20160742 Ver 6_Monitoring Report_20230502

Cedar Cliff Hydroelectric Development
Auxiliary Spillway Upgrade Project -
Spillway Excavation,
Summary of Water Quality Monitoring Results.
Prepared for: Duke Energy Carolinas, LLC
Prepared by: Jon C. Knight, Ph.D. and Josh R. Quinn
May 2023

Introduction
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.
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). Based on the
boreholes drilled during the geological/geotechnical site investigation, it was estimated that
approximately 26% of the total excavated material (73,600 cubic yards) will be comprised of rock
lithologies containing 2% to 7% pyrite by volume (HDR 2017). Even though there are no known
instances of acid -drainage related to the to the site lithologies, rocks with greater than 1 % pyrite
and/or pyrrhotite by volume are considered to be potentially acid -producing. Even though HDR
(2017, 2018a, 2018b) has discussed the project in detail and has projected minimal, if any,
acidification impacts from pyrite oxidation. 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. Subsequently, NCDEQ issued Section 401 Water Quality Certifications
(#WQC004077), and the permit (SAW-2015-02543) issued by the USACE dated June 21, 2019
required Duke Energy to adhere to the water quality monitoring plan.
The summary of the water quality data collected during the 26-month baseline period' (July 2018—
September 2020) was reported by Knight and Quinn, (2021) and was submitted to NCDEQ as the
first annual (baseline) report. Water Quality sampling resumed in March 2021, just prior to rock
excavation, and continued through March 2023 while the rock was excavated and spoiled into the
lake.2 The required 2021 and 2022 annual reports were not submitted due to medical issues with
the primary author.
In 2023, Duke Energy submitted a modification request to the approved Clean Water Act (CWA)
Section 404 (Action ID 20215-02542) and Section 401 Individual Permit (DWR # 20160742 Ver 4)
for design changes related to the Cedar Cliff Auxiliary Spillway Upgrade Project. Since the NC
Division of Water Resources and the USACE will review the request, this summary report of the
water quality monitoring at Cedar Cliff will highlight the principal findings of the monitoring program
for agency review. A complete detailed report comparing the baseline data to the entire period of
rock excavation is planned after excavation is complete (expected mid-2023).
The Duke Energy monitoring plan was designed to evaluate the extent and influence of pyrite
oxidation on the pH in the waters of Cedar Cliff reservoir and the East Fork of the Tuckasegee River
down stream of Cedar Cliff Hydro. Pyrite can react in the presence of oxygen and water to form
ferrous sulfate and sulfuric acid (2FeS2 + 702 + 2H2O --+ 2FeSO4 + 2H2SO4). Further oxidation of
ferrous iron would produce ferric hydroxides and/or ferric carbonates. The stoichiometry of
complete oxidation of one mole of pyrite would produce two equivalents of hydrogen ions.
Most natural freshwaters are buffered by the bicarbonate -carbonate system, the following equation
is applicable:
' When referenced in this report, the 'baseline' period refers to the time period of July 2018 through September 2020.
2 The final rock placement in the lake was on April 14, 2023.

Where:
1 _ [H+] [HCO3 1]
K1 _[CO2]
Ki' = First equilibrium constant as a function of temperature
H" = Hydrogen ion concentration (moles/L) (10-p")
HCO3-' = Bicarbonate concentration (moles/L)
CO2 = Carbon Dioxide concentration (moles/L)
Bicarbonate concentrations usually result from the weathering and subsequent dissolution of parent
rock material within the watershed. The pH is a function of the ratio of carbon dioxide to bicarbonate
concentrations, the relative rates of biological respiration or photosynthetic rates determine the
carbon dioxide concentrations.
Other minor acid -base reactions may occur as water percolates through the soil or rock formations.
Chemical precipitation and/or chemical adsorption onto clays also influence pH. Therefore, the
purpose of the monitoring plan is to identify the various processes controlling the pH in the project
waters, in particular pyrite oxidation influencing pH.
Site Description and Phase II 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. 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 (Figure 1). Knight and Quinn
(2021) describe in detail the Phase I construction activity of the Auxiliary Spill Channel Upgrade
project.
In the first quarter of 2021, Phase I activities were completed and the commencement of Phase II
spillway excavation began. Auxiliary spillway excavation and spoiling of rock was originally planned
to span less than 12 months. Initially, a test blast program involved small excavations of the
auxiliary spillway rock wall as well as trials to spoil the excavated material into Cedar Cliff
Reservoir. The preliminary barging and subsequent dumping of excavated material in the reservoir
revealed increased turbidity in the East Fork turbine flow. In an attempt to maintain turbidity levels
below the NC state turbidity standard of 10 NTU for trout waters, barging rates, spoil placement,
and hydro operations were varied and compared to the observed tailrace and reservoir turbidity
levels.
These trials led to the use of a tracked mobile screen to minimize the fine material deposited in the
reservoir. It was used to separate the excavated material into rocks larger than 6 inches, material
less than 6 inches but greater than 1'/2 inches, and material less than 1'/2 inches. After blasting the
rock from the auxiliary spillway `wall', large rocks were reduced to manageable size, put into the
mobile screen, and separated into the 3 size fractions. Sizes greater than 1'/2 inches were loaded
into barges and spoiled in Cedar Cliff reservoir. Material less than 1'/2 inches was temporally stored
in the auxiliary spill channel until loaded into trucks and removed from the site to an authorized spoil
site. As a routine, the area of rock excavation and temporary rock storage was sprayed with water
to control dust.

Figure 1. Cedar Cliff Development Site Features and Water Quality Sampling Locations
Additional plans to reduce turbidity levels downstream of Cedar Cliff hydro, approved by NCDWR
and the USACE, included:
• An underwater weir constructed at the downstream end of the 8.5-acre rock spoil
footprint. The weir and spoil repository footprint was located further upstream in the
reservoir than the originally planned in 2019. This change was proposed to help
reduce turbidity levels in the downstream tailrace.
• The weir and turbidity curtains assisted in mitigating sediment and turbidity levels
downstream of the spoil repository footprint.
• The design of the 1951 Access Road was revised to reduce the volume of material
excavated as well as placement of the rip rap (rock) material on shore while the lake
was drawn down. These plans eliminated the need to drop the material through the
water column, also reducing turbidity.
The permitted rock spoil area was divided into grids. Each barge was equipped with GPS and depth
transducers to accurately place the spoiled rock in the reservoir; ultimately creating the submerged
weir with an elevation of 2250 ft-msl. Beginning In 2021, rock was spoiled at the most downstream
portion of weir, slowly building the slopes of the weir from the channel depth of 2210 ft-msl to the
top of the weir at 2250 ft-msl (Figure 2).
4

c 1Pm zan rr -,o .,. pb Pare se TYIetl INtl, Cedar Cliff Iiii etry Lake toUM
10-Foot Luke
are
kmemne.ani
Figure 2. Cedar Cliff Reservoir Features and Water Quality Sampling Locations
—Rock Placed in the Lake —Truck Loads of Fines Deposited Off -Site —Truck Loads of Mixed Size Placed On -Site
180000
160000
u 120000
to
VI
a 100000
m
O
m 00000
at
m
� 6000D
a,
m
40000
u
LI
W
20000
Lake Placement Trials Began 14 Mav 2021
Production Placement Began 21 June 2021
Production Placement Ended 14 April 2023
Q I I I
M J J A 5 0 0 N D J F M A M J J A 5 0 N D J
2020 2021
F M A
2023
Figure 3. Record of Excavated Material (Rock Spoil into the Lake and Fine Material Removed
from the Site, May 14, 2021 — Mar 31, 2023).
With the exception of a few trial barge dumps during the "experimental period", active spoiling of the
excavated rock began on May 14t", 2021. Trucking the fines off -site began about a week later. The
average daily barging rate was 263 cubic yards per day (yd3 /day), but ranged from 0 to 972
yd3/day. Trucking rates were equally variable with an average of 199 yd3/day, and ranged from 0 to
885 yd3/day. Both material disposal rates were a function of rainfall, crew availability and excavation
rates. Barging rates were also impacted by hydro operations.
5

