NC0004979_Report_20220201 (2)

DUKE Allen Steam Station
V' ENERGY® 253 Plant Allen Road (NCSR 2525)
Belmont, NC 28012
o:828.478.7600
January 27,2022 RECEIVED
NC Division of Water Resources
WQ Permitting Section-NPDES r C 0 1 2022
1617 Mail Service Center
Raleigh,NC 27699-1623 NCDEQ/DWR/NPGCS
Subject: Duke Energy,LLC.
Allen Steam Station
NPDES Permit NC0004979
Dear Dr. Sergei Chernikov,
This letter and the attached materials are provided in support of Duke Energy Carolinas,LLC's (Duke
Energy)application to continue the thermal variance stated in the Allen Steam Station(Allen)NPDES
permit as required by condition A. (21.).The continuation of Duke Energy's thermal variance at Allen is
based on the enclosed comprehensive 316(a) studies undertaken in accordance with permit condition A.
(21.).
Duke Energy (then Duke Power Company) sponsored an initial 316(a)demonstration study for Allen
during 1973-1974 soon after the Clean Water Act(CWA) legislation was enacted in 1972.This included
intensive studies of the lake's ecology and chemical properties. Since then,Duke Energy has performed
fisheries and water quality sampling in Lake Wylie at varying frequencies from 1978 to the late 1980s,
and annually since 1993.These studies also included benthic macroinvertebrates and primary production
assessments at varying frequencies.The most recent balanced and indigenous community(BIC)report for
this sampling was submitted under the previous permit in 2014.
The current NPDES permitted thermal limits under§316(a) of the CWA for Allen's effluent include a
monthly average discharge temperature limit of 38.9°C during June 1 through September 31,and a
monthly average temperature limit of 35°C during October 1 through May 31. To maintain this variance
and in accordance with section A. (21)in the current NPDES permit, Duke Energy has conducted 316(a)
studies as outlined in the approved Study Plan and thus, is submitting the report within 3.5 years from the
effective date of the permit.
Results from the study found that current Allen operations will ensure the survival,reproduction,
development, and growth of representative important species(RIS). Moreover,the Allen thermal plume
has not blocked or inhibited access to any potential spawning habitat, spawning activities, or the
development of early juveniles of RIS.Despite warm water temperatures,the lake was found to have a
balanced and indigenous fish community.

If there are any questions,please contact either:
• Mr. Maverick Raber(Environmental Science Manager)980.875.2021,maverick.raber@duke-
energy.com
• Mr. Scott Fletcher(Environmental Science Manager)980.875.6014, scott.fletcher@duke-
energy.com
I certify, under penalty of law, that this document and all attachments were prepared under my direction
or supervision in accordance with a system designed to assure that qualified personnel properly gather and
evaluate the information submitted.Based on my inquiry of the person or persons who manage the system,
or those persons directly responsible for gathering the information, the information is, to the best of my
knowledge and belief true, accurate, and complete. I am aware that there are significant penalties for
submitting false information, including the possibility of fines and imprisonment for knowing violations.
Sincerely,
Jeffr lanagan
General Manager III
UPS Tracking: 1Z X67 601 24 9158 2777

CWA §316(a) Balanced and Indigenous
Community Study Report (2014-202 1)
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ALLEN STEAM STATION
Lake Wylie, Belmont, North Carolina
NPDES Permit# NC0004979
Duke Energy Environmental Sciences
Huntersville, NC
January 2022
a.) DUKE
ENERGY

CWA§316(a)Balanced and Indigenous Community Study Report(2014-2021)
ALLEN STEAM STATION
Contents
Executive Summary 1
1 Introduction 3
1.1 Physical Description and Background 3
1.2 316(a) Demonstration Studies 4
1.3 Station Operations and Thermal Characteristics 4
2 Methods 14
2.1 Water Quality 14
2.2 Planktonic Community 18
2.3 Habitat Formers 19
2.4 Benthic Macroinvertebrate Community 19
2.5 Fish Community 19
2.5.1 Spring Electrofishing Survey 19
2.5.2 Fall Electrofishing Survey 20
2.6 Other Vertebrate Wildlife 20
3 Results and Discussion 21
3.1 Water Quality 21
3.1.1 Water Temperature and Dissolved Oxygen Profiles 21
3.1.2 Water Chemistry 26
3.1.3 Lake Productivity and Trophic Status 30
3.2 Planktonic Community 32
3.3 Habitat Formers 32
3.4 Benthic Macroinvertebrate Community 34
3.5 Fish Community 34
3.5.1 Spring Electrofishing Survey 34
3.5.2 Fall Electrofishing Survey 43
3.6 Other Vertebrate Wildlife 48
4 Balanced and Indigenous Assessment 50
5 References 51
Tables
Table 1-1. Net capacity factors, expressed in percent(%), and monthly average discharge water
temperatures for Allen during 2014-2021.. 4
Table 2-1. Limnological parameters and monitoring frequency. 15
Table 2-2.Analytical methods and reporting limits for parameters monitored in Lake Wylie in 2014-
2021 18
Table 3-1.Summary of surface water quality measurements made in Lake Wylie during 2014-2021
monitoring. 24

