Text

Annual Lake Norman Maintenance Monitoring Program: 2004 Summary
	ML060320087
Person / Time
Site:	McGuire, Mcguire
Issue date:	01/24/2006
From:	Gordon Peterson; Duke Power Co
To:	; Document Control Desk, Office of Nuclear Reactor Regulation
References
	NC0024392
	Download: ML060320087 (148)
	v • d • e

I PkDuke GARY R. PETERSON MEPowerv Vice President McGuire Nuclear Station A Duke Energy Company Duke Power MGO1VP / 12 700 Hagers Ferry Road Huntersville, NC 28078-9340 704 875 5333 704 875 4809 fax grpeters@duke-energy. corn January 24, 2006 U. S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555

Subject:

McGuire Nuclear Station Docket Nos. 50-369, 50-370 Please find attached a copy of the annual "Lake Norman Maintenance Monitoring Program: 2004 Summary," as required by the National Pollutant Discharge Elimination System (NPDES) permit NC0024392. The report includes detailed results and data comparable to that of previous years. The report was submitted to the North Carolina Department of Environment and Natural Resources on January 12, 2006.

Questions regarding this submittal should be directed to Kay Crane, McGuire Regulatory Compliance at (704) 875-4306.

Gary R. Peterson

%jI.Ez $

www. duke-energy. corn

U. S. Nuclear Regulatory Commission Document Control Desk January 24, 2006 Page 2 cc: Mr. J. F. Stang, McGuire Project Manager Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Mr. W. D. Travers, Regional Administrator U.S. Nuclear Regulatory Commission Region II Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlanta, Georgia 30303 Mr. Joe Brady Senior Resident Inspector McGuire Nuclear Station

LAKE NORMAN MAINTENANCE MONITORING PROGRAM:

2004

SUMMARY

McGuire Nuclear Station: NPDES No. NC0024392 Duke Power A Duke Energy Company December 2005

TABLE OF CONTENTS Page EXECUTIVE

SUMMARY

i LIST OF TABLES vi LIST OF FIGURES vii CHAPTER 1: McGUIRE NUCLEAR STATION OPERATION Introduction 1-1 Operational data for 2004 1-1 CHAPTER 2: WATER CHEMISTRY Introduction 2-1 Methods and Materials 2-1 Results and Discussion 2-3 Future Studies 2-12 Summary 2-12 Literature Cited 2-14 CHAPTER 3: PHYTOPLANKTON Introduction 3-1 Methods and Materials 3-1 Results and Discussion 3-2 Future Studies 3-9 Summary 3-9 Literature Cited 3-10 CHAPTER 4: ZOOPLANKTON Introduction 4-1 Methods and Materials 4-1 Results and Discussion 4-2 Future Studies 4-6 Summary 4-6 Literature Cited 4-8 CHAPTER 5: FISHERIES Introduction 5-1 Methods and Materials 5-1 Results and Discussion 5-3 Future Studies 5-8 Summary 5-8 Literature Cited 5-9

EXECUTIVE

SUMMARY

As required by the National Pollutant Discharge Elimination System (NPDES) permit number NC0024392 for McGuire Nuclear Station (MNS), the following annual report has been prepared. This report summarizes environmental monitoring of Lake Norman conducted during 2004.

McGUIRE NUCLEAR STATION OPERATION The monthly average capacity factor for MNS was 101.3 %, 101.2 %, and 101.9 % during July, August, and September of 2004, respectively (Table 1-1). These are the months when conservation of cool water and discharge temperatures are most critical and the thermal limit for MNS increases from a monthly average of 95.0 'F (35.0 0 C) to 99.0 0 F (37.2 0 C). The average monthly discharge temperature was 97.7 'F (36.5 0C) for July, 97.6 'F (36.4 0 C) for August, and 94.2 'F (34.6 0 C) for September 2004. The volume of cool water in Lake Norman was tracked throughout the year to ensure that an adequate volume was available to comply with both the Nuclear Regulatory Commission Technical Specification requirements and the NPDES discharge water temperature limits.