Water Quality Sites and Sampling Methodology
The water quality sampling sites, or Environmental Monitoring Points (EMPs) were the same as
described in the baseline report. (Knight and Quinn, 2021). Those sites (Figures 1 and 2) were
chosen to represent the various hydrology, construction activities, and excavated material storage
or spoiling areas. A summary of those monitoring sites is presented in Table 1.
Table 1. Water Quality Monitoring Sites for the Cedar Cliff Auxiliary Spillway Upgrade
Auxiliary Spillway Upgrade Project Monitoring Sites
Description
Symbol
Latitude (°)
Longitude (°)
water Sample
SamplingartofDeploymentLogger
Cedar Cliff Lake - Forebay
EMP 4
35.25486
-83.09882
16-Jul-18
N/A
Hydrolab
Van Dorn
Cedar Cliff Lake - Upstream of Construction
EMP 7
35.25030
-83.09201
16-Jul-18
N/A
Hydrolab
Van Dorn
Aupliary Spillway Sampling Site
Conductivity
Hydrolab
(flows into Upper Sediment Basin)
EMP 3
35.25233
-83.09914
28-Aug-18
Water Level
Grab Sample
Single Stage
Upper Sediment Basin Sampling Site
Conductivity
Hydrolab
(flows into upper Bypassed Reach)
EMP 5
35.25250
-83.09931
28-Apr-20
Water Level
Grab Sample
Single Stage
Conductivity
Hydrolab
Upper Bypassed Reach Sampling Site
EMP 6
35.25212
-83.09951
14-Jul-20
Water Level
Grab Sample
Single Stage
Conductivity
Hydrolab
Lower Bypassed Reach Sampling Site
EMP 2
35.25295
-83.10299
28-Aug-18
Water Level
Grab Sample
Single Stage
Minimum Flow Unit Discharge
EMP 1
35.25344
-83.10274
28-Aug-18
Conductivity'
Hydrolab
Grab Sample
Modified Rain Gage
Rain
35.25344
-83.10274
24-Mar-21
N/A
Hydrolab
Grab Sample
East Fork Upstream of West Fork Confluence
EMP 8
35.26893
-83.11633
28-Aug-18
N/A
Hydrolab
Grab Sample
Conductivity Logger Placed at Minimum Flow Gage

Field Instrument Calibration
Prior to each sampling, the Hydrolab data sonde was laboratory calibrated 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 Methodology4
Parameter
Units
Method
Calibration Method
Manufacturer's
S ecified Accurac
Depth
m
Pressure
In -field immersion
±0.05 m
Temperature
°C
Thermistor
Checked with NIST
± 0.10 °C
tracable thermometer
Dissolved Oxygen
mg/L
Luminescence
Barometric pressure of
± 0.01 mg/L
air saturated water
Specific Conductance
psi
Electrical bridge
Calibrate to 75 pSi
± 1% of reading
checked with 25 psi
Calibrate to 100 NTU
Turbidity
NTU
Nephelometric
checked with 10 NTU
± 5% of reading
ORP
my
Platinum
Calibrate with Zorbell's Solution
± 20 my
electrochemical
corrected for temperature
pH glass
Calibrate to 7.00 pH
pH
units
electrochemical
± 0.2 units
Calibrate to 4.00 pH
Reference electrode
n/a
Saturated KCI
Shared with ORP and pH
(see Appendix B,
Baseline Report)
3 The instrument was allowed to achieve thermal equilibrium in the lab prior to calibration.
4 Hach Company 2005.

Chemical Analysis of Water Samples
Upon collection of a water sample, it 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 until delivery to the laboratory. All sample
analyses (Table 3) were performed within the recommended holding times.
Table 3. Monthly Laboratory Analysis of Cedar Cliff Auxiliary Spillway Upgrade Water
Samples
Ionic
Chemical
Type of
Bottle Type
Summary of
Analytical
Parameter
Category
Symbol
Sample
Preservative
Analysis
Method
Alkalinity
i 2
HCO3- CO3-
Whole water
PET
Titration (0.025N HCl),
SM 23206
Ice
Fixed end -point
Alkalinity
HCO3' CO3.2
Whole water
PET
Titration 0. 01036 N HCISM
23206
Ice
Complete Titration
Cn
.0
Choride
Cr'
Whole water
PCe
Ion chromatography
EPA 300.0
Q
Sulfate
SO,-
Whole water
PCe
Ion chromatography
EPA 300.0
Nitrate
NO,-'
Field filtered
Colorimetric
EPA 353.2
SuIHDPE
ric
Calcium
Whole water
HDPE
ICP
Ca"
EPA 200.7
Dissloved Ca
Field filtered
Nitric Acid
total recoverable
Magnesium
Whole water
HDPE
ICP
M g 2
EPA 200.7
Dissloved Mg
Field filtered
Nitric Acid
total recoverable
Sodium
Whole water
HDPE
ICP
Na
EPA 200.7
Dissloved Na
Field filtered
Nitric Acid
total recoverable
Potassium
Whole water
HDPE
ICP
N
K j
EPA 200.7
Dissloved K
Field filtered
o
Nitric Acid
total recoverable
U
Aluminum
Whole water
HDPE
ICP
AI 3
EPA 200.7
Dissloved AI
Field filtered
Nitric Acid
total recoverable
Manganese
Whole water
HDPE
ICP -mass spec
Mn"
EPA 200.7
Dissloved Mn
Field filtered
Nitric Acid
total recoverable
Iron
3
Whole water
HDPE
ICP -mass spec
Fe
Nitric Acid
total recoverable
EPA 200.8
Dissolved Iron
Field filtered
Reduced Iron
Fe+2
Whole water
60 ml BOD
Colorimetric
SM 3500 Fe B
water sealed
Note: PET = Polyethylene terephthalate; HDPE = High -density polyethylene; BOD = Biological Oxygen Demand;
ICP = Inductively Coupled Plasma; EPA = U.S. Environmental Protection Agency; SM = Standard Methods. Colored cells
represent samples added in 2021 compared to the baseline period.
In the 2020 Baseline Report, rain chemistry was estimated from the literature and rainwater was
assumed to contribute to lower pH values and to the dissolution of local substrates. Beginning in
2022, rainwater was collected in a modified rain gage between sampling dates. Since the modified
rain gage only held 1.25 liters, not all samples had enough water volume to analyze all parameters.
The priority of analytes for the rainwater samples were alkalinity, Hydrolab parameters, anions, and
cations.
As suggested in the Baseline Report, commencing in 2021 additional parameters or procedures
were performed to address the chemical imbalance of the cation -anion totals.