CWA§316(a)Balanced and Indigenous Community Study Report(2014-2021)
ALLEN STEAM STATION
Table 3-2.Summary of surface water chemistry results in Lake Wylie during 2014-2021 monitoring 28
Table 3-3. Summary of bottom depth water chemistry results in Lake Wylie at Zone C during 2017-2021
monitoring. 29
Table 3-4.Summary of summer chlorophyll a concentrations (µg/L) in samples from Lake Wylie during
2014-2021. 31
Table 3-5. Mean (and range) of water quality parameters for each zone(C and D) and lake-wide in Lake
Wylie during spring 2014-2021 electrofishing. 35
Table 3-6. Number(No.) and biomass(kg) of fish collected from electrofishing within two zones(C and
D) and all of Lake Wylie during spring 2014-2021 35
Table 3-7. Percent pollution tolerance,trophic guild, and percent of hybrids for fish collected from
electrofishing within two zones and lake-wide in Lake Wylie during spring 2014-2021 38
Table 3-8.Table 3-8. Mean (and range) of water quality parameters for each zone (C and D) and lake-
wide in Lake Wylie during fall 2017-2019 electrofishing. 44
Table 3-9. Number(No.) and biomass(kg) of fish collected from electrofishing within two zones(C and
D) and lake-wide in Lake Wylie during fall 2017-2019. 44
Table 3-10. Location, behavior, and number of vertebrate wildlife observed in the Allen discharge area
during summer surveys in 2016-2021 49
Figures
Figure 1-1. Mean monthly air temperatures recorded at CNS during the current study period compared
to 1989-2013 average.. 8
Figure 1-2.Total annual precipitation recorded at CNS during the current study period compared to
1985-2013 average(horizontal line) 9
Figure 1-3.Total monthly precipitation recorded at CNS during current study period compared to 1985-
2013 monthly averages 9
Figure 1-4. Average winter thermal plume prediction using CE-QUAL-W2 Model with 2007 hydrology
and meteorology and actual 2007 operations at Allen and Catawba Nuclear Station. 11
Figure 1-5. Average summer thermal plume prediction using CE-QUAL-W2 Model with 2007 hydrology
and meteorology and actual 2007 operations at Allen and Catawba Nuclear Station 12
Figure 2-1. Limnological (water quality and chemistry) sampling locations and zones in Lake Wylie. 14
Figure 2-2. Fish sampling locations and zones in Lake Wylie 15
Figure 3-1. Seasonal temperature profile plots of Lake Wylie main channel locations from 2014 to 2018
26
Figure 3-2.Seasonal temperature profile plots of Lake Wylie main channel locations from 2019 to 2021
23
Figure 3-3.Seasonal dissolved oxygen profile plots of Lake Wylie main channel locationsfrom 2014 to
2018. 25
Figure 3-4.Seasonal dissolved oxygen profile plots of Lake Wylie main channel locations from 2019 to
2021 26
Figure 3-5. Distribution of aquatic plants in Lake Wylie during the 2019 survey 33
ii

CWA§316(a)Balanced and Indigenous Community Study Report(2014-2021)
ALLEN STEAM STATION
Figure 3-6. Mean catch rate (CPUE) by number and by weight of all species collected within two zones
and lake-wide from electrofishing in Lake Wylie during spring 2003-2021. 37
Figure 3-7. Mean catch rate (CPUE) by number of stock size and larger Largemouth Bass collected
within two zones and lake-wide from electrofishing in Lake Wylie during spring 2003-2021 39
Figure 3-8. Mean catch rate (CPUE) by number of stock size and greater Bluegill collected within two
zones and lake-wide from electrofishing in Lake Wylie during spring 2014-2021. 40
Figure 3-9. Mean catch rate (CPUE) by number of stock size and greater Redbreast Sunfishand stock
size and larger Redear Sunfish collected within two zones and lake-wide from electrofishing in
Lake Wylie during spring 2014-2021 41
Figure 3-10. Length-frequency of Largemouth Bass and Bluegill collected within two zones and lake-
wide from electrofishing in Lake Wylie during spring 2014-2021. 42
Figure 3-11. Length-frequency of Redbreast Sunfish and Redear Sunfish collected within two zones and
lake-wide from electrofishing in Lake Wylie during spring 2014-2021. 43
Figure 3-12. Largemouth Bass condition by zone of Lake Wylie and by length category for fish collected
during fall 2017-2019 electrofishing. 46
Figure 3-13. Figure 3-13. Bluegill and Redear Sunfish condition (relative weight) by zone of Lake Wylie
and by length category for fish collected during fall 2017-2019 electrofishing. 47
Figure 3-14. Redbreast Sunfish condition by zone of Lake Wylie and by length category for fish collected
during fall 2017-2019 electrofishing. 48
Appendices
Appendix A. 2019 Lake Wylie 316(a)Study Plan—Allen Steam Station.
Appendix B. Box and whisker plots comparing historical (2000-2013) analytical data to 2014-2021.
Appendix C. Initial 1976 winter and summer thermal plume models for Lake Wylie.
Appendix D.Table of fish captured by electrofishing from Lake Wylie since 1976.

