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Home My WebLink AboutNC0004961_Review-Ass of Balanced & Indigenous Popultions_20091117Yt1�� NCDENR North Carolina Department of Environment and Natural Resources Division of Water Quality Beverly Eaves Perdue Governor Allen Stowe Water Management, Duke Energy EC13K PO Box 1006 Charlotte, NC 28201-1006 Coleen H. Sullins Director November 17, 2009 Dee Freeman Secretary Subject Review of Duke Energy Carolinas, NPDES Permit NC0004961, "Assessment of Balanced and Indigenous Populations in Mountain Island Lake near Riverbend Steam Station", August 2009 Environmental Sciences Section staff have reviewed the subject document which was received on August 28, 2009 We apologize for the delay on communicating our comments back to you Jeff DeBerardinis, Eric Fleek, Debra Owen, and Bryn H Tracy reviewed the sections on trace element analyses in fish, macroinvertebrates, water and sediment chemistry, and fish, respectively By agreement with the Department of Environment and Natural Resources (NCDENR), Duke Energy conducts annual monitoring of Mountain Island Lake in the vicinity of the Riverbend Steam Station to support NPDES Permit NC0004961 (A.(1) Effluent Limits ions an'Monitoring Requirements – Final ("The Regional �- Administrator has determined pursuant to Section 316(a) of the Act 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 body of water") The power plant operates under an DWQ- and EPA -approved §316(a) thermal variance The report does fulfill the permit obligations for reporting the results of the biological monitoring Based on a review of the current dates, it is our opinion that tl�e iverbend Steam Station is unlikely in having an impact to the benthic macroinvertebrate ,and fish communit P► -s �n Mountain Island Lake We also conclude t a t e twFi—o aquatic communities currently qualify as balanced, indigenous communities We do have some comments and observations and analysis requests for future reports Comments and Observations 1 Nutrient concentrations in Mountain Island Lake were similar to those previously observed during DWQ's lake sampling However, nutrient loading appears to be increasing from McDowell Creek Total phosphorus and specific conductance are generally greater in the McDowell Creek cove as compared with the rest of the reservoir The entire 11 6 mile long McDowell Creek, from its source to its confluence with the lake, is listed as impaired for biological integrity on DWQ's 2006 EPA -approved §303(d) list 2 Aqueous concentrations of metals were low and consistent with the low levels of turbidity and suspenderLsolids se measu n s aree wih th egte surface metal sampling conducted by DWQ However, sample of total recoverable arsenic 11 4 ug/1.)-�eater than the state water quality standard of 10 pg/L This water sample was collected on August 20, 2008 near the bottom near the forebay of thq Mountain Island Hydropower Station 3 The fish assemblage in this multi-purpose reservoir is comprised of 22 indigenous and 13 nonindigenous species (Tables 5-1 and 5-2) The nonindigenous species have been introduced for one reason or another either accidentally or to manage the reservoir's fishery and aquatic since impoundment of the Catawba River Section 316(a) of the Clean Water Act does allow for " Such a community may include historically non-native species introduced in connection with a program of wildlife management and species whose presence or abundance results from substantial, irreversible environmental modification" (40CFR 125 71(c) 1621 Mail Service Center, Raleigh, North Carolina 27699-1621 Location 4401 Reedy Creek Road, Raleigh, North Carolina 27607 Phone 919-743-84001 FAX 919-743-85171 Customer Service 1-877-623-6748 Internet htto //h2o enr state nc uslesb/ An Equal Opportunity 1 Affirmative Action Employer NonrthCarohna Naturally ► - Allen Stowe November 17, 2009 Page 2 4 Concentrations of trace elements, especially mercury, selenium, and arsenic, in the tissue of Common Carp, sunfish, and bass continued to be less than concentrations of regulatory concern and have remained low for the past decade All selenium concentrations were well below the North Carolina Department of Health and Human Services (NCDHHS) criterion of 10 pg/g (parts per million) All arsenic concentrations were less than the US EPA criterion of 1.2 pg/g for recreational fishermen, no criterion exists in NC All mercury concentrations were less than the NCDHHS criterion of 0 4 pg/gm for recreational fishermen There are no state or federal criterion for zinc concentrations in fish tissue Analysis Requests For the 2014 report, it would also be advantageous if you could provide additional information to aid in our interpretation of the data 1 In addition to Tables 4-1 through 4-3, please include a taxonomic table comparing taxa occurrences for the current sampling year for each station so that a direct side-by-side comparison can be more easily conducted Please see Table 1 as an example Table 1. Waterbody Licklog Branch Sugarloaf Creek Scott Creek Date 8/9/2007 8/9/2007 8/9/2007 Location SR 1706 off SR 1708 off SR 1556 County Jackson Jackson Jackson Taxon Ephemeroptera Acentrella spp R Plaud►tus dub►us gp C A Baetts flawstr►ga R Pseudocloeon propinguum R 2 In addition to Figures 4-1 through 4-5, please Include the following graphs for each station and year (in the same format as currently presented) for the following groups. Non-Chironomid Diptera, Ephemeroptera, Plecoptera, Trichoptera, Coleoptera, Odonata, Megaloptera, Crustacea, and Mollusca Again, this will allow for a more direct side-by-side comparison for each station and each taxonomic group 3 In addition, EPT taxa richness and EPT density should also be reported for each station going forward These metrics can be reported in accordance with current graphical formats If you have any questions, please do not hesitate to contact me or my staff. Yours truly, Jay Sauber Acting Chief, Environmental Sciences Section cc Jeff DeBerardinis, Environmental Sciences Section Eric Fleek, Environmental Sciences Section Rob Krebs, Mooresville Regional Office Debra Owen, Environmental Sciences Section Jeff Poupart, Surface Water Protection Section Bryn H Tracy, Environmental Sciences Section Charles Weaver, Surface Water Protection Section ME ASSESSMENT OF BALANCED AND INDIGENOUS POPULATIONS IN MOUNTAIN ISLAND LAKE NEAR RIVERBEND STEAM STATION NPDES Permit No. NC0004961 Principal Investigators: Michael A. Abney John E. Derwort Keith A. Finley DUKE ENERGY Corporate EHS Services McGuire Environmental Center 13339 Hagers Ferry Road Huntersville, NC 28078 August 2009 ACKNOWLEDGMENTS The authors wish to express their gratitude to a number of individuals who made significant contributions to this report. First, we are much indebted to the EHS Scientific Services field staff in carrying out a complex, multiple -discipline sampling effort that provides the underpinning of this report. We would like to thank Glen Long for support in water quality and sediment sample collections. Mark Auten, Kim Baker, Bob Doby, James Hall, Bryan Kalb, Glenn Long, and Todd Lynn were vital contributors in completing fisheries collections and sample processing. James Hall, Aileen Lockhart, Shannon McCorkle, and Jan Williams contributed in macroinvertebrate sampling, sorting and taxonomic processing. We would also like to thank multiple reviewers; including Penny Franklin, Duane Harrell, Ron Lewis, and John Velte. The insightful commentary and suggestions from these individuals and also between co-authors have benefited the report in myriad ways. ii I TABLE OF CONTENTS EXECUTIVESUMMARY......................................................................................... .... v LISTOF TABLES............................................................................................................... vii LIST OF FIGURES .. . ................................................................................................ viii CHAPTER 1- INTRODUCTION........................................................................................1-1 REGULATORY CONSIDERATIONS .......................................................... .......... 1-2 CHAPTER2- STATION OPERATION............................................................................ 2-1 METHODS..................................................................................................................... 2-1 RESULTS AND DISCUSSION..................................................................................... 2-1 StationOperation......................................................................................................... 2-1 ThermalCompliance.................................................................................................. 2-2 Compliance with EPA Nomograph -Related Thermal Limits ..................................... 2-2 CHAPTER 3- WATER AND SEDIMENT CHEMISTRY ............................................... 3-1 MATERIALS AND METHODS.................................................................................... 3-1 Collection of Field Parameters, Water, and Sediment Chemistry Samples ................. 3-1 AnalyticalMethods...................................................................................................... 3-2 RESULTS AND DISCUSSION..................................................................................... 3-3 WaterQuality.............................................................................................................. 3-3 RSS Ash Basin Effluent Selenium and Arsenic Mass Loading Estimates .................. 3-8 Sediment Elemental Analyses...................................................................................... 3-9 CONCLUSIONS........................................................................................................... 3-10 CHAPTER 4- MACROINVERTEBRATES...................................................................... 4-1 MATERIALS AND METHODS.................................................................................... 4-1 RESULTS AND DISCUSSION..................................................................................... 4-1 Substrate....................................................................................................................... 4-1 Density......................................................................................................................... 4-2 TaxaAbundance.......................................................................................................... 4-2 CONCLUSIONS............................................................................................................. 4-3 CHAPTER5- FISH.............................................................................................................. 5-1 MATERIALS AND METHODS.................................................................................. 5-1 Winter and Summer Electrofishing Surveys................................................................ 5-1 Spring Electrofishing Surveys..................................................................................... 5-1 Fall Hydroacoustics and Purse Seine Surveys............................................................. 5-2 Trace Element Analyses............................................................................................. 5-2 Balanced and Indigenous Assessment........................................................................ 5-2 RESULTS AND DISCUSSION................................................................................... 5-3 Winter Electrofishing Surveys.................................................................................... 5-3 ff Summer Electrofishing Surveys............................................................................. 5-3 Spring Electrofishing Surveys................................................................................ 5-4 Fall Hydroacoustics and Purse Seine Surveys.......................................................... 5-5 CONCLUSIONS......................................................................................................... 