20160742 Ver 3_Monitoring Report_20210112

Cedar Cliff Hydroelectric Development
Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Prepared for: Duke Energy Carolinas, LLC
Prepared by: Jon C. Knight, Ph.D. and Josh R. Quinn
January 2021

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Table of Contents
ExecutiveSummary ........................................................................................................
1
ProjectOverview .............................................................................................................
4
Site Description and Construction Activities ....................................................................
6
Water Quality Sites and Sampling Methodology .............................................................
9
Field Instrument Calibration ..........................................................................................
11
Chemical Analysis of Water Samples ............................................................................
12
HydrologicalData ..........................................................................................................
13
Reservoir Sediment Characterization ............................................................................
13
Cedar Cliff Site Hydrology and Water Sampling Dates .................................................
14
CedarCliff Reservoir .....................................................................................................
19
Seasonal Forebay Water Quality ...........................................................................................
19
Temperature......................................................................................................................
19
Dissolved Oxygen and Oxidation Reduction Potential .......................................................
20
CarbonDioxide and pH .....................................................................................................
22
Conductivity and Turbidity .................................................................................................
24
Comparison between Reservoir Forebay and Up -lake Water Quality ....................................
25
Characterization of Cedar Cliff Reservoir Sediments ....................................................
28
Auxiliary Spillway Channel and Sediment Basin ...........................................................
30
Principal Spillway Channel and Bypassed Reach .........................................................
31
EastFork .......................................................................................................................
32
Chemical Characterization of Cedar Cliff Site Drainages ..............................................
34
AnalyticalEvaluation .............................................................................................................
34
Evaluation of Analytical Results to pH ...................................................................................
37
Predicted pH at Various Pyrite Oxidation Rates ............................................................
47
Summary.......................................................................................................................
51
References....................................................................................................................
53
List of Figures
Figure 1. Gantt Chart of Major Phase I Construction Activities during the Baseline Water
Quality Monitoring for the Cedar Cliff Auxiliary Spillway Upgrade ................................... 7
Figure 2. Cedar Cliff Development Site Features and Water Quality Sampling Locations .......... 8
Figure 3. Cedar Cliff Reservoir Features and Water Quality Sampling Locations ....................... 8
Figure 4. Cedar Cliff Operations, East Fork Flow, Reservoir Level, and Water Sampling
Dates............................................................................................................................. 15

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Figure 5. Cedar Cliff R6servoir Storage Curve ..........................................................................
16
Figure 6. Cedar Cliff Reservoir Retention Times Compared to Rainfall .....................................
16
Figure 7. Cedar Cliff Bypassed Reach Water Level and Water Sampling Dates .......................
17
Figure 8. Auxiliary Spillway Channel and Sediment Basin Water Level and Water Sampling
Dates.............................................................................................................................
18
Figure 9. Cedar Cliff Reservoir 2018-2019 Water Column Temperatures (Upper Panel)
Compared to Bear Creek Hydro Operations and Daily Air Temperatures (Lower
Panel) ............................................................................................................................
19
Figure 10. Cedar Cliff Reservoir 2018-2019 Water Column Dissolved Oxygen (Upper
Panel) Compared to Water Column Oxidation Reduction Potential (Lower Panel) ........
21
Figure 11. Cedar Cliff Reduction Reactions in Relation to Eh ....................................................
21
Figure 12. Cedar Cliff Reservoir 2018-2019 Water Column pH (Upper Panel) Compared to
Water Column Carbon Dioxide (Lower Panel) ...............................................................
23
Figure 13. Cedar Cliff Reservoir 2018-2019 Water Column Conductivity (Upper Panel)
Compared to Water Column Turbidity (Lower Panel) .....................................................
24
Figure 14. Comparison of Cedar Cliff Forebay and Up -Lake Temperature, Dissolved
Oxygen, and Oxidation Reduction Potential Profiles ......................................................
26
Figure 15. Comparison of Cedar Cliff Forebay and Up -Lake pH, Conductivity, and Turbidity
Profiles..........................................................................................................................
27
Figure 16. Particle Size Distribution of Cedar Cliff Forebay Sediments .....................................
28
Figure 17. Scanning Electron Microscopy Elemental Spectra of Cedar Cliff Forebay
Sediments.....................................................................................................................
29
Figure 18. Conductivity of the Cedar Cliff Auxiliary Spillway and Sediment Basin .....................
30
Figure 19. Turbidity of the Cedar Cliff Auxiliary Spillway and Sediment Basin ...........................
31
Figure 20. Conductivity of the Cedar Cliff Principal Spillway and Bypassed Reach ...................
31
Figure 21. Turbidity of the Cedar Cliff Principal Spillway and Bypassed Reach .........................
32
Figure 22. Conductivity of the East Fork ....................................................................................
33
Figure 23. Turbidity of the East Fork .........................................................................................
33
Figure 24. Relationship between Median Ionic Strength and Median Conductivity ....................
34
Figure 25. Median pH values from all Cedar Cliff Sampling Sites ..............................................
38
Figure 26. Median Carbon Dioxide Concentrations Calculated from all Cedar Cliff Sampling
Sites..............................................................................................................................
39
Figure 27. Median Concentrations of Anions and Cations from All Cedar Cliff Sampling
Sites..............................................................................................................................
40
Figure 28. Median Concentrations of Iron Fractions from Cedar Cliff Sampling Locations ........
43
Figure 29. Median Molar Ratios of the Products of Pyrite Oxidation Measured at the Cedar
Cliff Sampling Locations ................................................................................................
44
Figure 30. Median Concentrations of Calcium, Magnesium, Sulfate, and Aluminum .................
46
Figure 31. Unoxidized Hydrogen Ions Remaining from Excavated Pyritic Material ....................
48

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Figure 32. Volume of Water Required to Dilute the Oxidized Hydrogen to the Equivalents at
VariouspH Levels ......................................................................................................... 49
Figure 33. Number of Days to Deliver a Volume of Water at the Baseline Average East Fork
Flow Required to Dilute the Oxidized Hydrogen to the Equivalents at Various pH
Levels............................................................................................................................ 50
List of Tables
Table 1. Baseline Water Quality Monitoring Sites for the Cedar Cliff Auxiliary Spillway
Upgrade......................................................................................................................... 9
Table 2. Hydrolab DS5 Data Sonde Specifications and Calibration Methodology ...................... 11
Table 3. Laboratory Analysis of Cedar Cliff Auxiliary Spillway Upgrade Water Samples ........... 12
Table 4. Analytical Results (Median Concentrations) from all Samples Collected from the
Cedar Cliff Sampling Sites Prior to the Spoiling of Excavated Rock in the Reservoir
(July 2018—September 2020) ........................................................................................ 35
Table 5. Summary of Total Anions, Cations, and Charge -Balance Error from the Cedar Cliff
Reservoir Sampling Sites .............................................................................................. 36
Table 6. Average Ionic Composition of Rainwater Compared to Cedar Cliff Surface Water ...... 45
List of Appendices
Appendix A: Pre- and Post -Construction Photos and Water Quality Sampling Sites of the
Cedar Cliff Spillway Upgrade Project
Appendix B: Selection and Maintenance of ORP and pH Reference Electrode

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Executive Summary
In 2014, the Federal Energy Regulatory Commission (FERC) established the Inflow Design
Flood (IDF) for Duke Energy Carolinas, LLC's (Duke Energy) Cedar Cliff Hydroelectric
Development (Cedar Cliff Development) as the Probable Maximum Flood (PMF). The existing
spillway discharge capacity is insufficient to pass the PMF without overtopping the dam,
resulting in the potential failure of the structure.
Following the completion of various dam and spillway remediation studies, Duke Energy
selected a construction plan that involves lowering the existing fuse plug sill elevation
approximately 10 feet (ft) after removing the two fuse plugs and a single concrete splitter wall,
and excavating rock (approximately 283,200 cubic yards) from the mountain hillside east of the
existing fuse plugs and along the bottom of the auxiliary spillway channel. During construction,
the Cedar Cliff Reservoir will be lowered 30 to 40 ft to accommodate construction activities
including staging the excavated material within the footprint of the existing fuse plug approach
channel. The excavated material will be loaded onto barges and spoiled into Cedar Cliff
Reservoir upstream of the dam. As specified in the U.S. Army Corps of Engineers (USACE)
Section 404/401 permit for the project, a 5 to 10 ft floating turbidity barrier will be installed at all
work areas that are in or adjacent to reservoir surface waters.
Pyrite (FeS2) was identified in rock exposures at the site and in the rock core from boreholes
drilled during the subsurface investigation. Subsequent petrographic analyses of the Tallulah
Falls Formation (TFFm) collected from the rock cores found that lithologies for garnet mica
schist, mica schist, and schistose biotite gneiss contained 2% to 7% pyrite by volume, and
approximately 26% of the total excavated material (73,600 cubic yards) will be comprised of
those rock lithologies. Even though there are no known instances of acid -drainage related to the
metasedimentary rocks of the TFFm, rocks with greater than 1 % pyrite by volume are
considered to be potentially acid -producing. Pyrite can react in the presence of atmospheric
oxygen and water to form ferrous sulfate and sulfuric acid (2FeS2 + 702 + 2H20 --* 2FeSO4 +
2H2SO4). The stoichiometry of complete oxidation of one mole of pyrite would produce two
equivalents of hydrogen ions.
Construction activities may exacerbate the oxidation of pyrite and subsequent acid production
by exposing large volumes of rock containing sulfide minerals to atmospheric oxygen.
Subsequent leaching of the oxidation products by rainfall/groundwater can result in the
formation of acid drainage, which is characterized by low pH values, high concentrations of
sulfate, and mobilization of metals such as iron, aluminum, and manganese. Even though
estimates have projected minimal, if any, acidification impacts from pyrite oxidation, the
potential does exist for an alteration of the reservoir's water quality. The North Carolina
Department of Environmental Quality (NCDEQ), Division of Water Quality, requested a
monitoring plan throughout the construction period.
Duke Energy submitted a water quality monitoring plan to NCDEQ on May 19, 2019.
Subsequently, NCDEQ issued a Section 401 Water Quality Certifications (#WQC004077 being
the most recent received by Duke Energy, dated September 14, 2020), and the resulting permit
(SAW-2015-02543) issued by the USACE on June 21, 2019 required Duke Energy to adhere to
the water quality monitoring plan.
As specified in the monitoring plan, reservoir and stream channel water quality sampling began
in July 2018 and continued on a monthly basis through September 2020. During this 'baseline'
monitoring period, Phase I construction activities included site preparation, road improvements,

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
bypassed reach channel sediment controls, and unit outages. Also, during the Phase I
construction period, erosion control measures installed by Duke Energy proved very effective,
as the turbidities rarely exceeded the 10 Nephelometric Turbidity Unit (NTU) state water quality
standard for trout waters at any sites during the monitoring period.
Monthly water quality sampling will resume just prior to rock excavation (Phase 11 construction
activities) and continue monthly for at least 36 months. As specified in the Section 401 Water
Quality Certifications (#WQC004077 being the most recent received by Duke Energy, dated
September 14, 2020), an annual report will be submitted to NCDEQ in December of each year
after sampling resumes. Each annual report will compare baseline water quality data to the
water quality data collected throughout the Phase 11 rock excavation period. This report
summarizes the water quality data collected during the 26-month baseline period (July 2018—
September 2020).
Eight water quality sampling sites were established in the Cedar Cliff Development's major
drainages,' which have the potential for existing and future pyrite acidification. Cedar Cliff
Reservoir, the auxiliary spillway channel, the principal spillway channel, and the bypassed reach
all contribute water to the East Fork Tuckasegee River (East Fork). Each site exhibited its own
hydrology, which influenced not only the concentration of water quality parameters within each
drainage, but the volume -weighted concentration of water quality parameters for the East Fork
concentrations.
During normal operations, the Cedar Cliff Powerhouse supplied the majority of water into the
East Fork; the Principal Spillway Tainter gate at Cedar Cliff Dam only sporadically released
water during heavy rains or supplied water to the East Fork. The Cedar Cliff Development's
minimum flow unit is required to supply at least 35 cubic feet per second (cfs) of flow during the
summer and fall months and 10 cfs of flow during the winter and spring months. During the
baseline sampling period, Unit 1 released a daily average of 178 cfs, Unit 2 (the minimum flow
unit) averaged 21.3 cfs per day, and the flow from the Principal Spillway released an average of
93.7 cfs per day. However, these flows were not representative of normal operations, since the
Powerhouse incurred an outage for 127 days in spring 2020 while the transformers and
transformer yard were being replaced. During the outage, flow through the Tainter gate channel
into the Principal Spillway was the only means to supply water to the East Fork.
The amount of water released from the Cedar Cliff Development and the storage volume in the
reservoir determined the average retention time of water in the reservoir. The longer retention
times allowed the biochemical reactions to exert a greater impact on the reservoir water
chemistry. Retention times ranged from over 150 days during low rainfall periods and high
reservoir levels to less than a week during higher rain periods and low reservoir levels. During
the late spring, summer, and fall months, the deep -water withdrawal from the Cedar Cliff
penstock prevented normal reservoir stratification since the water was constantly pulled deep as
the units were operating. The Powerhouse had very limited access to water deeper than the
penstock invert (approximately 26 acre-ft volume below the invert). Since this very deep water
had a long retention time, the biological metabolism had time to reduce the oxygen
concentrations to anoxic conditions, where additional anaerobic respiration allowed chemically
reduced forms of iron and other substances to diffuse from the sediments into the overlying
water. Sulfur compounds were not detected in the sediments and sulfate concentrations were
I Minimum flow unit discharge, lower bypassed reach, auxiliary spillway, reservoir forebay, upper sediment basin,
upper bypassed reach, reservoir upstream of construction, and East Fork Tuckasegee River upstream of the East
Fork confluence.