CWA§316(a)Balanced and Indigenous Community Study Report(2014-2021)
ALLEN STEAM STATION
Executive Summary
This report satisfies the Clean Water Act(CWA) §316(a) monitoring requirement for continuance of the
existing thermal variance for Allen Steam Station (Allen)through demonstration of no prior appreciable
harm on the biological community of Lake Wylie. In accordance with the National Pollutant Discharge
Elimination System (NPDES) permit(No. NC0004979)for Allen and the North Carolina Department of
Environmental Quality(NCDEQ) approved 2019 Lake Wylie 316(a) Study Plan, biological surveys and
supporting monitoring was conducted at Lake Wylie to demonstrate the continued protection and
propagation of a balanced, indigenous community(BIC) of aquatic wildlife.The study conformed to the
specifications outlined in 40 CFR 125 Subpart H,the U.S. Environmental Protection Agency's(USEPA)'s
DRAFT 316(a) Guidance Manual (USEPA 1977), and the USEPA Region 4 letter to NCDEQ(2010).
This report presents operational and environmental data collected since the last 316(a) assessment of
balanced and indigenous populations in Lake Wylie near Allen (Duke Energy 2014). As defined in 40 CFR
125.71(c),the term BIC is synonymous with the term balanced, indigenous populations referenced in
the CWA and in previous Allen 316(a) reports.The current study period spanned seven years and six
months(2014 through the second quarter of 2021), and included an update in the monitoring program
effective in 2019. Information from the study period was compared with historical data, and biological
data were also evaluated against the four primary BIC criteria defined in 40 CFR 125.71,which state that
BICs are biotic communities typically characterized by:
• Having diversity and representative trophic levels within expectations,
• The ability to self-sustain through successful reproduction and recruitment over seasonal
changes,
• Having adequate food items, and
• A lack of domination by pollution tolerant species.
Duke Energy has two permitted thermal discharges to Lake Wylie,one from Catawba Nuclear Station
(CNS) down-lake near Wylie Dam and one up-lake at Allen. To evaluate the impacts of the Allen thermal
discharge on Lake Wylie,two distinct zones(Zones C and D)were delineated.Zone C begins in the South
Fork Catawba River arm of the lake where Allen's thermal discharge is located and extends down into
the mid-lake region of Lake Wylie. Zone D is located up-lake in the mainstem Catawba River arm and
represents non-thermally influenced background conditions for comparison to Zone C.Additional
sampling occurred throughout the lake, downstream of Zone C,to better represent lake-wide conditions
that could affect an overall BIC.
Lake Wylie continued to be classified as mesotrophic based on long-term and 2014-2020 nutrient and
chlorophyll a concentrations, consistent with historical trophic classifications of the reservoir. Seasonal
limnological data continued to affirm that Lake Wylie provides a suitable physicochemical environment
for sustaining a BIC. Similarly, data collected from other biological communities(e.g., plankton, habitat
formers, other vertebrate wildlife, macroinvertebrates) or literature surveys conducted for other biotic
categories also support that Lake Wylie is suitable for sustaining a BIC.
A total of 30,538 fish representing 37 distinct species (plus two hybrid complexes) and nine families
were collected from Lake Wylie during the eight years of spring electrofishing. Bluegill were the most
1

CWA§316(a)Balanced and Indigenous Community Study Report(2014-2021)
ALLEN STEAM STATION
abundant species(56%of the fish captured), and Largemouth Bass had the highest biomass collected of
any species (1,371 kg or 45%of the total biomass).This was comparable with historical lake-wide
sampling results,for which Bluegill represented 65%of individuals collected, and Largemouth Bass 45%
of the overall biomass.The annual catch rates of fish during spring 2014-2021 were generally similar to
those noted since 2003.The fish community found in the thermally influenced zone of Lake Wylie (Zone
C) encompassed multiple trophic guilds(e.g., insectivores, omnivores,and piscivores) indicative of a
balanced fish community.Additionally,fish captured in the thermally influenced zone had similar
proportions of pollution tolerance to the associated reference zone, and no zones were dominated by
pollution-tolerant species.The proportion of sunfish identified as hybrids was less than 0.5%with no
pattern between thermally influenced and non-influenced zones.
Catch rates and sizes of representative important species(RIS; Largemouth Bass, Bluegill, Redbreast
Sunfish, and Redear Sunfish) indicated multiple age classes of each species throughout the lake.
Condition factors, an indication of fish health, suggested the RIS populations had capacity to be
sustained across seasons. No population metrics were observed in lake Wylie which were related to
operations at Allen.This assessment demonstrated that the Lake Wylie fish community was balanced
and composed mostly of indigenous species(84% native species) expected from a reservoir located in
the North Carolina Piedmont.
Under the current thermal variance conditions, no prior appreciable harm was present against the
survival, reproduction, development, and growth of the BIC due to Allen operations. Additionally, no
observations indicated that the Allen thermal plume has blocked or inhibited access to any potential
spawning habitat, spawning activities,or the development of early juveniles of RIS and the BIC.
Consequently,the current thermal limits and Allen operations have ensured the protection and
propagation of a BIC in Lake Wylie.
2