First, was the additional analysis of alkalinity utilizing the measurement of a titration curve with an
acid of = 20% lower concentration than during the baseline period (see Table 3). Beginning in 2021,
alkalinity was calculated from the inflection point of the titration curve, rather than a fixed end point.
In 2022, an acidity titration (APHA, 1998, SM-4500-CO2 C) was performed on each sample to
measure the amount of base (NaOH) required to neutralize the sample as well as the measurement
Of CO2, to a pH of 8.3 standard units.
Second, again beginning in 2021, the routine cation measurements in the baseline period were
performed on whole water samples, yielding a total elemental concentration. The calculation of the
anion -cation balance assumed the parameters were dissolved. Since the baseline period, the cation
samples were filtered yielding a more direct measurement of dissolved cations (see Table 3).
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; pyrite may have formed in the water column or sediments if sufficient
chemical reduction of iron and sulfur (sulfate--).sulfite--+sulfide) had occurred, enabling FeS to form
and precipitate, or the spoiling of material excavated from the auxiliary spill channel.
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 100°C, 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.
The SEM analysis on all sediment samples revealed trace amounts of iron and no sulfur, indicating
no pyrite (or extremely small amounts) present in the lake sediments. The sediment samples were
composed of extremely fine grained material with 16.8% organic content. 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.
SEM spectra analysis 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 (< pm). 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.1966). 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.
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.
Hvdroloaical Data
Duke Energy Regulated Renewables Operations Center (RROC) provided the following operations
data from the 2018-2023 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)5
• Cedar Cliff Primary Spillway Flow (cfs)6
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?
5 During normal operations, the lake levels were managed to achieve target lake levels of 95-96 ft local datum, the lake
level is greater than the 75 foot level, as the tainter gate opens, water flows under the tainter gate. Based on the gate
opening and lake elevation, the original engineering calculations provided the flow into the principal spill channel. The
water released (cfs) into the principal spill channel was calculated and recorded in the RROC PI data base.
6 Beginning in September, 2020, the lake levels were lowered to accommodate tainter gate maintenance and to
accommodate baring activities. From this date through 2023, lake levels were managed to achieve levels of 60-70 ft local
datum. During this time, the tainter gate was fully open and, if lake levels rose above the tainter gate sill (75 ft ;local
datum), reservoir surface water entered the principal spillway as an open flow channel over the tainter gate sill. Water
height over the Tainter Gate sill was determined by subtracting 75 ft from the PI reported reservoir level. Flows were then
calculated for this report from a rating curve provided by HDR, When the reservoir level was less than 75 ft DE level, no
reservoir water entered the principal spillway
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.
10

Cedar Cliff Site Hydrology
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
• Water Sprayed for Dust Control of Excavation Site
3. Principal Spillway Channel and Bypassed Reach
• Reservoir surface water via the Tainter Gate channel
• Tributary, Overland Runoff, and Groundwater
• Seepage from Sediment Basin, via the Auxiliary Spillway Channel
• 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 (including tainter gate channel releases)
• 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 rate of the formation of the of oxidation products, but also the volume of water
the reactions occur. Mathematically, the volume -weighted concentration of the water quality
parameters in all contributing flows accounts for downstream concentrations.
Cedar Cliff Reservoir and East Fork of the Tuckasegee River
In 2018, Cedar Cliff reservoir was managed to achieve a target lake level of 95-96 ft local datum
while Bear Creek was drawndown for maintenance and construction. Prior to the auxiliary spillway
construction, both Cedar Cliff and Bear Creek lake levels were managed to achieve normal
seasonal target levels. However, during the auxiliary spillway construction project the reservoir level
was being managed between 60 and 70 ft local datum to accommodate barging the spoiled rock.
To manage these lower lake levels relied solely on the generators. When significant rainfall and/or
increased releases from Bear Creek caused Cedar Cliff reservoir levels to rise above the 75 ft level,
water would flow down the principal spillway as an open channel flow (Figures 4 and 5).
On August 16 and 17, 2021, the Tuckasegee River received significant rainfall from Tropical Storm
Fred, causing Cedar Cliff Hydro Unit 1 to trip due to water backing up into the powerhouse and
flooding the unit. The Unit was returned to service September 8. During that time the East Fork only
received water via the principal spillway. Also, after that forced outage, Unit 1 was de -rated to 4 MW
due to lower lake levels. The de -rating was reflected in lower discharges from Unit 1 after
September 8, 2021. The de -rating will continue throughout the auxiliary spillway project.
11

As expected, the volume of water in Cedar Cliff reservoir paralleled the lake level (Figure 6). The
volume of water released through the hydro station varied reflecting the lake management strategy
to maintain the lake level between 60 and 70 ft (local datum).
Weekly average water retention times were calculated by dividing the average weekly reservoir
storage by the average weekly volume of water released from the reservoir (Figure 6). The longer
the time water is retained in the reservoir, the greater effect biochemical reactions have on the
observed water quality in the water column.
Principal Spillway Channel and Bypassed Reach Water Levels
The level loggers were placed in small depressions in the channel, which enabled continuous
recording of water level and were used to measure the intermittent water rise over the level logger,
indicating the timing of increased flows (Figures 7 and 9). 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. The average bypassed reach flows without spill from the
reservoir were estimated to be 7-8 cfs8 in the baseline report (Knight and Quinn, 2021). Almost
negligible flows entered the East Fork of the Tuckasegee River from the Bypassed Reach
compared to flows recorded at the minimum flow gage, located immediately downstream of Cedar
Cliff Hydro.
Typically, the higher flows in the Bypassed Reach originated from the spill into the principal spillway
and, to a much lesser extent, from rainfall. These higher flows, especially from the main spill
channel, flushed the Bypassed Reach. As flows decreased and water receded, the pools drained
slowly through the check dams providing flows into the lower Bypassed Reach. All pools were
subject to significant evaporation until the next high-water event.
The high water spilling into the primary spill channel through the tainter gate opening periodically
destroyed the single stage samplers and the level logger located in the lower Bypassed Reach
(EMP 2). If destroyed, each logger and the single stage sampler were replaced on each return
sampling trip.
Auxiliary Spillway Channel and Sediment Basin Water Levels
The auxiliary spill channel and the sediment basin were at a higher elevation than the primary spill
channel and therefore were not impacted by the highwater levels spilling from the lake. Periodic
high water in the Principal Spillway and/or construction activities prevented crossing the Bypassed
Reach to sample the auxiliary spillway channel and sediment basin.
Rainfall, and subsequent groundwater seepage, and as excavation progressed, water sprayed on
the excavated material to control dust were the major sources of water into the auxiliary spill
channel (Figure 7). As designed, this water flowed into the constructed sediment basin. The rapid
rise of water and subsequent rapid decline of water in both the auxiliary spill channel and the
sediment basin illustrated the permeability of both channel substrates. After excavation began,
rarely was surface water collected from either site; only periodic samples from the single stage
samplers were available for chemical analysis, 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 9). The basin rapidly lost water as it filtered and drained through the sediment basin
dam into the Bypassed Reach at the EMP 6 site. Only water samples retained in the single stage
samplers were collected for analysis.
s The Bypassed Reach flow was calculated using a flow -weighted conductivity from the bypassed reach and the East
Fork
12