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
generally less than 1 milligram per liter (mg/L) in the water column. This indicated that little, if
any, products of pyrite oxidation or pyrite formation were associated with the increase of ferrous
iron.
During the fall and winter periods, the reservoir continually lost heat to the atmosphere to the
point where convective cooling mixed the reservoir, resulting in uniform concentrations of all
analytes throughout the water column.
Overall, Cedar Cliff Reservoir had excellent water quality above the penstock invert with very
low concentrations of dissolved compounds. Conductivity ranged from 14 to 15 pSi, dissolved
oxygen concentrations ranged from 3.3 to 10.9 mg/L, and pH ranged from 5.7 to 8.5.
The primary source of water in the auxiliary spillway channel was rain that fell directly into the
auxiliary spillway catchment, The rain infiltrated, percolated, and seeped into the groundwater,
with surface flows only occurring during heavy rains. Prior to Phase I construction activities,
water samples were collected by digging into the soil near the outlet of the auxiliary spillway to
collect groundwater as it flowed to the surface. After construction of the sediment basin, water
flowed on the surface at a very low flow rate, likely due to increased rainfal in 2020 after the
sediment basin was completed. The water was more acidic than other sites and was
characterized by high concentrations of sulfate, calcium, magnesium, and aluminum but low
levels of iron compared to other sites. These ionic compositions and concentrations resembled
ground water originating from limestone and/or gypsum formations rather than from pyrite
oxidation. Although these formations were not observed in the metasedimentary rock samples
from the auxiliary spillway, the molar ratios of the primary products of pyrite oxidation indicated
other processes controlled the chemical composition of the subsurface auxiliary spillway water
The relatively small amount of water from the auxiliary spillway channel, as well as other rain -
induced seepage, entered the primary spill channel and bypassed reach. Flows in the bypassed
reach were variable since the bypassed reach does not have a minimum flow requirement.
Higher flows derived from Tainter gate releases and/or from rainfall flushed the bypassed reach.
As the water receded, the pools drained slowly and were subject to significant evaporation, only
to be flushed again by the next high-water event. The water chemistry in the bypassed reach
was subjected to all of these varying physical events.
Since the East Fork received most of its flow from Powerhouse generation or the Principal
Spillway flows from the surface of the reservoir, the river's water chemistry resembled that of
Cedar Cliff Reservoir during the baseline monitoring period. The average flow of 7.02 — 7.72 cfs
for the bypassed reach was calculated from the flow -weighted ionic concentrations between the
reservoir water, bypassed reach, and the East Fork. At these bypassed reach flows, the
bypassed reach water quality had a very minuscule impact on the river's water quality. Also, at
these bypassed reach flow rates, a very high rate of pyrite oxidation would have to occur to
impact water chemistry of the East Fork.
Based on calculations using assumed pyrite oxidation rates of the pyrite containing rock, more
than enough water flows through the system to keep the pH of the Cedar Cliff reservoir and the
East Fork well within the NC state water quality standards of pH 6.0 — 9.0. In addition, the
normal, very low flows from the bypassed reach suggest that any increased acidification
originating from pyrite oxidation in the auxiliary spillway channel would have minimal, if any,
impact on the East Fork water quality.

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Promect Overview
In 2014, the Federal Energy Regulatory Commission (FERC) established the Inflow Design
Flood (IDF) for Duke Energy Carolinas, LLC's (Duke Energy) Cedar Cliff Hydroelectric
Development (Cedar Cliff Development) as the Probable Maximum Flood (PMF). Prior to the
FERC notice, the OF had been 40% of the PMF. The existing spillway discharge capacity is
insufficient to pass the PMF without overtopping the dam, resulting in the potential failure of the
structure. Engineering design and analyses have indicated that expanding the auxiliary spillway
channel (width and depth), installing Hydroplus Fusegates as the spillway control mechanism,
and replacing the existing parapet wall with a taller PMF wall (additional storage) will provide the
necessary physical site measures to safely pass the OF without overtopping Cedar Cliff Dam.
Duke Energy's selected construction plan specified excavating rock (approximately 283,200
cubic yards) from the mountain hillside east of the existing fuse plugs. During construction,
Cedar Cliff Reservoir will be lowered 30 to 40 feet (ft) to accommodate construction activities
including staging the excavated material within the footprint of the existing fuse plug approach
channel. The excavated material will be loaded onto barges and spoiled into Cedar Cliff
Reservoir upstream of the dam (for discussion and review of submerged disposal, see HDR
2018a). As specified in the U.S. Army Corps of Engineers (USACE) Section 404/401 permit for
the project, a 5 to 10 ft floating turbidity barrier will be installed at all work areas that are in or
adjacent to reservoir surface waters.
As discussed by HDR (2018a), pyrite (FeS2) was identified in rock exposures at the site and in
the rock core from boreholes drilled for the subsurface investigation (HDR 2017). Subsequent
petrographic analyses of metasedimentary rocks of the Tallulah Falls Formation (TFFm)
collected from the rock cores found that the garnet mica schist, mica schist, and schistose
biotite gneiss lithologies contained 2% to 7% pyrite by volume (HDR 2017). Based on boreholes
drilled during the geological/geotechnical site investigation for the auxiliary spillway upgrades,
approximately 26% of the total excavated material (73,600 cubic yards) will be comprised of
these three rock lithologies.
Even though there are no known instances of acid -drainage related to the metasedimentary
rocks of the TFFm in the region surrounding the site, rocks with greater than 1 % pyrite and/or
pyrrhotite by volume are considered to be potentially acid -producing. Pyrite can react in the
presence of atmospheric oxygen and water to form ferrous sulfate and sulfuric acid (2FeS2 +
702 + 2H20 --* 2FeSO4 + 2H2SO4). The stoichiometry of complete oxidation of one mole of
pyrite would produce two equivalents of hydrogen ions. Although some acid -drainage is
produced by natural weathering, construction activities can expose large volumes of rock
containing sulfide minerals to oxidizing conditions. The oxidation of pyrite and subsequent acid
production increase significantly when exposed to atmospheric oxygen, and particle sizes
becomes smaller and smaller (Pugh et.al. 1984). Subsequent leaching of the oxidation products
by rainfall/groundwater result in the formation of acid drainage, which is characterized by low pH
values, high concentrations of sulfate, and mobilization of metals such as iron, aluminum, and
manganese.
Even though HDR (2017, 2018a, 2018b) has discussed the project in detail and has projected
minimal, if any, acidification impacts from pyrite oxidation, and the reservoir characteristics
suggest a lack of accumulation of acidic water, the potential does exist for an alteration of the
water quality. Due to the potential of pyrite oxidation and subsequent acidification of surface
waters, Duke Energy submitted a water quality monitoring plan to the North Carolina
Department of Environmental Quality (NCDEQ), Division of Water Quality, on May 19, 2019.

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Subsequently, NCDEQ issued Section 401 Water Quality Certifications (#WQC004077), and the
permit (SAW-2015-02543) issued by the LISACE dated June 21, 2019 required Duke Energy to
adhere to the water quality monitoring plan.
As specified in the monitoring plan, reservoir and stream channel water quality sampling began
in July 2018. However, start of rock excavation has been delayed until the first quarter of 2021
and baseline water quality monitoring continued on a monthly basis through September 2020.
This report summarizes water quality data collected during the 26-month baseline period2 (July
2018—September 2020).
Monthly sampling will resume just prior to rock excavation and will continue monthly for at least
36 months. As specified in the most recent Section 401 Water Quality Certification, an annual
report will be submitted to NCDEQ in December of each year after sampling resumes. Each
annual report will compare water quality baseline data to the water quality data collected
throughout the rock excavation period.
2 When referenced in this report, the 'baseline' period refers to the time period of July 2018 through September 2020.

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Site Description and Construction Activities
Since July 2018, activities at the Cedar Cliff Development have centered on the routine
maintenance and repair of the hydro station, installation of the new hydro station transformer,
principal spillway gate maintenance and installation of the new gate hoist and gate hoist
building, and the implementation of the Phase I auxiliary spillway upgrade construction (Figure
1). Phase I construction began in late -December 2019 and involved site preparation, road
improvements, installation of the Sediment Basin Dam at the upstream end of the bypassed
reach channel, installation and maintenance of erosion sediment control measures, tree
clearing, and construction tasks involving the installation of the Soldier Pile Wall above the
auxiliary spillway channel and placement of vertical rock anchors in the left abutment of the
Cedar Cliff Dam. Phase 11 spillway construction is expected to begin in the first quarter of 2021
and will involve enlarging the auxiliary spillway channel, spoiling the excavated material into
Cedar Cliff Reservoir, and construction of appurtenant concrete structures for the Fusegate
infrastructure and PMF Wall.
Hydro maintenance and repair work in 2019 involved constructing a new bridge across the
principal spillway entrance channel and drawing the reservoir down to install the new hoist and
gate cables, controls, and seals to the Tainter gate. In addition, the circa-1 951 access road to
the hydro intake gate was graded while erosion controls were placed. In early 2020, a four -
month outage at the hydro station was required to replace the hydro station transformers and
transformer yard.
During Phase I of the project, access roads were improved, a sediment basin was installed, the
principal spillway outfall channel -upper bypassed reach was re -configured adjoining the
sediment basin dam and along the lower access road, two check dams were installed in the
bypassed reach in support of site erosion and sediment control, and laydown and equipment
storage areas were installed 3 . Bypassed reach channel banks adjoining the sites lower access
road were cleared of some trees and stabilized with washed rip-rap4. Erosion and sediment
control measures were installed to support these activities.
Additional preparatory Phase I activities included tree removal from the steep side channel walls
above the auxiliary spillway channel and on the peninsula for the access road. In addition, a
construction ramp was built for reservoir access at the upstream Cedar Cliff Access off Shook
Cove Road. The left abutment vertical rock anchor installations and the soldier pile wall were
completed in December 2020. The 1951 Access Road work is partially graded and will be
completed in late-2021 as part of the Phase 11 work scope.
The locations of Phase I activities are presented in Figures 2 and 3, and photos of the pre- and
post -construction at the Cedar Cliff Development are compared in Appendix A.
3 When not in use, all heavy equipment was stored on plastic containment pads.
4 The three 12 ft diameter x 110 ft long culverts referenced in the permit were not placed in the bypassed reach.

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Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Figure 2. Cedar Cliff Development Site Features and Water Quality Sampling Locations
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edar CFrlT Dam
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N

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Water Quality Sites and Sampling Methodology
The water quality sampling sites, or Environmental Monitoring Points (EMPs) as identified in
Figures 2 and 3, Table 1, and Appendix A, were selected based on their proximity to the
proposed rock excavation and the in -reservoir spoiling of the excavated material.
Table 1. Baseline Water Quality Monitoring Sites for the Cedar Cliff Auxiliary Spillway
Upgrade
Auxiliary Spillway Upgrade Project Monitoring Sites
Latitude
Longitude
Start of
Logger
Description
Symbol
WaterSample
(0)
( 0)
Sampling
Deployment
Cedar Off Reservoir - Forebay
EMP4
35.25486
-8109882
1l
WA
Hydrclah
Van Dorn
Cedar Cliff Reservoir - Upstream of
Hydrolab
Spoil Area
FMP 7
35.25030
-8100201
ll
N/A
Van Dorn
Auxiliary Spillway Sampling Site
Conductivity
Hydmlah
(flows into Upper Sediment Basin)
EMP 3
35�25233
-83.09914
28-Aug-1 8
LevelLogger
Grab Sample
Single Stage
Upper Sediment Basin Sarnpl Ing Site
Conductivity
Hydrolab
(flows into upper Bypassed Reach)
EMP 5
35.25250
-8109931
28-Apr-20
LevelLogger
Grab Sample
Single Stage
Conductivity
Hydriflab
Upper Bypassed Reach Sampling Site
EMP 6
35.25212
-83.09951
14-Jul-20
Grab Sample
Level Logger
Single Stage
Lower Bypassed Reacln Sampling Site
Col
Hydrolab
(flows into East Fork)
EMP 2
35.25295
-83.10299
28-Aug-18
LevelLogger
Grab Sample
Single Stage
Minimum Flow LJnit Discharge
FMP 1
35.25344
-83.10274
28-Aug-1 8
Corl
Hydrolab
Grab Sample
East Fork Upstream of West Fork
Hydrolab
Confluence
EMP 8
3526893
-83.11633
28-Aug-1 8
NfA
Grab Sample
' East Fork conductivity logger placed at minimum flow gage
The forebay site (EMP 4) was established in the old thalweg of the East Fork Tuckasegee River
(East Fork), which was the deepest portion of Cedar Cliff Reservoir. This site is approximately
200 feet downstream of the proposed excavated material spoil area.
The reservoir sampling site (EMP 7) was established upstream of the spoil area and served as
a water quality control site where the change in water quality is expected to be minimal, if any.
Reservoir water samples were taken from the surface (0.3 m) and from 1 meter above the
reservoir sediment with a Van Dorn sampler. Water column profiles were taken in situ at 1 -
meter intervals with a Hydrolab DS5 Data Sonde@.
In the bypassed reach (sites EMP 2, EMP 3, EMP 5, and EMP 6), water grab samples were
collected from the pools that formed in the channel. These pools typically had very low flow (1 to
2 cfs, see Appendix A, Photos 7 and 8). However, some rain storms added significant flow to
the channel, whereas flows from the principal spillway added relatively large flows (see
Appendix A, Photo 12). At each bypassed reach site, a modified U.S. Geological Survey single-

