6
0.3
• RM 457.6
RM 472
0.25
J
hC.0
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Figure 4
Snake River TP concentrations at Swan Falls Reservoir inflow (river mile [RM]472.0), Swan Falls
Reservoir outflow(RM 457.6), and Celebration Park (RM 447.6).
FERC Project No. 1971 Page 19

Phosphorus Reduction Reasonable Assurance Idaho Power Company
1.0e+5 1.0e+5
Inflow Inflow
_ 0 Outflow O Outflow
M 8.0e+4 8.0e+4
� v
o a
N 6.0e+4 J 6.0e+4
0 0
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Figure 5
Monthly 2005 total, orthophosphorus, and particulate phosphorus loads. Note: Estimated phosphorus
loads from drains and tributaries are not included in plots (Naymik and Hoovestol 2008).
Page 20 FERC Project No. 1971

Idaho Power Company Phosphorus Reduction Reasonable Assurance
Inflow Inflow
2.0e+5 0 Outflow 2.0e+5 O Outflow
� v
0 1.5e+5 a 1.5e+5
J O
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7
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1.5e+5
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Figure 6
Monthly 2006 total, orthophosphorus, and particulate phosphorus loads. Note: Estimated annual TP loads
from drains and tributaries are not included in these plots (Naymik and Hoovestol 2008).
FERC Project No. 1971 Page 21

Phosphorus Reduction Reasonable Assurance Idaho Power Company
40000
35000
30000
25000
U
0 20000
!_
m
N
`^ 15000
10000
5000
0
ZZ/9 '09 /�0�5 /��05 00E 9j3"'0 1 ��OS'' , 0�6 Zp006 Z �O> 4 �O>
Figure 7
2005 and 2006 streamflow below C.J. Strike Reservoir.
Page 22 FERC Project No. 1971

Idaho Power Company Phosphorus Reduction Reasonable Assurance
25,000
20,000
POR
w ■ 2003
15,000
2004
V ~ 1 ♦ 2005
E 1
10,000 ~� • 2006
Q 5,000
c
R �
m �
0
0% 10% 20% 300,0 40% SO% 60010 70% 80% 90% 100%
Percent Exceedance
Figure 8
1912 through 2017 Snake River near Murphy, Idaho, period of record (POR) average annual flow
exceedance curve. Streamflow percent exceedance for 2003 through 2006 average annual flows.
FERC Project No. 1971 Page 23