WATER CHEMISTRY Annual precipitation in the vicinity of MNS in 2004 totaled 44.6 inches or 17.1 inches less than observed in 2003, but similar to the long-term precipitation average for this area (46.3 inches). Air temperatures in 2004 were generally warmer than measured in 2003, as well as the long-term mean. The most pronounced differences occurred in May when 2004 temperatures averaged 3.5 'C warmer than 2003, and 2.6 'C warmer than the long-term average.

Temporal and spatial trends in water temperature and DO in 2004 were similar to those observed historically, and all data were within the range of previously measured values.

Water temperatures in 2004 were generally warmer than observed in 2003 in both the mixing and background zones. Winter temperatures averaged about 0.3 'C warmer throughout the water column in 2004 versus 2003. Summer temperatures averaged about 2 to 3 'C warmer in 2004 versus 2003, with the primary differences observed in the upper 10 m of the water column. Interannual differences in water temperatures, especially in the surface waters, typically paralleled differences exhibited in air temperatures between 2004 and 2003.

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Reservoir-wide isotherm and isopleth information for 2004, coupled with heat content and hypolimnetic oxygen data, illustrated that Lake Norman exhibited thermal and oxygen dynamics characteristic of historical conditions and similar to other Southeastern reservoirs of comparable size, depth, flow conditions, and trophic status. Availability of suitable pelagic habitat for adult striped bass in Lake Norman in 2004 was generally similar in distribution and amount to historical conditions observed annually since 1983. Despite similarities in habitat conditions to previous years, the largest striped bass die-off ever observed in the reservoir (2599 fish) occurred in the summer of 2004.

All chemical parameters measured in 2004 were within the concentration ranges previously reported for the lake during both preoperational and operational years of MNS.

Concentrations of metals in 2004 were also low, and often below the analytical reporting limits. Manganese and iron concentrations in the surface and bottom waters were generally low in 2004, except during the summer and fall when bottom waters became anoxic, and the release of soluble forms of these metals into the water column was observed. In contrast to previous years, at no time during 2004 did iron concentrations exceed NC's water quality standard (1.0 mg/L). Manganese levels, however, did exceed the State standard (200 ug/L) in the bottom waters throughout the lake in the summer and fall, and are characteristic of historical conditions.

PHYTOPLANKTON Lake Norman continues to support highly variable and diverse phytoplankton communities.

No obvious short term or long term impacts of station operations were observed.

In 2004 lake-wide mean chlorophyll a concentrations were generally in the mesotrophic range with the exception of May, when chlorophyll concentrations averaged in the oligotrophic range. Chlorophyll concentrations during 2004 were generally within the same ranges as those of 2003. Lake Norman continues to be classified as oligo-mesotrophic based on long term, annual mean chlorophyll concentrations. The highest chlorophyll value recorded in 2004, 10.57 ug/L, was well below the NC State Water Quality standard of 40 ug/L.

In most cases, total phytoplankton densities and biovolumes observed in 2004 were higher than those observed during 2003, and standing crops were within ranges established over previous years. Phytoplankton densities and biovolumes during 2004 never exceeded the NC ii

guidelines for algae blooms. Standing crop values in excess of bloom guidelines have been recorded during six previous years of the Program. As in past years, high standing crops were usually observed at up-lake locations; while comparatively low values were noted down-lake.

Seston dry and ash-free weights were more often higher in 2004 than in 2003, and down-lake to up-lake differences were apparent most of the time. The proportions of ash-free dry weights to dry weights in 2004 were higher than those of 2003, indicating an increase in organic composition among 2004 samples.

Secchi depths reflected suspended solids, with shallow depths related to high dry weights.

The lake-wide mean secchi depth in 2004 was slightly higher than in 2003 and was within historical ranges recorded since 1992.

Diversity, or numbers of taxa, of phytoplankton had decreased since 2003, when the total number of individual taxa was the highest yet recorded. The taxononic composition of phytoplankton communities during 2004 was similar to those of many previous years.

Cryptophytes were dominant in February, while diatoms were dominant during May and November. Green algae dominated phytoplankton assemblages during August. Blue-green algae were slightly more abundant during 2004 than during 2003; however, their contribution to total densities rarely exceeded 5 %.

The most abundant alga, on an annual basis, was the cryptophyte Rhodomonas minuta.