CWA§316(a)Balanced and Indigenous Community Study Report(2014-2021)
ALLEN STEAM STATION
1 Introduction
1.1 Physical Description and Background
Allen Steam Station (Allen) is a five-unit, coal-fired, electric-generating facility with a nameplate capacity
of 1,145 megawatts(MW). Units 1 and 2 are rated at 165 MW each and began operation in 1957. Units
3,4, and 5 are rated at(in order) 265 MW, 280 MW, and 270 MW, and these units began commercial
operation in 1959, 1960, and 1961.All units operate in a once-through cooling mode, and water is
withdrawn from Lake Wylie via a shoreline-situated cooling water intake structure (CWIS).
Lake Wylie was initially formed in 1904 by the impoundment of the Catawba River with a hydroelectric
dam near Fort Mill,South Carolina, creating a reservoir that extends into portions of North and South
Carolina. It is the third largest reservoir in the 13-hydropower station, 11 reservoir system called the
Catawba-Wateree Hydroelectric Project(FERC No. 2232).The dam was rebuilt in 1924, expanding the
lake's surface to approximately 12,177 ac at a full pond elevation of 569.4 ft above mean sea level.The
lake has a shoreline length of approximately 348.5 mi and a mean depth of 23.0 ft.The drainage area is
roughly 3,020 square miles with a mean annual inflow of 1,570 cubic meters per second (cms) and
outflow of 2,100 cms at the dam, and a hydraulic retention time of 32 days(Duke Energy 2017).The
South Fork Catawba River accounts for approximately 1%of the inflow into Lake Wylie.
Lake Wylie provides Allen and Duke Energy's Catawba Nuclear Station (CNS)with cooling water, as well
as other"designated uses"for local communities such as a municipal water supply for the cities of
Belmont, North Carolina and Rock Hill, South Carolina. Lake Wylie is classified as a eutrophic waterbody
(NCDENR 2013a) and is managed for recreational fishing. Popular sport fish on Lake Wylie include
Largemouth Bass Micropterus salmoides,crappie, and catfish (SCDNR 2014).
The condenser cooling water(CCW) system of Allen utilizes a once-through flow pattern where raw
water,withdrawn from the Catawba River arm of Lake Wylie, is pumped over condensers to cool Allen
system components and then discharged back to the lake in the South Fork Catawba River arm.The
discharge of this heated water, referred to as"thermal discharge", requires a Clean Water Act(CWA)
316(a)thermal variance,which is regulated through a National Pollutant Discharge Elimination System
(NPDES) permit maintained by Allen (No. NC0004979).The NPDES permit for Allen effective during the
years covered in this report(2014-2021)was issued on August 1, 2018 and had monthly average
thermal discharge limits of 35°C(95°F) during October—May and 38.9°C(102°F)during June—September.
These temperature limits are expected to be protective of biological communities in the receiving
waterbody(i.e., Lake Wylie).
Assessment of the potential effects of thermal discharges on biological communities is a key component
of a thermal discharge variance (EPA and NRC 1977, NCASI 2013).Section A. (21)of the 2018 NPDES
permit specifies the reapplication basis for continuation of the 316(a)thermal variance, including
demonstrating"...no changes in the biotic community of the receiving water body which would impact
the previous variance determination."As such, Duke Energy conducted annual biological surveys on
Lake Wylie during the previous permit term as a continuation of annual surveys since the early 1990's.
3

CWA§316(a)Balanced and Indigenous Community Study Report(2014-2021)
ALLEN STEAM STATION
1.2 316(a) Demonstration Studies
The original Allen 316(a) demonstration study concluded that"...the heated discharge from Plant Allen is
such that the protection and propagation of a balanced indigenous aquatic community(BIC) in and on
Lake Wylie is assured" (Duke Power Company 1976). Since annual studies began in the early 1990's,
Duke Energy has submitted four biological monitoring reports supporting the continuation of Allen's
thermal variance with the same conclusion (Duke Energy 2001, 2004, 2009, 2014), and within each
subsequent NPDES permit,the NCDEQ has agreed. For example, in the notes of Section A. (1) of the
2018 NPDES permit,that the "...thermal component of the discharge assures the protection and
propagation of a balanced, indigenous, population of shellfish,fish, and wildlife in and on the receiving
water body."A similar statement exists in the most recent NPDES permit issued on August 1, 2018.
This report covers comprehensive water quality and biological studies conducted from January 2014 to
July 2021, in support of the 2018 NPDES permit. Monitoring results presented herein include data for
Allen's operation, meteorological conditions, physicochemical reservoir condition, and an assessment of
thermal effects on plankton, habitat formers, macroinvertebrates, fisheries, and other vertebrate
wildlife data. Information provided in EPA's Technical Guidance Manual (EPA 1977) and NCASI's
Considerations and Requirements for Biological Impact Determinations Related to Thermal Discharges
(NCASI 2013)were used in the assessment.
1.3 Station Operations and Thermal Characteristics
Power generation at coal facilities has declined significantly in recent years,giving way to natural gas
and renewables.As a result,Allen's capacity factor has decreased, having a direct on the resulting
thermal discharge into the lake. During the study period, net station capacity dropped from 23.4% in
2014 to 8.1% in 2018 (Table 1-1). Average annual unit capacity during this time also dropped with a
maximum annual unit capacity of 27.6%(Unit 5) in 2014, compared to 14.4% (Unit 5) in 2018.This
drop in operations over the study period has further reduced any potential for thermal effects on
aquatic populations in Lake Wylie.
The NPDES thermal compliance discharge limit for Allen, expressed as a monthly average,was 35.0°C
(95°F)for October 1-May 30 and 38.9°C(102°F)for June 1-September 31.Thermal discharge limits
were met throughout the study period (Table 1-1).The maximum monthly average discharge
temperature of 37.2°C(99.0°F)was reported in July 2016(Table 1-1).
Table 1-1.Net capacity factors,expressed in percent(%),and monthly average discharge water temperatures for
Allen during 2014-2021. NA represents a month in which no flow was passed through outfall 001 from units 1-5.
Monthly Avg
Net capacity factor Discharge
Temp
Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Station °C °F
2014
January 34.2 32.8 44.4 47.1 43.1 40.3 18.3 64.9
February 24.7 21.3 34.0 44.8 42.1 33.4 18.9 66.0
March 5.9 10.3 43.7 45.6 26.2 26.4 18.9 66.0
April 0.0 0.0 0.0 0.0 0.0 0.0 NA NA
May 17.6 21.3 34.1 10.2 38.7 24.4 30.0 86.0
June 52.4 45.5 57.2 43.2 37.4 47.2 35.6 96.1
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N N N