5-6 LITERATURE CITED..................................................................................................... L-1 APPENDIXTABLES...................................................................................................... A-1 IV EXECUTIVE SUMMARY Per agreement with the North Carolina Department of Environment and Natural Resources (NCDENR), annual monitoring of macroinvertebrates and fish was initiated in 1990 at selected locations in Mountain Island Lake to evaluate potential impacts of the Riverbend Steam Station (RSS) condenser cooling water discharge on balanced and indigenous populations in Mountain Island Lake. Water quality and sediment samples collected also provided information relative to the biological assessment. This report compares monitoring data collected from 2004 — 2008 and past studies. As in the past, during 2004 — 2008, RSS operated primarily as a peaking facility. Electric generation, occurred on 81% of available days, with the entire station operating at an average of 48% of capacity over the period. Thermal limits specified in the RSS National Pollutant Discharge Elimination System (NPDES) permit were not exceeded. Average monthly condenser cooling water (CCW) discharge temperatures ranged from 4.9 °C (58.9 °F) in February 2005, to 34.7 °C (94.4 °F) in August 2007. These temperatures followed a regular seasonal pattern and were within the range of previously reported values. The discharge water temperature of RSS was continually monitored to ensure compliance and to assist in the investigation of potential impacts to downstream biota. Water quality in Mountain Island Lake during 2004 — 2008 was similar to previous years. Seasonal thermal stratification, and dissolved oxygen concentrations were representative of historical ranges. Lake -wide, concentrations of major nutrients, similar to historical levels, continued to result in Mountain Island Lake being classified as oligotrophic to mesotrophic during 2004 — 2008. Typically elevated concentrations of dissolved and suspended material, as well as nutrients entering the lake from the McDowell Creek drainage were slightly lower during 2004 — 2008. Mass loading of selenium and arsenic from the RSS ash basin outfall during 2004 — 2008 was similar to historical trends, except for reductions observed in arsenic loading over the 2007 — 2008 period. Mountain Island Lake concentrations of aqueous trace elements remained generally low, consistent with low levels of turbidity and suspended solids. March 2008 arsenic concentrations in fine surficial sediments were elevated downstream of RSS in the forebay of Mountain Island Hydroelectric Station (MIHS) with respect to uplake v concentrations, with samples dust downstream of the RSS ash basin effluent confluence yielding the highest concentrations. While the 2008 samples were likely influenced by a slight relocation of the sampling s_te due to difficulty in obtaining material other than coarse sand at the former location, MIHS forebay sediment sampling continues to indicate a slight, gradual increase in arsenic concentrations over recent years. Sediment concentrations of selenium were consistently low lake -wide. As a whole, 2004 — 2008 Mountain Island Lake water and sediment chemistry continue to indicate the waterbody remains capable of sustaining balanced and indigenous aquatic communities. Trace element concentrations measured in Mountain Island Lake common carp, sunfish, and largemouth bass since 1988 remain well below values of regulatory concern. As in previous years, annual samples of the macroinverterbrate community collected uplake, downlake, and adjacent to the RSS discharge area during 2004 — 2008 were comprised primarily of Oligochaeta, Diptera, and Corbicula. Comparison of macroinvertebrate densities and taxa abundance continues to indicate no apparent adverse effect of the heated discharge on the macroinvertebrate community in the vicinity of the discharge. Electrofishing samples have shown a persistent and stable fish community present in the littoral portions of Mountain Island Lake around RSS from 2004 to 2008. The assorted fish species typically found in Mountain Island Lake encompass a range of trophic groups including insectivores, omnivore:, and piscivores that indicate a balanced and indigenous fish community. Forage fish population densities were comparable to those measured previously at Mountain Island Lake and to other Catawba River reservoirs of similar trophic status. The introduction of alewife, the inherent, temporal variability of clupeid populations, and the historical flux of Mountain Island Lake between oligotrophic and mesotrophic water quality classifications are all factors contributing to the unpredictable nature of forage fish densities. Based on the diversity and numbers of individuals in the Mountain Island Lake littoral fish community during winter, spring, and summer; the range of trophic groups represented; the lack of accumulation of selenium, arsenic, mercury, or zinc in fish flesh; and the regular availability of forage fish to limnetic predators; it is concluded that the operation of RSS has not impaired the protection and propagation of a balanced and indigenous fish community in Mountain Island Lake. vi h_ LIST OF TABLES Table Title Page 1-1 Biological and water quality monitoring locations on Mountain Island Lake............ 1-5 2-1 RSS monthly units 4 through 7 (U4 — U7), monthly average (Av), and annual station coal-fired capacity factors (percent) during 2004 — 2008 ............................... 2-3 3-1 Analytical methods used to determine chemical and physical constituents in Mountain Island Lake during 2004 — 2008.............................................................. 3-12 4-1 Densities (number/m2) of macroinvertebrates collected annually from Location B (upstream of RSS) from 2000 — 2008........................................................................ 4-5 4-2 Densities (number/m2) of macroinvertebrates collected annually from Location F (RSS discharge) from 2000 — 2008............................................................................. 4-9 4-3 Densities (number/m2) of macroinvertebrates collected annually from Location G (downstream of RSS) from 2000 — 2008................................................................. 4-12 5-1 Number of individuals and number of species in winter electrofishing surveys from three locations (B, F, and G) in Mountain Island Lake, 1994 — 1999, 2000 — 2003, and 2004 — 2008................................................................................................ 5-8 5-2 Number of individuals and number of species in summer electrofishing surveys from three locations (B, F, and G) in Mountain Island Lake, 1991 — 1993, 1994 — 1999, 2000 — 2003, and 2004 — 2008.......................................................................... 5-9 5-3 Number of individuals, biomass, and number of species collected during spring electrofishing of five 300-m transects downlake and five 300-m transects uplake of the RSS discharge canal in Mountain Island Lake, 1993 —1997, 1999 — 2008... 5-10 5-4 Number of individuals and number of species collected during spring electrofishing of ten 300-m transects in the vicinity of the RSS discharge canal in Mountain Island Lake, 1994 —1997 and 1999, 2000 — 2003, and 2004 — 2008...5-11 5-5 Number, percentage, average length, average density, and forage fish population estimates in Mountain Island Lake, 1993 — 1997, 1999 — 2008, from mid- September purse seine and hydroacoustic surveys ................................................... 5-12 vii LIST OF FIGURES y Figure Title Page 1-1 Sampling locations on Mountain Island Lake. Duke Energy historical location identifiers are listed in parentheses . . ...... ...... ................................ ........................... 1-6 2-1 Average monthly CCW discharge temperatures (solid circles) and monthly range daily average temperatures (open circles), displayed over days per month of RSS coal-fired generation during 2004 — 2008 ............................................ .................... 2-4 2-2 Average monthly downstream temperatures (solid circles) and monthly range of daily average temperatures (open circles).................................................................. 2-4 3-1 Winter profiles of temperature (°C; ■) and dissolved oxygen (mg/L; ❑) at the viii Mountain Island Lake forebay, Location G.............................................................. 3-15 3-2 Summer profiles of temperature (°C; ■) and dissolved oxygen (mg/L; ❑) at the Mountain Island Lake forebay, Location G.... ............... ......................................... 3-16 3-3 Semi-annual specific conductance profiles in Mountain Island Lake, 2004 — 2008........................................................................................................................ 3-17 3-4 Semi-annual pH profiles in Mountain Island Lake, 2004 — 2008 ............................ 3-18 3-5 Distribution of Mountain Island Lake specific conductance ..................................... 3-19 3-6 Distribution of Mountain Island Lake pH................................................................. 3-19 3-7 Distribution of Mountain Island Lake total alkalinity concentrations ..................... 3-19 3-8 Distribution of Mountain Island Lake turbidity........................................................ 3-20 3-9 Distribution of Mountain Island Lake total suspended solids concentrations........... 3-20 3-10 Distribution of Mountain Island Lake ammonia nitrogen concentrations ................. 3-20 3-11 Distribution of Mountain Island Lake nitrate+nitrite nitrogen concentrations......... 3-21 3-12 Distribution of Mountain Island Lake total nitrogen concentrations ........................ 3-21 3-13 Distribution of Mountain Island Lake soluble orthophosphate concentrations........ 3-21 3-14 Distribution of Mountain Island Lake total phosphorus concentrations ................... 3-22 3-15 Distribution of Mountain Island Lake calcium concentrations ................................. 3-22 3-16 Distribution of Mountain Island Lake magnesium concentrations ........................... 3-22 3-17 Distribution of Mountain Island Lake sodium concentrations .................................. 3-23 3-18 Distribution of Mountain Island Lake potassium concentrations ............................. 3-23 3-19 Distribution of Mountain Island Lake chloride concentrations ................................. 3-23 3-20 Distribution of Mountain Island Lake sulfate concentrations ................................... 3-24 3-21 Distribution of Mountain Island Lake iron concentrations ....................................... 3-24 3-22 Distribution of Mountain Island Lake manganese concentrations ............................ 3-24 3-23 Distribution of Mountain Island Lake aluminum concentrations .............................. 3-25 3-24 Distribution of Mountain Island Lake silica concentrations ..................................... 3-25 3-25 Distribution of Mountain Island Lake arsenic concentrations ................................. 3-25 3-26 Distribution of Mountain Island Lake barium concentrations .................................. 3-26 3-27 Distribution of Mountain Island Lake copper concentrations ................................... 3-26 viii r. LIST OF FIGURES, Continued Figure Title Page 3-28 Distribution of Mountain Island Lake soluble copper concentrations ...................... 3-26 3-29 Distribution of Mountain Island Lake mercury concentrations ................................ 3-27 3-30 Distribution of Mountain Island Lake zinc concentrations ....................................... 3-27 3-31 Average annual RSS ash basin discharge and arsenic loading to Mountain Island Lake, 1992 — 2008..................................................................................................... 3-28 3-32 Average annual RSS ash basin discharge and selenium loading to Mountain Island Lake, 1992 — 2008........................................................................................ 3-28 3-33 Distribution of arsenic concentrations in sediment fines sampled from Mountain Island Lake upstream (US) and downstream (DS) of the RSS ash basin outfall...... 3-29 3-34 Distribution of selenium concentrations in sediment fines sampled from Mountain Island Lake upstream (US) and downstream (DS) of the RSS ash basin outfall........................................................................................................................ 3-29 4-1 Density (number/m2) of macroinvertebrates collected annually during 2000 — 2008 from Mountain Island Lake.............................................................................. 4-16 4-2 Total number of macroinvertebrate taxa collected annually during 2000 — 2008 from Mountain Island Lake....................................................................................... 4-16 4-3 Density (number/m2) of Oligochaeta, Diptera, and Corbacula collected annually during 2000 — 2008 from Location B in Mountain Island Lake ............................... 4-17 4-4 Density (number/m2) of Oligochaeta, Diptera, and Corbacula collected annually during 2000 — 2008 from Location F in Mountain Island Lake ................................ 4-17 4-5 Density (number/m) of Oligochaeta, Diptera, and Corbicula collected annually during 2000 — 2008 from Location G in Mountain Island Lake ............................... 4-18 5-1 Number of fish (a), and fish species (b) collected from electrofishing a 100-m transect at each of three locations (B, F, and G) during winter electrofishing in Mountain Island Lake, 1994 — 2008......................................................................... 