Cedar Cliff Reservoir
■ Sampling Dates — — —Tainter Gate Sill Level — — —Full Pond Lake Level Generation Flow Tainter Gate Spill Flo}r5,
100
90
80
L<J 70
60
a�
D 50
J
40
J 30
20
10
0
3510
3DDD
Z5ff[3
_-L8
c�
LL
lvvv
5�..
J A 5 0 N Q J F M A M J J A 5 0 N d J F M A M J J A 5 0 N d J F M A M J J A 5 0 0 N d J F M A M J J A 5 0 N d J F r.1
2018 2019 2020 2021 2022 2023
Figure 4. Cedar Cliff Lake Level and Outflows
Bear Creek Reservoir
Lake Level — — —Full Pond Bear CreekTotal Outflow
100
90
80
U1 TO
G0
a�
� 50
J
aD 40
_J 30
20
10
0
3500
3000
2500
2000
1500 2
LL
1000
500
0
J A S O N Q J F M A M J J A S 0 N D J F M A M J J A 5 4 N 6 J F M A M J J A S 0 4 N D J F M A M J J A S O N C J F M
2018 2019 2020 2021 2022 2023
Figure 5. Bear Creek Lake Level and Outflow
13

100
� 90
rl
80
70
Q 60
50
40
30
J 20
10
0
Cedar Cliff Reservoir
• Sampling Dates Percent Lake Volume Average WeeWy Retention Time
250 >,
as
MOE
F-
c
0
150
as
'D
ioa-2
ID
50 a�
as
as
4
_ C rd = r_i _ r_i _ _ _ S C rJ C J F r.1 = NI J J _ C N C J F M= ra J, P 5 C C rd v J F r'+1 = r.l J J .` C rj C J F rv1
2018 2019 2020 2021 2022 2023
Figure 6. Percent of Cedar Cliff Reservoir Volume and Weekly Average Reservoir Water Retention Time
14

10
9
7
as 6
J 5
aJ 4
3
2
1
Q
Cedar Cliff
A Sample Dates Auxilary Spill Channel Water Level —Lower Bypass Water Level East Fork Water Level -Daily Rainfall
5.00 n
c
2.00 0�
1-00 t4
0.00
1-ao
-2 -00
-3 -00
-4-00
-5.00
J ` 0 N D J F N1 A M J J A S U N D J F M A het J J A S 0 N D J F M A M J J A 5 0 0 N D J F M A M J J A S C N D J F M
2018 2019 2020 2021 2022 2023
Figure 7. Rainfall Compared to Water Levels in the Auxiliary Spill Channel, Lower Bypass, and East Fork Downstream of the Hydro.
Cedar Cliff
Auxiliary Spill Channel CondtictIVIN' Lower Bypass Conductivity East Fork Conductivity
1000 +
•
•
100 * i 0 • 0 •r r • • •
* • • 0
10 -. r
1 --
J A S O N D J F M A M J J A S O N D J F M A M J J A S 0 N D J F M A M J J A S 0 4 N D J F M A M J J A S 0 N D J F M
2018 2019 2020 2021 2022 2023
Figure 8. Conductivity of the Auxiliary Spill Channel, Lower Bypass, and East Fork Downstream of the Hydro (Circles Represent Conductivity
Values Collected at the Time Water Samples Were Collected)
15

w
J
W
10
9
7
6
5
A
3
2
1
0
Cedar Cliff
Auxilary Spill Channel Water Level Sediment Basin Water Level — East Fork Water Level daily Rainfall
J A S 0 N❑ J F M A Art J J A S 0 N❑ J F M A M J J A S 0 N Q J F M A M J J A 5 0 0 N❑ J F M A h•1 J J A 5 0 N❑ J= PO
2018 2019 2020 2021 2022 2023
Figure 9. Rainfall Compared to Water Levels in the Auxiliary Spill Channel, Sediment Basin, and East Fork Downstream of the Hydro.
10000
-_ 10 00
v]
21
.> 100
3
CJ
10
Cedar Cliff
Auxilary Spill Channel Conductivity Sediment Basin Conductivity Upper Bypass Conductivity East Fork Conductivity
p OOp O D 0 0C.
1
J= S C N o J
2018
I
_. MI � 141 11 . �. I F M A M J J A 5 0 N 6 J F M A Art J J A S O N❑ J F M zi. p.1 ; J A S 0 0 N❑ J F M A M J J A S 0 N D J F M
2019 2020 2021 2022 2023
Figure 10. Conductivity Measured in the Auxiliary Spill Channel, Sediment Basin, and East Fork Downstream of the Hydro (Circles Represent
Conductivity Values Collected at the Time Water Samples Were Collected)
16

Conductivity of the Auxiliary Spillway Channel, Sediment Basin, Bypassed Channel, and
the East Fork East Fork Tuckasegee River
The conductivities (an indirect measure of dissolved solids) measured in the East Fork at the
minimum flow gage were similar throughout the entire monitoring period. (Figures 8 and 10)
indicating little change in the total dissolved solids, both in the lake and the East Fork. The
conductivities measured in all of the Bypassed Reach channels were substantially higher than
the East Fork, especially after excavation of the auxiliary spillway began. These data indicated
little, if any, influence from the spill channels on the East Fork chemistry.
The sporadic readings from the conductivity loggers (Figure 10) usually resulted from the
conductivity loggers being on the surface and not well submerged. However, the conductivity
loggers were prone to failure preventing a complete data set.
The conductivity from the auxiliary spill water was substantially higher than from any other site.
The higher conductivities in the auxiliary spill channel likely resulted from seepage flows through
the rock and soil substrate. The dissolved solids in the auxiliary spill channel increased
substantially after the fine material separated from the excavated material was temporarily
stockpiled in the auxiliary spill channel. The water sprayed for dust control in the auxiliary
spillway likely added to the increased conductivity.
Also, 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. Periodic rain events, and especially spills from the lake through
the primary spillway, temporally diluted the sediment basin dissolved solids in the Bypassed
Reach. The dilution and/or precipitation of dissolved compounds continued through the bypass
reach (Figure 11). Low flows and reduced dissolved solids in the bypass reach had little, if any,
impact on the East Fork conductivities, as evidenced by the similarity of East Fork values to
those measured from the reservoir (Figure 11).
■Baseline Period ■Excavation Period
1000
100
10
Figure 11. Median Conductivities Calculated During the Baseline and Excavation Periods,
Measured at All Sampling Sites.)
17

Turbidity of the Auxiliary Spillway Channel, Sediment Basin, Bypassed Channel, and the
East Fork East Fork Tuckasegee River
The turbidities of the bypassed reach and East Fork rarely exceeded the state water quality
standard of 10 NTU. More excursions of 10 NTU occurred prior to rock excavation (Figure 12).
Higher turbidities generally resulted from higher flows associated with tainter gate releases
which suspended material from the river bed. This material rapidly settled out of the water when
flows subsided.
Cedar Cliff
♦ Upper Bypass ♦
Lower Bypass
East Fork at Hydro
• East Fork above Confluence — — —State N!Q Standard
20
18
Excavation Period
16
■
14
•
•
12
•
,a10
—————————————
————————
————————————
———————————————————————— — — — —_.
8
■
■
-2
J A S O N❑ J F M A M J J A S O N❑ J F M A M J J A S O N❑ J F
M A r.1 A 5 Q Q N❑ J F M A M J J A S Q N❑ J F M
2018 2019
2020
21i21 2022 2023
Figure 12. Turbidity Measured in the Upper and Lower Spill Channel, and both East Fork Sites
Down Stream of the Hydro
IN