CWA§316(a)Balanced and Indigenous Community Study Report(2014-2021)
ALLEN STEAM STATION
Monthly Avg
Net capacity factor Discharge
Temp
Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Station °C °F
November 0.0 0.0 0.0 4.1 0.0 0.8 19.7 67.5
December 0.0 0.0 21.7 39.5 0.0 12.2 22.3 72.1
2020 Avg 1.0 6.8 2.6 10.4 9.2 6.0 21.8 71.3
2021
January 0.0 0.0 0.0 0.0 0.0 0.0 9.9 49.9
February 0.0 0.0 0.0 0.0 0.0 0.0 9.1 48.3
March 0.0 0.0 0.0 0.0 0.0 0.0 13.2 55.7
April 0.0 0.0 0.0 0.0 0.0 0.0 17.2 62.9
May 0.0 0.0 0.0 0.0 0.0 0.0 22.2 71.9
June 0.0 0.0 0.0 0.0 0.0 0.0 26.8 80.3
Meteorological forces can exert significant influences, both directly and indirectly, on the physical,
chemical, and biological characteristics of aquatic ecosystems, and documentation of local and regional
meteorology can often provide insight into the spatial and temporal dynamics in these characteristics
(Wetzel 2001).Two important meteorological parameters are air temperature and precipitation, and
data for these two variables were obtained from a meteorological monitoring site established near CNS,
located down lake approximately 10 miles south of Allen.The data also serve to document localized
temporal trends in air temperatures and rainfall patterns.
Air temperatures influence variability in a waterbody's thermal regime via seasonal water column
heating and cooling.Air temperatures during the study period were generally above average compared
to data collected since 1989. Notably higher than average air temperatures were also recorded in
January 2017, February 2017 and 2018, March 2016,and December 2015 with monthly means 3.0-6.0°C
greater than the average (Figure 1-1).
7

CWA§316(a)Balanced and Indigenous Community Study Report(2014-2021)
ALLEN STEAM STATION
30
25 i:��� r � '%•■� I 11989-2013 Average
/,' � ` —•— 2014
0 20Nt4Nc�( •
•. `� —•— 2015
■
; —.—2016
15 ■ •
•••••• 2017
a Ai� •; •..,.. 2018
.1;N.
ai
10 :fir■ / • • —•— 2019
Q A
•� /• T —■—2020
5 ,VI"
—•—
� • 2021
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Figure 1-1. Mean monthly air temperatures recorded at CNS during the current study period compared to 1989-
2013 average.
Precipitation affects hydrologic characteristics in aquatic ecosystems by controlling water volume, inflow
rates, and water column mixing. This hydrodynamic influence can be additionally magnified or modified
by reservoir outflow characteristics, resulting in variations in spatial and temporal water quality and
biological regimes. In addition to influencing hydrologic and hydraulic characteristics, precipitation can
impact water quality by direct chemical loading associated with atmospheric chemistry or indirectly via
constituent loading associated with watershed runoff.The rainfall totals in 2014, 2015, 2018, 2019,and
2020 were all above the long-term (1985-2013)average of 107.1 cm,whereas rainfall in 2016 and 2017
was below average (Figure 1-2).Two major hurricanes impacted the CNS area during fall 2018(Florence
in September and Michael in October)that contributed to the above average rainfall in those months
(Figure 1-3).These rainfall patterns directly affected the inflow to the reservoir and discharge out of the
reservoir.
8

CWA§316(a)Balanced and Indigenous Community Study Report(2014-2021)
ALLEN STEAM STATION
160
140 -
120 - -
- - -
— 100 - -
E
u _
o 80 - -
ra
Y -
a
'0 60
0)
a
40
20
0
V1 m u'1 N cn r♦ m Un N 01 ei m V1 N CT r 1
00 00 00 C11 CT C l In 01 0 0 0 0 0 '-1 r•1 e-1 e-1 N
01 01 T C11 Ci m C71 CIl 0 0 O O O O O 0 O O O
e-1 e-I e-I e-I e I e-1 '-1 i-I N N N N N N N N N N N
Figure 1-2.Total annual precipitation recorded at CNS during the current study period compared to 1985-2013
average(horizontal line).
30
25 •
/ \ I 11985-2013 AVG
/ —•— 2014
E 20 • •
• —••— 2015
2016
I ::
• � • M • 1 / ■ •
•• '/ 1 `1 1 •/ •�
•/ �• —•— 2019
• Y 1 • • PI
• 1 • � • •• 2020
■ •�2021
5 •1 1 L.
,
0 •
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Figure 1-3.Total monthly precipitation recorded at CNS during current study period compared to 1985-2013
monthly averages.
9