5-13 5-2 Number of fish (a), and fish species (b) collected from electrofishing a 100-m transect at each of three locations (B, F, and G) during summer electrofishing in Mountain Island Lake, 1994 — 2008......................................................................... 5-14 5-3 Selenium concentrations in muscle tissue from common carp (a), sunfish (b), and bass (c) from four locations (A, B, C, and G) in Mountain Island Lake, 1994 — 2008. The only complete common carp samples were Locations A (2004 — 2006) and C (2005).................................................................................................. 5-15 5-4 Arsenic concentrations in muscle tissue from common carp (a), sunfish (b), and bass (c) from four locations (A, B, C, and G) in Mountain Island Lake, 1994 — 2008. The only complete common carp samples were Locations A (2004 — 2006) and C (2005)................................................................................................... 5-16 ix LIST OF FIGURES, Continued I Figure Title Page 5-5 Mercury concentrations in muscle tissue from common carp (a), sunfish (b), and bass (c) from four locations (A, B, C, and G) in Mountain Island Lake, 1995 — 2008. The only complete common carp samples were Locations A (2004 — 2006) and C (2005)................................................................................................... 5-17 5-6 Zinc concentrations in muscle tissue from common carp (a), sunfish (b), and bass (c) from four locations (A, B, C, and G) in Mountain Island Lake, 1997 — 2008. The only complete common carp samples were Locations A (2004 — 2006) and C(2005).................................................................................................................... 5-18 x IL - CHAPTER 1 INTRODUCTION Riverbend Steam Station (RSS) is located northwest of Charlotte, in Gaston County, North Carolina on 25 -km Mountain Island Lake, one of the 11 Catawba River reservoirs (Figure 1- 1) The RSS began commercial service in 1929. Three of the oldest generating coal-fired units (I — 3) were retired from service in the 1970s. The station presently has four operating coal-fired units (4 — 7), with a combined generating capacity of 454 MWe-net. Units 4 and 5 began commercial operation in 1952, and units 6 and 7 followed in 1954. In recent years RSS generation has typically been used to meet peak electric power demand, and as such, short-term and cyclic operation of selected units is common In the 1990s, the four coal-fired units were modernized to improve reliability in light of their role in meeting electrical load peaks; the above -listed unit capacities reflect those modifications. Four additional combustion turbine units located at the RSS site, each of 30 MWe-net capacity, are not condenser -cooled and therefore do not reject heat to Mountain Island Lake. The RSS coal-fired units 4 — 7 utilize Mountain Island Lake as a source for once -through condenser cooling water (CCW). The CCW intake and discharge structures for RSS are located approximately 10.6 and 22.0 river km, respectively, downstream of Cowans Ford Hydroelectric Station (CFHS; impounding Lake Norman). The RSS CCW discharge structure is approximately 2.7 km upstream of Mountain Island Hydroelectric Station (MIHS). Each generating unit has two CCW pumps that can be operated independently. Station operators run either one or two pumps per unit depending on intake water temperature, discharge temperature limits, and operational efficiency. The four RSS once - through -cooled units are capable of withdrawing CCW at a combined maximum rate of 18.2 m3/s (642 cfs). 1-1 REGULATORY CONSIDERATIONS _y Current National Pollutant Discharge Elimination System (NPDES; NCDENR 2005) permitted thermal limits for RSS CCW effluent, based upon an approved 316(a) thermal variance, are: • a monthly average CCW discharge (i.e., end -of -pipe) temperature limit of 35 °C (95 °F), and • a daily average downstream water temperature limit of 32 0 °C (89.6 °F) measured at Mountain Island Hydroelectric Station. The RSS NPDES permit stipulates additional delta temperature (OT) thermal effluent limits (i.e., maximum permissible temperature increase above ambient, or upstream conditions), based on the. Environmental Protection Agency (EPA) nomograph (USEPA 1976), under specific operational conditions. The EPA nomograph limits are intended to protect warmwater fish from "cold shock" in the event of a winter season plant shutdown. These operational constraints (paraphrased below) were originally approved by the North Carolina Department of Environment and Natural Resources NCDENR in 1993, and incorporated into subsequent RSS NPDES permits, including the present permit: • when only one RSS control system is operating and the inlet water temperature ranges from 2.5 'C (36.5 °F) to < 12.8 `C (55 °F), then the average daily discharge water temperature limit is two times the inlet temperature (°F) minus 23, and • when only one RSS control system is operating and the inlet water temperature is < 2.5 ° C (36.5 °F), then the average daily discharge water temperature limit is 10 'C (50 °F). Assessment of the potential influence of thermal discharges on biological communities is a key component of thermal discharge variances granted under section 316(a) of the Clean Water Act (CWA). The term "balanced, indigenous community" [40CFR125.71(c)] is synonymous with the term "balanced, indigenous population" in the CWA, and refers to a biotic community typically characterized by diversity, the capacity to sustain itself through cyclic seasonal changes, presence of necessary food chain species and a lack of domination by pollution tolerant species. Such a community may include historically non-native species introduced in connection with a program of wildlife management and species whose presence or abundance results from substantial, irreversible environmental modifications (USEPA 1977). 1-2 r Pursuant to an agreement with the NCDENR, annual monitoring of macroinvertebrates and fish was initiated in 1990 at selected Mountain Island Lake locations in the vicinity of RSS. The objectives of this ongoing monitoring program were to assess macroinvertebrate and fish populations with respect to operation of RSS, and provide an indication of the suitability of approved thermal limits as defined in the RSS NPDES permit. Additionally, water quality and sediment samples were evaluated to provide information relevant to the biological assessment, but also to characterize potential impacts to the reservoir relating to the permitted RSS ash basin discharge. Water quality and biological samples are collected each year from established Mountain Island Lake sample locations (A — G) upstream, within the immediate influence of, and downstream of the RSS thermal discharge. Additionally, fish are collected from 10 shoreline segments in the vicinity of RSS in the spring (Table 1-1 and Figure 1-1). Finally, sediment samples are collected generally once per permit period at selected locations upstream and downstream of the RSS ash basin discharge. Conventional Duke Energy sample location numbers associated with Locations A through G are provided in Table 1-1 and Figure 1-1 for reference to previously submitted reports. Locations A and B are upstream of the RSS thermal discharge (Location A is also upstream of the station CCW intake) and for the purposes of the 316(a) monitoring program, these two locations were considered reference sites. Location C is immediately downstream of the RSS ash basin discharge. This location is used in conjunction with Location B to evaluate water quality and sediment chemistry in relation to the potential impacts of the RSS ash basin discharge. Location D is situated in the McDowell Creek arm of Mountain Island Lake and is utilized to characterize potential water quality impacts resulting from inflows from that extensively developed sub -catchment. Location E represents the area where Charlotte -Mecklenburg Utilities Department (CMUD) withdraws raw lake water for drinking water supply; water chemistry is sampled to assist in characterizing Mountain Island Lake water quality at the site. Location F is adjacent to the RSS CCW thermal discharge and is utilized to evaluate potential near -field effects on aquatic biota from heated effluents. Finally, Location G is situated at the Mountain Island Lake forebay and represents a far -field site for evaluating impacts of the RSS thermal discharge. Previous studies of this site have established that the existing limits on the thermal component of the discharge of RSS have assured the protection and propagation of balanced, indigenous populations in Mountain Island Lake (Duke Power Company 1994; Duke Power 2001 and 2004). This report presents results related to RSS operations from data collected since submittal of the previous (2004) summary report and includes data collected from 2004 1-3 Table 1-1. Biological and water quality monitoring locations on Mountain Island Lake. 1 Latitude/longitude data obtained from TOPOI USGS mapping software (National Geographic Holdings, Inc 2001) River km (mi) Report Duke County Description Assessments Upstream of Location Energy Mountain Latitude' Longitude' Designation Location Island N W No. Hydroelectric Station A 16.0 Gaston / Catawba River at entrance to Duck Cove Water quality 17.2 35° 22 894' 80° 58 817 Mecklenburg Sediments (10.7) Fish Mecklenburg Catawba River upstream and north of RSS ash Water quality 116 35° 22 358' 80° 57 363' B 2776 basin discharge, eastern side of lake Sediments (7 2) Macroinvertebrates Fish C 2775 Gaston / Catawba River downstream of RSS ash basin Water quality 108 35° 22 009' 80° 57 085' Mecklenburg discharge and upstream of McDowell Creek Sediments (6.7) confluence; western side of lake D 277.3 Mecklenburg McDowell Creek cove, approx. 250 m upstream Water quality 100 35° 22.240' 80° 56.510' from Catawba River mainstem confluence (6 2) E 277.0 Mecklenburg Catawba River at Charlotte -Mecklenburg Water Water quality 5.8 35° 20 922' 80° 56 621' Treatment lant intakes (3 6) F 2765 Gaston RSS condenser cooling water discharge canal Water quality 27 35° 21.320' 80° 58.171' Macroinvertebrates (1.7) Fish G 275.0/ Gaston Mountain Island Dam forebay (275.0), Water quality 0.2-0.6 35° 20 069' 80° 59 203' 2755 Cove upstream of the Mt. Holly Water Treatment Sediments (01-04) 35° 20 099' 80° 59 428' plant intake (275.5) Macroinvertebrates Fish 1 Latitude/longitude data obtained from TOPOI USGS mapping software (National Geographic Holdings, Inc 2001) Yr ... ,. t,,, ,_ " -,. {tt A2i .+ r^ei •" vp.. n; Y�.is, id _ ot4 ,Figure 1-1, Sampling locations on N Lintain'Island Lake, Mike Energy hiswrical location identifiers are, listed in parentheses, 1-6 CHAPTER 2 STATION OPERATION METHODS Riverbend Steam Station (RSS) intake, discharge, and downstream water temperatures were continuously monitored during 2004 — 2008 to ensure thermal permit compliance. Thermal compliance data were obtained from National Pollutant Discharge Elimination System (NPDES) discharge monitoring reports. Station generating unit capacity data were compiled from the Duke Energy MicroGads and predecessor databases. Until April 9, 2008, RSS downstream water temperatures were measured at the Mountain Island Hydroelectric Station (MIHS) tailrace. During periods of very low Catawba River flow, however, particularly as experienced during recent drought years, MIHS generation was limited. In the absence of hydroelectric generation during warmer months, daytime temperatures in the quiescent tailwater pool could be appreciably warmed by incident solar radiation, in excess of upstream (upper pool) thermal conditions in deeper lake strata which correspond to MIHS penstock elevations. Therefore, Duke Energy sought and was granted permission from North Carolina Department of Environment and Natural Resources (NCDENR) to relocate the RSS downstream thermal compliance point upstream of the MIHS. On April 9, 2008 the downstream thermal sensor was relocated to the Mountain Island Dam forebay at a depth of 9 in; a depth that historical monitoring data indicated corresponded to tailwater temperatures during periods of hydroelectric generation. RESULTS AND DISCUSSION Station Operation The RSS has in recent years operated as a peaking facility, and operation during January 2004 through December 2008 was consistent with this role of peak electric load generation. Electric generation (from one or more coal-fired units) occurred on 81% of days between January 1, 2004 and December 31, 2008 (Figure 2-1). For the entire five-year period, RSS 2-1 coal-fired units operated at an average of about 48% of capacity (i e., actual/potential station generation), ranging from 39.6% in 2004 to 56.3% in 2007 (Table 2-1). Month-to-month generation