Common and abundant diatoms were Fragillaria crotonensis in May and Tabellaria fenestrata in November. The small desmid, Cosmarium asphearosporumvar. strigosum was dominant in August 2004. All of these taxa have been common and abundant throughout the Maintenance Monitoring Program.

The phytoplankton index (Myxophycean) characterized Lake Norman as oligotrophic during 2004, and was slightly higher than the annual index for 2003. Quarterly index values decreased from the highest in February to the lowest in November. Quarterly values did not reflect maximum and minimum chlorophyll concentrations and phytoplankton standing crops. Location index values tended to reflect increases in chlorophyll and phytoplankton standing crops from down-lake to mid-lake.

iii

ZOOPLANKTON Lake Norman continues to support a highly diverse and viable zooplankton community.

Zooplankton densities, as well as seasonal and spatial trends were generally consistent with historical precedent during 2004, and no impacts of plant operations were observed.

Maximum zooplankton densities occurred in May at three locations and in February at two other locations. Minimum zooplankton densities were most often noted in August. As in past years, epilimnetic densities were higher than whole column densities. Mean zooplankton densities tended to be higher among Background Locations than among Mixing Zone Locations during 2004. In the Mixing Zone, a long term trend of increasing year-to-year densities was observed for May. In addition, long term trends showed much higher year-to-year variability at Background Locations than at Mixing Zone Locations.

One hundred and seventeen zooplankton taxa have been recorded from Lake Norman since the Program began in 1987 (Fifty-two were identified during 2004). Four previously unreported taxa (three cladocerans and one rotifer) were identified during 2004.

Overall relative abundance of copepods in 2004 had decreased since 2003, and they were dominant in ten samples collected during August and November. Cladocerans were dominant in only two samples in August, while rotifers were dominant in 70% of all samples.

Overall, the relative abundance of rotifers had increased since 2003, and their relative abundances were somewhat similar to those of 1995. Historically, copepods and rotifers have most often shown annual peaks in May; while cladocerans continued to demonstrate year-to-year variability.

Copepods were dominated by immature forms with adults rarely accounting for more than 10% of zooplankton densities. The most important adult copepod was Tropocyclops, as was the case in previous years. Bosmina was the predominant cladoceran, as has also been the case in most previous years of the Program. Bosminopsis dominated most cladoceran populations in August. The most abundant rotifers observed in 2004, as in many previous years, were Polyarthra,Conochilus, and Karetella, while Asplanchna and Syncheata were occasionally important among rotifer populations.

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FISHERIES In accordance with the Lake Norman Maintenance Monitoring Program for the NPDES permit for MNS, specific fish monitoring programs were coordinated with the NCWRC and continued during 2004. Spring electrofishing indicated that 17 to 21 species of fish and 2 hybrid complexes comprised fish populations in the 3 sampling areas, and numbers and biomass of fish in 2004 were generally similar to those noted since 1993. Declines in largemouth bass numbers, which were first observed in 2000, appear to be an exception.

In 2004, considerable striped bass mortality was observed during summer in Lake Norman and this mortality appeared to be related to a combination of unique events triggered by an unusually warm May and the abundance of prey in the hypolimnion. Mean Wr for Lake Norman striped bass collected in November and December 2004 was similar to that observed previously and indicated little change in the overall condition of this fish.

Trapnetting indicated little change in the crappie populations in Lake Norman in 2003-2004.

Hydroacoustic and purse seine sampling indicated that there was a decline in the number of prey fish and a change in species composition from 2003 to 2004.

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LIST OF TABLES Table # Title Page #