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
stage sampler (Graczyk, et.al., 2000) was placed to capture water during higher flow events.
Each water sample was placed in a large Ziploc' bag where the Hydrolab data sonde was
immersed to record the in -situ parameters. In addition to water samples, a level logger and
conductivity logger (programmed to record data at 15-minute intervals) were placed at each
bypassed reach site (Table 1).
Sampling site EMP 3 was established in the auxiliary spillway channel immediately downstream
of the proposed rock excavation site. The auxiliary spillway channel had very low seepage flow
(less than 0.1 cfs, see Appendix A, Photo 4)5 ; higher flows were only observed and collected
with the single stage sampler during and after heavy rain S6.
Sampling site EMP 5 was established in the sediment basin as soon as the basin was
completed (May 2020). Similarly, the upper bypassed reach site (EMP 6) was established in
July 2020 after lower access road construction and upper bypassed reach modifications were
finished (see Appendix A, Photo 6 and 9)). Both sites are intended to observe any water quality
changes, if any, as residual runoff occurs within the immediate auxiliary spillway channel
drainage area, or if rare (unanticipated) residual water from the reservoir flows from the auxiliary
spillway channel, through the sediment basin and into the bypassed reach.
The lower bypassed reach sample location (EMP 2) was established to determine the water
quality entering the East Fork (see Appendix A, Photo 10). These samples capture the
'integrated' (flow weighted) water quality from all sources contributing water to the bypassed
reach.
All generation flows from the Cedar Cliff Powerhouse (Unit 1 and the Unit 2 minimum flOW7)
originate from a common, low level intake penstock tunnel (see Appendix A, Photos 11 and 14
for withdrawal elevations). Unit 1 has a rated generation capacity of 6.375 megawatts (MW)
(555 cfs) at full pond (elevation 2,330 ft), while Unit 2 supplies a continuous minimum flow to the
East Fork and has a rated capacity of 395 kilowatts (kW) (35 cfs) (Duke Energy Carolinas, LLC.,
2018). A minimum flow valve, capable of releasing 10 cfs, originates from the common penstock
and was used to supplement required minimum flow downstream of the powerhouse during unit
outages in conjunction with flow from the principal spillway and bypassed reach.
Since all of the hydro units were supplied from a common penstock, water samples and in situ
Hydrolab readings were taken from the discharge trough of the minimum flow unit (EMP 1). A
conductivity logger was also employed at the minimum flow gage downstream of the
powerhouse to record changes in the ionic strength of the combined flow of the bypassed reach
and the Powerhouse releases.
An additional sampling site (EMP 8) in the East Fork was established 1.7 miles downstream
from the Cedar Cliff Development which would capture the mixed flow from the Powerhouse
and the Bypassed Reach. Consistent with other sites, water samples and in situ Hydrolab
readings were taken. This sampling location allowed for quantification of any water quality
changes in the East Fork prior to its confluence with the West Fork Tuckasegee River (West
Fork).
Prior to construction of the sediment basin, water samples were typically collected by digging into the sand.
The single -stage sampler, level logger, and conductivity logger were temporally removed while the sediment basin,
sediment dam, upper bypassed reach, the check dams, and lower auxiliary spill were under construction.
7 The FERC license requires a minimum flow of 35 cfs from July 1 through 30 November, and 10 cfs the remainder of
the year.
IN

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Field Instrument Calibration
Prior to deployment (Table 1 for locations of level logger deployments), all water level loggers
were subjected to water depths ranging from zero to 5 ft, spanning the expected range of water
pressures. The slight individual pressure deviations were corrected for each logger to the
pressures recorded by the logger selected as the barometric pressure sensor. These
corrections of the individual loggers enabled an accurate calculation of water depth when the
barometric pressure sensor was subtracted from the deployed logger's pressure.
Prior to deployment at each site (Table 1 for locations of conductivity loggers), each conductivity
logger was checked using 0 and 75 pSi standards. An NIST traceable thermometer was used to
check the temperature accuracy.
Prior to each sampling, the Hydrolab data sonde was laboratory calibrated 8 with various
standards (Table 2). If the instrument did not calibrate within the manufacturer's stated
accuracy, the sensing electrodes were cleaned and/or complete maintenance was performed as
recommended by the manufacturer. If any sensor failed to calibrate again, the instrument was
returned to the manufacturer for repair or sensor replacement. After sampling, each Hydrolab
sensor was checked using the same standards.
Table 2. Hydrolab DS5 Data Sonde Specifications and Calibration Methodology9
Manufacturer's
Paramete r
Units
Method
Calibration Method
Specifiedhc�.
Depth
motors (m)
Pressure
In -field immersion
0.05 m
Temperature
C
Thermislor
Checked with IN I ST
0.10 IC
treGoble thermometer
Dissolved Oxygen
mg/L
Luminescence
Barometric pressure of
+ G.01 mWL
air saturated Water
Calibrate to 75 psi
Specific Conductance
psi
Electrical bridge
+ 10/6 of reading
��heckod with 25 psi
Calibrate to 100 NTIJ
Turbidity
NTIJ
Nophelornotric
+ 5% of reading
checked with 10 NTU
Oxidation Reduction
Platinum
Calibrate with ZorbellN Solution
milli volts (mv)
+ 20 mv
Potential (ORP)
electrochemical
corrected for temperature
pH glass
Calibrate to 7 00 pH
pH
units
+ 0 2 units
Calibrate to 4 00 pH
electroc�hemical
Reference electrode
l
Saturated KCI
Shared with ORP and pH
(see Appendix 13)
8 The instrument was allowed to achieve thermal equilibrium in the lab prior to calibration.
9 Hach Company 2005.
11

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Chemical Analysis of Water Samples
Upon collection of a water sample, the whole water was either poured into a pre -labeled bottle
with the appropriate preservative or field -filtered through a 0.45 pm membrane filter and then
added to the sample bottle. All of the sample bottles were stored on ice upon return to the
laboratory. All sample analyses (Table 3) were performed within the recommended holding
times.
Table 3. Laboratory Analysis of Cedar Cliff Auxiliary Spillway Upgrade Water Samples
Ionic
Dissolve Ion
Type of
Bottle Type
Summary of
Analytical
Parameter
Category
Symbol
Sample
Preservative
Analysis
Method
Alkalinity
HCO3-1 CO3-2
Whole water
PET
Titration (0.025N HGI);
SM 2320B
Ice
Inflection and -point
(n
Choride
cl-1
Whole water
PET
[on chromatography
EPA 300.0
Ice
<
Sulfate
SO4 -2
Whole water
PET
[on chromatography
EPA 300.0
Ice
Nitrate
NO3-1
Field fifteried
HDPE
Golorimetric
EPA 353.2
Sulfuric Acid
Calcium
Ca"
Whole water
HDPE
ICP
EPA 200.7
Nitric Acid
total recoverable
Magnesium
Mg 12
Whole water
HDPE
ICIP
EPA 200.7
Nitric Acid
total recoverable
Sodium
Na"
Whole water
HDPE
CIP
EPA 200.7
Nitric Acid
total recoverable
Potassium
K+J
Whole water
HDPE
CIP
EPA 200.7
Nitric Acid
total recoverable
Aluminum
AI'3
Whole water
HDPE
CIP
EPA 200.7
Nitric Acid
total recoverable
Manganese
Mn +3
Whole water
HDPE
CIP -mass Spec
EPA 200.8
Nitric Acid
total recoverable
Total Iron
Fe 13
Whole water
HDPE
CIP -mass Spec
EPA 200.8
Nitric Acid
total recoverable
Dissolved Iron
Fe+'
Field fifteried
HDPE
CIP -mass Spec
EPA 200.8
Nitric Acid
total recoverable
Reduced Iron
Fe +2
Whole water
60 ml SOD
colorimetric
SM 3500 Fe B
water sealed
Note: PET = Polyethylene terephthalate; HDPE = High -density polvethylene-1 BOD = Biological Oxygen Demand-,
ICP = Inductively Coupled Plasma-, EPA = U.S. Environmental Protection Agency-, SIM = Standard Methods
Reduced iron samples were collected in 60 ml Biological Oxygen Demand (BOD) bottles and
sealed with water to prevent oxygen from entering the sample. Within 24 hours, the samples
were analyzed utilizing the Hach phenanthroline method and measured with a
spectrophotometer.
Chloride, potassium, sodium, and magnesium parameters were added after the original
monitoring plan was submitted. In addition to those originally proposed, these elements would
permit a more complete characterization of the water chemistry.
12

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Hydrological Data
Duke Energy Regulated Renewables Operations Center (RROC) provided the following
operations data from the Plant Information (PI) database:
Recorded at 15-minute intervals:
• Cedar Cliff Unit 1, Primary Generation (MW)
• Cedar Cliff Unit 1 Flow (cfs)
• Cedar Cliff Unit 2, Minimum Flow Generation, (MW or KW)
• Cedar Cliff Unit 2 Flow (cfs)
• Cedar Cliff Reservoir Level (ft)
• Cedar Cliff Tainter Gate Position (ft)
• Cedar Cliff Tainter Gate Flow (cfs)10
Recorded at 1 -hour intervals:
• Bear Creek Reservoir Level (ft)
• Bear Creek Unit Generation (MW)
• Bear Creek Unit Flow (cfs)
• Bear Creek Tainter Gate Flow (cfs)
• Cedar Cliff rainfall"
Reservoir Sediment Characterization
Reservoir sediments either receive material settling from the water column or may diffuse
compounds into the water column, with the latter occurring especially under chemically reduced
(low ORP) conditions. In addition to the sampling protocol presented in the original monitoring
plan, reservoir sediments were collected in the Cedar Cliff Reservoir forebay (EMP 4) to further
characterize pyrite dynamics, if present. Sediment pyrite could have been present from the
original construction of the Cedar Cliff Development in 1951-1952; or, pyrite may have formed in
the water column or sediments if sufficient chemical reduction of iron and sulfur
(sulfate--*suIfite--*suIfide) had occurred, enabling FeS to form and precipitate.
A sediment sample was collected in either October or late September of each year with a ponar
grab sampler. Particle size analysis was performed on a portion of the sample. Another portion
was dried at 1 OOOC, and then ashed at 5000C to remove organic carbon. Both dried samples
were analyzed using a scanning electron microscope (SEM) with a backscatter (BSe) detector
and energy dispersive spectrometer (EDS) to determine their elemental composition.
10 The Tainter Gate sill is 25 ft deeper than full pond (DE level = 75 ft). During normal operations, the tainter gate
opening and the water released (cfs) are recorded in the RROC PI data base. When the Tainter Gate is fully open,
the reservoir surface water enters the Principal Spillway Channel as an open flow channel over the Tainter Gate sill.
These open channel flows were not recorded in the PI database. Water height over the Tainter Gate sill was
determined by subtracting 75 ft from the PI reported reservoir level. Flows were then calculated by a rating curve
provided by HDR, When the reservoir level was less than 75 ft DE level, no reservoir water entered the principal
spillway.
11 A rain gage was installed on the Cedar Cliff Dam in January 2019. Rain gage data were recorded in the RROC PI
database as inches per hour.
13

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Cedar Cliff Site Hydrology and Water Sampling Dates
The four distinct Cedar Cliff site drainages and sources of water contributing to each are:
1. Cedar Cliff Reservoir
Bear Creek Reservoir (Tainter Gate and Unit Generation)
Tributary, Overland Runoff, and Groundwater
Direct Rainfall
2. Auxiliary Spillway Channel and Sediment Basin
Seepage and Leakage
Overland Runoff and Groundwater
Direct Rainfall
3. Principal Spillway Channel and Bypassed Reach
Reservoir surface water via the Tainter Gate channel
Tributary, Overland Runoff, and Groundwater
Auxiliary Spillway Channel
Seepage from Sediment Basin
Direct Rainfall
4. East Fork
Cedar Cliff Hydro: Unit 1 (0-555 cfs)
Cedar Cliff Hydro: Unit 2 (0-35 cfs)
Minimum Flow Control Valve (0-10 cfs)
Bypassed Reach Channel
Tributary, Overland Runoff, and Groundwater
Direct Rainfall
Each of the drainages has the potential to influence water quality of the reservoir and East Fork;
however, the potential for water quality changes due to pryite oxidation in the various drainages
is not only a function of concentration of oxidation products, but also the relative contribution of
the volume of water to the downstream areas. Mathematically, the volume -weighted
concentration of the water quality parameters accounts for downstream concentrations. This
comparison will be made in future reports after rock excavation begins.
Based on the operations data supplied by RROC for the baseline period, Unit 1 released a daily
average of 177.8 cfs, Unit 2 (minimum flow) averaged a discharge of 25.3 cfs, while the
principal spill channel released an average of 93.7 cfs per day. However, these flows are not
representative of normal operations, since the Powerhouse incurred an outage for 127 days in
spring 2020 while the transformers and transformer yard were being replaced. During the
outage, flow through the Principal Spillway was the only means to supply water to the East Fork.
During normal operations, the Powerhouse supplied the majority of water into the East Fork; the
Principal Spillway only sporatically released water during heavy rains (Figure 4).
Normally, the target reservoir level is 98 DE-ft 12, with an operating range of 95-100 ft. Beginning
in September 2019, the reservoir level was lowered 30 to 35 ft (65 to 70 DE-ft) to accommodate
12 Duke Energy reports reservoir levels relative to full pond, which equals 100 ft (DE-1 00 ft).
14