CWA§316(a)Balanced and Indigenous Community Study Report(2014-2021)
ALLEN STEAM STATION
The thermal influence of Allen was originally determined through field measurements and thermal
temperature modeling as part of the original 1976 316(a) demonstration (Duke Power Company 1976).
Winter and summer thermal plume maps of hypothesized "extreme"years were developed from this
effort using actual data from 1953, 1967 and 1968 (Appendix C).The delineated thermal plume here was
defined as the difference in epilimnetic temperatures from background of 2.8°C(5 °F) in North Carolina
and 1.7°C(3°F) in South Carolina (Duke Power Company 1976).The hypothetical "extreme"years
shown in Appendix C represent worst-case scenarios that would occur under baseload operational
conditions. Given the fact that Allen's operations and thermal loading to Lake Wylie have decreased
substantially over the years(Table 1-1),the hypothetical "extreme"years analyzed during the 1976
316(a) demonstration represent worst-case scenarios that could most likely only occur under old
operational scenarios.
The thermal influence of Allen was re-assessed in 2020 using a calibrated hydrodynamic model (CE-
QUAL-W2).The model was configured using the hydrological and meteorological data from 2007,which
was a very dry year in the Catawba River watershed. During 2007, flows in the Catawba River
downstream of Wylie Dam were in the bottom 10th percentile of the historical record dating from 1942-
2019.Therefore,the W2 model utilized conditions in 2007 to simulate lake temperatures in an extreme
meteorological year when summer and winter thermal plumes would be expected to cover the largest
areal extent.The thermal plume was defined as"3°F (1.7°C)delta-t above background lake temperature
in South Carolina and 5°F (2.8°C) delta-t in North Carolina".The "background"temperature is based on
intake temperature data from Allen and is estimated to be 52°F(11.1°C) in the winter and 85°F(29.4°C)
in the summer.The latest modeling simulations estimated the thermal plume by comparing monthly
average model-predicted temperatures in the surface layer of Lake Wylie using the W2 model with 2007
hydrology and meteorology as well as actual 2007 operations at Allen and CNS. Figure 1-4 is a contour
plot of the February delta-t calculated by comparing monthly average model-predicted temperatures in
the surface layer of Lake Wylie using the W2 model with 2007 hydrology and meteorology as well as
actual 2007 operations at Allen and CNS. Figure 1-5 shows the calculated delta-t from comparing the
September predictions from the two models to simulate the "summer" plume.These plume maps show
the extent of both the 3°F plume and the 5°F plume.
10

CWA§316(a)Balanced and Indigenous Community Study Report(2014-2021)
ALLEN STEAM STATION
Catawba River Inflow
S. Fork Catawba River Inflow
Plant Allen
Plant Allen Discharge—
Area Shaded in Purple has Delta-T>5°F(2.78 oC)
4.411. Area Shaded in Blue has Delta-T>3°F(1.67°C)
a
Catawba Nuclear -
!wr"
Wylie Dam
Figure 1-4.Average winter thermal plume prediction using CE-QUAL-W2 Model with 2007 hydrology and
meteorology and actual 2007 operations at Allen and Catawba Nuclear Station.
11

CWA§316(a)Balanced and Indigenous Community Study Report(2014-2021)
ALLEN STEAM STATION
Catawba River Inflow
S. Fork Catawba River Inflow
Plant Allen
Plant Allen Discharge.—_
°K
Area Shaded in Purple has Delta-T>5°F(2.78°C)
Area Shaded in Blue has Delta-T>3°F(1.67°C)
Catawba Nuclear �- -
�f
kNyi;,: i ar
Figure 1-5.Average summer thermal plume prediction using CE-QUAL-W2 Model with 2007 hydrology and
meteorology and actual 2007 operations at Allen and Catawba Nuclear Station.
12

CWA§316(a)Balanced and Indigenous Community Study Report(2014-2021)
ALLEN STEAM STATION
For purposes of this report and the assessment of the Lake Wylie biological communities, zones of study
were established as they relate to thermal plume characteristics. Based on the results from the 2020
thermal plume model, lake sampling zones were determined based on the thermal plume delineations
from the most recent model confirmations.These zones are described below and depicted in Figures 1-6
and 1-7.
Zone A—Catawba Nuclear Station thermally influenced area
Zone B—Catawba Nuclear Station non-thermally influenced reference area
Zone C—Allen thermally influenced area
Zone D—Allen non-thermally influenced reference area
13