1-1 Average monthly capacity factors for McGuire Nuclear Station 1-2 2-1 Water chemistry program for McGuire Nuclear Station 2-18 2-2 Water chemistry analytical methods and reporting limits 2-19 2-3 Heat content calculations for Lake Norman in 2003 and 2004 2-20 2-4 Comparison of Lake Norman with TVA reservoirs 2-21 2-5 Lake Norman water chemistry data in 2003 and 2004 2-22 3-1 Mean chlorophyll a concentrations and secchi depths in Lake Norman 3-13 3-2 Duncan's multiple range test for chlorophyll a 3-14 3-3 Total phytoplankton densities and biovolumes from Lake Norman 3-15 3-4 Duncan's multiple range test for phytoplankton densities 3-16 3-5 Duncan's multiple range test for dry and ash free dry weights 3-17 3-6 Phytoplankton taxa identified in Lake Norman from 1990 - 2004 3-18 3-7 Dominate classes and species of Phytoplankton 3-28 4-1 Total zooplankton densities and composition 4-10 4-2 Duncan's multiple range test for zooplankton densities 4-12 4-3 Zooplankton taxa identified in Lake Norman from 1987 - 2004 4-13 4-4 Dominant taxa and percent composition of selected zooplankton 4-16 5-1 Common and scientific names of fish collected in Lake Norman 5-11 5-2 Numbers and biomass of fish collected in April, 2004 5-12 5-3 Lengths and age of largemouth bass collected in Lake Norman 5-13 5-4 Comparison of length and age for largemouth bass from near MSS and 5-13 MNS from data collected 1971 - 2004 5-5 Dead or dying striped bass in Lake Norman July-August 2004 5-14 5-6 Fish collect from gill nets in July 2004 5-16 5-7 Prey fish densities from September 2004 5-16 5-8 Prey fish statistics from purse seine samples collected late summer or 5-17 early fall 1997 - 2004 vi

LIST OF FIGURES Figure # Title Page 2-1 Map of sampling locations on Lake Norman 2-25 2-2a Annual precipitation totals near McGuire Nuclear Station, 1975 - 2004 2-26 2-2b Monthly precipitation totals near McGuire Nuclear Station for 2003 and 2-26 2004 2-2c Monthly mean air temperatures (1989 - 2004) near McGuire Nuclear 2-27 Station 2-3 Monthly mean temperature profiles in background zone 2-28 2-4 Monthly mean temperature profiles in mixing zone 2-30 2-5 Monthly temperature and dissolved oxygen at the MNS discharge 2-32 2-6 Monthly mean dissolved oxygen profiles in background zone 2-33 2-7 Monthly mean dissolved oxygen profiles in mixing zone 2-35 2-8 Monthly temperature isotherms for Lake Norman 2-37 2-9 Monthly dissolved oxygen isopleths for Lake Norman 2-40 2-1 Oa Heat content of Lake Norman 2-43 2-1Ob Dissolved oxygen content of Lake Norman 2-43 2-11 Striped bass habitat in Lake Norman 2-44 2-12 Lake levels for 2002, 2003, and 2004 for Lake Norman 2-46 3-1 Chlorophyll a measurements, densities, biovolumes, and seston weights 3-29 3-2 Mean chlorophyll a concentrations for 1987 - 2004 3-30 3-3 Chlorophyll a concentrations by location for 1988 - 2004 for February 3-31 3-4 Chlorophyll a concentrations by location for 1987 - 2004 for August 3-32 and November 3-5 Class composition of phytoplankton at Locations 2.0 3-33 3-6 Class composition of phytoplankton at Locations 5.0 3-34 3-7 Class composition of phytoplankton at Location 9.5 3-35 3-8 Class composition of phytoplankton at Location 11.0 3-36 3-9 Class composition of phytoplankton at Location 15.9 3-37 3-10 Myxophycean index values from 1988 - 2004 3-38 4-1 Zooplankton density by sample location in Lake Norman 4-18 4-2 Zooplankton community composition in Lake Norman 4-19 4-3 Zooplankton densities during February and May 1988 - 2004 4-20 4-4 Zooplankton densities during August and November 1987 - 2004 4-21 4-5 Quarterly zooplankton community composition from 1990 - 2004 4-22 4-6 Annual lake-wide zooplankton community composition, 1988 - 2004 4-23 4-7 Zooplankton community composition from mixing zone locations, 1988 4-24

- 2004 4-8 Zooplankton composition from background locations, 1988 - 2004 4-25 5-1 Lake Norman sampling zones 5-18 Vii

5-2 Numbers and biomass of fish in Lake Norman 1993 - 2004 5-19 5-3 Numbers and biomass of largemouth bass in Lake Norman 1993 - 2004 5-20 5-4 Size distributions of largemouth bass in Lake Norman in 2004 5-21 5-5 Relative weights for largemouth bass in Lake Norman in 2004 5-22 5-6 Lengths and relative weights for striped bass in Lake Norman 5-23 5-7 Lakewide population estimates for pelagic fish 5-24 5-8 Size distribution of forage fish from purse seine surveys 5-25 viii