capacity factors varied substantially by season and year, depending on load demand and unit outages Maximum monthly average capacity was achieved during the June — August period in each of the five years, reflecting greater utilization of RSS for periods of peak summertime electric demand. Thermal Compliance The thermal limits of the NPDES permit of RSS were not exceeded during the 2004 — 2008 period. The average monthly CCW discharge water temperature ranged from 14.9 °C (58.9 °F) in February 2005, to 34.7 °C (94.4 °F) in August 2007 (Figure 2-1). These temperatures followed a regular seasonal pattern and were within thermal ranges previously reported (Duke Power Company 1993, 1994; Duke Power 2004). Likewise, daily average downstream temperatures measured at MIHS reflected typical seasonal variability, ranging from 8.1 °C (46.5 °F) on January 29, 2004 to 31.9 °C (89.5 °F) on August 10, 2007 (Figure 2- 2). During 2004 — 2008, maximum average monthly CCW outlet and downstream daily average temperatures were recorded in August 2007. These thermal maxima were influenced by below normal total precipitaticn in August 2007 (1.04 cm versus a normal 9.45 cm), as well as appreciably warmer than normal ambient August 2007 air temperatures (587 cooling degree-days versus a normal of 415; NOAA 2008a). Compliance with EPA Nomograph -Related Thermal Limits The EPA nomograph thermal limits (see Chapter 1) apply during times of relatively low receiving stream temperatures, and when only one of the RSS coal-fired units control systems is operational. A nomograph limit is calculated by applying a maximum permissible temperature increase (OT) above ambient, i.e., CCW inlet temperature. These limits were established to protect resident warmwater fish from potential "cold shock" in the event of a unit trip or sudden unit shutdown, which would lead to rapid cooling in the portion of Mountain Island Lake affected by the RSS thermal plume. Coincident wintertime operation of more than one RSS control system frequently restricted the applicability of nomograph thermal limits. During 2004 — 2008, thermal effluent temperatures complied with applicable nomograph thermal restrictions at all times. 2-2 Table 2-1 RSS monthly units 4 through 7 (U4 — U7), monthly average (Av), and annual station coal-fired capacity factors (percent) during 2004 — 2008. N W 2004 2005 2006 2007 2008 Month U4 U5 U6 U7 Av U4 U5 U6 U7 Av U4 U5 U6 U7 Av U4 U5 U6 U7 Av U4 U5 U6 U7 Av Jan 668 661 763 277 580 357 404 419 423 404 00 00 51 54 29 179 164 324 543 325 594 538 592 589 581 Feb 708 672 743 00 503 174 454 322 390 339 304 308 452 462 394 469 520 637 625 57.4 464 455 505 589 511 Mar 299 449 464 29 299 715 682 472 773 654 364 341 423 519 422 313 312 320 313 315 413 644 692 642 610 Apr 594 51 1 452 688 563 305 579 00 655 374 673 525 745 775 693 473 493 578 539 527 76 1 78 8 742 825 780 May 540 704 740 774 701 423 387 169 174 268 349 363 426 469 410 643 637 647 645 644 689 637 654 657 659 Jun 340 65 8 745 802 660 496 485 639 642 578 684 646 673 767 697 587 579 615 624 604 853 836 750 822 810 Jul 422 498 630 653 566 717 674 645 578 646 780 789 810 789 793 775 725 710 682 718 701 592 668 512 614 Aug 524 457 454 58 1 50,6 756 727 732 785 751 789 747 813 743 774 788 763 757 76 1 76.6 472 430 570 544 513 Sep 119 100 265 268 202 619 621 689 687 660 37 41 190 129 110 630 327 634 734 599 244 238 293 331 282 Oct 00 00 79 102 51 357 421 368 480 410 597 603 570 122 451 781 52 439 755 522 00 00 104 127 66 Nov 00 00 04 30 08 209 256 149 00 138 665 657 60 699 496529 658 698 612 629 104 124 262 382 236 Dec 136 19 159 135 118 469 410 375 33 301 355 352 462 417 404 563 595 569 467 543 173 160 257 269 223 Annual 39.6 46.2 47.3 56.4 49.0 N W U a> ca E 9 30 20 25 20 N 15 CU 10 5 0 113 104 95 86 CD 77 �a CD v 68 -TiCD 59 50 41 32 2004 2005 2006 2007 2008 Date Figure 2-1 Average monthly CCW discharge temperatures (solid circles) and monthly range daily average temperatures (open circles), displayed over days per month of RSS coal-fired generation during 2004 — 2008. U a> m Q E F2 95 86 77 CDA 68 -a m c 59 m TI 50 41 32 2004 2005 2006 2007 2008 Figure 2-2. Average monthly doNAnstream temperatures (solid circles) and monthly range of daily average temperatures (open circles) 2-4 CHAPTER 3 WATER AND SEDIMENT CHEMISTRY MATERIALS AND METHODS Collection of Field Parameters, Water, and Sediment Chemistry Samples Mountain Island Lake water quality was monitored at six locations (A, B, C, D, E, and G; Figure 1-1 and Table 1-1) semiannually (summer and winter) during 2004 — 2008. Sample locations ranged (as ordered above) from the furthest upstream site at Cowans Ford Hydroelectric Station (CFHS) tailwater to the furthest downstream site at the Mountain Island Hydroelectric Station (MIHS) forebay. Locations were the same as those monitored in prior years (Duke Power Company 1994; Duke Power 2001 and 2004). In-situ analyses were performed by Duke Energy Scientific Services personnel? At each location, vertical profiles of in-situ parameters (temperature, dissolved oxygen, pH and specific conductance) were collected with a Hydrolab DataSonde°. Water samples for the laboratory analyses listed in Table 3-1 were collected with a Kemmerer bottle at surface (0.3 m) at each location, and approximately one meter above bottom at the MIHS forebay (Location G). Samples for soluble nutrients (i.e., ammonia -N, nitrtate+nitrite-N, and orthophosphate) were filtered (0.45-µm) in the field. Additional samples collected for the analysis of soluble copper, beginning in 2005, were also field - filtered. All samples were preserved (acidified or iced) in the field immediately following collection. Mountain Island Lake sediment sampling was conducted on March 6, 2008 (data from sediment samples collected January 30, 2004 were summarized previously; Duke Power 2004). Sediment cores were obtained from four locations (A, B, C, and G; Figure 1-1 and Table 1-1), including an upstream reference site (Location A), locations immediately upstream and downstream of the ash basin outfall (Locations B and C, respectively) and the MIHS forebay (Location G). Ten replicate cores were obtained from each location with a K- 2 The Duke Energy Scientific Services organization is presently certified by the North Carolina Division of Water Quality (DWQ) under the Field Parameter Certification program (certificate number 5193) However, all field chemistry data represented in this report are uncertified data, i e , not collected for effluent compliance monitoring purposes 3-1 B° gravity corer, or in shallower depths, a hand corer fitted with cellulose acetate butyrate core liner tubes. Upon collection, sediment cores were sealed with polyethylene end caps, with site water overlaying the intact water -sediment interface. Cores were maintained in an upright position to preserve the sediment -water interface, stored on ice, and subsequently refrigerated upon return to the laboratory. Analytical Methods Analytical methods and sample preservation techniques employed during 2001 — 2005 are summarized in Table 3-1. Since 2001, trace element concentrations of water samples have been analyzed as "total recoverable" elemental concentration, which incorporates a dilute acidic digestion of the sample (USEPA 1994). This technique was distinct from the analytical method for trace elements employed during the period 1988 — 2000, when acid - preserved samples were analyzed by atomic absorption spectroscopy direct injection, i.e., samples were not acid -digested. With minor exceptions, laboratory water quality analyses were performed by Duke Energy Corporate EHS Analytical Laboratory, Huntersville, NC (North Carolina DWQ Laboratory Certification program, certificate number 248). In several instances, selected parameters were analyzed by an alternate state -certified commercial laboratory. Prism Laboratories, Inc., Charlotte, NC (NC DWQ certificate number 402) provided turbidity analyses (except for February 2004 samples), total solids analyses for 2005 — 2008, total suspended solids for 2005 samples, and mercury analyses for February 2007 and February 2008 samples. Because the uppermost sediment strata was of primary concern in evaluating recent deposition and trace element bioavailability, sediment core samples were processed in the laboratory to remove surficial material (i.e., silt + clay fractions) from the uppermost stratum of each core. Upon return to the laboratory, fine-suspendable sediments were siphoned from the uppermost 2 mm of each sediment core, sieved through a 63-µm plastic (Nitex) screen, and then deposited onto a pre -weighed 0.45-µm Millipore° acetate membrane filter. Filters were subsequently dried at room temperature and analyzed by non-destructive neutron activation analysis at the Nuclea- Services Laboratory, North Carolina State University, Raleigh, NC. Quality assurance measures for dry weight -based selenium and arsenic concentrations (expressed as µg element/g sediment) employed analyses of filter blanks, internal standards, and National Institute of Standards and Technology or International Atomic Energy Agency reference materials for calibration. 3-2 Data analyses employed both statistical and graphical methods. Time series plots were used to assess seasonal and inter -annual trends in CCW and lake temperatures. Box and whisker plots (showing median, 25% and 75% quartiles, and data range) were produced for selected water chemistry analytes, by sample location and pre -defined year groupings, to permit temporal and spatial comparisons with historical data. Trace element concentrations in Mountain Island Lake sediments were analyzed by non -parametric procedures (Wilcoxon rank sum and Kruskal-Wallis tests) for effects by year and location, respectively (SAS Institute Inc. 2002 — 2004) where statistical treatment of analytical results was not limited by the prevalence of below -detection values. In all instances where analyte concentrations were less than the laboratory reporting limit, the reporting limit value was represented graphically. RESULTS AND DISCUSSION Water Quality Because of the relatively small catchment and short hydrologic retention time of Mountain Island Lake (e.g., < 1 to 12 days; Bales et al. 2001), the thermal structure of the reservoir is substantially influenced by the linkage of controlled releases from the upstream CFHS and outflows from MIHS, combined with the thermal plume from RSS. A submerged weir immediately upstream of Cowans Ford Dam results in inflows to Mountain Island Lake during summer hydro generation that are thermally representative of the warmer Lake Norman epilimnion. The high flow-through rates, small reservoir catchment, and relatively shallow reservoir morphometry all serve to limit the establishment of a strong thermal gradient, particularly in areas of the lake upstream of RSS. Typical seasonal trends during 2004 — 2008 were observed for Mountain Island Lake temperature and dissolved oxygen (Figures 3-1 and 3-2). Forebay thermal profiles were similar to results of previous monitoring (Duke Power Company 1994; Duke Power 2001, 2004). During the summers of 2004 — 2008, the deeper regions of the reservoir became weakly stratified thermally, and dissolved oxygen levels declined gradually with increasing depth below the uppermost mixed layer (i.e., top 3 to 5 m) of the water column (Figure 3-2). As in previous years, the occurrence of summertime hypolimnetic anoxia at the MIHS forebay was variable year-to-year, with anoxic conditions occurring most years at elevations in the reservoir corresponding to the lower limit of the MIHS penstocks, i.e., normally in the bottom 3 to 4 meters of the water column. Thermal stratification was slightly less 3-3 pronounced for the August 2005 sampling compared to other years, and can be linked to lack of anoxic conditions at the time in chose bottom waters. Surface specific conductance (Figures 3-3 and 3-5) ranged lake -wide from 49.9 to 227 µS/cm, with maximum values typically occurring in the McDowell Creek cove (Location D). This finding is consistent with recent monitoring trends and is in agreement with data reported by other researchers (Bales et al. 2001; Buetow 2003). McDowell Creek receives a substantial point source discharge from the recently enlarged Charlotte -Mecklenburg Utilities 12 -MGD McDowell Creek Wastewater Treatment Plant (WWTP), as well as non - point source contributions due to increasing (primarily residential) development in the watershed. Specific conductance values measured in the lower water column (i.e., 3 to 4 in deep) at Location D were frequently among the greatest encountered lake -wide. Near - surface specific conductance values at this location were exceptionally greater in February 2005, however, likely reflecting warmer, buoyant inflows from McDowell Creek relative to cooler ambient lake temperatures at the time of sampling (Figure 3-3). Based