Water Quality - Cedar Cliff Reservoir In Situ Measurements
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 13) driven by the seasonal meteorological conditions (air
ter
2018 2019 2020 2021 2022 2023
Figure 13. Cedar Cliff Reservoir Water Column Temperatures, 2018 - 2023
The reservoir did not develop a classical epilimnion or hypolimnion separated by a thermocline
with strong horizontal thermal gradients. Rather, weak vertical thermal gradients developed,
indicating that the deep- water removal via the penstock removed the cooler bottom water as it
was replaced by warmer water originating near the surface. Hence, the development of the
vertical thermal gradients followed the rate of the Cedar Cliff hydro generation flows.
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)9 exhibited characteristics similar to a traditional hypolimnion with vertical
exchange of heat and compounds limited by diffusion and low turbulence.
Dissolved Oxygen and Carbon Dioxide
The water column dissolved oxygen (DO) concentrations followed the pattern established by the
temperature distribution; namely, DO decreased as the water column temperatures increased
(Figure 14). The most consistent pattern of DO loss was in the water below the invert of the
hydro penstock. Water below this level had reduced vertical mixing and was not removed or
replaced until fall cooling was sufficient to mix that water. Until that water was mixed, either
9 Calculated from the invert elevation and the storage curve presented in Figure 5, Knight and Quinn, 2020..
19

aerobic or anaerobic respiration continued until the DO was completely depleted in that deep
water.
Even with periodic high retention times (Figure 6), primary production appeared to be limited
since summer oxygen concentrations in the water column decreased rather than exhibiting high
oxygen in the upper, euphotic zone. Below the surface of Cedar Cliff Reservoir, the DO
decreased due to warmer temperatures, coupled with 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 warmer water along with the associated lower DO
concentrations. With the initiation of fall cooling and subsequent mixing, DO increased as
temperatures decreased and atmospheric oxygen exchange progressed.
1 ii1f1-
l l'3f1
2280
W 2270 -
-y 22so -
C
4
� 2259 -
n
a
:Li 22an-
2230 -
2220 -
2210-
2209 -
%1'3I1 -
2018 2019 2020 2021 2022 2023
Figure 14. Cedar Cliff Reservoir Water Column Dissolved Oxygen, 2018 - 2023
2330 _ y
2320 ' 7
10 a
2]10 0.
2300 .r ►�+1[y.11J �a
2290
2280 �db � c
• Ou
n, 2270 � � �•44
2250 N v[yjjY•
1!J 2240
220 h. 1:0
2220 I II
2210
2200 hC L e t �. III �
2018 2019 2020 2021 2022
Figure 15. Cedar Cliff Reservoir Water Column Carbon Dioxide, 2018 - 2023
The water column carbon dioxide values (Figure 15) throughout the entire sampling period
exhibited lower values deeper in the water column during the summer/fall season. The highest
CO2 values were observed in the surface waters during the spring/summer months as a result of
the limited photosynthetic activity.
:I
2023
C

According to Hutchinson (1975), most natural freshwaters are buffered by the bicarbonate -
carbonate system; whereas pH is controlled by the ratio of CO2 to bicarbonate. Since the
reservoir pH values ranged from 5.69 to 8.45 units (Figure 16), there is no evidence of strong
acids influenced the pH rather biological respiration (production of CO2) dominated the buffering
system.
Additionally, if CO2 was produced from autochthonous production, DO and CO2 concentrations
would show opposite concentration trends. The timing of high CO2 generally precedes that of
lower DO indicating an organic source other than algae produced in the reservoir. The timing of
high CO2 generally follows higher releases of water from Bear Creek indicating the organic
substrates originate from Bear Creek reservoir.
Mir
233C
232c ,Y . pH
23tC • • m ill i • :
i
229C � � • • • • w • • • . •
225C • • • •pi• • i i • • i
.--. 227C • • • : :� �
225C • : . � � : • • F -
fb
- -
223C
: E{
2200: rn. ; ; •
2018 2019 2020 2021 2022 2023
Figure 16. Cedar Cliff Reservoir Water Column Carbon Dioxide, 2018 - 2023
Conductivity and Turbidity
Conductivity values were generally less than 20pSi, indicating waters of very low ionic
concentrations (Figure 17). However, conductivity values were significantly higher in the water
below the penstock invert. 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.
233L
2s�r. Conductivity
231C
MU • -
• • • : : :'
229C � • • � � • � � � �
228L : • : � � • �
i � 226L • • -
225C
661 W 224L i ; • • • • • i
223C ..
222L • • • • • • • � • •
225C
220C vq,�,: • = E • : : i • • • • i
2190 �1lJl.�1771� • : ' . !� • _ • • =!'� • - 2Q-L .
2018 2019 2020 2021 2022 2023
Figure 17. Cedar Cliff Reservoir Water Column Conductivity, 2018 - 2023
a

235�
2320 - - : Turbidity
2300
2290 � • : :
2280 : e
2270 • • • : • • '
i
2260
22so : .
u, 22ao ; � • • • :
• • i '
2230 . •
2220 • ■ • �
• • • : : ::
22to
2-110
2018 2019 2020 2021 2022 2023
Figure 18. Cedar Cliff Reservoir Water Column Turbidity, 2018 - 2023
Cedar Cliff Reservoir had very low turbidity levels, only exceeding the state standard for trout
waters of 10 NTU (Figure 18) in 2018 (i.e., before spoil placement began). These higher
turbidity values originated from water released from Bear Creek Reservoir during the extensive
drawdown and maintenance of Bear Creek.
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.
Very little water quality differences were observed between the two sites. 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.
22

Rock Experiment
In October 2022, a random selection of unwashed rocks greater than 1'/2 inches were placed in
a 5-gallon bucket. Another bucket was filled with 10 liters of lake water. A calibrated Hydrolab
data sonde was placed in the lake water and set to record pH and conductivity every 5 seconds.
At approximately 2-3-minute intervals, a pre -weighed rock was placed in the lake water and
agitated to dislodge the rock dust into suspension. A total of 3 kg of rock was added to the 10
liters of lake water. The 3 kg of rock, dislodged 26,000 mg of material (2,600 mg/L suspended
solids).
55
6-4
U-3
6-2
CL
6-1
£7
5-9
�. H Conductivity —Suspended Solids
Cl 5 10 15 20 25 30 35 40
Elapsed Time (min)
45
3506
35
3000
30
J
131
230D
25
{fi
3
p
2i30G (�7
20
wr
m
75G0
a
-
�
1060
m
10
o
0
540 ~
5
J-0
O
50
Figure 19. Conductivity and pH Compared to Suspended Solids from Rock Samples Greater
than 1'/2 inches
The pH and conductivity exhibited little change from the rock dust until the suspended solids
reached a concentration of over 100 mg/L (Figure 19). Even at this concentration of solids,
which far exceeded Total Suspended Solids (TSS) concentration in the lake, showed minimum
change in pH and conductivity. With the addition of more solids the pH increased slightly until a
concentration of 1,500 mg/L TSS, at which point the pH decreased until the original pH of 6.1
standard units was reached at a TSS level of 2,600 mg/L.
SEM analysis of the suspended solids again showed trace amounts of iron and no sulfur but
rather showed the dominance of aluminum -silicate clays.
This experiment illustrated that the rock dust originating from spoiled material into the Cedar
Cliff Reservoir had little, if any, impact on the pH and conductivity in the lake. Trace amounts of
iron and no detectable sulfur compounds were in the rock dust. The rock dust temporarily
contributes clays to the water column and added to the existing lake sediment.
23