CHAPTER 1 McGUIRE NUCLEAR STATION OPERATION INTRODUCTION As required by the National Pollutant Discharge Elimination System (NPDES) permit number NC0024392 for McGuire Nuclear Station (MNS) issued by the North Carolina Department of Environment and Natural Resources (NCDENR), the following annual report has been prepared. This report summarizes environmental monitoring of Lake Norman conducted during 2004.

OPERATIONAL DATA FOR 2004 The monthly average capacity factor for MNS was 101.3 %, 101.2 %, and 101.9 % during July, August, and September of 2004, respectively (Table 1-1). These are the months when conservation of cool water and discharge temperatures are most critical and the thermal limit for MNS increases from a monthly average of 95.0 'F (35.0 'C) to 99.0 'F (37.2 'C). The average monthly discharge temperature was 97.7 'F (36.5 'C) for July, 97.6 'F (36.4 0C) for August, and 94.2 'F (34.6 0 C) for September 2004. The volume of cool water in Lake Norman was tracked throughout the year to ensure that an adequate volume was available to comply with both the Nuclear Regulatory Commission Technical Specification requirements and the NPDES discharge water temperature limits.

1-1

Table 1-1. Average monthly capacity factors (%) and monthly average discharge water temperatures for McGuire Nuclear Station during 2004.

MONTHLY AVERAGE MONTHLY AVERAGE CAPACITY FACTORS (%) NPDES DISCHARGE TEMPERATURES Month Unit 1 Unit 2 Station OF °C January 105.1 105.1 105.1 68.0 20.0 February 105.1 104.9 105.0 67.5 19.7 March 16.7 104.8 60.8 67.9 19.9 April 61.1 104.3 82.7 73.3 22.9 May 103.9 103.7 103.8 84.0 28.9 June 102.2 102.3 102.3 93.1 33.9 July 101.3 101.3 101.3 97.7 36.5 August 101.3 101.0 101.2 97.6 36.4 September 101.9 102.0 101.9 94.2 34.6 October 55.7 103.3 79.5 84.2 29.0 November 64.7 104.0 84A 78.1 25.6 December 105.1 104.6 104.9 75.2 24.0

[ Averages 85.3 103.4 94A 81.7 27.6 1-2

CHAPTER 2 WATER CHEMISTRY INTRODUCTION The objectives of the water chemistry portion of the McGuire Nuclear Station (MNS)

NPDES Maintenance Monitoring Program are to:

1. maintain continuity in Lake Norman's chemical data base to allow detection of any significant station-induced and/or natural change in the physicochemical structure of the lake; and

2. compare, where applicable, these physicochemical data to similar data in other hydropower reservoirs and cooling impoundments in the Southeast.

This report focuses primarily on 2003 and 2004. Where appropriate, reference to pre-2003

.data will be made by citing reports previously submitted to the North Carolina Department of Environment and Natural Resources (NCDENR).

METHODS AND MATERIALS The complete water chemistry monitoring program for 2004, including specific variables, locations, depths, and frequencies is outlined in Table 2-1. Sampling locations are identified in Figure 2-1, whereas specific chemical methods and associated analytical reporting limits, along with the appropriate references, are presented in Table 2-2. Measurements of temperature, dissolved oxygen (DO), DO saturation, pH, and specific conductance were taken, in situ, at each location with a Hydrolab Data-Sonde (Hydrolab 1986) starting at the lake's surface (0.3m) and continuing at lm intervals to one meter above lake bottom. Pre and post-calibration procedures associated with operation of the Hydrolab were strictly followed, and documented in hard-copy format. Hydrolab data were captured and stored electronically, and following a data validation step, converted to spreadsheet format for permanent filing.

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Water samples for laboratory analysis were collected with a Kemmerer water bottle at the surface (0.3m), and from one meter above bottom, where specified (Table 2-1). Samples not requiring filtration were placed directly in single-use polyethylene terephthalate (PET) bottles which were pre-rinsed in the field with lake-water just prior to obtaining a sample.