on conductance profiles, elevated dissolved solids inflows from McDowell Creek frequently appear to suffuse into the lake at depths below 3 meters. Elevated summer specific conductance values observed in the deepest waters of Mountain Island Lake forebay (Location G) are primarily linked to increased concentrations of the dissolved fraction of redox -sensitive metals (e.g., reduced iron and manganese), reflective of the influence of thermal stratification and seasonal anoxia at that particular site. From a temporal perspective, slightly elevated specific conductance was observed lake -wide during 2008, with August 2008 values similar to increased conductance levels encountered during the 1998 — 2002 regional drought. A drought period spanning spring 2007 through the summer of 2008 likely contributed to the elevated dissolved solids, driving the conductance readings upward (NCDENR 2009). However, marginally increased Lake Norman dissolved solids concentrations, linked to a new discharge of flue gas desulfurization wastewater at Marshall Steam Station on Lake Norman, may also be a contributor to recently elevated lake -wide conductance va" ues (Duke Energy, unpublished data). In-situ pH (Figures 3-4 and 3-6) in the main channel of Mountain Island Lake tended to be circum -neutral, with a median pH of 7.1, and a range of pH 6.1 to 7.9 during 2004 — 2008. A general increase in reservoir -wide pH, and to some extent, total alkalinity (see discussion below; Figure 3-7) is apparent over the 19 years of monitoring summarized in this report. These gradual increases may be related to slight increases in calcium (Figure 3-15) as well as decreases in sulfate concentrations (Figure 3-20) over a similar time period. While added 3-4 calcium inputs are likely attributable to increased Mountain Island Lake'and Catawba River Basin watershed development over the past two decades, similarly timed reductions in sulfate concentrations in Southeastern surface waters have been observed. These sulfate reductions are thought to be related to lower sulfate deposition attributable to air emissions control measures implemented at numerous up -wind coal -electric generating facilities (USEPA 2003). Surface (0.3 m) pH values ranged from 6.6 to 7.9 lake -wide. Lowest pH values were observed during the August 2005 sampling. Drought -associated summer 2007, and particularly 2008 pH values in the McDowell Creek cove (Location D) ranged from 7.5 to 7.9, displaying a tendency toward slightly more alkaline conditions compared to other lake - wide sample locations. Likewise, forebay (Location G) euphotic zone (e.g., depths < 3 m) pH values were marginally more alkaline (pH 7.4 to 7.8) my August 2008 than the earlier 2004 • 2007 samplings. These forebay pH values were - coincident ,with slightly supersaturated dissolved oxygen concentrations (e.g., 109 to 111%) measured at 0.3 to 3 in depth and were probably linked to increased densities of phytoplankton and resultant photosynthetic activity occurring due to the warm and relatively dry weeks prior to the August 20 sampling date (NOAA 2008b). Total alkalinity as CaCO3 ranged from 12 to a maximum of 60 mg/L (the latter value from a forebay bottom sample in 2008) during 2004 — 2008 (Figure 3-7). Greatest alkalinity concentrations lake -wide were measured during the August 5, 2004 sampling, ranging from 23 to 29 mg CaCO3/L. From a spatial perspective, total alkalinity values associated with the McDowell Creek cove (ranging from 12 to 29 mg CaCO3/L) were usually slightly elevated with respect to surface (0.3 m) samples collected from other Mountain Island Lake locations. As discussed above, total alkalinity concentrations have displayed a long-term, but very slight increasing trend over the years of this monitoring program. While some of the noted increase is undoubtedly linked to drought conditions prevalent during several of the years over the past decade, other watershed -linked contributions may also be important, given the dynamic changes in land use and population over time. Mountain Island Lake turbidity ranged from 1.6 to 16.5 NTU in 2004 — 2008 (Figure 3-8). No samples exceeded the applicable state water quality standard (25 NTU; NCDENR 2007a). Reservoir -wide, turbidity was slightly less spatially variable, compared to prior reporting periods. Total suspended solids (TSS) concentrations were also generally low (ranging from 1 to 10 mg/L for mainstem locations) during 2004 — 2008 (Figure 3-9). A maximum TSS concentration of 16 mg/L occurred in the McDowell Creek arm of Mountain 3-5 Island Lake during the February 2007 sampling, a site where greatest TSS concentrations have frequently been observed in the past (Bales et al. 2001; Duke Power 2001, 2004). Nutrient concentrations throughout 2004 — 2008 reflected historical trends and were consistent with formerly documented, time -variable transitions between oligotrophic and mesotrophic water quality classifications for Mountain Island Lake (USEPA 1975; Weiss and Kuenzler 1976; Bales et al. 2001; Duke Power 2001; Buetow 2003; NCDENR 2004). Ammonia -nitrogen (Figure 3-10), nitrate+nitrite (Figure 3-11), and total nitrogen concentrations (Figure 3-12) were similar to previous years. Maximal ammonia -nitrogen concentrations were consistently measured during summer in the deeper waters of the MIHS forebay; Location G (maximum of 1.3 mg NH3-N/L August 20, 2008). This was the only sample location where near -bottom samples were obtained in this monitoring program. Seasonally elevated ammonia -nitrogen concentrations noted for deep samples collected at this site can be linked to anoxia -induced strongly reducing conditions, which result, in..an increased release of nutrients from lake sediments, as well as limitation of oxygen -dependent microbial nitrification processes. Such seasonal increases in ammonia -nitrogen concentrations have been reported previously in Mountain Island Lake, and other Catawba River reservoirs (Bales et al. 2001; Duke Power 2004). These seasonal increases in the reservoir hypolimnetic ammonia -nitrogen were also reflected in 2004 — 2008 total nitrogen concentrations. Lake -wide, phosphorus concentrations were similar to those observed in recent years. Concentrations of soluble orthophosphate (Figure 3-13) and total phosphorus (Figure 3-14) in the McDowell Creek arm of Mountain Island Lake (Location D) have for many years provided a consistent indication of nutrient loading via the McDowell Creek WWTP. Bales et al. (2001) observed, based on 1996 — 1997 monitoring, that on average approximately one half of the loading of total phosphorus to Mountain Island Lake entered the reservoir from McDowell Creek. Six individual exceedances of the Mecklenburg County Water Quality Program (MCWQP) action level (0.04 mg/L) for total phosphorus were reported for the McDowell Creek arm of Mountain Island Lake during 2007, as well as a sample exceeding the action level in the Gar Creek arm of the lake, during the same drought -impacted year (Buetow 2008). During 2004 — 2008, both orthophosphate and total phosphorus concentrations were reduced in the McDowell Creek arm with respect to prior years of monitoring. Loading of nutrients to Mountain Island Lake during 2004 — 2008, while reduced overall, remained evident from spatial trends in nitrate+nitrite (Figure 3-11) and total phosphorus 3-6 (Figure 3-14) concentrations. As for phosphorus, the MCWQP action level for nitrate+nitrite (0.65 mg/L) was exceeded on three occasions in the McDowell Creek arm of the lake during 2007; no exceedances were observed elsewhere in the reservoir (Buetow 2008). McDowell Creek was listed as impaired for biological integrity in the most recent (2006) 303(d) evaluation of state water quality use attainment (NCDENR 2007b). Continuing nutrient enrichment and excessive solids loading from the McDowell Creek WWTP and the extensively developed catchment further upstream undoubtedly contribute to this impairment. During 2004 — 2008, concentrations of major cations, including calcium (Figure 3-15), magnesium (Figure 3-16), sodium (Figure 3-17), and potassium (Figure 3-18); and anions, including chloride (Figure 3-19) and sulfate (Figure 3-20) were generally consistent with previous trends. Median concentrations of these major dissolved ionic constituents, as for specific conductance (Figure 3-5), were slightly lower than the marginally elevated concentrations observed during the prolonged 1998 — 2002 regional drought. As discussed previously for calcium, long-term temporal trending appears to also indicate a slight increase in magnesium concentrations over the years 1990 — 2008, whereas sulfate concentrations appear to be in slight decline over the same timeframe. Mountain Island Lake iron (Figure 3-21) and manganese (Figure 3-22) concentrations during 2004 — 2008 were typical of previous years. Surface concentrations of the two metals remained low and showed minimal variation among the locations. However, as is commonly observed, substantially elevated summertime iron and manganese concentrations in the minimally oxygenated water near the lake bottom at the forebay location (G) were evident, as expressed by maxima on Figures 3-21 and 3-22 (note log concentration scale). Aluminum concentrations (Figure 3-23) have, over time, displayed a clear decreasing trend. It is possible, although presently unconfirmed for this site, that the observed decreases in aluminum may be linked to reduced regional atmospheric sulfate deposition and lessened watershed acidification over recent years, due to the increasing implementation of coal-fired power plant emission controls. Similar aluminum concentration reductions have been demonstrated in northeastern U.S. lakes in response to power plants air emission controls and reduced acid deposition of sulfur (Warby et al. 2008). Soluble silica concentrations (Figure 3-24) were comparable to long-term monitoring data. Median silica concentrations were marginally greater in the McDowell Creek cove (Location D) and further down -lake mainstem sites (Locations E and G) relative to further up -lake. 3-7 I Aqueous concentrations of trace elements were typically near or below laboratory reporting limits during 2004 — 2008. No spatial trends were evident in the lake -wide trace element concentrations, with the exception that samples collected from the lake bottom at the MIHS forebay (Location G) yielded 2004 — 2008 maximum concentrations of total recoverable arsenic (maximum of 11.4 µg2 August 20, 2008; Figure 3-25) and barium (maximum of 0.14 mg/L, Figure 3-26). A maximum total recoverable copper concentration of 5.49 µg/L was measured at surface (0.3 m) at the forebay location (G) August 5, 2004 (Figure 3-27). Of these three trace elements, only a single August 2008 lake forebay (Location G) bottom sample exceeded a state water quality standard (arsenic; 10 µg2 based on human health) or action level (NCDENR 2007a). Total recoverable cadmium, chromium, lead, nickel, silver, and selenium concentrations consistently remained below method reporting limits (Table 3- 1) and applicable water quality standards or action levels throughout 2004 — 2008, and are not depicted graphically. Two mercury samples exceeded laboratory reporting limits during 2004 — 2008. Mercury in a sample collected August 5, 2004 from the lake mainstem at the CMUD water intake (Location E) had a concentration of 0.35 µg/L, and a second sample collected August 4, 2005 from the bottom at the MIHS forebay (Location G) yielded a concentration of 0.32 gg/L. The cause of this pair of elevated mercury concentrations, which exceeded water quality standard of 0.12 µg/L, was undetermined (NCDENR 2007a). RSS Ash Basin Effluent Selenium and Arsenic Mass Loading Estimates For the five-year period, 2004 — 2008, loading of arsenic (Figure 3-31) from the NPDES- permitted RSS ash basin discharge averaged 895 g/day, and selenium loading (Figure 3-32) averaged 47.5 g/day. As described previously (Duke Power 2001), the post -1995 estimated increase in arsenic or selenium loading, depicted in Figures 3-31 and 3-32, should be considered artifacts of modified discharge flow calculations implemented in 1995, rather than being attributed to any operational changes at RSS. Estimates of arsenic mass loading to Mountain Island Lake were near or below historical averages, ranging from 336 g/day (2007) to 1,556 g/day (2006). Arsenic loading increased approximately two -fold over the y -.ars 2004 — 2006, after a minimum level of loading was achieved in 2003. Subsequently in 2007 and 2008, loading was substantially reduced to levels not observed in recent years. Arsenic loading reductions in 2003 were in part linked to significantly greater precipitation event -driven watershed contributions to the ash pond (Duke Power 2004). Reductions in effluent arsenic concentrations driving the 2007 — 2008 3-8 loading estimates lower, however, may be related