Chemical Characterization of Cedar Cliff Sites
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 ionic composition in the reservoir
and East Fork were very similar for both the baseline period and the excavation period (as the
rock experiment suggested). The most notable difference was the lower HCO3' concentrations
since the methodology was changed to yield a lower detection limit during the excavation period
(Figures 20 and 21).
The chemistry of the auxiliary spill channel during the baseline period could be classified as a
calcium -sodium: bicarbonate sulfate system. However, during the excavation period the water
changed to a primarily a sodium: sulfate system. The temporary storage and subsequent
leaching of the fine material temporarily stored in the auxiliary spill channel transported the
dissolved compounds, primarily sodium and sulfate, to the surface and into the sediment basin.
The sodium and sulfate dissolution and/or ion exchange were indicative of the chemical
composition of the parent rock. Even though sulfate was the dominant anion, only trace
amounts of iron were detected indicating very little, if any, pyrite oxidation occurred in the fine,
excavated material. No ferrous iron was detected in any of the samples collected during the
excavation period; again, indicating a minimal potential for pyrite oxidation.
Both sodium and chloride decreased throughout the bypassed reach, and since both ions are
extremely soluble (Stumm and Morgan, 1981) with no interaction with other compounds, the
decreased sodium and chloride concentrations were diluted with inflowing accretion water
throughout the Bypassed Reach.
24

Table 4. Analytical Results (Median Concentrations) from all Samples Collected from the Cedar Cliff Samplinq Sites
Median Concentration
Anions
Median
Concentration
Cations
Baseline
HCO3
Cir,
2
SO4
NO3"
TOTAL
Na
j
K
+2
Ca
.z
Mg
.3
Mn
.3
Fe
.z
Fe
A+ 3
TOTAL
Location
(2018 - 2020)
Excavation
Anions
Cations
(2021 - 2023)
(meq/L)
(meq/L)
(meq/L)
(meq/L)
(meq/L)
(meq/L)
(meq/L)
(meq/L)
(meq/L)
(meq/L)
(meq/L)
(meq/L)
(meq/L)
(meq/L)
2018-2020
0.100
0.030
0.690
0.009
0.828
0.089
0.087
0.411
0.122
0.0121
0.00035
0.00000
0.084
0.806
Auxiliary Spill Channel
EMP 3
2021 - 2023
0.079
0.056
5.855
0.052
6.095
1.096
0.609
3.857
0.593
0.090
0.002
0.000
0.024
6.696
2018-2020
0.100
0.023
0.386
0.001
0.511
0.058
0.061
0.214
0.068
0.0022
0.00091
0.00011
0.050
0.454
Auxilary Spill Channel High
EMP 3
2021 - 2023
0.028
0.020
1.431
0.010
1.577
0.665
0.298
1.332
0.740
0.194
0.012
0.000
0.799
4.803
2018-2020
0.100
0.015
0.528
0.001
0.644
0.099
0.119
0.386
0.132
0.0134
0.00449
0.00000
0.098
0.853
Sediment Basin High
EMP 5
2021 - 2023
0.001
0.100
0.041
0.032
6.204
0.477
0.033
0.005
6.312
0.614
0.730
0.104
0.524
0.054
2.852
0.325
0.873
0.107
0.117
0.0120
0.003
0.00107
0.000
0.00000
1.060
0.070
6.448
2018 - 2020
0.673
Upper Bypassed Reach
EMP 6
2021 - 2023
0.001
0.042
2.876
0.019
2.978
0.362
0.204
1.370
0.394
0.066
0.000
0.000
0.300
2.913
2018-2020
0.100
0.026
0.614
0.004
0.744
0.078
0.050
0.368
0.096
0.0200
0.00066
0.00000
0.053
0.666
Upper Bypassed Reach High
EMP 6
2021 - 2023
0.027
0.039
0.865
0.010
0.918
0.119
0.062
0.486
0.137
0.023
0.002
0.000
0.107
0.934
2018-2020
0.111
0.057
0.174
0.003
0.345
0.102
0.031
0.170
0.073
0.0017
0.00121
0.00019
0.011
0.390
Lower Bypassed Reach
EMP 2
2021 - 2023
0.105
0.062
0.378
0.003
0.530
0.141
0.043
0.309
0.119
0.002
0.001
0.000
0.002
0.626
2018-2020
0.118
0.044
0.110
0.001
0.273
0.089
0.040
0.135
0.087
0.0016
0.00193
0.00079
0.032
0.387
Lower Bypassed Reach High
EMP 2
2021 - 2023
0.079
0.030
0.060
0.019
0.332
0.090
0.024
0.055
0.029
0.002
0.001
0.000
0.004
0.202
2018-2020
0.100
0.028
0.019
0.002
0.149
0.054
0.015
0.048
0.028
0.0017
0.00292
0.00090
0.017
0.167
East Fork
EMP1
2021 - 2023
0.060
0.028
0.022
0.001
0.122
0.053
0.016
0.045
0.026
0.001
0.003
0.000
0.005
0.156
2018-2020
0.100
0.030
0.021
0.002
0.153
0.056
0.016
0.048
0.029
0.0020
0.00294
0.00069
0.019
0.173
East Fork
EMP 8
2021 - 2023
0.079
0.031
0.024
0.001
0.132
0.055
0.016
0.046
0.028
0.001
0.003
0.000
0.005
2018-2020
0.100
0.028
0.019
0.001
0.149
0.055
0.014
0.052
0.028
0.0006
0.00192
0.00093
0.013
0.164
Forebay Surface Aerobic
EMP 4
2021 - 2023
0.055
0.027
0.020
0.001
0.110
0.052
0.013
0.046
0.027
0.000
0.002
0.000
0.005
0.151
2018-2020
0.100
0.028
0.019
0.001
0.149
0.055
0.014
0.056
0.029
0.0007
0.00193
0.00095
0.013
0.170
Uplake Surface Aerobic
EMP 7
2021 - 2023
0.080
0.027
0.019
0.001
0.127
0.054
0.013
0.050
0.027
0.000
0.002
0.000
0.005
0.153
2018-2020
0.100
0.026
0.019
0.001
0.146
0.051
0.012
0.042
0.027
0.0013
0.00258
0.00018
0.020
0.156
Uptake Bottom Aerobic
EMP 7
2021 - 2023
0.054
0.025
0.019
0.001
0.102
0.050
0.012
0.043
0.025
0.001
0.003
0.000
0.006
0.143
2018-2020
0.100
0.028
0.020
0.002
0.150
0.051
0.013
0.050
0.029
0.0056
0.00623
0.00228
0.033
0.190
Forebay Bottom Aerobic
EMP 4
2021 - 2023
0.065
0.026
0.022
0.001
0.115
0.051
0.013
0.045
0.027
0.001
0.004
0.000
0.005
0.152
2018-2020
0.205
0.027
0.015
0.001
0.247
0.052
0.015
0.087
0.042
0.1102
0.19303
0.02138
0.019
0.540
Forebay Bottom Anaerobic
EMP 4
2021 - 2023
0
0
0
0
0
0
0
0
0
0
0
0
0
0
25