Samples for the analysis of soluble nutrients (orthophosphate, nitrite-nitrate, and ammonia) were processed in the field by filtering a known volume of water through a 0.45um glass-fiber filter which was pre-rinsed in the field with a 100 mL portion of the filtrate. Upon collection, all water samples were immediately preserved and stored in the dark and on ice to minimize the possibility of physical, chemical or microbial transformation.

Water quality data were subjected to various graphical and statistical techniques in an attempt to describe spatial and temporal trends within the lake, and interrelationships among constituents. Whenever analytical values were obtained that were equal to or less than the method reporting limit, these values were set equal to the reporting limit for statistical purposes. Data were analyzed using two approaches, both of which were consistent with earlier Duke Power Company (DPC), and Duke Power (DP) studies on the lake (DPC 1985, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997; DP 1998, 1999, 2000, 2001, 2002, 2003, 2004). The first method involved partitioning the reservoir into mixing, background, and discharge zones, consolidating the data into these sub-sets, and making comparisons among zones and years. In this report, the discharge includes only Location 4; the mixing zone, Locations 1 and 5; the background zone includes Locations 8, 11, and 15.

The second approach, applied primarily to the in-situ data, emphasized a much broader lake-wide investigation and encompassed the plotting of monthly isotherms and isopleths, and summer-time striped bass habitat. Several quantitative calculations were also performed on the in-situ Hydrolab data; these included the calculation of the areal hypolimnetic oxygen deficit (AHOD), maximum whole-water column and hypolimnion oxygen content, maximum whole-water column and hypolimnion heat content, mean epilimnion and hypolimnion heating rates over the stratified period, and the Birgean heat budget.

Heat content (Kcal/cm ), oxygen content (mg/cm 2 ), and mean oxygen concentration (mg/L) of the reservoir were calculated according to Hutchinson (1957), using the following equation:

Lt = Ao-I TO

Az

dz where; 2-2

Lt = reservoir heat (Kcal/cm ) or oxygen (mg/cm 2 ) content Ao = surface area of reservoir (cm )

TO = mean temperature (fC) or oxygen content of layer z Az = area (cm2 ) at depth z dz= depth interval (cm) z= surface Zm = maximum depth Precipitation and air temperature data were obtained from a meteorological monitoring site established in lower Lake Norman, near MNS, in 1975. These data are employed principally by Duke Power as input variables into meteorological modeling studies to address safety issues associated with potential radiological releases into the atmosphere by MNS (Duke Energy Company 2004), as required by the Nuclear Regulatory Commission. The data also serve to document localized temporal trends in air temperatures and rainfall patterns.

Data on lake level and hydroelectric flows were obtained from Duke Power's Fossil/Hydroelectric Department, which monitors these metrics hourly.

RESULTS AND DISCUSSION Precipitation and Air Temperature Annual precipitation in the vicinity of MNS in 2004 totaled 44.6 inches (Figures 2-2a, b) or 17.1 inches less than observed in 2003 (61.7 inches), but similar to the long-term precipitation average for this area (46.3 inches), based on Charlotte, NC airport data. In 2003, greater than 80% of the yearly rainfall occurred over the first eight months of the year.

In contrast, greater than 80% of the yearly rainfall in 2004 occurred over the last eight months of the year. The highest total monthly rainfall in 2004 occurred in September (7.73 inches), in concert with the occurrence of Hurricanes Frances and Ivan, both of which bypassed the greater Charlotte area but exerted a considerable effect on the North Carolina mountains and foothills.

Air temperatures in 2004 were generally warmer than measured in 2003, and the long-term mean, based on monthly average data (Figure 2-2c). The temporal difference was most pronounced in May when 2004 temperatures averaged 3.5 0 C warmer than 2003, and 2.6 'C warmer than the long-term average.

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Temperature and Dissolved Oxygen Water temperatures measured in 2004 illustrated similar temporal and spatial trends in the background and mixing zones (Figures 2-3 and 2-4), as they did in 2003. This similarity in temperature patterns between zones has been a dominant feature of the thermal regime in Lake Norman since MNS began operations in 1983.

