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Home My WebLink AboutNC0004979_Report_20220201 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) -r 4 �. 14 i. € a ' i�` .ve 4,,,,„ ... , __,_„,________________..„...7,.„.„.:...„....__ _.....,..._..„,.. ..t.,_-. ‘ ALLEN STEAM STATION Lake Wylie, Belmont, North Carolina NPDES Permit# NC0004979 Duke Energy Environmental Sciences Huntersville, NC January 2022 a.) DUKE ENERGY 1 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 4 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 July 11.1 27.9 34.7 39.0 37.1 30.0 34.4 93.9 August 32.7 4.8 5.8 13.1 12.1 13.7 32.8 91.0 September 23.0 9.3 13.4 3.3 0.0 9.8 35.6 96.1 October 0.0 0.0 0.0 7.8 10.8 3.7 27.2 81.0 November 19.7 19.4 31.7 48.6 56.8 35.2 25.0 77.0 December 5.5 9.3 18.2 24.8 26.4 16.8 21.7 71.1 2014 Avg 18.9 16.8 26.4 27.3 27.6 23.4 27.1 80.8 2015 January 8.3 9.8 12.2 23.1 17.4 14.2 15.6 60.1 February 42.4 49.1 53.3 64.3 46.7 51.1 15.6 60.1 March 0.0 13.3 4.8 3.7 14.7 7.3 13.9 57.0 April 0.0 0.0 0.0 0.0 0.0 0.0 NA NA May 0.0 0.0 24.3 0.0 8.5 6.6 28.9 84.0 June 35.4 35.4 45.3 22.9 44.5 36.7 36.7 98.1 July 41.3 32.3 30.9 57.4 36.5 39.7 36.7 98.1 August 16.9 15.8 29.5 62.0 49.5 34.7 35.6 96.1 September 7.1 6.9 0.0 8.7 8.6 6.3 33.9 93.0 October 3.9 2.0 0.0 0.0 0.0 1.2 25.0 77.0 November 0.0 0.0 0.0 0.0 0.0 0.0 20.0 68.0 December 5.1 1.1 0.0 0.0 0.0 1.2 21.7 71.1 2015 Avg 13.4 13.8 16.7 20.2 18.9 16.6 25.8 78.4 2016 January 14.6 10.7 6.0 18.7 8.1 11.6 19.4 66.9 February 13.2 12.5 14.2 31.4 21.1 18.5 18.3 64.9 March 2.0 1.5 0.0 53.6 0.0 11.4 25.0 77.0 April 7.1 6.9 0.0 4.6 0.0 3.7 24.4 75.9 May 0.0 4.3 0.0 0.0 0.0 0.9 32.8 91.0 June 31.3 30.0 46.2 0.0 0.0 21.5 33.9 93.0 July 60.3 54.4 52.6 0.0 36.9 40.8 37.2 99.0 August 18.0 36.9 70.2 3.7 59.0 37.6 36.7 98.1 September 7.2 28.4 15.0 24.8 53.7 25.8 35.0 95.0 October 2.8 4.0 7.9 0.0 7.9 4.5 31.1 88.0 November 0.0 0.0 0.0 0.0 0.0 0.0 NA NA December 0.3 2.1 14.8 12.8 0.0 6.0 17.6 63.7 2016 Avg 13.0 16.0 18.9 12.5 15.6 15.2 28.3 83.0 2017 January 22.8 19.8 17.2 19.1 22.0 20.2 21.3 70.3 February 0.0 0.0 3.2 0.0 0.0 0.6 16.7 62.1 March 4.5 6.3 0.0 4.1 10.4 5.1 22.1 71.8 April 7.4 7.6 0.0 9.0 11.8 7.2 23.6 74.5 May 0.0 0.0 0.8 9.7 11.0 4.3 25.2 77.4 June 0.0 0.0 1.7 0.0 16.5 3.6 29.9 85.8 July 18.5 18.2 27.5 25.3 40.5 26.0 35.4 95.7 August 0.0 0.0 17.0 16.8 28.2 12.4 31.6 88.9 5 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 September 11.4 7.1 21.2 17.0 20.5 15.4 28.9 84.0 October 5.3 6.2 12.7 17.8 17.7 11.9 26.1 79.0 November 0.0 0.0 0.0 0.0 0.0 0.0 17.2 63.0 December 7.8 4.4 10.1 0.0 0.0 4.5 13.4 56.1 2017 Avg 6.5 5.8 9.3 9.9 14.9 9.3 24.3 75.7 2018 January 38.2 51.5 33.2 31.8 39.1 38.7 17.7 63.9 February 0.0 0.0 0.0 0.0 0.0 0.0 10.9 51.6 March 0.0 0.0 0.0 0.0 0.0 0.0 12.1 53.8 April 0.0 0.0 0.0 1.6 0.0 0.3 17.7 63.9 May 8.3 5.2 9.5 3.7 11.0 7.5 25.2 77.4 June 7.2 8.2 9.1 9.9 20.4 10.9 30.9 87.6 July 0.0 0.0 0.0 0.0 11.4 2.3 30.4 86.7 August 0.0 0.0 0.0 0.0 21.0 4.2 31.2 88.2 September 0.0 0.0 15.8 25.3 33.9 15.0 33.8 92.8 October 8.6 9.0 12.4 17.8 29.1 15.4 28.4 83.1 November 0.0 0.0 0.0 0.0 0.0 0.0 15.4 59.7 December 0.0 0.0 2.0 4.8 6.8 2.7 12.5 54.5 2018 Avg 5.2 6.2 6.8 7.9 14.4 8.1 22.2 71.9 2019 January 0.0 0.0 0.0 0.0 3.8 0.8 11.7 53.1 February 0.0 0.0 0.0 0.0 0.6 0.1 10.9 51.7 March 0.0 0.0 0.0 0.0 0.0 0.0 12.2 54.0 April 0.0 0.0 6.6 6.5 0.6 2.7 19.1 66.4 May 0.0 0.0 1.6 6.1 8.3 3.2 25.4 77.8 June 9.1 19.7 8.6 7.8 21.7 13.4 30.9 87.6 July 15.6 5.2 0.0 13.0 42.4 15.2 35.3 95.6 August 24.3 9.2 0.0 0.0 35.8 13.9 34.5 94.1 September 42.0 34.1 42.5 35.2 54.0 41.6 36.6 97.9 October 7.6 7.6 8.4 8.1 8.6 8.1 24.9 76.9 November 5.6 5.0 8.5 9.5 10.3 7.8 17.3 63.2 December 0.0 0.0 0.0 10.1 0.0 0.0 13.7 56.7 2019 Avg 8.7 6.7 6.3 8.0 15.5 9.0 22.7 72.9 2020 January 0.0 0.0 0.0 0.0 0.0 0.0 11.2 52.1 February 0.0 0.0 0.0 0.0 0.0 0.0 11.2 52.2 March 0.0 0.0 0.0 0.0 0.0 0.0 14.2 57.6 April 0.0 0.0 0.0 0.0 0.0 0.0 17.9 64.2 May 0.0 0.0 0.0 0.0 0.0 0.0 20.4 68.7 June 0.0 0.0 0.0 7.2 10.2 3.5 26.7 80.1 July 4.5 5.3 5.5 47.6 44.9 21.6 36.2 97.1 August 7.3 8.3 0.0 0.0 33.4 9.8 32.2 90.0 September 0.0 0.0 3.0 6.7 2.1 2.4 27.5 81.5 October 0.0 0.0 1.1 19.3 19.2 7.9 22.2 71.9 6 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