2018 - 2020 Baseline Period
■ HCO3-1 ■ CI-1 ■ SO4-2 ■ NO3-1
10.00
S_
t` off.
`'
5z`y
e ipc aJ aJ �¢ ,tie
cpa
JQQ
`��Qa o�z
`��Q
F��a
e e
Qo JQ�a JQ�
9
JQQe
pie
Sam
cam,
F,a
10.00
J
1.00
0
2018 - 2020 Baseline Period
w Na+1 ■ K+1 w Ca+2 E Mg+2 ■ Mn+3 ■ Fe+3 ■ Fe+2 ■ AI+3
iiiiiiiii N
U
_
U 0.10
O
O.Ol
a�yd \ �c
e,�a
0a QQe
pig
°�2 6'�Qa
d`F,D `oc
as
av e
P \<,-0 e
aicc J
a
apt
¢ Qua
Fo J
Q�`f
J
PJ+a
JQQ
�o �,D2;�
F1:0-
Figure 20. 2018 — 2020, Baseline Period - Median Dissolved Anionic and Cationic Species from all Sampling Sites
10.00
J
N
1.00
O
N
V
0
2021 - 2023 Excavation Period
■ HCO3-1 ■ CI-1 ■ SO4-2 ■ NO3-1
cP°co
ace°�
ea�O
JQ�av
�a
2021 - 2023 Excavation Period
m Na+1 m K+1 ■ Ca+2 m Mg+2 m Mn+3 ■ Fe+3 m Fe+2 ■ AI+3
10.00
1 I I
N
O .
s=
U
ca
0
0.01
PJcy�� �0
S;a°ca
�a
Figure 21. 2021 — 2023, Excavation Period - Median Dissolved Anionic and Cationic Species from all Sampling Sites
26

Evaluation of Analytical Results to pH
The median pH values from the various sampling sites ranged from 4.5 to 7.0 standard units
(Figure 22), with the lowest values observed in the auxiliary spillway channel, the sediment
basin, and the upper Bypassed Reach. Highest pH values were 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), coupled with high
sulfate concentrations; undectable ferrous iron could not be associated with dissociated pyrite of
the exposed pyritic rock and fine excavated material stored 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:
• Major pH Buffering in Most Surface Water (Alkalinity): (Stumm and Morgan 1981)
H2O H H+ + OH-
CO2 + H2O H H2CO3 H H+ + HCO3'- H H+ + C032-
0 Overall Reaction of Pyrite Oxidation (Stumm and Morgan 1981)
H2O H H+ + OH-
2FeS2 + 702 + 2H2O --)- 2FeSO4 + 2H2SO4
■ Baseline (2018 - 2020) Excavation (2021 - 2023)
8.0
7.5
7.0
v
6.5
I 6.0
5.5
N
5.0
4.5
4.0
Im
¢t�� ay5
PJ+� \a�e�� J�� et�� `Dya e��aq
Figure 22. Median pH values from all Cedar Cliff Sampling Sites
27

Alkalinity (Bicarbonate/Carbon Dioxide Buffering System)
The alkalinity (HCO3-') measured during the baseline period was a consistent 0.1 meq/L) from
all samples. In addition, carbon dioxide concentrations seemed unusually high at most sites
(Figures 23 and 24). During the baseline period, alkalinity was measured at a fixed pH endpoint
with an unknown acid normality. To provide for a more accurate alkalinity method, during the
excavation period, alkalinity was determined by a titration utilizing 0.01036 N HCI with the
alkalinity calculated from the maximum slope of the titration curve (Figure 25). The titration
curves from samples collected from the Lower Bypassed Reach, the East Fork, and Cedar Cliff
Reservoir all had titration curves that followed the titration curve of the standard solution. This
trend indicated that the pH from those samples was controlled by the bicarbonate -carbon
dioxide buffering system.
The total alkalinity (HC031) calculated from the titration curves performed during the excavation
period revealed much lower concentrations than from the analyses performed during the
baseline period (Figure 26). Bicarbonate concentrations were similar in all sites except the
sediment basin and upper bypassed reach. The pH at these two sites was less than 4.5
standard units, which is lower than the endpoint of the alkalinity titration curve, hence very little
alkalinity. However. at the lower bypass the alkalinity (and pH) exhibited values substantially
higher than the upper bypassed reach. The significant changes in alkalinity and pH between the
Upper and Lower Bypassed Reaches suggest that accretion flows containing higher
bicarbonate contribute to the extremely low flows upstream of the Lower Bypassed Reach.
The 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 and gaseous exchange with the atmosphere. For
example, median CO2 concentrations from the lake surface samples were lower than the
median concentrations observed in the deeper depths, which would correspond to
photosynthetic and respiratory activity, respectively. Whereas the auxiliary spill channel and the
Lower Bypassed Reach the CO2 concentrations appear to be dominated by gaseous exchange
with the atmosphere since the concentrations approximated the CO2 atmospheric equilibrium
concentration.
51 0.09
0.00
■ Baseline Period 2018 - 2021 Excavation Period 2021-2023
m
41
S x�
Figure 23. Median Alkalinity (HCO31) at all Sites during the Baseline and Excavation Periods
a:]

1000.0 ,
J
U
E 1000
m
a
10.0
`m
G
C
m L0
m
0.1
■ Baseline Period 2018 - 2021 Excavation Period 2021-2023
IIIIJIlllIl
,4a fo�
a v�
,a
Figure 24. Median Carbon Dioxide (CO2-) at all Sites during the Baseline and Excavation
Periods Relative to Saturation with the Atmospheric CO2.
• 0.16 IN NaCd3 Standard —Slope of Standard
• Forebay Sample —Slope of ForebaySample
nr Upper Bypass Sample —Slope of Upper Bypass Sample
7.00
6.50
5.00
5.50
Q 5.00
4.50
4.00
3.50
3.00
0.00 1.00 2.00 3.00 4.00 = 00
Volume Acid (ml) Slope of Ttration Curve
Figure 25. Alkalinity Determination Utilizing a Titration Curve and Endpoint (maximum slope)
Comparing Titration with a Known Standard, a Sample from Cedar Cliff Forebay, and a sample
from the Upper Bypassed Reach.
W