CWA§316(a)Balanced and Indigenous Community Study Report(2014-2021)
ALLEN STEAM STATION
2 Methods
2.1 Water Quality
Water quality and water chemistry data were collected to evaluate the limnological characteristics of
the reservoir and how they may influence aquatic communities.These data were collected to help
provide an understanding of the primary productivity of the reservoir ecosystem and potential chronic
or acute changes in aquatic communities. Water quality and chemistry data were also evaluated in
consideration of cumulative influences with the thermal discharge on a BIC.
Water quality and chemistry monitoring performed in Lake Wylie during 2014-2021 is outlined in Tables
2-1 and 2-2. Field parameter measurements of temperature, dissolved oxygen (DO), pH, and specific
conductivity were taken in situ at each sampling location with a multiparameter data sonde such as a
Hydrolab (OTT Hydromet, Loveland, Colorado) or an Aqua TROLL 600 multiparameter sonde (In-Situ,
Inc. Fort Collins,Colorado). Measurements started at the lake surface (0.3 m) and continued atone-
meter eo e
meter intervals to 10 m,then two-meter intervals to the lake bottom. Pre-and post-calibration
procedures associated with operation of the Hydrolab and Aqua TROLL were documented in both
electronic and hard-copy format. Hydrolab and Aqua TROLL data were captured and stored
electronically and converted to spreadsheet format following data validation.
Lake water samples for laboratory analysis were collected with a peristaltic pump, or by direct grab at
the surface (0.3 m). Samples were collected semi-annually in 2014 and 2015, quarterly from 2016 to
2018,and semi-annually from 2019 to 2021 (Table 2-1). Chlorophyll a samples were collected semi-
annually from 2014 to 2017. In 2018,the sampling strategy changed based on guidance from the
updated 316(a) requirement, and chlorophyll a sampling frequency changed to summer collection only
at select sites. If at any time observed field conditions indicated an active bloom (i.e., D.O. Sat. %>120
and pH >9), then additional chlorophyll a and phytoplankton samples were collected (Table 2-1).
Surface samples not requiring filtration were discharged directly into high-density polyethylene(HDPE)
or polyethylene terephthalate (PET) sample bottles. Dissolved-fraction samples were field-filtered with a
0.45-µm in-line filter capsule and peristaltic pump. Filter capsules were pre-rinsed by running a
minimum of 500 mL of sample water through the filter prior to filling the sample bottles. Filtered and
unfiltered sample bottles were pre-acidified where applicable. Chlorophyll a and nutrient samples were
collected from the measured photic zone using a depth integrated sampler.The photic zone was
determined as twice the secchi depth,which was measured by lowering a secchi disk to extinction prior
to sampling.Samples were stored on ice and in the dark immediately following collection to minimize
the potential for physical, chemical, and/or microbial transformation.
Laboratory analytical methods, reporting limits,and sample preservation techniques are included in
Table 2-2. Most water chemistry samples included in this study were analyzed by the Duke Energy
Analytical Laboratory located in Huntersville, NC(North Carolina Division of Water Resources [NCDWR]
Certification#248). Chlorophyll a samples were analyzed by ETT Environmental laboratories in Greer,SC
(South Carolina Department of Health and Environmental Control [SCDHEC] Certification#23104).
Standard chain of custody procedures and documentation were followed throughout these analyses.
Water quality and analytical chemistry data were subjected to various numerical and graphical
techniques to evaluate spatial and temporal trends within the lake, interrelationships among
constituents, and the potential effect on lake biota. One particular metric evaluated,the trophic state
14

CWA§316(a)Balanced and Indigenous Community Study Report(2014-2021)
ALLEN STEAM STATION
index(TSI; Carlson 1977), assesses the overall productivity of the lake as a whole.TSI values for
phosphorus, Secchi depth,and chlorophyll a were calculated to standardize these select physiochemical
variables for comparison.TSI values range on a scale of 0 to 100 and are considered in relation to the
intended use of the waterbody and BIC support.
Data were evaluated using seasonal comparisons between zones and historical comparisons within
zones.Also, data within each zone were compared to lake-wide values for context. Comparisons for
assessing potential impacts within the Allen thermal influence zone (Zone C) were allowed by the
availability of the non-thermally influenced reference area (Zone D).Analytical results reported to be
equal to or less than the method reporting limit were evaluated at the reporting limit for numerical and
statistical assessments.
The 2014-2021 data were compared to historical data to evaluate changes in the waterbody during the
study period and detect long-term trends (Appendix B). For the purposes of this report, historical water
quality and analytical data included the years 2000-2013.These years had Allen discharge limits
consistent with current years.
Table 2-1. Limnological parameters and monitoring frequency(Q=quarterly,SA=semi-annually,A=annually)
in Lake Wylie during 2014-2021(S=Surface only,PZ= Photic zone).
2014 2015 2016 2017 2018 2019 2020 2021
WATER QUALITY
NUTRIENTS
Total phosphorus SA-S SA-S Q-S Q-S Q-PZ SA-PZ SA-PZ SA-PZ
Orthophosphorus SA-S SA-S Q-S Q-S Q-PZ SA-PZ SA-PZ SA-PZ
Ammonia nitrogen SA-S SA-S Q-S Q-S Q-PZ SA-PZ SA-PZ SA-PZ
Nitrate+nitrite nitrogen SA-S SA-S Q-S Q-S Q-PZ SA-PZ SA-PZ SA-PZ
Total Kjeldahl nitrogen SA-S SA-S Q-S Q-S Q-PZ SA-PZ SA-PZ SA-PZ
Chlorophyll a SA-PZ SA-PZ SA-PZ SA-PZ - A-PZ A-PZ A-PZ
MAJOR IONS
Calcium SA-S SA-S Q-S Q-S Q-S SA-S SA-S SA-S
Magnesium SA-S SA-S Q-S Q-S Q-S SA-S SA-S SA-S
Potassium SA-S SA-S Q-S Q-S Q-S SA-S SA-S SA-S
Sodium SA-S SA-S Q-S Q-S Q-S SA-S SA-S SA-S
Chloride SA-S SA-S Q-S Q-S Q-S SA-S SA-S SA-S
Sulfate SA-S SA-S Q-S Q-S Q-S SA-S SA-S SA-S
PHYSICAL
Secchi SA-S SA-S Q-S Q-S Q-S SA-S SA-S SA-S
Turbidity SA-S SA-S Q-S Q-S Q-S SA-S SA-S SA-S
Hardness(Calculated) SA-S SA-S Q-S Q-S Q-S SA-S SA-S SA-S
Alkalinity(TIP) SA-S SA-S Q-S Q-S Q-S SA-S SA-S SA-S
METALS(TOTAL AND DISSOLVED)
Copper SA-S SA-S Q-S Q-S Q-S SA-S SA-S SA-S
Lead SA-S SA-S Q-S Q-S Q-S SA-S SA-S SA-S
Zinc SA-S SA-S Q-S Q-S Q-S SA-S SA-S SA-S
15