to changes in coal supply, as the reductions show no clear linkage with RSS coal-fired electric generation capacity (Table 2-1). Mass loading of selenium via the RSS ash basin outfall displayed somewhat less inter -annual variability, in contrast to arsenic. Annual average selenium loading ranged from 36 g/day (2004) to 56 g/day (2006). As observed previously, selenium loading from the ash pond effluent appeared more closely linked to effluent discharge rates than did arsenic loading rates (Duke Power 2001, 2004). Mean annual Se concentrations in ash pond effluents during 2004 — 2008 were only marginally above the laboratory reporting limit, ranging from 2.3 to 3.1 µg/L. Sediment Elemental Analyses Neutron activation analysis of surficial fine (< 63 µm; silt+clay fraction) Mountain Island Lake sediments sampled March 6, 2008 resulted in arsenic concentrations of similar magnitude as observed previously at the two sites upstream of the RSS ash basin discharge (Locations A and B), but increased arsenic concentrations down -lake (Locations C and G), compared to previous years (Figure 3-33). Arsenic results for sediments collected immediately downstream of the RSS ash basin discharge (Location C) were particularly elevated in 2008 with respect to historical data, with a median arsenic concentration of 77.7 µg/g, i.e., more than three -fold the median 2004 arsenic concentration (see following discussion). Results of Kruskal-Wallis tests showed that for all 1988 — 2008 sediment samples combined, sample location had a highly significant effect (P < 0.001) on the magnitude of arsenic concentrations in sediment fines. For 2008 samples, Wilcoxon rank sum scores indicated arsenic concentrations in fine surficial sediments collected at the two sites downstream of the RSS ash basin outfall were significantly (Location C: P < 0.001; Location G: P < 0.01) greater than up -lake concentrations. Atypically elevated sediment arsenic concentrations from Location C, immediately downstream of the RSS ash basin outfall are thought to be an artifact of a slight change in the sampling site in 2008. Sediments sampled from the customary sites within the river channel in recent years have been exposed to substantial currents during upstream CFHS generation, so that samples frequently yield primarily coarse sand (virtually no fines present). This was particularly the case at Location C in 2008. To facilitate collection of sediment fines, an area was sampled approximately 250 in upstream, very near to the mouth of a cove where RSS ash pond effluent flows into the lake. Presumably, over the years, relatively arsenic -rich ash pond effluent -associated particulates have settled in this cove, including the region sampled near the point of confluence with the river channel. Therefore, the 2008 Location C samples W may be considered largely indicative of material entering the mainstem from the cove impacted by RSS ash basin effluents, rather than indicative of the mainstem of the lake itself (where deposits of sediment fines were virtually absent in 2008). The scarcity of sediment fines in the river channel at Location C is linked, conversely, to the gradual increases observed in sediment arsenic concentrations at the Mountain Island Lake forebay (Location G). Lower velocities encountered in this deepest portion of the lake facilitate an ultimate sink for fine particulates. Location G trace element analyses therefore serve to provide a window on the long-term arsenic mass loading from all upstream sources, including the RSS ash basin outfall. Similar to the 2004 sampling, sediment selenium concentrations (Figure 3-34) from samples collected in 2008 were mostly below sample -specific detection limits (i.e., 33 of 40 samples), so statistical methods were not employed for this analyte. (Selenium concentrations less than detection limits were represented graphically as the detection limit in Figure 3-34.) No overall location -dependent relationship was apparent in the combined set of 1988 — 2008 samples for selenium. This observation is consistent with the relatively low concentrations of selenium typical of the RSS ash basin discharge. CONCLUSIONS Water quality in Mountain Island Lake during 2004 — 2008 was similar to previous years. Seasonal thermal stratification, dissolved oxygen concentrations, and pH were representative of historical ranges. Specific conductance values had increased by the end of the monitoring period in 2008, achieving values similar to those recorded during the drought earlier in the decade. Lake -wide, concentrations of major nutrients, similar to historical levels, indicated spatial variability, but continued to result in Mountain Island Lake being classified as oligotrophic to mesotrophic durir_g 2004 — 2008. Typically elevated concentrations of dissolved and suspended material, as well as nutrients entering the lake from the McDowell Creek drainage, were slightly lessened during 2004 — 2008. This impaired tributary, however, continued to produce a localized degradation of water quality, typically limited to the McDowell Creek cove of the lake. Mass loading of selenium and arsenic from the RSS ash basin outfall during 2004 — 2008 was similar to historical trends, except for reductions observed in arsenic loading over the 2007 — 2008 period. Mountain Island Lake concentrations of aqueous trace elements remained generally low, consistent with low levels of turbidity and suspended solids. One sample (total recoverable arsenic of 11.4 µg/L, 3-10 collected in August 2008) yielded the singular exceedance of a state water quality standard or action level for trace elements during 2004 — 2008. March 2008 arsenic concentrations in fine surficial sediments were elevated downstream of RSS with respect to uplake concentrations, with samples just downstream of the RSS ash basin effluent confluence yielding the highest concentrations. While the 2008 samples were likely influenced by a slight relocation of the sampling site due to difficulty in obtaining material other than coarse sand at the former location, MIHS forebay sediment sampling continues to indicate a slight, gradual increase in arsenic concentrations over recent years. Sediment concentrations of selenium were consistently low lake -wide. As a whole, 2004 — 2008 Mountain Island Lake water and sediment chemistry continue to indicate the waterbody remains capable of sustaining balanced and indigenous aquatic communities. Trace element concentrations measured in Mountain Island Lake common carp, sunfish, and largemouth bass since 1988 remain well below values of regulatory concern (Chapter 5). 3-11 Table 3-1. Analytical methods used to determine chemical and physical constituents in Mountain Island Lake during 2004 — 2008. Parameter Method (EPAIAPHA)3 Preservation Reporting Limit Alkalinity, Total Total inflection point titration 4 °C 0 01 meq/L EPA 310 1 as CaCO3 Aluminum Atomic emission/ICP 0 5% HNO3 0.05 mg/L EPA 200 7 Arsenic, Total ICP Mass Spectrometry 0 5% HNO3 2 0 pg/L Recoverable EPA 200 8 1 0 pg/L4 Arsenic, Sediment Neutron Activation Analysis 4 °C 0 0002 pg/g sample Barium Atomic emission/ICP 0 5% HNO3 0 005 mg/L EPA 200 7 Cadmium, Total ICP Mass Spectrometry 0 5% HNO3 0 5 pg/L Recoverable EPA 200 8 1 0 pg/L4 Calcium - Atomic emission/ICP 0 5%_HNO3 0 03 mg/L EPA 200 7 Carbon, Total Organic EPA 415 1 4 °C, 0 1 mg/L 0 5% H2SO4 Chloride Ion Chromatography 4 °C 1 0 mg/L EPA 300 0 Conductance, Temperature -compensated in-situ 0 1 pS/cm6 Specific nickel or graphite electrode APHA 2510 Chromium, Total ICP Mass Spectrometry 0 5% HNO3 1 0 pg/L Recoverable EPA 200 8 Copper, Dissolved ICP Mass Spectrometry 0 5% HNO3 2 0 pg/L EPA 200 8 1 0 pg/L4 Copper, Total ICP Mass Spectrometry 0 5% HNO3 2 0 pg/L Recoverable EPA 200 8 1 0 pg/L4 Iron, Total Atomic emission/ICP 0 5% HNO3 0 01 mg/L Recoverable EPA 200 7 Lead, Total ICP Mass Spectrometry 0 5% HNO3 2 0 pg/L Recoverable EPA 200 8 Magnesium Atomic emission/ICP 0 5% HNO3 0 03 mg/L EPA 200 7 3 References 1 USEPA 1983 2 APHA et al 1998 4 August 2008 only 5 Optimal conditions, no interfering elements in sample matrix 6 Instrument sensitivity furnished in lieu of laboratory reporting limit 3-12 Table 3-1. (Continued). Parameter Method (EPA/APHA) Preservation Reporting Limit Manganese ICP Mass Spectrometry 0 5% HNO3 1 0 pg/L EPA 200 8 Nitrogen, Ammonia EPA 350 1 40C 0 02 mg/L 0 5% H2SO4 Nitrogen, Nitrate+Nitrite EPA 353 2 4 °C 0 02 mg/L 0 5% H2SO4 Nitrogen, Total EPA 351 2 40C 0 1 mg/L Kjeldahl 0 5% H2SO4 Nickel ICP Mass Spectrometry 0 5% HNO3 2 0 pg/L EPA 200 8 Phosphorus, EPA 365 1 40C 0 005 mg/L Orthophosphate Phosphorus, Total EPA 365 1 40C 0 01 mg/L 0 5% H2SO4 Oxygen, Dissolved Temperature -compensated in-situ 0 01 mg/L6 polarographic cell APHA 4500-0-G pH Temperature -compensated in-situ 0 01 units glass electrode APHA 4500-H+ Potassium Atomic emission/ICP 0 5% HNO3 0.25 mg/L EPA 200 7 Selenium ICP Mass Spectrometry 0 5% HNO3 2 0 pg/L EPA 200 8 1 0 pg/L4 Selenium, Sediment Neutron Activation Analysis 40C 0 02 pg/g sample Silica (as Si) APHA 4500Si-F 40C 0.5 mg/L Silver ICP Mass Spectrometry 0 5% HNO3 0 5 pg/L 1 0 pg/L4 EPA 200 8 Sodium Atomic emission/ICP 0 5% HNO3 1 5 mg/L EPA 200 7 Solids, Total Gravimetric, dried at 103-105 °C 4 °C 20 mg/L EPA 160 3 12 mg/L' Solids, Total Gravimetric, dried at 103-105 °C 4 °C 0 10 mg/L Suspended" EPA 160 2 / APHA 2540 D Sulfate Ion Chromatography 40C 1 0 mg/L EPA 300 0 ' August 2005, 2006 samples " Modified Seston method for 1-L samples 3-13 Table 3-1. (Continued). Parameter Method (EPA/APHA) Preservation Reporting Limit Temperature NTC Thermistor in-situ 0 01 °C6 APHA 2550 Turbidity Turbidimetric 4 °C 0 05 NTU EPA 180 1 Zinc ICP Mass Spectrometry 0 5% HNO3 1 0 pg/L EPA 200.8 3-14 2004 2005 0 5 10 15 20 0 5 10 15 20 0 5 10 Qr (1) ❑ 15 20 0 0 5 10 1Z 0) ❑ 15 20 2006 2007 5 10 15 20 0 5 10 2008 0 5 10 15 20 0 5 E -S 10 Q 0) ❑ 15 20 15 20 Figure 3-1. Winter (February) profiles of temperature (°C, ■) and dissolved oxygen (mg/L; ❑) at the Mountain Island Lake forebay, Location G 3-15 2004 0 5 10 15 20 25 30 35 0 5 E L 10 Q N ❑ E 15 2005 0 5 10 15 20 25 30 35 0 -1 - I 1 20 2006 0 5 10 15 20 25 30 35 0 --ti 5 15 �zl E 20 ' 2007 0 5 10 15 20 25 30 35 0 5 10 d N 15 20 2008 0 5 10 15 20 25 30 35 0 5 15 20 Figure 3-2 Summer (August) profiles of temperature (°C, ■) and dissolved oxygen (mg/L; ❑) at the Mountain Island Lake forebay, Location G. 3-16 Location A µS/cm 0 25 50 75 100 125 150 175 200 225 250 0 ♦ o Feb2004 1 -'_` t - - - Aug 2004 Feb 2005 2 __ t >- _ �Aug2005 o Feb2006 3 a' __ _ - _ Aug 2006 Feb 2007 - Aug 2007 4 _ _ - _ # _ _ _ _ _ __ ,_ _ __ t Feb2008 •-Au 2008 N ■ • 7 8 Location C µS/cm 0 25 50 75 100 125 150 175 200 225 250 0 Feb2004 -o-Aug 2004 ¢ Feb2005 2 __ - _ - - _ --o--Aug 2005 o Feb 2006 _- _ _ _ - _ __ �Aug2006 3 • Feb 2007 Aug 2007 4 Feb 2008 • •-Auq 2008 t 5 Q e N � 6 7 g Location E µS/cm 0 25 50 75 100 125 150 175 200 225 250 0 Feb 2004 1 Aug 2004 a Feb2005 2 ♦ Aug 2005 o Feb2006 3 r_- _ a -o-- Aug 2006 • Feb 2007 -•- Aug 2007 r 4 _ -__ _ _a __ _ _ - _ _ _-_ • Eeb2008 C -+- Aug 2008 - Q e 7 fl �♦ Location B µS/cm 0 25 50 75 100 125 150 175 200 225 250 0 Qe ■ Feb 2004 1 - _ - 1♦ - - - - - - _" -o- Aug 2004 Feb 2005 2 _ _ _ # _ _ _ _ _ ___ Aug 2005 o Feb 2006 3 _z _ _ #_ _ _ <_ _ _ _ _ _ -Aug 2006 • Feb 2007 •- Aug 2007 4 - - - - i -- - -- + Feb2008 Aug2008 g_ 5 Q 7 8 Location D µS/cm 0 25 50 75 100 125 150 175 200 225 250 0 o ■ o o Feb 2004 1 Aug 2004 O - • a - - - Feb2005 2 -c- Aug 2005 a It- o Feb2006 3 -Aug 2006 • Feb2007 Aug 2007 4 a Feb2008 �. -♦- Aug2008 L 5 Q N 7 in Location G µS/cm 0 25 50 75 100 125 150 175 200 225 250 0 5 t 10 Q N 15 20 q ♦ ♦ q Feb2004 ♦ -o- Aug 2004 q ♦ a Feb2005 'Aug 2005 ♦ o 1eb2006 -o- Aug 2006 * • Feb2007 ♦ - -•- Aug 2007 'M ♦ • Feb2008 ♦ -Au 2008 w a a ♦1 0■ b 0 1 Figure 3-3 Semi-annual specific conductance profiles in Mountain Island Lake, 2004 — 2008 3-17 Location A Location B pH SU pH SU 5 6 7 8 9 5 6 7 8 9 0 1 2 3 C 4 Q 0) � 5 6 7 8 Location C pH SU 5 6 7 8 0 . 1 2 3 4 C 5 CL N 6 7 8 9 10 1 2 3 E 4 L 5 Q 0) � 6 7 8 9 10 -o- Feb 2004 �Aug2004 --Feb2005 —Aug2005 -d-Feb2006 --o--Aug2006 -• Feb2007 Aug 2007 -+-Feb 2008 -♦-Au 2008 -0-Feb2004 _o -Aug 2004 t— - — b2004 --0--Feb2005 —M92005 -- _Aug2004 -♦- Feb2005 -°-Feb 2006 b —Au92006 Aug2005 o--Aug2005 - --- — - ° Feb2006 1 -+--Au 2008 -°-Aug2006 ' -• Feb2007 -- - Aug 2007 -♦--Feb2008 --- -•-Aug 2007 Aug 2008 ° --+- Feb 2008 I� -r Aug2008 it t a � Location C pH SU 5 6 7 8 0 . 