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
the Tainter gate construction 13 (Figure 4). Beginning in late January 2020, the reservoir level
rose above the Tainter gate sill to deliver water to the East Fork during the powerhouse
transformer replacement outage. After the outage, the reservoir level was reduced to between
60 and 65 ft to accommodate Phase I construction activities. Water samples were collected in
the bypassed reach and East Fork during this time, however due to extended drawdown the
reservoir could not be sampled until the construction ramp (boat ramp) was available in April,
2020.
Tainter Gate Flow —Unit 2 Unit 1 Flow —Minimum Flow Unit (2) A EMP 1 Watef Semple o visit —Reservairl-evel
5000
4500
4000
3500
3000
Ep
2500
2000
1500
1000 a Q C& �k �k �k I
500
0
1DD
95
9D
85 ��
80
75
7D 0?
65
6D
55
5G
J A S 0 IN D J F M A M J J S 0 IN D J F M A M J J A S
2018 2019 2020
Figure 4. Cedar Cliff Operations, East Fork Flow, Reservoir Level, and Water Sampling
Dates
During the 2019 drawdown period, prior to the Powerhouse outage, the reservoir storage was
reduced to 50-64% of full pond storage (average DE-ft. = 66.7). The reduced reservoir storage
percentage is based on the reservoir elevation — reservoir storage capacity relationship
provided in Figure 5 along with the measured reservoir elevation shown in Figure 4. However, in
2020, the reservoir was lowered to between 60 and 65 DE-ft, which further reduced the
reservoir storage to between 43 and 45% of full pond storage.
The various reservoir levels, as well as the deep penstock intake, significantly impacted the
water retention time in the reservoir during the baseline monitoring period (Figure 6), which, in
turn, greatly impacted the time for biochemical reactions occurring in the water column. Ten-day
average water retention times were calculated by dividing the reservoir storage (above the
invert) by the water released from the reservoir. A 1 0-day running average release flow was
used to minimize the daily variability of hydro operations. Retention times were also a function
of rain events (i.e., the more rain, the greater the water release). Based upon the rain recorded
at the Cedar Cliff rain gage, 28.43 inches of rain fell between the months of February and
October 2019, while during the same period in 2020, 60.2 inches fell.
Throughout the baseline sampling period the 1 0-day average retention time ranged from 2.43 to
180.4 days. In 2018, the higher average retention time of 53.1 days was the result of high
reservoir levels and relatively low water release rates. By contrast, the 2020 average retention
time of water in the reservoir was 8.53 days indicative of low reservoir levels and high reservoir
release rates. In 2019, the calculated retention time averaged 24.3 days.
13 The Tainter gate sill is 25 ft below full pond, or 75 DE-ft.
15

a Full Pond
0 Ave20119Drawdown
7MI)
LITKISE4
6 5000
a) 4000
0
U) 3000
KIM
k"I
0
2190
Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
—Penstock Opening Tainter Gate Opening
0 2020 Outage Drawdown H Ave 2020 Drawdown
2210 2230 2250 2270 2290 2310 2330
Reserv6r Flevation (ft-USCGS)
Figure 5. Cedar Cliff Ri5servoir Storage Curve
—-Retention Time with Powerhouse and Primary Spillwav Flow
—Retention Time with Only Powerhouse Flow
Ramfall
200
-j,- 180
>1
ca
_C3 160
(D
E
F-
140
_(�P 120
0)
fl�
i 0o
(D
> so
so
40
20
0
0.8
0.6
0.4
0.2
0 <
A S 0 N D J F M A M J J A S 0 N D J F M A M J J A S 0
2018 2019 2020
Figure 6. Cedar Cliff Reservoir Retention Times Compared to Rainfall
16

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Unlike flows from the Powerhouse or Tainter gate channel, no rating curves were developed for
any of the spill channel sites; primarily since the flows were so low and were very intermittent
when not subjected to Principal Spillway flows. Any spill channel flows presented in this report
are estimated floWS14 because level loggers were mainly employed to measure the intermittent
water rise over the level logger, indicating the timing of increased flows (Figures 7 15 and 8). The
level loggers were placed in small depressions in the channel, which enabled continuous
recording of water level. During most of the sample collections, the EMP 2 site (lower bypassed
reach) had estimated flows less than 2 to 3 cfs, while the auxiliary spillway (EMP 3) typically had
less than 0.1 cfs.
Typically, higher flows from the principal spillway and/or from rainfall flushed the bypassed
reach. As flows decreased and water receded, the pools drained slowly and were subject to
significant evaporation until the next high-water event.
ii
06
M
9
8
7
4
3
2
—Taintef Gate Opening —EMP 2 Bypnsed Reach Level
* EMPMaterSample EMP 2 High Water Sampla
* EMP 6 Water Sample EMP 6 High Water Sample
Q
el
A.
a.
J A 9 0 IN D J F M A M J J A S 0 A D J F M A M J J A S
2018 2019 2020
Figure 7. Cedar Cliff Bypassed Reach Water Level and Water Sampling Dates
EMP 6 SWassed Reach Level
V isit
Rainfall
46
40
35
2.5
2-0
-2,0
-2-5
-3-0
-3-5
-4,0
-4-5
In 2019, the USGS single -stage samplers (high water sample) at the lower bypassed reach site
(EMP 2) rarely filled except from Tainter gate releases. In 2020, while the tainter gate was fully
opened, the reservoir level was raised to allow reservoir water to flow over the Tainter Gate sill
into the principal spillway thereby supplying water to the East Fork during the powerhouse
outage. During this time, level loggers, conductivity loggers, and the single -stage samplers
could not be safely retrieved due to high water. In addition, high water from the Principal
Spillway prevented crossing the bypassed reach to sample the auxiliary spillway channel. At the
completion of the powerhouse outage the reservoir was lowered to stop the Principal Spillway
flows and water was supplied to the East Fork by Powerhouse generation. After the principal
See page 41 for calc-ulated Bypassed Reach flow based on flow -weighted ionic concentrations
Prior to the lake drawdown in September 2019, the Tainter gate opening in Figure 7 represented normal operations
when the opening under the Tainter gate was recorded by RROC. After the lake drawdown the Tainter gate was fully
opened, and the water level in Figure 7 was the depth of the open channel flow, i.e. water height above the Tainter
gate sill.
17

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
spillway flow ceased, the USGS samplers in the spillway channels at both EMP 2 and EMP 6
were filled from rain -driven higher flows (Figure 7).
After the sediment basin was constructed, the auxiliary spillway channel was re-routed into the
basin. The auxiliary spillway channel flows were entirely dependent upon intermittent rain
events falling within the auxiliary spillway catchment 16 . The heavier rains in 2020 increased the
sub -surface seepage flow (Figure 8) compared to previous years. In 2020, after the construction
of the sediment basin, the auxiliary channel seepage flows were observed as very low surface
flows (Appendix A, Photo 4).
The rain -driven flow events from the auxiliary spillway channel rapidly entered the basin to a
level above the USGS sampler, allowing the sampler to fill (Figure 8). The basin rapidly lost
water as it filtered and drained through the sediment basin dam into the bypassed reach at the
EMP 6 site. No standing water in the basin was observed when water samples were taken.
—Auxiliary Spill (EMP 3� Level Sed iment Basin (El-d P 5 � Leve I EMP 3 Water Sample EMP 3 High Water Sample
EMP 5 Water Sample EMP 5 High Water Sample visit Rainfall
� 5. 0
d)
45
'F5 40
CU
ED
35
E
O-U
25
20
10
0.5
0 0
11) 0 0 a 0 0 0 9 6
J A S 0 N D J F M A M J J A S 0 N D J F M A M J J A S
2018 2019 2020
Figure 8. Auxiliary Spillway Channel and Sediment Basin Water Level and Water
Sampling Dates
4.5
40
35
30
25 co
2.0 ib
1.5 Oc
10
0 5
0 - 0
16 Wishon (2002) reported in a 1996 Seepage Report', zero seepage flows measured from either the dam or the fuse
plug when the reservoir level was two feet below full pond and after weekly rain totals ranging from 0 to 2.6 inches.
M

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Cedar Cliff Reservoir
Seasonal Forebay Water Quality
Temperature
Reservoir water temperatures are typically driven by meteorological conditions, primarily solar
energy and wind. Advective inflows may also significantly impact water temperatures. Cedar
Cliff Reservoir is located in a steep valley that is sheltered from wind by the surrounding terrain,
which minimized the surface wind shear, limiting wind -induced stratification. The rate of heat
exchange with the atmosphere is a function of the difference between the water temperature
and the equilibrium temperature". Cedar Cliff reservoir water temperatures followed the
seasonal heating and cooling pattern (Figure 9, upper panel)18 driven by the seasonal
meteorological conditions (air temperatures; Figure 9, lower panel).
The reservoir did not develop a classical epilimnion or hypolimnion separated by a thermocline
with strong horizontal thermal gradients. Rather, vertical thermal gradients developed, indicating
that the deep- water removal via the penstock removed the cooler bottom water and was
replaced by warmer water originating near the surface. Development of the vertical thermal
gradients followed the rate of the Cedar Cliff hydro generation flows.
2330
232f)
2310
2200
2290
2280
2270
2260
2250
2240
2230
DJ 2220
2210
2200
2190
� C-. a, � t - :
Aug I Sept t Oct � Nuv I Dec I Jan 1 Feb 1 Mar I Apr I May I Jun I Jul I Aug I Sept I Oct
2D1 8 2019
Daily Average Air Temps 0 Lake Sampling Dates —Bear Greek Tainter Cate —Bear Greek Generation
F-I
a 31)
20
IT 10
It
E 0
Feb ?,laF Apr May Jun Jul Auq F�ept Oct
2n­� 2919
250G
2000 �!
1600
1000 _.
EGG 0
0
ED
Figure 9. Cedar Cliff Reservoir 2018-2019 Water Column Temperatures (Upper Panel)
Compared to Bear Creek Hydro Operations and Daily Air Temperatures (Lower Panel)
11 Equilibrium temperature is the water temperature at which the net heat exchange with current atmospheric
conditions is zero. This temperature is approximated with the measured air temperatures.
18 2020 data were not plotted since the 127 days of low reservoir level prevented boat access to the reservoir.
19

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Even though a traditional thermocline did not develop, the strongest horizontal gradients were
observed at and below the penstock invert, indicating that the penstock had very limited access
to the water below the penstock and reduced vertical mixing below that level. This small volume
of water (26 acre-ft)19 exhibited characteristics similar to a traditional hypolimnion with vertical
exchange of heat and compounds limited by diffusion and low turbulence.
In the summer of 2019, Cedar Cliff Reservoir exhibited the importance of advective density flow
as described by Thornton et al. (1990). The warm, deeper reservoir water was rapidly replaced
with cool water. This cool water was not derived from surface heat exchange, as evidenced by
warm surface water and warm air temperatures, but rather from a sudden release of cool water
from the upstream Bear Creek Reservoir. An outage at the Bear Creek Powerhouse from
February to May 2019 required the Tainter gate at Bear Creek to pass water downstream. This
surface water release from Bear Creek Reservoir allowed the cold water to be retained in the
deeper areas of Bear Creek Reservoir. Once the outage was over, the generating units began
utilizing the deep penstock opening with subsequent release of the bottom, cold water into
Cedar Cliff. Once this cold, deep water from Bear Creek Reservoir was depleted in Cedar Cliff
Reservoir, warm water from Bear Creek Reservoir again entered Cedar Cliff Reservoir. As
Cedar Cliff hydro continued generation, the cooler water from Bear Creek Reservoir was
depleted and replaced by warmer surface water again pulled down via Powerhouse generation.
As the summer progressed, the deep -water warming continued until the reservoir began to cool
following the fall meteorological cooling (see Figure 9).
Dissolved Oxygen and Oxidation Reduction Potential
The 2018 water column dissolved oxygen (DO) concentrations followed the pattern established
by the temperature distribution; namely, DO was higher in the surface layer due to atmospheric
oxygen exchange and photosynthetic activity (Figure 10, upper panel). Below the surface of
Cedar Cliff Reservoir, the DO decreased due to respiration by algae and bacteria. Like
temperature, as Cedar Cliff hydro continued generation, the water was removed from the lower
reservoir levels and was replaced by water above the penstocks. As respiration continued, DO
continued to decrease. Even though the horizontal thermal gradients were minimal, the water
column was stable enough to prevent atmospheric oxygen exchange. As respiration continued,
the DO continued to decrease while water was being removed from the generation. With the
initiation of fall cooling and subsequent mixing, DO increased as atmospheric oxygen exchange
progressed.
In the late spring/early summer 2019 period, the advective density inflow from Bear Creek hydro
(as described in the previous section) was also apparent as the inflow water had slightly less
DO than Cedar Cliff Reservoir. Once this water was depleted from Cedar Cliff hydro, a similar
pattern of oxygen decreases and distribution occurred as in 2018.
As mentioned previously, water below the penstock invert was not removed or replaced until fall
cooling was sufficient to mix that water. Until that water was mixed, either aerobic or anaerobic
respiration continued until the DO was completely depleted in that deep water.
The continued biological respiration in the deep water resulted in continued depression of the
oxidation reduction potential (ORP) (Figure 10, lower panel). Redox potential (Eh) is the
measurement of the tendency of an environment to oxidize or reduce substrates. Most redox
19 Calculated from the invert elevation and the storage curve presented in Figure 5.
ORN