CWA§316(a)Balanced and Indigenous Community Study
ALLEN ReportSTEAM(2014-2021)STATION
GAfou1PNTYf r a�'
NORTH CAROLINA
rf
SOUTH FORK �i =',
CATAWBA RIVER 249.0 _ .�
Legend
is Water Quality } MIEN
Sampling Location 0 STEAM
STATION
Duke Energy 250.0
Facility
'tif" 242.0 ,,r
NC 4
SC L *
235.0
,o
B
225.0
CATAWBA
NUCLEAR � � --
STATION
t B
f F
a 215.0 •r � : ley
I
, �; �200.0 N
A .. 9;I,`55,
fok,DUKE
ENERGY 0 2 5 5 7 5 10
ammi■m Kilometers
Figure 2-1.Limnological sampling locations and zones in Lake Wylie.
16

CWA§316(a)Balanced and Indigenous Community Study Report(2014-2021)
ALLEN STEAM STATION
GASTON COUNTY D
NORTH CAROLINA
SOUTH FORK
CATAWBA RIVER
El
Legend
ALLEN El
0 Fish Sampling STEAM
Location STATION 1
UDuke Energy D .;
Facility
a El
o E
NC
SC J„
B
CATAWBA
NUCLEAR
1-1
STATION -
5
o N
A 0 } El
DUKE ENERGY, 25 5 75 10
>• immomm simmommi Kilometers
Figure 2-2. Fish sampling locations and zones in Lake Wylie.
17

CWA§316(a)Balanced and Indigenous Community Study Report(2014-2021)
ALLEN STEAM STATION
Table 2-2.Analytical methods and reporting limits for parameters monitored in Lake Wylie in 2014-2021.
Reporting
Parameter Method(EPA/APHA) Preservation
Limit
Temperature Thermistor,APHA 2550 In situ 0.1°C
Oxygen, Dissolved Luminescent(LDO)cell,ASTM D888-09-C In situ 0.1 mg/L
pH Glass Electrode, EPA 150.2 In situ 0.1 unit
Conductance,Specific Thermistor, EPA 120.1 In situ 1 µS/cm3
Secchi Hutchinson 1975 N/A N/A
Turbidity Turbidimetric, EPA 180.1 56°C 0.05 NTU
Chlorophyll a SM 10200H Ice,darkness 2 µg/L
Ammonia Colorimetric, EPA 350.1 56°C, H2SO4, pH<2 0.02 mg/L
Total Kjeldahl Nitrogen Colorimetric, EPA 351.2 56°C, H2SO4, pH<2 0.1 mg/L
Nitrate+Nitrite Colorimetric, EPA 353.2 56°C, H2SO4, pH<2 0.01 mg/L
Phosphorus,Total Colorimetric, EPA 365.1 56°C, H2SO4, pH<2 0.005 mg/L
Orthophosphorus Colorimetric, EPA 365.1 5.6°C 0.005 mg/L
Calcium ICP, EPA 200.7 56°C, HNO3, pH<2 0.01 mg/L
Magnesium Atomic Emission/ICP, EPA 200.7 56°C, HNO3, pH<2 0.005 mg/L
Potassium Atomic Emission/ICP, EPA 200.7 56°C, HNO3, pH<2 0.1 mg/L
Sodium Atomic Emission/ICP, EPA 200.7 56°C, HNO3, pH<2 1.5 mg/L
Chloride Ion Chromatography, EPA 300.0 56°C 0.1 mg/L
Sulfate Ion Chromatography, EPA 300.0 56°C 0.1 mg/L
Total Hardness Calculation, EPA 200.7 N/A N/A
Alkalinity Calculation,SM 2320B4d 56°C 5 mg/L
Copper,Total Recoverable ICP Mass Spectroscopy, EPA 200.8 56°C, HNO3, pH<2 1.0 p.g/L
Copper, Dissolved ICP Mass Spectroscopy, EPA 200.8 56°C, HNO3, pH<2 1.0 µg/L
Lead,Total Recoverable ICP Mass Spectroscopy, EPA 200.8 56°C, HNO3,pH<2 0.2 µg/L
Lead, Dissolved ICP Mass Spectroscopy, EPA 200.8 56°C, HNO3, pH<2 0.2 µg/L
Zinc,Total Recoverable ICP Mass Spectroscopy, EPA 200.8 56°C, HNO3, pH<2 5 µg/L
Zinc, Dissolved ICP Mass Spectroscopy, EPA 200.8 56°C, HNO3, pH<2 5 µg/L
2.2 Planktonic Community
Phytoplankton and zooplankton are generally considered to be low potential impact (LPI) biotic
categories,therefore narrative assessments of these components were made and included within the
framework of the Lake Wylie BIC.The assessment of plankton as LPI was performed using scientific
literature and historical planktonic community data collected from Lake Wylie (Duke Energy 2020a).The
validity of using a narrative approach can be found in the most recent 316(a) review by Coutant(2013).
18