1 2 3 4 C 5 CL N 6 7 8 9 10 1 2 3 E 4 L 5 Q 0) � 6 7 8 9 10 Location D pH SU 9 5 6 7 8 9 -o- Feb 2004 �Aug2004 --Feb2005 —Aug2005 -d-Feb2006 --o--Aug2006 -• Feb2007 Aug 2007 -+-Feb 2008 -♦-Au 2008 -0-Feb2004 _o -Aug 2004 t— - — --0--Feb2005 —M92005 -- _ i q • -°-Feb 2006 b —Au92006 Aug2005 -•-Feb2007 * �Aug2007 -+ -Feb2008 * 1 -+--Au 2008 i -+ Feb2007 A pet - Aug 2007 -♦--Feb2008 466*1 p❑tia �e a J. Aug 2008 Location D pH SU 9 5 6 7 8 9 1 2 3 E 4 C 5 a 0) � 8 7 8 9 10 41 j -o- Feb 2004 �Aug2004 --Feb2005 —Aug2005 -d-Feb2006 --o--Aug2006 -• Feb2007 Aug 2007 -+-Feb 2008 -♦-Au 2008 - -- * t— - — ♦— _ _ i q • 0 b _ Aug2005 1 2 3 E 4 C 5 a 0) � 8 7 8 9 10 41 j --o- Feb2 004 Aug 2004 Feb2005 — — �Aug2004 d -¢-Aug2005 Feb2006 �Aug2006 Feb2007 -•-Aug2007 --Feb2008 _Au 2008 -a-Feb2005 b _ Aug2005 - o Feb2006 * -o-Aug2006 465 w Location E Location G pH SU pH SU 5 6 7 8 9 5 6 7 8 9 0 1 2 3 4 L 5 CL (D 0 6 7 8 9 10 0 5 E t 10 Ia. W 15 20 Figure 3-4. Semi-annual pH profiles in Mountain Island Lake, 2004 — 2008. 3-18 Feb2004 4 4 0 �Aug2004 d -a-Feb2005 b Aug2005 - o Feb2006 * -o-Aug2006 465 w -+ Feb2007 A pet - Aug 2007 -♦--Feb2008 466*1 p❑tia �e a J. Aug 2008 Figure 3-4. Semi-annual pH profiles in Mountain Island Lake, 2004 — 2008. 3-18 c 250 - - - 200 E ' 100 -- I a ' I I I I I I i l i t O - - 0 0 0 0 0 0 0 0 0 o a n o A B C D B G Sample Dates / Location Figure 3-5 Distribution of Mountain Island Lake specific conductance 10 — I —;— T ---`---_ — I I I 1 I I ' i i I I 9 -- ------' - -- - -- ------ -_-_ 8 -- -- ----- - - --- --- N a 7 A B C D E G Sample Dates / Location Figure 3-6 Distribution of Mountain Island Lake pH, 70 =- -- - - -- -_- ---- - ' -60 so ' I R I I I i I i I I I I i I I I I ' 30 3 l l i U x i x i —J 20TI�j � rlj.j T O A B c D e c Sample Dates / Location Figure 3-7 Distribution of Mountain Island Lake total alkalinity concentrations 3-19 50 45 40 - - -- - - .. - ---- - ------- t 35 I e i ~' 25 - - -- -' ---- 1- - -- - - --' _- -- - ------------- --- - - - - - . z - - ---- - T I ! �_- I r '20I I t I t r t . . 10 5 O -- o o 0 0 0 0 0 0 0 0 0 0 A B C D F- G Sample Dates / Location Figure 3-8 Distribution of Mounta n Island Lake turbidity 8 - . 60 so E i I I I I I I I I i A 1 I S I I I I J 1 1! 1 1 1 1 1 1 I I I 40 A ' - -- -- 30 - - � 20E E { � I I E 10 o - A B C D E G Sample Dates / Location Figure 3-9 Distribution of Mountaln'Island Lake total suspended solids concentrations. 1 I T I I I I 1 O r s m E � E 1-k- 0 ii I I i I l i l i i! I 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 A B c D E G Sample Dates / Location ,Figure 3-10 DlstrlbUtlon of Mountain Island 'Lake ammonia nitrogen concentrations 3-20 C 1 6 1 4 - - - - - - - -- - i -- -- I 1 O , .. .- } - '-- - + --+ -- r '-- '- ---- i ---' I I 0.6 F- -- - 0,4 0', v0 $ i l _ I 1 I JJJ m I T— A B C D E G Sample Dates / Location Figure 3-11 Distribution of Mountain Island Lake nitrate+nrtrlte nitrogen concentrations 30 25 - E i a _ _ 20 4 1 5 - - - - - - - -E - --- --' - - -- - - . i T I i I ( I I I I I I I T 00 o N o o o c. 0 0 0 0 A B C D E G Sample Dates / Location Figure 3-12 Distribution of Mountain Island Lake total nitrogen concentrations 007 j I jP- - ----- -- ---- - -- --- 0 06 ( 1 I� «j.- 005 . o0s .� 0,04- 1I 0,03 s 1 000 — - c', c:� A B c D E G Sample Dates / Location Figure 3-13 Distribution of, Mountain Island ,Lake soluble orthophosphate concentrations_ 3-21 y O 16 0_.24 s a h 0 12 010 E, o'008 r i 006 0.04, 0 02 LD 0,00 ---- - v - -- _- - - F-1 - --- 0 0 0 o 0 0 0 0 A 6 C D E G Sample Dates / Location Figure 3-14 Distribution of Mountain Island Lake, total phosphorus concentrations 14 - 9_2 - i - Er i �_ -4- 1 11 T 11 ' 1 I L 4 1 l �i_ _Ty'�e„_ I�1AI l I i I I j i : I� 2 r i �- I � -r r r r i r r o- Fao-,� F- F -5-T - o 0 A 6 C D E G Sample Dates / Location Figure 3-15 Distribution of Mountain 'Island Lake calcium concentrations 30 2,5 J 20 _ - `-_ __ t �y _ - - - - � , �� I : �� : X77 � - h, � � - . _ •-� rt ,- :. � I I 0,5 00 A E3 C D 1 Sample Dates / Location Figure 3-16 ;Distribution of Mountain `Island Lake magnesium concentrations-, 3'-22 r 12 - -- — - - - -- - - - a '-- I i I i b I I i a 0 6 I 2 y tel- A B C D E G Sample Dates / Location Figure 3-17 Distribution of Mountain Island ,Lake sodium concentrations. 35 - - --- - - - - -- -- -- -- 1I i I I W � I I I I I i f f I I I I f I 2 5 - -- { I { I G { { F{ j � . l { - J ---i' I 20 { _ { _ I _ _ j _1 !_11 { { {_ I I I __a1!L I ! I 1 o 05 f 00 I Ti� 0 0 0 o 0 0 0 0 0 A B C' D E G Sample Dates / Location Figure 3-18 Distribution of Mountain Island Lake potassium concentrations. 16 --- - - - -- - - - T -- - -- ---- - - -- -- -- - ------ - 14. ---- - l l 12 t m I ! I 10 q 1 I i 1 O A B C D E G Sample Dates / Location Figure 3-19 Distribution of Mountain Island Lake chloride concentrations 3-23 16 14 12 ,1O R �-f�l� f 0 i b a � �' -- ----- p. - o --�! �- o 0 0T;g 0 - 2? 02 � ��3 - - - 0 0- - - - 0 0- - - - 0 o 0 0 0 0 0 A B C D E G Sample Dates / Location Figure, 3-20 Distribution of Mountain Island Lake sulfate concentrations ho " l ! =1---J ----+----- - Ll= 1 01 0 01 I I� 0 0 0 0 0 0 0 � o 0 0 0 0 0 0 0 S 0 0 9 o 0 Sample Dates / Location Figure 3-21 Distribution of Mountain Island ,'Lake iron concentrations 10 --3 E0 1 ----- - - -- - ------ -- - - - - - - 0 01 0001 A Sample Dates / Location Figure 3-22 DistrlbUtlOU of Mountain Island sake manganese concent>;ations, 3-24 I 1�� T1 Sample Dates / Location Figure 3-22 DistrlbUtlOU of Mountain Island sake manganese concent>;ations, 3-24 I 0,60 r ' ' ra i 040 , • ' I I I I a� __.,. ,�___ _ _. , _ ,. 0 X11 0 0 00 ( _ 25� M 9� A B C D E G Sample Dates / Location Figure 3-23 Distribution of Mountain Lsland Lake aluminum concentrations 9 -- -- - ^- v -• -- - - - -- - -- -- • - ---• - ---- I f f y I I I I I 7 -- -- -- I --- =- - - • - -- �- --- T - I i i i --- I i- - I I I i I 6 , er It - - - I I — I ; i } ! 1 1 i 1 1 F -1 =-1 --t ! a O II it I I_ I I A B C D E G Sample Dates / Location Figure 3-24 D1strlbUtlon of Mountain Island Lake silica concentrations ,z - x= - - - ----- 1 6 t ! I 2 I _. -- -- 1 1 i I I-T rm 1 S� 2 �s f-1 Z" a M E n AM�13 C D E G Sample Dates / Location Figure 3-25 Distribution of'Mountaln Island Lake arsenic concentrations 3-25 016 ----- - - O 14 - -------- -----------�-- ---- --- ----- --- i - -- - -------------- ------ 012 -----O12 - I -- - - - - -4-1 ---- -------- ;- ----- -----------�- i i I I I i ii i I iI I I f O06 ,-----------------------*-------!----- -- !-----I -- - !-- --� O 04 --I i�- � �- ti ---ii -�I-�----i�� f�lIi 002 - �- i�i�l�l 'moi 000 0 0 o N N O O o 0 0 0 A B C D E G Sample Dates / Location Figure 3-26. Distribution of Mountain Island Lake barium concentrations. 12 --- ------ ------ -------T--- ----- --- -- ---- --- -- ---- --- - - ------ ---1O10 -- --- ---- - - ------ -f �- - - - -- -- - - - -�—i- - rn 6 ------------------- ---- ---- i ------ ----- --- --- ------------------------------ -------}----- I 2 0 o O N N N c N N N o O O O N N O O o 0 o N A B c D E G Sample Dates / Location Figure 3-27. Distribution of Mountain Island Lake copper concentrations. 12 ------------------ ------- ------------ ------ - -- -, -- - ------- ---- - 1 i I I --- -------------------- ------- ------ ------ -- - -----,------ ------ ------- ----- --}-- ---- ---- --- (i I it i II - - - - - - ------ -4- ----- 4 - - �- - ------------ ------ -------- - --- - - - - - - - - - -- - ----- { - --- { 2 -+-+ - t- T - - --�- - - -- - - j - -T - -+------- ----- - i i j I I i i i i i 0 O o O o N O o o N O T_;R a0 A B C D E G Sample Dates / Location Figure 3-28. Distribution of Mountain Island Lake soluble copper concentrations. 3-26 1 0000 Y 01000 1 �0-0100 00010 ........ t 00001 E A E) F Sample Dates Location Figure 3-29 Distribution of Mountain Island Lake mercury concentrations 35 - --- - ------ - - -- ------- - --- ---- Z5------ - ---- - ----------- 20L i L L I i -1 Ir 10 5 ------ T1- i T 11' `1-� UL� 1 0 S� 2 A B C 1) Sample Dates / Location Figure 3-30 Distribution of Mountain Island Lake zinc concentrations. 3-27 Zb,000 T S>3 -0 20,000 E 15,000 m U N 10,000 T ❑ 5,000 a� 0 "I'bUU 1,600 1,400 D (n 1,200 r 0 s� 1,000 Q 800 (C] Q 600 w 400 200 0 N C`7 V LO (D 1- 00 m ON M .Q- LO (D I-- CO 62 m m O m CS m C3) OCD O O O O O O O (T O) C3) M M (' O) M O OO O O O O O O higure 3-31 Average annual RSS ash basin discharge and arsenic loading to Mountain Islaod Lake, 1992 — 2008 25,000 El Discharge Flow ■ Se Loading Ca 20,000 F, a� 15,000 CU v ❑ 10,000 T C 0 5,000 Q) WE 50 Cf) 40 r- 0 0 m Q 30 m 0 0 N C) "Y Lf) CO I- CO m O N C-0 ' LO (O r- 00 O) m O) m O O) O) 6) O O O O O O O O O O) CT 0) OO 62 6) O- O O O O O O O O O � .- N N N C'4 N N N N N Figure 3-32, Average annual MS ash basin discharge and selenium loading, to Mountain Island bake. 1992-2008 3-28 100 ;- -- - --- --- --- ?--- --�- --- ----r -- -- -- -- -- -rT T ----. I � I ------ ---T ----- r-- I I I I I I ! I I ! I I I ! -- ' I I I 1 1 I I I I I I I I I I I I I I I t 'I 'I I I I I I I I I I I I 70 ' I i 60- - -i -� - - I I - I I I I T50 ----+----f----+--- ----r----f-----t----+---- - --*---- - + ---+-----+-----+----+-----i----- —I --i a> 40 --j-----t-----t--- ----- fi-- i l i i i i i i t i l l i I i i i - i N 30 + -+i ------- -- ---- t--- +-----t-----+20 in 1! 10 I I I I ! ! I I ODrn o v m v m m rn o v rn v o eo rn o v rn v w ao rn o v rn v a6 ao CO rn rn rn o o m a6 rn rn rn o o a6 co rn rn rn o o m oo rn 0)rn o 0 a,rn rn rn rn o o rn rn rn rn rn o o rn rn rn rn rn o o rn m rn rn rn o 0 r < r r N, N �-- < < < < N N < r r < r N N r < < r < N N A (4 S km US) B (0 5 km US) C (0 6 km DS) G (10 1 km DS) Sample Dates / Location Figure 3-33. Distribution of arsenic concentrations in sediment fines sampled from Mountain Island Lake upstream (US) and downstream (DS) of the RSS ash basin outfall. 40 ----7 T ---T----7 ------- - T - -- - - --- - T - -- T --<---- i i! i i i i i l i i i l — r— r - T - T r --T- - - - —r— - - i l 35T-1-1 i i i l i l -------r---t - rt ; - t - * +- y -t - i i i 4-- -- - 30 -r---r------r-----r----- r----- --- -- 25 ---�----F---F---F---+---,-----F--t---F----j�----t----t----t---t----r- I • t-----t---t—t--t--+---i----r----i----=----i----i---- a 20 —t - � 15 I + +- --- - +-- t—+--- a --;- --- --- - -; -- - -- -; -�- - i 10...............-r i ! ! ! I I I +-�-+--;-;- +-+- � N 5 CO �I I I 1-14-4- ! ! i 1 -- I I ! !- I I- �y r , iii 0 M O O V' OJ V' OD OD T O v D) DD 00 O) O V' O v DD O O V D) QO OD N O) a) W O O W W W D7 � O O DD N O) W Q) O O W N O D) W O O O m O O O O m D) O) OA C":,O m Q) O W O W m Q) O O O O r < r r N N r r < < < N N r r < r < NO N < r r r < N N A(4 S km US) B (0 5 km US) C (0 6 km DS) G (10 1 km DS) Sample Dates / Location Figure 3-34. Distribution of selenium concentrations in sediment fines sampled from Mountain Island Lake upstream (US) and downstream (DS) of the RSS ash basin outfall. 3-29 CHAPTER 5 FISH MATERIALS AND METHODS Winter and Summer Electrofishing Surveys Electrofishing surveys were conducted in Mountain Island Lake near Riverbend Steam Station (RSS) in January and July (2004 — 2008) uplake from the RSS intake (Location B), in the discharge canal (Location F), and downlake from the RSS discharge near Mountain Island Dam (Location G; Table 1-1 and Figure 1-1). The locations surveyed consisted of 100-m transects on both the left and right shorelines. Surface water temperature (°C) and dissolved oxygen (mg/L) were measured with a calibrated thermistor and dissolved oxygen probe, respectively, at each location. Stunned fish were collected by two netters, identified to species, and measured for total length (mm). Catch per unit effort (CPUE, number of fish/100 m) and the number of species were calculated for each sampling location. Spring Electrofishing Surveys Electrofishing surveys were conducted in Mountain Island Lake near RSS in April or May (2004 — 2008) uplake and downlake from the RSS discharge canal (Figure 1-1). The locations surveyed were identical to historical locations surveyed since 1993 and consisted of five 300-m shoreline transects at each location. Transects included habitats representative of those found in Mountain Island Lake. Shallow flats where the boat could not access within 3-4 in of the shoreline were excluded. All sampling was conducted during daylight, when water temperatures were expected to be between 15 and 20 °C. Stunned fish were collected by two netters and identified to species. Fish were enumerated and weighed in aggregate by taxon, except for largemouth and spotted bass, where total lengths (mm) and weights (g) were obtained for each individual collected. Surface water temperature (°C) was measured with a calibrated thermistor at each location. Catch per unit effort (CPUE, number of fish/1,500 m) and the number of species were calculated for each sampling location. 