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
reactions are biologically mediated (catalyzed), sometime by very specific organisms, as energy
is available for their metabolism (Gibbs Free Energy, AGO, Figure 11).
2330
2320
2310
2300
2290
Z. 2280
- 2270
2260
2250
2240
LL 2230
2220
2210
2290
2190
Dissolved Oxygen (mgilL)
Aug I Sept I Oct I Nov I Dec Jan I Fet� ' Mar I Apr
201 B
011P (mv)
9.
May Jun Jul
2019
4:
Aug I Sept I ;_�'t
2330 9
2320
1 '+
. *
I
Go
-
4" -
2310
2300
2290
2280
2270
2260
2251)
2 240
V
22301
222"
2210
2 200
2190—*
I'D
Aug Sept Oct
NOv Dec
Jan Feb
Mar
Apr May
Sept OCt
2018
2019
Figure 10. Cedar Cliff Reservoir 2018-2019 Water Column Dissolved Oxygen (Upper
Panel) Compared to Water Column Oxidation Reduction Potential (Lower Panel)
E
h
0
Oxidant
A G
MV
(accepts el
(energy available)
Aerobic Respration
-686
kcal/mole
Asstm ilatory N il rate Reduc I �on
rjo,`�H` ---;, NH. -organic
Fe.fOH)(HCOI,XPO.) (S)
NanfKation
NH.11 + 3f2O-. <---> NO�' 0 2H" H:O
-657
r4 0." +--1- N 0
-175
kcallmo,le
+600--
(��) Fe-) SO4-;
DeniInf�catton
Fe�(OHXHCO))(PO4) (S)
CH-0 -NO,"4—)-CO� 2HO
-649
kcallmole
IronReciuction
Fe-.(0K)(HCO3XP0.)
Fe(X)3 + 3 K"' 01(E��
_E!>
HPO��; -300
(s)
kcal;nnale
-150--
Suifate keducw>n
2C H 0 + 5Q.-2 + 3H 2CO. H S- 2K:O
-1 9D
kcallmolo
Fe -I + V res -4, (Pynte)
K., - 10-'S
0 measured f--]
CalCu[ated
Note: Eh=Oxidation Reduction Potential (mv), AGO = Gibs Free Energy, K�p= Solubility Product
Figure 11. Cedar Cliff Reduction Reactions in Relation to Eh
21

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
The redox reactions that are most important in the evaluation of pyrite chemistry involve carbon,
oxygen, nitrogen, iron, and sulfur (Figure 11). In aerobic conditions, oxygen is the primary
electron acceptor, represented by the first three reactions in Figure 11. Although denitrification
reactions occur at slightly less ORP, the aerobic conditions persist. As oxygen and nitrate are
consumed, the Eh decreases. As biological respiration continued, ferric iron (Fe +3 ) became the
primary electron acceptor as the ferric iron was reduced to ferrous iron. Although ferric iron may
exist as a free ion, most ferric iron is complexed with hydroxide (iron hydroxide) and/or
bicarbonate (iron bicarbonate) and/or phosphorus (iron phosphate). As ferric iron is reduced and
becomes soluble, the associated ions of the hydroxide, bicarbonate, or phosphoru S20 become
soluble. As anaerobic respiration continues, the Eh continues to decrease when sulfate may
become the terminal electron acceptor for the organisms as sulfide is produced. Sulfide and
ferrous iron will combine (without biological mediation) to form the insoluble ferrous disulfide 21
(pyrite).
These reactions occur in the water column, but are most prevalent in sediments, especially with
organic material available to micro -organ isms. As these reduction products become solubilized
and concentrations build in anaerobic sediments, diffusion from the sediments increases the
concentrations of these compounds in the water above the sediments.
In Cedar Cliff Reservoir, the ORP values generally follow the DO trends. Aerobic respiration
reduced the water column DO concentrations with a corresponding decrease in ORP levels.
Water above the penstock invert maintained a year-round oxidizing environment, primarily
because of the reservoir's relatively low retention times and deep -water withdrawal
characteristics. However, in the water below the penstock invert, Eh levels continued to
decrease as anaerobic metabolism continued. Reduction products accumulated either from
metabolism in the water column or diffusion of reduction products from the sediment. Sulfate
reduction would likely not have occurred since the lowest water column ORP measurement
recorded was -3 mv.
Carbon Dioxide and pH
The water column pH values (Figure 12, upper panel) throughout the entire baseline sampling
period exhibited little variability, with the lower values observed deeper in the water column
during the summer/fall season. The highest pH values were observed in the surface waters
during the spring/summer months as a result of photosynthetic activity.
Since the reservoir pH values ranged from 5.69 to 8.45 units, there is no evidence of strong
acids influencing pH and, according to Hutchinson (1975), within those pH ranges, most natural
freshwaters are buffered by the bicarbo n ate -carbon ate system, the following equation was
applied:
K1 _ [H+] [HCO3
1 K021
Where:
Kil = First equilibrium constant as a function of temperature
H+1 = Hydrogen ion concentration (moles/L) (10-PH)
HCO3-1 = Bicarbonate concentration (moles/L)
2 1 This phosphorus is usually considered 'internal' loading to the water body and may become available for algal
uptake.
21 The reaction of ferrous iron plus sulfide yields FeS2 (pyrite) has a pKsp = 18,which is very insoluble and tends to
precipitate as a solid.
22

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
CO2 = Carbon dioxide concentration (moles/L)
pH (units)
2330
2220
2310
2�Qo
2
2290
2280
F 2270
2254)
2240
L 2230
EI
2220
2210
2200
2191)
r
ALIg
Sept
Oct
Nov Dec
Jan
Feb
Mar
Apf
Aug Sept Oct
2018
2019
Carbon Dioxide (nngfL)
233D
2320
'I-D15
2JIU:
2200
71,
4?
2290
E 22�0
2250
2240
2230
P
LL
2210
0
22 U
2
io
Aug
Sept
Oct
Nov I Dec I
Jan I
Feb—T
Mar
Apr
Aug I Sept T Oct
2018
2019
Figure 12. Cedar Cliff Reservoir 2018-2019 Water Column pH (Upper Panel) Compared to
Water Column Carbon Dioxide (Lower Panel)
Since the pH was a function of the ratio of carbon dioxide to bicarbonate, the influence of the
relative rates of respiration or photosynthesis on pH may be estimated by calculating the carbon
dioxide concentrations from the bicarbonate equilibrium equation. While respiration occurred
throughout the water column, photosynthesis only occurred in the lighted, euphotic zone
(Figures 10 and 12). Photosynthetic activity resulted in higher oxygen levels coinciding with low
carbon dioxide concentrations; the converse suggests that carbon dioxide produced by
respiration lowered the pH. Indeed, higher oxygen and lower carbon dioxide were observed in
the surface waters, while the opposite was observed in the deeper water.
The summer of 2018 exhibited pH trends similar to the summer of 2019 (Figure 12, upper
panel). Oxygen concentrations during both summers indicated that respiration occurred in the
deeper water; however, carbon dioxide concentrations were much higher in 2019. The Cedar
Cliff Reservoir surface water oxygen and carbon dioxide data suggest that photosynthetic
activity was more pronounced in the summer of 2019. In 2019, the influx of bottom water from
Bear Creek Reservoir may have stimulated higher primary production as well as increased the
organic loading to Cedar Cliff. Both of which increased respiratory rates and allowed carbon
dioxide to exceed the concentrations observed in 2018.
23

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Conductivity and Turbidity
Conductivity values, a measure of dissolved compound and relative ionic strength, were
generally less than 20pSi, indicating waters of very low ionic concentrations (Figure 13, upper
panel). However, conductivity values were significantly higher in the water below the penstock
invert. As mentioned previously, this water was not readily available for generation and had a
long retention time. The conductivity values strongly support this conclusion, since the relatively
high concentration of ions did not originate from the upper water, but rather from ionic diffusion
from the sediments. The conductivity increase persisted until the water temperatures cooled and
mixed the bottom water.
2330
232C
2310
230C
22 9C
22 BC
E 2270
22%
22 5C
2240
2230
22 X
221C
22 DO
219C
2MO
2320
2310
23CO
2290
m 2280
F
2270
2260
2240
2230
2220
2210
2200
21 UO
Conductivity (pSi)
so
Aug Sept Oct Hov Dec Ja Apr Mav I Auq SEpt Oct
2018 2019
Turbidity (NTU)
2018 2019
Figure 13. Cedar Cliff Reservoir 2018-2019 Water Column Conductivity (Upper Panel)
Compared to Water Column Turbidity (Lower Panel)
Turbidity is a relative measure of suspended solids (particles). Cedar Cliff Reservoir has very
low turbidity, rarely exceeding the state standard for trout waters of 10 NTU (Figure 13, lower
panel). The only exception was during the winter of 2018-2019 when surface turbidity was
slightly greater than 10 NTU. The higher turbidity values at the bottom of the reservoir during
this time suggest that the solids were transported into the reservoir and rapidly settled to the
bottom. Sources of these solids could have originated from surface runoff since these higher
turbidity values occurred during high rainfall events (see Figure 6). More likely, the higher
turbidity values originated from water released from Bear Creek Reservoir during the extensive
drawn down (40-90 ft below full pond) in the last quarter of 2019 to facilitate the installation of
the Bear Creek hoist and allow divers to repair the Bear Creek intake gate rail system.
24

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Comparison between Reservoir Forebay and Up -lake Water Quality
The sampling site (EMP 7) was a reservoir location upstream of the proposed rock spoil area.
This site was included in the monitoring proposal to serve as a 'control' site for comparison to
the forebay site (EMP 4) after the rock from the excavation area was spoiled in the reservoir.
Rather than plotting all of the profiles, the January, 2019, and the August samplings at each
reservoir site for each baseline year were compared. Very little water quality differences were
observed between the two sites (Figures 14 and 15). The obvious difference between the two
sites was with the water quality below the forebay penstock invert. Water at the same elevation
from both sites had almost identical quality, with the minor exception of slightly higher turbidities
at the up -lake location.
25

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(ISW-4) U01leAal::l

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Characterization of Cedar Cliff Reservoir Sediments
The sediment samples were composed of extremely fine grain material (Figure 16) with 16.8%
organic contents. This material overlaid the original bottom, which existed when the reservoir
was built. The particle size distribution indicates that over time, clays and organic material were
transported into the reservoir and, along with organic material produced in the reservoir (e.g.,
phytoplankton), settled to the bottom. Also, the amount of organic material in the sediment
would provide the necessary substrate for both aerobic and anaerobic respiration. Consumption
of these organics would no doubt contribute to the formation of reduced compounds and the
subsequent diffusion of those products into the overlaying water.
100
90
80
70
60
50
40
30
20
10
PD�ark (Gray Silty ClaV
Natural Moisture = 271%
i i i i i i i i i i
Organic Content = 16.8%
Specific Gravity = 2.58
I 6=09
100
10
Particle Size (prn)
Figure 16. Particle Size Distribution of Cedar Cliff Forebay Sediments
SEM spectra analysis (Figure 17) showed the bulk of the material to be alumina -silicate
minerals, such as kaolinite clay enriched with feldspar and mica. A few very small titanium -
enriched particles were scattered throughout, and even fewer iron -enriched particles were
observed. Very little sulfur was present and no particles consistent with iron pyrite were
identified.
Most soils of the world contain kaolinite in the clay size fraction (<2pm). In highly weathered
soils, such as those of Southeastern U.S., kaolinite is usually the dominant clay mineral
because of its relative resistance to chemical weathering. Kaolinite has a large cation -exchange
capacity (adsorption) (Millar et al.1 966). When formed in well -weathered soils and transported
into water, the hydrogen ions adsorbed unto the kaolinite may be exchanged with other cations,
especially multi-valent cations such as iron. Approximately 25% of the particles were less than
1.5 pm, suggesting a very high cation exchange capacity of the sediments.
The lack of sulfur in the sediments suggests that pyrite was not formed in the chemically
reduced environment. As mentioned previously, sulfide formation was not favored since the
oxidation-reduction potential did not favor sulfate reduction. The trace amount of sulfur observed
in the dried sample was likely associated with the organic fraction in the sediment since no
sulfur was observed in the sediment sample ashed at 500'C, which eliminated the organics.
0m,

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Also noteworthy was the lack of phosphorus in the sediments and the presence of carbon in the
ashed sample. These spectra indicate that the primary compounds associated with iron were
bicarbonates, hydroxides, or oxides, rather than phosphates or sulfides.
Cedar Cliff Forebay Sediment Sample Dried at 1OOPC
6141-100 sern03 BRIGHT
C1 6111 100 sviT104 LARGE
0 6141 - i on setrO4 PL ATY
Material is alumina -silica minerals with small amounts of
magnesium, potassium, and iron. A trace amount of sulfur
S1 was identified. Higher weight particles are enriched with
either titanium or iron.
C Ti Fe
Tt M n Fe
JO., A,
2 4 6 8 keV
Cedar Cliff Forebay Sediment Sample Ashed at 5001C
wr 6141- 500 sernOi PLATY
F) 6141 500 sem03 BRIGHT
0 6141-500 semO3 BRIGHT 2
Material is alumina -silica minerals with small amounts of
magnesium, potassium, and iron. No sulfur was identified -
Higher weight particles are enriched with titanium or iron.
At
I Ti Fe
C Fe mq K LKL7, i a
V J K 7i M11 Fe
-rT-r , I I I I I I
kev
Figure 17. Scanning Electron Microscopy Elemental Spectra of Cedar Cliff Forebay
Sediments
29

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Auxiliary Spillway Channel and Sediment Basin
The conductivity of the water samples collected from the auxiliary spillway channel (EMP 3)
ranged from 88 to 185 pSi (Figure 18), while conductivities from the storm events (the high
water) ranged from 34 to 63 pSi. Prior to the construction of the sediment basin, auxiliary
spillway channel samples were collected by creating a small stilling well (3-inch depth) in the
sand to obtain the water seeping to the surface. After the auxiliary spillway channel was re-
routed to the newly constructed sediment basin, a small surface flow enabled water collection.
The sporadic readings from the conductivity logger (Figure 18) and the deviations from the
water samples prior to construction resulted from the conductivity logger being on the surface
and not well submerged. After construction, there was good agreement between the logger and
samples since the logger was continually submerged in the small surface flow.
The conductivity from the auxiliary spill water was substantially higher than the upper water in
Cedar Cliff Reservoir, indicating that the seepage and leakage flows were the primary sources
of water, with periodic rain events diluting the groundwater seepage. As the auxiliary spillway
channel flowed into the sediment basin during the rain events, the water from the sediment
basin rapidly filtered through the sediment basin dam, carrying dissolved compounds with it.
7
4)
_J
C
Z 6
cu
CD
4
UcL 3
2
­uxolar� SplWay (EMP Jj Le-�LN G e J rie N Basin (EM P 5� Lev e I
Auxiliary SpilhNay (EM PI 3) Cond Logger —Seciment Basin (EMP 5) Cond Logger
A ux I i ary S 0 1 Way (EM P 3) Cc nd So mple & Auxiiary SpilWay (EMP 3) High Water Cond Sample
J A S 0 N D J F M A M J J A S 0 N D J F M A M J J A S
2018 2019 2020
Figure 18. Conductivity of the Cedar Cliff Auxiliary Spillway and Sediment Basin
200
190 =
160 (1)
140
120
100
so
W
0
40
20
0
Prior to and after the construction of the sediment basin and re-routing the auxiliary spillway
channel, the suspended solids, as measured by turbidity, in the auxiliary spillway channel were
at or below the 10 NTU North Carolina water quality standard (Figure 19). The two spikes of
turbidity observed in the auxiliary spillway channel were associated with high rainfall events.
The August 2020 high turbidity spike in the auxiliary spillway channel was reduced to less than
2 NTU by the newly constructed sediment basin (Figure 19).
KE