Pyrite Oxidation
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,
the sediment basin, and the upper bypass (Figure 26) suggest that the low pH levels were the
result of pyrite oxidation. The evaluation of the extent of pyrite oxidation centers on the ratios of
the pyrite oxidation products. Even though the very soluble ferric sulfate is a product of pyrite
oxidation, the oxidized iron reacts to form relatively insoluble ferric hydroxides and ferric
carbonates (Stumm and Morgan, 1981). Since the particulate iron, which was approximately 2
orders of magnitude greater than soluble iron, could have originated from pyrite oxidation, it is
included in the molar ratio analysis.
The molar chemical pyrite oxidation reaction yields 4 sulfates to 4 hydrogens (or 1:1), 4 sulfates
to 2 irons (or 2:1), and 4 hydrogens to 2 irons (or 2:1). Even though some ratios may
approximate the ratio of individual pyrite oxidation products, if the concentration ratios
approximate all three ratios, pyrite oxidation would be considered the primary reaction
controlling pH.
The ratios involving sulfate and iron (Figure 27) illustrate that most of the ratios are at least and
order of magnitude greater than the pyrite oxidation reaction would imply. The exception was
observed in the single stage sampler from the auxiliary spill channel, however, that ratio was an
order of magnitude less that the chemical equation predicts.
The hydrogen ion molar ration to sulfate and iron fractions (Figure 28) showed the sulfate to
hydrogen ion ratio was again orders of magnitude greater than the pyrite oxidation reaction
predicted. Hydrogen ion ratios to particulate iron were extremely low whereas hydrogen ion to
filterable iron approximately equaled the reaction prediction in the auxiliary spill channel single
stage sampler, and of the median of samples collected at the lower bypassed reach location.
None of the locations exhibited the predicted ratios all three ratios of 4 sulfates to 4 hydrogens
(or 1:1), 4 sulfates to 2 irons (or 2:1), and 4 hydrogens to 2 irons (or 2:1). Therefore, pyrite
oxidation is not considered the primary reaction controlling pH at any of the sites.
all

■H+1 Sulfate ■Particulate ■Filtered IRON
Iran
10.0000
1.0000
m
m
0
E 0.1000
0
m 0.0100
C:
as
ci
0
U 0.0010
0.0001 ILI.
-P , *__ ..
■ ■ ILI 1 1 1
I .I I I 1 .1
Or
Figure 26. Molar Concentrations of Hydrogen Ions, Sulfate, and Iron Fractions from all Cedar
Cliff Sampling Sites
1 E+05
1. E+04
1. E+43
0 1. E+02
tr
1. E+41
0
1. E+00
1-E-01
1.E-02
1E-03
Particulate Fe ■ Filtered Fe+3 Pyrite Oxidation Ratio
SO4-2 - Fe SO4-2 : Fe+3
e
Figure 27. Molar Ratios of Sulfate to Iron Fractions from all Cedar Cliff Sampling Sites
31

■ SO4-2 - H+1 ■ Filtered Fe+3 ■ Particulate Fe
H+1 : Fe H+1 Fe
1-E+45
1. E+4i
1.E+43
O 1-E+42
tu
1. E+41
`m
a
� 1.E+pp
1.E-01
1.E-02
1. E-03
#: Q
Pyrite Oxidation Ratio-- SO4-2: H+1
Pyrite Oxidation Ratio - H+1 : Fe
Figure 28. Molar Ratios of Sulfate and Iron Fractions to Hydrogen Ions from all Cedar Cliff
Sampling Sites
32

Summary
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. to evaluate the
extent and influence of pyrite oxidation on the pH in the waters of Cedar Cliff reservoir and the
East Fork Tuckasegee River downstream of Cedar Cliff Hydro before and after the Auxiliary
Spillway Upgrade Project. Therefore, the purpose of the monitoring plan is to identify the various
processes controlling the pH in the project waters, in particular pyrite oxidation as it influences
ph. This report covers the data collection from the baseline period (2018-2020) through the
excavation period (2021-2023).
The methods and sampling sites during the excavation period were the same as during the
baseline period, with the following exceptions:
• Samples for most parameters consisted of a whole water sample and a filtered sample
• Alkalinity titration curves were performed where alkalinity was determined from the
inflection point
• A laboratory experiment was performed measuring the direct effect of spoiled rock
Rock barging consisted of spoiling rocks greater than 1'/2 inches into the lake. The fines were
removed with a mobile screen. Material less than 1'/2 inches (fines) were temporarily stored in
the auxiliary spill channel until trucked to other locations, both off -site and on -site. Barging
material into the lake commenced on May 14, 2021 and ended April 14, 2023 with
approximately 164,000 yds3 spoiled. A total of approximately 130,000 yds3 of screened fines
were trucked from the auxiliary spill channel to off -site and on -site locations.
The lake level was lowered to approximately 50-60% of its total capacity on September 4, 2019,
and was managed at this level through most of the excavation period to accommodate barging
and other construction activities. Since this lower lake level was below the tainter gate sill, lake
water only flowed down the principal spillway when lake levels rose above the tainter gate sill
during heavy rains or outages. During these heavy rains, the chemistry at the upper and lower
bypassed reach sites resembled that of lake water. During the remainder of time, the principal
spill way only received water from the auxiliary spill channel via the sediment basin and, above
the lower bypassed reach site, accretion water entered the spillway. The average flow from the
bypassed reach into the East Fork Tuckasegee River was calculated to be 7-8 cfs.
Due to the temporary storage of the screened rock fines, the auxiliary spill channel had higher
conductivity values (dissolved solids) during the excavation period than the baseline period.
Primarily sulfate and sodium ions contributed to the increased conductivity values. The
sediment basin water collected in the single stage samplers and the upper bypassed reach
samples were reflective of these higher values. By the time the water slowly moved down the
bypassed reach and accretion water entered the channel, the values were only slightly greater
than the East Fork levels.
Cedar Cliff Reservoir water quality during the excavation period resembled that during the
baseline period. Conductivity and turbidity levels were very low throughout the entire 5 years of
sampling turbidity values only approximated the state standard of 10 NTU during the 2019 Bear
Creek maintenance. Since retention times of the water was significantly shorter during the lake
drawdown period, the influence of biological reactions (photosynthesis and respiration) was
reduced during this period. pH values varied little in the lake, median of 6.9 standard units at the
surface and 6.1 standard units at the bottom. A laboratory experiment adding rocks greater than
33

1'/2 inches from the rock separator, illustrated that the rock dust had no influence on pH or
conductivity.
Detailed analyses of alkalinity, and subsequent pH values, revealed that the pH's from the lower
bypassed reach location, the East Fork River, and all of the lake samples were controlled by the
carbon dioxide -bicarbonate buffering system. Even though sulfate was high in the auxiliary spill
channel, sediment basin, and upper bypassed reach locations, molar ratios of hydrogen ions,
sulfate, and iron fractions did not support the pyrite oxidation mechanism of controlling pH. The
auxiliary spill channel and upper bypassed reach were heavily influence by the temporary
storage of the screened rock fines. This influence should be diminished as material is removed.
Overall conclusion is that there was no evidence of pyrite oxidation which impacted the pH of
Cedar Cliff waters. In addition, the increase of ionic concentrations during the excavation period
originating from the auxiliary spill channel due to the temporary storage of screened fines should
return to baseline conditions once the auxiliary spill channel returns to exposed bedrock.
34

References
American Public Health Association (APHA). 1998. Standard Methods for the Examination of Water
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.
Hach Company. 2005. Hydrolab DSSX, DS5, and MS5 Water Quality Multiprobes, User Manual,
Catalog Number 003078HY.
HDR. 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.
2018b. 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
Knight, JC. and JR Quinn, 2020. Cedar Cliff Hydroelectric Development, Auxiliary Spillway
Upgrade Project Baseline (Pre -Auxiliary Spillway Excavation) Monitoring Results. Duke
Energy Carolinas, LLC
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.
35