5-1 Fall Hydroacoustics and Purse Seine Surveys The abundance and distribution of pelagic forage fish in Mountain Island Lake were determined using mobile hydroacoustic (Brandt 1996) and purse seine (Hayes et al. 1996) techniques. An annual mobile hydroacoustic survey from the Mountain Island Hydroelectric Station (MIHS) to approximately Location C was conducted in mid-September to estimate forage fish populations (Figure 1-1). Hydroacoustic surveys employed multiplexing, side - and down -looking transducers to detect surface -oriented fish and deeper fish (from 2.0 in depth to the bottom), respectively. Both transducers were capable of determining target strength directly by measuring fish position relative to the acoustic axis. Purse seine surveys were also collected in mid-September from the forebay of the MINS (near Location G). The purse seine measured 118 x 9 m, with a mesh size of 4.8 mm. A subsample of forage fish collected from each area was used to estimate taxa composition and size distribution. Trace Element Analyses Selenium, arsenic, mercury, and zinc concentrations were measured in epaxial muscle tissue of common carp Cyprinus carpio, sunfish (typically redbreast sunfish Lepomis auritus), and bass (typically largemouth bass Micropterus salmoides) collected by electrofishing in July (2004 — 2008) at Locations A, B, C, and G (Figure 1-1). Muscle tissue was dissected from each of five fish from a particular taxon, where available, and trace element concentrations (µg/g, wet weight) were determined individually by neutron activation analysis at the Nuclear Services Laboratory at Ncrth Carolina State University, Raleigh, NC. Graphical methods were used to examine spatial and temporal trends in trace element concentrations. Balanced and Indigenous Assessment Annual sampling protocols are designed to assess the balanced and indigenous nature of the Mountain Island Lake fish community and provide information relative to potential RSS impacts. The assessment includes a comparison of CPUE and number of species data from locations uplake of, in the discharge canal of, and downlake of RSS during winter and summer electrofishing. These electrofishing surveys are part of the required RSS 316(a) annual monitoring program. Additionally, trace element accumulation in fish muscle is 5-2 evaluated in relation to the ash basin discharge. Spring electrofishing and hydroacoustic surveys near RSS are part of the Catawba-Wateree hydroelectric relicensing activities. RESULTS AND DISCUSSION Winter Electrofishing Surveys Winter electrofishing surveys from 2004 to 2008 produced 5,078 individuals comprising eight families, 21 species, and two hybrid centrarchid combinations (Table 5-1). The species composition for the combined winter electrofishing surveys was dominated by clupeids (47.5%), centrarchids (45.1%), and cyprinids (6.9%), with the remaining families representing less than 1.0% each. Data from winter 2000 — 2003 documented a lower percentage of clupeids (5.3%) and cyprinids (2.0%) and a higher percentage of centrarchids (91.4%, Table 5-1 and Duke Power 2004). Pollution tolerant species (i.e., longnose gar Lepasosteus osseus, grass carp Ctenopharyngodon adella, common carp, golden shiner Notemagonus crysoleucas, white catfish Ameaurus catus, eastern mosquitofish Gambusaa holbrooka, redbreast sunfish, and hybrid sunfish) represented 15.7% of the collected fish from winter 2004 — 2008. This percentage decreased from 41.6% of collected fish reported from winter 2000 — 2003. The CPUE and number of species at individual locations ranged from 41.5 (Location G in 2005) to 701 (Location B in 2006) fish/100 in and from four (Locations F and G in 2005) to 13 species (Location F in 2004), respectively (Figure 5-1, Appendix Tables A-1 to A-5). Spatial dissimilarities in CPUE (Location B in 2006 and Location F in 2007) and number of species (Location F in 2004 and 2008) were likely due to collecting schools of threadfin shad and discharge canal temperature, respectively. Winter electrofishing data are consistent with previous data (Duke Power 2001, 2004) and indicate no negative impact from RSS operations on Mountain Island Lake fish populations. Summer Electrofishm Says Summer electrofishing surveys from 2004 to 2008 produced 4,054 individuals comprising seven families, 17 species, and two hybrid centrarchid combinations (Table 5-2). The species composition for the combined summer electrofishing surveys was dominated by centrarchids (66.1%), clupeids (27.5%), and cyprinids (6.2%), with the remaining families 5-3 R 1 t representing less than 1.0% each. Data from summer 2000 to 2003 documented similar percentages of each: centrarchids (66.2%), clupeids (30.5%), and cyprinids (2.4%). Pollution tolerant species represented 30.3% of the collected fish during summer 2004 — 2008. This percentage decreased from 44.1 % of collected fish reported from summer 2000 — 2003. The CPUE and number of species at individual locations ranged from 29.5 (Location G in 2006) to 288.0 (Location F in 2006) fish/100 m and from five to seven species (multiple locations for each; Figure 5-2, Appendix Tables A-6 to A-10). Spatial dissimilarities were due to collecting a school of threadfin shad (Location F in 2006) and a large centrarchid population (Location G in 2007 and 2008). Summer electrofishing data are consistent with previous data (Duke Power 2001, 2004) and indicate no negative impact from RSS operations on Mountain Island Lake fish populations. Spring- Electrofishin Surveys urveys Spring electrofishing surveys from 2004 to 2008 were conducted at water temperatures ranging from 12.7 to 20.8 °C. Fish numbers and biomass per 1,500 m ranged from 468 to 2,140 and from 45.7 to 131.2 kg, respectively, uplake of the RSS discharge and 706 to 1,389 and 38.4 to 81.6 kg, respectively, downlake from the RSS discharge (Table 5-3). The number of fish species ranged from 12 to 19 uplake and from 10 to 13 downlake of the RSS discharge. Previous reports documented that numbers of fish, biomass, and number of species collected uplake were generally greater than those from downlake locations (Duke Power Company 1994; Duke Power 2001, 2004). For 2004 — 2008 the numbers of fish and biomass varied between uplake and downlake, even though the number of species collected uplake was generally higher. Spring electrofishing surveys, from 2004 to 2008, were dominated by centrarchids (89.8%) and cyprinids (8.3%), with the remaining families representing less than 1.0% each (Table 5-4). Pollution tolerant species represented 28.3% (97.4% of that being redbreast sunfish) of the collected fish during spring 2004 — 2008. One new species, rainbow trout Oncorhynchus mykass, was collected uplake in 2006. Most likely introduced by an angler, it would not be expected to survive the summer. Spring electrofishing survey data varied among years, similar to other Catawba River reservoirs. 5-4 I Fall Hydroacoustics and Purse Seine Surveys Similar to Mountain Island Lake and other Catawba River reservoirs since 1994, hydroacoustics from 2004 to 2008 showed no temporal trend in annual forage fish population estimates (range = 601,00 — 3,597,000; 603 — 3,611 fish/ha) (Table 5-5). Purse seine surveys from 2004 to 2008 indicated a shift back to a threadfin shad Dorosoma petenense dominated (range = 80.2 — 99.8%) forage fish community. Alewife Alosa pseudoharengus, first detected in low numbers in 1999 (Duke Power 2001), have comprised as much as 83.1% (2003) of mid-September pelagic, forage fish community surveys, but have remained relatively low since 2004 (range = 0.2 —19.6%). Trace Element Analyses Trace element concentration means for common carp were typically comprised of less than five fish due to the difficulty of collecting common carp. The four complete common carp samples (out of 20 attempts; Location A from 2004 to 2006 and Location C in 2005) since 2004 had element concentration means mostly within the ranges of sunfish and bass. An individual sunfish from Location C in 2005 was a statistical outlier for all trace element concentrations and not included in analyses. All 2004 — 2008 trace element concentration means for sunfish and bass decreased at all locations relative to 1993 — 2003 and were within ranges reported from 1988 to 2003 (Harden and Reid 1991; Duke Power Company 1994; Duke Power 2001, 2004). Mean selenium concentrations in fish muscle tissue from complete samples collected from 2004 to 2008 ranged from 0.31 to 1.03 µg/g, wet weight (Figure 5-3). Mean selenium concentrations since 2004 from sunfish (range = 0.33 — 0.86 µg/g, mean = 0.53 µg/g) and bass (range = 0.31 — 1.03 µg/g, mean = 0.59 µg/g) were slightly greater than the average value of 0.50 µg/g measured in largemouth bass muscle tissue from 26 sites throughout the entire Catawba River basin during 1993 (Coughlan 1995). Location C, downstream from the ash basin discharge, had the highest mean selenium concentration for three out of the five years for bass and sunfish, although the years did not coincide between species. All measured values in common carp, sunfish, and largemouth bass were well below the North Carolina Department of Health and Human Services (NCDHHS) Action Level of 10.0 µg/g for the protection of human health (NCDHHS 2007). 5-5 r Mean arsenic concentrations in fi3h muscle tissue from complete samples collected from 2004 to 2008 ranged from 0.03 to 0.17 µg/g, wet weight (Figure 5-4). Mean arsenic concentrations since 2004 from sunfish (range = 0.03 - 0.17 µg/g, mean = 0.09 µg/g) and bass (range = 0.04 - 0.17 µg/g, mean = 0.08 µg/g) were similar to the average value of 0.09 µg/g measured in largemouth bass muscle tissue from 26 sites throughout the entire Catawba River basin during 1993 (Coughlan 1995). All measured values in common carp, sunfish, and largemouth bass were well below the Division of Water Quality's tissue screening value of 1.20 µg/g (NCDENR 2006). Mean mercury concentrations in f_sh muscle tissue from complete samples collected from 2004 to 2008 ranged from 0.03 to 0.15 µg/g, wet weight (Figure 5-5). Mean mercury concentrations since 2004 from sunfish (range = 0.04 - 0.13 µg/g, mean = 0.07 µg/g) and bass (range = 0.06 - 0.15 µg/g, mean = 0.10 µg/g) were similar to the average value of 0.08 µg/g measured in largemouth bass muscle tissue from 26 sites throughout the entire Catawba River basin during 1993 (Coughlan 1995). All measured values in common carp, sunfish, and largemouth bass were well below the NCDHHS action level of 0.40 pg/g for the protection of human health (NCDHHS 2007). Mean zinc concentrations in fish muscle tissue from complete samples collected from 2004 to 2008 ranged from 2.39 to 8.31 pg/g, wet weight (Figure 5-6). Mean zinc concentrations since 2004 from sunfish (range = 239 - 5.54 µg/g, mean = 4.42 µg/g) and bass (range = 2.43 - 5.63 µg/g, mean = 3.81 µg/g) were below the average value of 6.71 µg/g measured in largemouth bass muscle tissue from 26 sites throughout the entire Catawba River basin during 1993 (Coughlan 1995). All measured values in common carp, sunfish, and largemouth bass were well below cancentrations (16 to 82 µg/g) reportbd for several taxa of omnivorous freshwater fish from other areas in the United States (Moore and Ramamoorthy 1984). CONCLUSIONS A diverse fish community was present in the littoral portions of Mountain Island Lake around RSS from 2004 to 2008; winter and summer electrofishing surveys documented 21 species (and two hybrid combinations) and 17 species (and two hybrid combinations), respectively. Both surveys were numerically dominated by clupeids and centrarchids, with cyprinids also being of numerical importance. Spring electrofishing documented 26 species 5-6 W F (and one sunfish hybrid combination), dominated by centrarchids and cyprinids. Pollution tolerant species, mostly redbreast sunfish, comprised 15 — 30% of the Mountain Island Lake fish community. The assorted fish species typically found in Mountain Island Lake near RSS encompass a range of trophic groups including insectivores, omnivores, and piscivores. Forage fish population densities, as measured by hydroacoustics, were variable and ranged from 603 to 3,611 fish/ha from 2004 to 2008. These densities are comparable to those measured previously at Mountain Island Lake and to other Catawba River reservoirs of similar trophic status. The introduction of alewife, the inherent, temporal variability of clupeid populations, and the historical flux of Mountain Island Lake between oligotrophic and mesotrophic water quality classifications (Chapter 3) are all factors contributing to the unpredictable nature of forage fish densities. Trace element concentrations have been measured in Mountain Island Lake common carp, sunfish, and bass since 1988. Trace element concentrations from 2004 to 2008 remained well below values of regulatory concern, where such values exist. Past studies have indicated that a balanced indigenous fish community exists near the RSS (Duke Power Company 1994; Duke Power 2001, 2004). The present study adds more years of comparable data to help reinforce that conclusion. Based on the diversity and numbers of individuals in the Mountain Island Lake littoral fish community during winter, spring, and summer; the range of trophic groups represented; the lack of accumulation of selenium, arsenic, mercury, or zinc in fish flesh; and the regular availability of forage fish to limnetic predators, it is concluded that the operation of RSS has not impaired the Mountain Island Lake fish community. 5-7