9
0) 6
FL 4
U)
3
< 2
Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Auxiliary Spillway (EM P 3) Level Se cli me 18 asin (EM P 5) Lev e I
A ux I i ary 3 pi I Way (E M P 3) T LFb 3 arriple Se d mert B asin (E M P 5) 4 gh Wate r Tu rb Sa mpl a
Auxiliary Sollway (EM P 3) High Water Turb SwTle ....... Tu r b VVQ STID
..................................................................................... .......................................... ..........
J A IS 0 N D J IF M A M J J A IS 0 N D J F M A M J J A
2018 2019 2020
Figure 19. Turbidity of the Cedar Cliff Auxiliary Spillway and Sediment Basin
Principal Spillway Channel and Bypassed Reach
150
45
40
35
30
25 el
20
15
10
5
0
Conductivity from the water samples ranged from 13 to 132 pSi from the upper bypassed reach
site (EMP 6) and 44 to 56 pSi from the lower bypassed reach location (EMP 2). The conductivity
logger data showed a similar pattern, with fairly good agreement between the two methods
(Figure 20). Lower conductivities in the high-water samples occurred immediately after Tainter
gate releases from the reservoir. The lowest conductivities recorded by the logger also
coincided with the Tainter gate releases.
A ux ill ary Spi I Way (Elyl P 3) Lev el Sedmert Basin (EMP 5) Level
Aux Ri ary Spiltway (EIVII P 3) C ond Lo gg er S edme I Ba sin (E VII P 5) Cc nd La gge r
Auxiliary Spillway (EMP 3) Cond Sample a Auxiliary Spillway (ENI P 3) High Water Gond Sarroe
9
7
in 6
5
4
60
2
200
190
160
140
120
'L LPU
60 CO
40 Q
20
0
0 1 11��� � -d . ..' .- .-L . L_ 'J_
J A S 0 IN D J F M A M J J A S 0 IN D J IF M A M J J A S
2018 2019 2020
Figure 20. Conductivity of the Cedar Cliff Principal Spillway and Bypassed Reach
CIE

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Higher conductivities at the upper bypassed reach site resulted from the auxiliary spill water
seeping through the sediment basin dam into the bypass during low bypass flows.
As mentioned previously, Tainter gate flows, or higher flows derived from rainfall, flushed the
bypassed reach. As the water receded, the pools drained slowly and were subject to significant
evaporation, as indicated by a gradual conductivity increase during the summer months.
Turbidity in the principal spillway and bypassed reach rarely exceeded the state turbidity
standard of 10 NTU (Figure 21). The only exceptions were during the Tainter gate releases or
higher rain -driven flows when higher flows increased the water velocity, causing suspension of
material from the river bed. The low turbidity values throughout the Phase I construction period
reflected the effectiveness of the erosion control measures employed during construction of
access roads, lay down areas, placement of check dams, and channel re-routing (Figure 1).
9
a
7
6
4
Zn
6L 3
M
2
0
_J I
0
Lowe r By passed Rea ch (E M P 2) Lev el
Lowe r By passed Rea ch (E M P 2) T urb S a mple
4 Lowe r By p assed Rea ch (E M P 2) H i gh W al: er Tu rb S ampi e
....... TUrb WO STE)
U pp e r By p assed Rea ch (E M P 5) Level
Upper Bypassed Reach (E:M P 6) Turb Sample
Upper eypassed Reach (FM P 6) Hrgh Water Turb Sample
+
................
:,w ....................... ...... .. . .....
L
J A S 0 N D J F M A M J J A S 0 N D J IF M A M J J A S
2018 2019 2020
Figure 21. Turbidity of the Cedar Cliff Principal Spillway and Bypassed Reach
East Fork
Since the East Fork received most of its water from the reservoir, either from the generation
flows or Tainter gate flows, conductivity in the river remained fairly constant (8-20 pSi) (Figure
22), following the reservoir conductivities (Figure 13).
140
120
D
10G
so
so
40
20
0
East Fork conductivities measured immediately upstream of the confluence with the East Fork
(EMP 8) were very similar to those measured at the powerhouse. Very slight conductivity
increases downstream were likely the result of small tributary inflow or bank seepage.
32

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Unt 2 + UNt 1 Flow
M i N rru m Fl ow Un it (2)
EmPlOondsample
4500
4000
3500
3000
0-2500
P
0
2000
r) 1500
1000
61010A
—Tairter Gate Flow
— EM P 1 C o ndu Ltv ity Logg er
0 East Fork Above Confluence (EMP 6)
0 L ---- I.L_ A�- - 10 -11 " WT
JASOl`J0JFfJArAJJA5OHDJ
2018 2019
Figure 22. Conductivity of the East Fork
F M A M J J A S
2020
The turbidity in the East Fork at the Powerhouse (EMP 1) was consistently below the state
standard of 10 NTU with the exception of one reading of 11.7 NTU during a very high water
Tainter gate release. Turbidity downstream at EMP 8 showed slightly higher readings, likely as
the streambed solids became suspended in the river. The low turbidities in the East Fork reflect
the effectiveness of the site erosion control measures during Phase I construction (Figure 23).
To ta I Ea st Fork Flo w East F o rk (EMP 1.) T LI rbi dity ....... Turb WQ STD 0 East Fork Above Confluence (EMP 5)
F_nnn
4500
4000
3500
Z 3000
2500
62000
1500
1000
500
0
J A S 0 N D J F NI A M J J A S 0 N D J
2018 2019
Figure 23. Turbidity of the East Fork
F M A M J J A S
2020
140
220
IDD
N
60
40 0
0
20
0
WN!,
20
15 -2
5
0
33

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Chemical Characterization of Cedar Cliff Site Drainages
Analytical Evaluation
A summary of the analytical procedures listed in Table 3 revealed a wide range of ionic
concentrations collected from the various sites (Table 4). The median ionic concentration S22
(from Table 4), had a very good correlation with conductivity (Figure 24), indicating good
consistency with the field measurements and laboratory analyses. This data also illustrates the
usefulness of conductivity loggers to track ionic changes in the water as Phase 11 of the upgrade
project progresses.
The auxiliary spillway channel (EMP 3), the upper bypassed reach channel (EMP 6), and lower
bypassed reach channel (EMP 2) all exhibited lower ionic concentrations and corresponding
lower conductivities in the samples collected with the USGS single stage samplers, indicating
that dilution was associated with higher flows. Additionally, the bottom reservoir samples during
anoxic periods had much higher ionic strengths and conductivities associated with the
compounds that diffused from the reservoir sediments.
140
120
—100
80
0
0 60
40
951
• Lake (EMP 4 and 7) �> East Fork (EMP 1 and 8) @ Lower Bypass (EMP 2)
• Upper Bypass (EMP 6) *Sediment Basin (EMP 5) PAuxNary Spill (EMP 3)
R 2 0,9667
EMP 3 High Water
EMP 6 High Water
EMP 2 High Water
EMP 4 anaerobic
EMP I and 8
1.0 1.5 2.0 2.,7
Median Ionic Strength (Z nneq)
Figure 24. Relationship between Median Ionic Strength and Median Conductivity
22 Median concentrations did not bias the results with intermittent high or low values as would a calculation of a mean
concentration. Median values allowed each individual sample to be statistically equivalent.
34

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CY)

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Another evaluation of analytical results is the calculation of the charge -balance error (CBE)
(Stumm and Morgan 1981) (Table 5). One fundamental law of nature is that aqueous solutions
must be electrically neutral. This means that in aqueous solutions, the total sum of all the
positive charges (cations) must equal the total sum of all negative charges (anions). The
calculated CBE can be positive or negative. A positive CBE indicates that the water sample has
a higher concentration of cations than anions. Conversely, a negative CBE indicates that anions
are more abundant. Low -concentrated waters are especially sensitive to small deviation
between total cations and anions. Acceptable water analyses have CBE less than ±5%.
Possible causes for electrical imbalances are:
• Some dissolved species (major ions) were not measured;
• Using unffltered samples that contain particulate matter, which may dissolve prior to
analysis, especially with acid preservative;
• Assumption that all the compounds measured were dissolved;
• Assumption that valences were those found in highly oxidized environments, particularly
multi-valent compounds associated with redox reactions; and/or
• Lab errors (serious or systematic errors during analysis), especially in low ionic strength
water where concentrations approached the detection limits of the technique.
Table 5. Summary of Total Anions, Cations, and Charge -Balance Error from the Cedar
Cliff Reservoir Sampling Sites
Charge
Number
Total
Total
Total Ions
Sample
Balance Error
of
Anions
Cations
(Cations * Anions)
Location
il
Samples
(ni
(meq/L)
(ni
(1/0
Auxiliary Spill Channel
14
0.828
0.806
1.634
-1.4
EMP 3
Auxilary Spill Channel High
3
0.511
0.454
0.965
-5.8
EMP 3
Sediment Basin High
3
0.644
0.853
1.497
139
PAP 5
Upper Bypassed Reach
5
0.614
0.673
1.287
4.6
EW 6
Upper Bypassed Reach High
4
0.744
0.666
1.410
-5.5
PAP 6
Lower Bypassed Reach
22
0.345
0.390
0.735
6.2
PAP 2
Lower Bypassed Reach Higl-
10
0273
0.387
0.660
174
EPOP 2
Fast Fork
22
0.149
0.167
0.317
5.6
POP 1
East Fork
24
0.153
0.173
0.326
6.4
EPOF 8
Furebay Surface Aerobic
18
0.149
0.164
0.313
4.9
EMP 4
Uplake Surface Aerobic
17
0.149
0.170
0.319
13. -
EMF 7
Forebay Bottom Aerobic
11
0 146
0.156
0.302
3.3
EMP 4
UpLake Bottom Aerobic
17
0.150
0.190
0.340
11 9
EMP 7
Forebav Boi Anaerobic
6
0.247
0.540
0.787
372
EPOF 4
W

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Of the 14 calculated CBEs from the Cedar Cliff drainage area median cation and anion
balances (Table 5), five of the CBEs were equal to or below the ±5% acceptance criterion. An
additional five analyses were within 7.5%; however, four of the analyses were greater than 10%
error, with the anoxic water from the bottom of Cedar Cliff Reservoir exhibiting a 37.2% CBE.
Even though many analyses were very good, the goal for the Phase 11 will be to improve the
analyses by evaluating the causes of potential errors.
The following recommendations will be implemented prior to Phase 11 sampling and analyses:
1 . Review each method with the analytical laboratory, especially with respect to detection
limits.
2. Include the calculation of pK' S23 during the alkalinity titration to verify carbonate
equilibrium, and/or independent measure, other than titration, of bicarbonate and
carbonate.
3. Include silicate (not silica) analysis in routine samples (silicate anion to be included in
CBE), and evaluate other potential missing anions.
4. Perform periodic total metal scans to evaluate potential missing cations.
5. Perform complete metal inductively coupled plasma (ICP) analyses on all unfiltered and
filtered samples (separate particles from dissolved compounds).
6. Establish a rainwater collection site, perform similar chemical analysis as grab
24
samples.
7. Employ chemical equilibrium software to determine ionic composition and speciation.
Evaluation of Analytical Results to pH
The median pH values from the various sampling sites ranged from 4.70 to 7.00 (Figure 25),
with the lowest values observed in the auxiliary spillway channel and the highest recorded from
the reservoir forebay surface water. The pH of water from the sampling sites suggests that the
low pH values in the auxiliary spillway channel (EMP 3) and the upper bypass site (EMP 6)
could be associated with pyrite oxidation of the exposed pyritic rock in the auxiliary spillway
channel. However, a detailed review of the analytical data is warranted to elucidate the probable
cause of the pH variability
An evaluation of the pH variability is based upon the following chemical equations:
Mamor PH Bufferinci in Most Surface Water (Alkalinity): (Stumm and Morgan 1981)
H20 +--> H+ + OH-
0O2 + H20 +-+ H2CO3 +-+ H+ + HC031- +-+ H+ + CO3 2-
Overall Reaction of Pyrite Oxidation (Stumm and Morgan 1981)
H20 +--> H+ + OH-
2FeS2 + 702 + 2H20 --)� 2FeSO4 + 2H2SO4
23 Negative logio of the first equilibrium constant of the carbon dioxide: bicarbonate chemical reaction.
24 See Table 6, rainwater has the potential to directly effect the chemistry of the low conductivity waters within the
Cedar Cliff Development, rather than estimating rainwater influence from the sparse literature, rain chemistry can be
measured directly.
37

Boo
700
CL
600
5_GQ
4-nn
Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
(b Cb
o
6,
Figure 25. Median pH values from all Cedar Cliff Sampling Sites
Using the first equation, median carbon dioxide concentrations were calculated for each
sampling location utilizing the equilibrium relationship presented previously (Figure 26).
Even though the calculated carbon dioxide concentrations were proportional to the pH values,
the data suggest that the pH values were within the range of the bicarbo nate-carbo n ate
buffering system (i.e., a strong acid was not necessary to achieve the observed low pH levels).
The higher carbon dioxide concentrations observed in the auxiliary spillway channel (EMP 3)
and the upper bypassed reach sites (EMP 6) could have resulted from high carbon dioxide in
the groundwater seepage that was prevalent at both sites. The groundwater seepage into the
bypassed reach would continually supply carbon dioxide to both sites, but since the
groundwater concentrations were greater than the atmospheric partial pressure saturation of
carbon dioxide, the carbon dioxide in the groundwater would have been lost to the atmosphere
as the water traveled through the sediment basin and moved downstream in the bypassed
reach.
The lower carbon dioxide concentrations in the lower bypassed reach (EMP 2), the East Fork
(EMP 1 and EMP 8), and the reservoir sites correspond to concentrations expected from
biological metabolism of respiration and photosynthesis.
IN

1GGOO
1000
0
V_
1.00
r)
0
-2
0 0.10
0.01
Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Cb
Z-Z
A; CP
" -, '�? '4 '5- 0 - &
&
Figure 26. Median Carbon Dioxide Concentrations Calculated from all Cedar Cliff
Sampling Sites
As discussed previously, the elevated levels of bicarbonate, iron, and nitrate in the bottom
waters of the forebay (Figure 27) resulted from diffusion from the reservoir sediments to the
overlying water, particularly during anoxic periods in the bottom water.
Since both the anionic and cationic concentrations in the East Fork (EMP 1 and 8) were very
similar to those concentrations observed in the reservoir surface water (Figure 27), the water
quality of the East Fork was dominated from the high flows originating from the reservoir, with
very little influence from the bypassed reach. The pH data (Figure 25) showed the same pattern
as the elevated ionic concentrations from the bypassed reach (EMP 2), exhibiting little influence
on the East Fork water chemistry.
As the chemical equation for pyrite oxidation implies, iron, sulfate, and hydrogen ions are the
final products of the reaction. The elevated concentrations of sulfate in the auxiliary spill water
(EMP 3), the sediment basin (EMP 5), and the upper bypass (EMP 6) (Figure 27, upper panel)
suggest that the low pH levels were the result of pyrite oxidation. However, calcium and
magnesium concentrations followed the same elevated levels as did sulfate (Figure 27, lower
panel), suggesting the sulfate was present as calcium and/or magnesium sulfate and not
associated with pyrite oxidation. The sulfate, calcium, and magnesium concentrations
decreased as the seepage water from the auxiliary spillway channel was diluted as the water
flowed downstream.
939

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Anions
HCO3-1 c4_1 SC4-2 NO3-1
(-eql) (Meol) (_eol) (­CV0
too
0.90
080
:a 0.70
060
G 50
040
G 30
020
D 10
0 W
I
(0 (0 CO rV rV Cb N
C6
C4
Cations
Na+I � K+1 Ga+2 Mg+2 @Mn+3 @Fe+3 Fe+2 mAI+3
(meol� (me4l) (rne0l) (meq(l) (me4l) [-e4l) (-ell) (-eqO
1.00
090
080
0.70
060
0
050
CD
E 0. 14WO
0
0.30
0.20
000
(1) Ib rV T.. N
Q �4z
1141, (4;
(6 6 Z�
IT- T T
Figure 27. Median Concentrations of Anions and Cations from All Cedar Cliff Sampling
Sites
40

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
The average flow of the Bypassed Reach at the EMP 2 site during the baseline period was
calculated from the following equation:
(QBP + QR) X T'EF = (QR X TIR) + (QBP X TlBp)
Solving for QBP,
QBP = KQR X TIR) (QR X T'EA
(TIEF TIBp)
where, (all values were calculated during the Baseline Period)
QBP = Average Flow of the Bypassed Reach
QR = Average Flow from Cedar Cliff Reservoir
(from page 14, 177.8 cfs + 25.3 cfs + 93.7 cfs = 296.8 cfs)
(QBP + QR) = Average Flow of the East Fork
TIR = Total Ion Concentration Cedar Cliff R6servoir (Table 5, EMP 4)
TIBP = Total Ion Concentration Bypassed Reach (Table 5, EMP 2)
TIEF = Total Ion Concentration East Fork (Table 5, Mean EMP 1 & EMP 8)
The total ion concentration of the Bypassed Reach grab samples yielded an average Bypassed
Reach flow of 7.02 cfs. Averaging both the grab sample and the high-water total ion
concentrations yielded a calculated flow of 7.72 cfs. At these flow rates, a direct measure of
acidification of the East Fork due to pyrite oxidation from the auxiliary spillway channel would be
very difficult to detect.
A comparison of the various forms of iron revealed that much of the iron is bound in the form of
particulates, likely as iron oxides or associated with the alumina -silica clay fractions. The
particulate iron was prevalent at all the sampled sites, most notably in the auxiliary spillway
channel and the upper bypassed reach sites (Figure 28, upper panel). The portion of total iron
that passed through a 0.45 pm filter was assumed to be dissolved, either as ferric or ferrous
iron 25 (Figure 28, lower panel). The oxidized ferric form was generally less than 1 pmole/L
concentration with the exception of the reservoir water deeper than the penstock invert. Ferrous
iron was present at all of the spill channel sites, but usually occurred during high water events.
Ferrous iron was detected at all East Fork and reservoir sites at levels usually less than 0.5
pmoles/L. Again, the notable exception was at the bottom of the forebay site during anoxic
conditions.
The contribution of pyrite oxidation as a major source of sulfate, hydrogen ions, and the various
forms of iron was ascertained by comparing the expected molar ratios of the three products
predicted by the chemical pyrite oxidation equation to the observed molar ratios measured in
the water samples (Figure 28). The three molar ratios calculated from sulfate, iron, and
hydrogen ions (Figure 29) were orders of magnitude different at the same locations, indicating
that processes other than pyrite oxidation controlled the abundance of the three compounds.
This was especially true for sulfate, since, except for the bottom of the reservoir during anoxic
25 Non-ionic iron may pass through a filter as colloidal forms, complexed with organic material, or adsorbed unto other
sub -micron particles.
41

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
periods, sulfate dominated the sulfate to iron and sulfate to hydrogen ratios at all sites. The
bypassed reach (EMPs 3, 5, and 6) exhibited high levels of sulfate. The oxidation of pyrite also
had little influence on the pH, as evidenced by the inconsistent hydrogen ion -to -iron ratios and
sulfate -to -hydrogen ratios. Pyrite oxidation played a minor role in the abundance of sulfate,
hydrogen ions, and the various forms of iron.
Even in the very low ionic strength water in the Cedar Cliff drainages, pyrite oxidation seems to
have played a very small role influencing the various concentrations of cations and anions.
Weathering of parent rocks other than pyrite, cation -exchange with clay particles, rainwater, and
other dissolution reactions had major influence on the abundance of those compounds.
42

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Total Iron
Particulate Filtered
[Fe] [Fe]
100.00
1000
0
E
a)
0 100
0
0.10
lb R A, A,
'J
Filtered Iron
[Fe+3] [Fe+2]
10000
1000
0 i.uo
2
0.10
O.U1
R lb R �O <0 rV OV
q "R
U C5, . C,
'(5 Cf o<
01:1
Figure 28. Median Concentrations of Iron Fractions from Cedar Cliff Sampling Locations
43

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Sulfate Total Iron 0 Hydrogen : Total Iron N Suffate: Hydrogen Ratio 2 -
4-2 4-2 44 Ratio I -
10
77 1
in,
10-1
10-3
(b 1z '�3 �b �0 "V �0 10, 1\ A, V
le;
01*
2FeS2 2FeSO4 + 2H2SQ4
Products
2[Fe+2] + 4[SO4-21 + 4[H+lj
Sulfate: Filterable Iron Hydrogen: FilterabIe Iron 0 Sulfate: Hydrogen Ratio - 2
42 42 44 Ratio - 1
IC)4
101
IC)2
Y
;5
0
�; I
lo-1
10-1
ELI
t �0 I-V A, 10,
1_z _4z
46
z
Figure 29. Median Molar Ratios of the Products of Pyrite Oxidation Measured at the Cedar
Cliff Sampling Locations
44

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
For example, some of the major ions found in rainwater 26 (Table 6) could contribute to the
observed concentrations in the surface waters, especially sodium, potassium, and magnesium;
most notably nitrate. Additionally, the acidic properties of rainwater, especially if strong acids
were in the clouds, lowered the pH of the rain beyond the formation of carbonic acid. This would
encourage cation -exchange with clays, weathering of parent rock, and dissolution of bound or
solid compounds. As rainwater percolates through the rock crevices or soil, carbon dioxide,
originating from microbial respiration, would add additional carbonic acid to the groundwater.
Table 6. Average Ionic Composition of Rainwater Compared to Cedar Cliff Surface Water
Median
Rain
Average Rain
Average Rain
of Surface
Analyte
Contribution
(mg/L)
(pmoles/L)
Samples
N)
__jpmoles,'L)
Na�'
0.31
13.7
76.26
17.9
K*1
0,13
3.3
45.39
7.2
Mg�2
0.30
12.3
36.39
33.9
Ca +2
0.77
0.019
100.61
0,019
HCO3-1
0.1
0.006
1.68
0.350
cl-1
0.25
0.007
31.26
0.023
So 4 -2
1.43
0.015
138.99
0,011
CO2
4.61
11047
1166-82
8.97
NO3-
3.14
50.6
11.357
445.53
Note- Average rain pH 57 assumed in equilibrium with CO2, lower if S02, H2SO4, HC1, HN(
Sou rc e � Ca rroll (11962) and Ga rrells a nd Mackenzie (197 1)
The lower concentrations of calcium, magnesium, sulfate, and aluminum measured in the
reservoir water and East Fork likely resulted from the weathering of metasedimentary and
granitic rocks found throughout the watershed (Figure 30). However, the auxiliary spill and
bypassed reach samples had significantly higher concentrations of those compounds.
The highest concentrations of these compounds were observed in the auxiliary spillway
samples and from the high-water events sampled from the sediment basin (Figure 30). The
relative ratios of calcium/magnesium/sulfate/aluminum resembled chemical composition of
water originating from limestone and/or gypsum formations (Hutchinson, 1957 and Stumm and
Morgan, 1981) rather than from pyrite oxidation. Although these formations were not observed in
from the metasedimentary rock samples collected from the auxiliary spillway, the molar ratios of
21 All references to the chemical composition of rainwater mention the variability of compounds and concentrations,
depending on the location of rain collections. These average values presented in Table 6 were taken from inland
sources, primarily from locations in the Mississippi and Ohio River Valleys. The concentrations presented in Table 6
are not intended to convey absolute values, but rather suggest that the contribution of rainwater to the low ionic
strength water in the Cedar Creek basin could contribute and influence the measured concentrations found in the
Cedar Cliff samples.
45

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
the primary products of pyrite oxidation indicated other processes controlled the chemical
composition of the subsurface auxiliary spillway water. For example, in addition to the acidic rain
trickling or percolating around soil or rock in the auxiliary spillway, hydrogen ions exchanged
with the kaolinite clays could have slowly dissolved the underground particulates into the
component ions. This solution would continue to percolate into the auxiliary spillway channel
substrate and seep to the surface at the lower end of the spillway channel (EMP 3).
After construction of the sediment basin, the auxiliary spillway water would continue to enter the
bypassed reach at the upper bypassed reach site (EMP 6). At higher flows, flow into the
sediment basin (EMP 5) would filter through the sediment basin dam to the upper bypassed
reach site (EMP 6). As the water moved downstream in the bypassed reach, concentrations
would decrease slightly, indicating precipitation, or, more likely, high flow events flushing the
bypassed reach.
[Ca+2] [Mg+2] [SO4-2] [AI+3]
1()3
1V
W
0
E
0
IIG
1
rt) (0 A,
10 4,Z
4F 4�F 4eF
Figure 30. Median Concentrations of Calcium, Magnesium, Sulfate, and Aluminum
46

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Predicted PH at Various Pyrite Oxidation Rates
The potential for acidification in the future may be calculated by the following basic equation:
[H+11 =
IFeSm X Pyrite Oxidation Rate X 2
Volume of Water
Where,
[H+I] = Total hydrogen ions originating from pyrite oxidation (equivalents
per Liter)
F-FeSm = total pyrite contained in the excavated rock (moles)
Pyrite Oxidation Rate = percent pyrite completely oxidized per year
2 2 equivalents H+I per mole pyrite
Volume of Water amount of water available per year for H+I dissolution (Liters)
The total moles of pyrite excavated was calculated by the following:
Where,
IFeSm = [[Rock X (0.26 X (FeS%)) X CIX FeSdI
FWFes
F-FeSm total pyrite contained in the excavated rock (moles)
Rock total volume of excavated rock (cubic yards)
0.26 26% percent of rock contained pyrite
FeS% either 0.02, 0.05, or 0.07 range of percent pyrite in the pyrite
containing rock
C conversion of cubic yards to cubic centimeters)
FeSd = pyrite density (gm per cubic centimeter)
FWFeS = Formula Weight of Pyrite
The amount of pyrite is a straight forward calculation. However, the actual pyrite oxidation is
unknown but may be inferred by the geological evidence collected from the petrographic
analyses of the metasedimentary rocks of the TFFm formation from the Cedar Cliff auxiliary spill
site. The garnet mica schist, mica schist, and schistose biotite gneiss lithologies are of the
massive (crystalline) morphology (very low surface to volume ratio). The results of the rock spoil
evaluation (HDR, 2018a) demonstrated a low potential for acid production due to the coarse
grain pyrite -bearing rocks in the TFFm formation. No mineral alteration/weathering, including the
oxidation of pyrite, was observed in any of the thin petrographic sections, including samples that
have been continuously submerged since the reservoir was filled, or from samples after 68
years of exposure since the auxiliary spillway excavation in 1952. There was no history of acid
production from the Cedar Cliff formations or from past site excavations, all of which indicated
extremely low oxidation rates.
For purposes of these predictions, the pyrite oxidation rates were assumed to be 1 % or 0. 1 %
pyrite oxidized per year 21 and were applied to calculate the amount of hydrogen ions released to
the overlying water each year from each of the rock formations containing 2%, 5%, and/or 7%
17 Based upon the observed weathering and crystalline structure of the exposed or submerged pyrite samples, these
percentages are a gross over -estimation of actual oxidation rates. These exaggerated oxidation rates were used to
calculate a highly improbable, extreme worst case release hydrogen ions and subsequent water requirements
necessary to maintain state water quality standards.
47

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
pyrite (HDR; 2018a). The remaining, unoxidized pyrite, expressed as equivalents of hydrogen
ions (Figure 31) were assumed available for the next year's oxidation and subsequent hydrogen
ion release.
I G,
2
101
0
0-
E
101
_2% Py r�te at 1 % 0xidatiur Rate —2% Pynte at 0-1% Oxidation R�tte
— 5% Pyrite at I % Oxidation Rate —5% Pyrite at 0-1% Oxidation Rate
_7% Pyrite at 1% Oxidation Rate —7% Pyrite at 0-1% Oxidation Rate
9 -- -- - - - - - - - - - - - - - - - - - - - - - A
20 30 40 K
Years from Completed Excavation
Figure 31. Unoxidized Hydrogen Ions Remaining from Excavated Pyritic Material
The volume of water 21 (expressed as acre-ft) necessary to dilute the hydrogen ions resulting
from the yearly oxidation of pyrite was calculated from the basic equation presented above.
Each percentage pyrite in the rock oxidized at either 0. 1 % or 1.0% diluted to a given pH
required different amounts of water (Figure 32). The volume of water required to dilute the acid
released from oxidized pyrite at 0. 1 % per year was similar regardless of percentage pyrite
content (hence, indistinguishable in Figure 32). For material with a pyrite content up to 7% and
an oxidation rate of 0. 1 % per year, an average of 37,880 acre-ft of water was necessary to
dilute the hydrogen ions to a pH of 7. This volume of water was 18% of the average annual flow
from the project. This percentage would decrease slightly with higher -than -average flows
through the project and, conversely, would increase slightly during low flow years.
At an assumed constant pyrite oxidation rate of 1% per year, the material with the highest pyrite
content required more water for dilution of the hydrogen ions (Figure 32). Even at those high
pyrite contents and with a high oxidation rate of 1 % per year, the annual average flow from the
project (vertical line in Figure 32) provided enough water to dilute the hydrogen ion to pH levels
greater than 6.3.
28 This calculation assumed no buffering capacity of the water-, even minimal buffering would reduce the volume of
water necessary to achieve a given pH.
48

Me
:M
��- 6. 0
91
C>
11
5.0
W
4.5
Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
--2% Pyrite at 1 % 0 x idation Rate
5% Pyrite at 1 % 0 x idation Rate
_7% Pyrite at 1 % Ox idat ion Rate
— Z o Pyrile at 0-1, Oo Ox i aai ion Rate
_5% Pyrite at 0- 1 % Ox idat ion Rate
_7% Pyrite at 0- 1 % Ox Idat ion Rate
102 101 104 10-. 101 101
Volume Water Required to Dilute H2SO4 to pH (acre-ft)
Figure 32. Volume of Water Required to Dilute the Oxidized Hydrogen to the Equivalents
at Various pH Levels
To put the volume of water required to dilute the hydrogen ions in perspective with hydro
operations, the number of days required to deliver the amount of water needed to dilute the
hydrogen ions from the various pyrite percentages and oxidation rates was calculated by
dividing the volume of water (Figure 32) by the average daily flows released from the projeCt29
(Figure 33). At an oxidation rate of 0. 1 % per year, only 66 days of average hydro operation was
necessary to discharge the equivalent volume of water to dilute the oxidation products to a pH
of 7. At an oxidation rate of 1 % per year and a pyrite content of 7%, a full year was required to
deliver enough water to dilute the hydrogen ions to a pH greater than 6.3.
29 The total East Fork Tuckasegee River flow was used, whether from Powerhouse generation or Principal Spillway
discharges.
49

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=11
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7:
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4,0
3.5
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Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
_2% Pyrite at 1 % Oxidation Rate — 2% Pyrite at 0- 1 % Oxidation Rate
. 5% Pyrite at 1 % Oxidation Rate _5% Pyrite at 0- 1 % Oxidation Rate
_7% Pyrite at 1 % Oxidation Rate _7% Pyrite at 0 1 % Oxidation Rate
HH� HM� HH� �
The number of days represented by the various
% pyrite and oxidation rates were based on the
—6nwdf
River -
at higher than average flows -the lines shift left
at lower than average flows -the lines shift right
1111111111
mill
1111111111111
10-1 10-1 10-1
10 101 101 101
Tme Required to Deliver Amount of Water to Dilute H2SO4 to PH (days)
Figure 33. Number of Days to Deliver a Volume of Water at the Baseline Average East
Fork Flow Required to Dilute the Oxidized Hydrogen to the Equivalents at Various pH
Levels
These calculations illustrate that even at extreme pyrite oxidation rates, the amount of water
flushed through the system will be more than adequate to dilute any acid originating from the
spoiled or exposed pyritic rock. However, acidification of the auxiliary spillway water may occur
due to the low flows (low flushing rate) as water percolates through the rock fissures and soil.
But, at such low flows, the higher East Fork flows would not be impacted by the extremely low
flows originating in the auxiliary spillway channel.
-M

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Summary
Water quality sampling sites were established in each of the Cedar Cliff Development's major
drainages, all of which showed no evidence of existing pyrite acidification. Cedar Cliff Reservoir,
the auxiliary spillway channel, the principal spillway channel, and the bypassed reach all
contributed water to the East Fork. Each site exhibited its own hydrology, which influenced not
only the concentration of water quality parameters within each drainage, but the volume -
weighted concentration of the water quality parameters accounted for the East Fork
concentrations.
Cedar Cliff Reservoir exhibited excellent water quality and supplied 99.9% of the water to the
East Fork, either via the deep -water penstock used for generation or releases from the Tainter
gate. The amount of water received from Bear Creek Reservoir, relative to the small storage of
Cedar Cliff Reservoir, resulted in high flushing rates through the reservoir. Even though
biochemical reactions had a major influence on water chemistry, the low productivity of the
system coupled with high flushing rates prevented the biochemical reactions from depleting the
dissolved oxygen, as is typical of many southeastern reservoirs.
The only poor water quality in Cedar Cliff Reservoir was observed during the summer/fall period
in the water below the penstock invert. This water was relatively unavailable for generation and,
consequently, exhibed anoxic water due to biochemical reactions depleting the oxygen.
Reduced compounds diffused from the sediments into this overlying water. Pyrite was not
present in this water or the sediments since no sulfur compounds were observed in sediment
samples. This anoxic water persisted until fall convective cooling mixed the reservoir, creating
uniform profiles of all water quality parameters.
The source of water in the auxiliary spillway channel was infiltration, percolation, seepage of
rainwater into the groundwater, and surface flows occurring during heavy rain (average flows
were less than 0.25 cfs). As this water percolated through the soil, complex reduction -oxidation
reactions such as aeration, precipitation, microbial communities, pore space, rates of organic
decomposition, and cation exchange capacity all influenced the ionic composition. The ionic
ratios suggested that pyrite oxidation had little, if any, influence on the water quality. Rather, the
grouting material used seal bore holes and rock fissures had a significant impact on the ionic
solution.
The relatively small amount of water from the auxiliary spillway channel, as well as other rain -
induced seepage, entered the primary spill channel and bypassed reach. Flows in the bypassed
reach were variable since the bypassed reach does not have a minimum flow requirement.
Higher flows were attributed to Tainter gate releases and/or from rainfall flushed the bypassed
reach. As the water receded, the pools drained slowly and were subject to significant
evaporation, only to be flushed again by the next high-water event. The water chemistry in the
bypassed reach was subjected to all of these varying physical events.
Since the East Fork received most of its flow from Powerhouse generation or Tainter gate flows
from the surface of the reservoir, the river's water chemistry resembled that from Cedar Cliff
Reservoir. The average flow of 6-7 cfs for the bypassed reach was estimated by calculating flow
from the flow -weighted ionic concentrations between the reservoir water, bypassed reach, and
the East Fork. At these bypassed reach flows, the bypassed reach water quality had a very
minuscule impact the East Fork water quality. Also, at these bypassed reach flow rates, a very
high rate of pyrite oxidation would have to occur to have any impact on the chemistry of the East
Fork.
51

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
All of the petrographic, water chemistry, and hydrological analyses support the conclusion that
the rates of pyrite oxidation have not impacted the water chemistry of any of the Cedar Cliff
drainages during the Phase I construction activities, nor is any significant impact expected from
pyrite oxidation originating from the Phase 11 construction activities, especially considering the
hydrological regime of the project.
52

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
References
American Public Health Association. 1998. Standard Methods for the Examination of Water and
Waste Water, 20th Edition. American Health Association. Washington, DC.
Carroll, D. 1962. Rainwater as a Chemical Agent of Geological Processes -A Review, Geochernistry
of Water, Geological Survey Water -Supply Paper, 1535, United States Government Printing
Office, Washington, DC.
Duke Energy Carolinas, LLC. 2018. East Fork Hydroelectric Project (FERC No. 2698) Cedar
Cliff Hydroelectric Development Auxiliary Spillway Upgrade Environmental Report and
Request for Approval for Temporary Variance from License Article 401 (Reservoir Level
Management) pp. E-3.
Garrells, R.M. and F.T. Mackenzie. 1971. Evolution of Sedimentary Rocks, Norton, New York, NY.
Graczyk, D.J., Dale M. Robertson, William J. Rose and Jeffrey J. Steuer. 2000. Comparison of
Water -Quality Samples Collected by Siphon Samplers and Automatic Samplers in
Wisconsin. U.S. Geological Survey, 8505 Research Way, Middleton, Wisconsin 53562.
Hach Company. 2005. Hydrolab DS5X, DS5, and MS5 Water Quality Multiprobes, User Manual,
Catalog Number 003078HY.
H DR. 2017. Geological and Geotechnical Subsurface Investigation, East Fork Hydroelectric Project
and Cedar Cliff Development (FERC No. 2698). Tuckasegee, North Carolina, Report for
Duke Energy of the Carolinas, LLC.
2018a. Cedar Cliff Rock Spoil Evaluation. East Fork Hydroelectric Project and Cedar Cliff
Development (FERC No. 2698) Tuckasegee, North Carolina.
2018 b. Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project Status
Update and Permitting Process. Power Point Presentation for Agency Briefing January 18,
2018.
Hutchinson, G.E. 1957. A Treatise on Limnology, Vol 1, Part 2— Chemistry of Lakes Pp. 1015. John
Wiley and Sons, Inc. New York, NY
Millar, C.E., L.M. Turk, and H.D. Foth. 1966. Fundamentals of Soil Science, Fourth Edition. John
Wiley and Sons, Inc. New York, NY.
Pugh, C.E., L.R. Hossner, and J.B. Dixon. 1984. Oxidation rate of iron sulfides as affected by
surface area, morphology, oxygen concentration, and autotrophic bacteria. Soil Science.
137:5, pp. 309-314.
Stumm, W. and J.J. Morgan. 1981. Aquatic Chemistry. John Wiley & Sons, Inc., New York, NY,
780p.
Thornton, K.W., B.L. Kimmel, and F.E. Payne. 1990. Reservoir Limnology: Ecological Perspectives,
John Wiley and Sons, Inc. New York, NY.
Wishon, John. 2002. Unpublished Seepage Report from Cedar Cliff. Duke Energy Corporation
53

Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Appendix A
Pre- and Post -Construction Photos and Water Quality Sampling
Sites of the Cedar Cliff Spillway Upgrade Project
Appendix A

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Cedar Cliff Hydroelectric Development Auxiliary Spillway Upgrade Project
Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results
Appendix B
Selection and Maintenance of ORP and pH Reference Electrode
pH and/or Oxidation- Reduction Potential (ORP) are potentiometric measurements where an
electrochemical signal is converted to a millivolt (mv) reading. The signal produced and
measured is a potential difference between the sensing and reference electrodes. Calibration of
a sensor is governed by the Nernst equation. Since the potentiometric signal produced is
electrochemical, the Nernst equation assumes good electrical conductivity between the sensor
and reference electrode. In most natural waters, and especially the buffers used to calibrate pH
or solutions used to calibrate ORP, electrical conductivity is not an issue since the ions
dissolved in solution provide ample electrical connection. However, in natural waters with very
low specific conductance, the low ionic concentration in those waters may inhibit the electrical
signal between the electrodes, yielding erroneous readings.
The reference electrode has a porous Teflon junction, which allows the reference electrode
solution to 'stream' into the sample, enhancing the electrical connection between the electrodes.
This is particularity important in low ionic strength waters. Since the Cedar Cliff Reservoir
typically exhibited conductivities less than 20 pSi, a reference electrode with a relatively large
porous junction (see below) was used for the Auxiliary Spillway Upgrade Project. In addition,
prior to each sampling trip, the porous junction was cleaned and the reference solution was
replaced with fresh saturated KCI solution. These steps maximized the performance of the
reference electrode to ensure accurate pH and ORP measurements.
iift I/
Appendix B