Water temperatures in 2004 were generally warmer than those observed in 2003 in both the mixing and background zone, and paralleled interannual differences exhibited in air temperatures (Figures. 2-2c, 2-3, and 2-4). Minimum water temperatures in 2004 were recorded in early February and ranged from 6.6 'C to 8.0 'C in the background zone, and from 7.4 'C to 13.1 0 C in the mixing zone. The average minimum temperature in 2004 was about 0.3 0 C warmer than that observed in 2003, and corresponded closely with the between-year difference in mean winter air temperature. Minimum water temperatures measured in 2004 were within the observed historical variability (DPC 1985, 1987, 1988a, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997; DP 1998, 1999, 2000, 2001, 2002, 2003, 2004).

Spring and summer water temperatures in 2004 ranged from about 1 to 5 0C warmer, on the average, than observed in 2003, with the primary differences occurring in the upper lOin of the water column (Figure 2-3, 2-4). The greatest between-year variability in summer water temperature was observed in June in both the mixing and background zones. Water temperatures in this portion of the water column ranged from 3.8 to 6.2 'C warmer in 2004 than 2003, and can be traced to the antecedent May air temperatures, which were the warmest recorded over the last 40 years (unpublished data, Charlotte airport). Maximum August surface water temperatures were also greater in 2004 than 2003 with interannual differences observed within each zone. The maximum surface temperature in the background zone in 2004 was 29.7 'C, whereas in 2003 the corresponding maximum temperature was 28.5 'C, or almost 1.2 'C cooler. Similarly, the maximum August surface temperature in the mixing zone in 2004 was 30.8 'C compared to a maximum of 29.1 0 C in 2003. Minimal differences in hypolimnetic (below 20m) temperatures were observed between 2004 and 2003 during the summer; the lone exception was in September when the deeper waters were warmer (and the surface waters were cooler) than observed in 2003, especially in the background zone. These thermal differences can be explained by differential cooling of the water column in 2004 versus 2003, in response to lower air temperatures in the preceding month of August (Figure 2-2c).

2-4

Fall and early winter water temperatures (October, November and December) in 2004 were generally similar to those measured in 2003, and followed the trend exhibited in air temperatures (Figure 2-3) Some differences were observed between years, and in certain portions of the water column, but overall cooling of the water column proceeded at a similar rate in 2004 and 2003.

Temperature data at the discharge location in 2004 were generally similar to 2003 (Figure 2-

5) and historically (DPC 1985, 1987, 1988a, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997; DP 1998, 1999, 2000, 2001, 2002, 2003, 2004). Temperatures in 2004 were typically equal to or cooler (by a maximum of 6.1 'C) in the spring, and warmer (by a maximum of 3.7 'C) in the summer and fall, than observed in 2003. The warmest discharge temperature of 2004 at Location 4 occurred in August and measured 38.8 'C, or 3.7 'C warmer than measured in August, 2003 (DP 2004).

Seasonal and spatial patterns of DO in 2004 were reflective of the patterns exhibited for temperature, i.e., generally similar in both the mixing and background zones (Figures 2-6 and 2-7). As observed with water column temperatures, this similarity in dissolved DO patterns between zones has been a dominant feature of the oxygen regime in Lake Norman since MNS began operations in 1983.

Winter and early spring DO values in 2004 were generally equal to or slightly lower, in both the background and mixing zones, than measured in 2003, except in January in the background zone which exhibited slightly higher oxygen concentrations in 2004 versus 2003 (Figures 2-6 and 2-7). The interannual differences in DO values measured during this period appeared to be related predominantly to the warmer water column temperatures in 2004 versus 2003. Warmer water would be expected to exhibit a lesser oxygen content because of the direct effect of temperature on oxygen solubility, which is an inverse relationship, and indirectly via a restricted convective mixing regime which would limit water column reaeration. February and March 2004 DO concentrations were about equal to or 0.5 mg/L less throughout the water column than measured in 2003.

Spring and summer DO values in 2004 were highly variable throughout the water column in both the mixing and background zones ranging from highs of 6 to 8 mg/L in surface waters to lows of 0 to 2 mg/L in bottom waters. This pattern is similar to that measured in 2003 and earlier years (DPC 1985, 1987, 1988a, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997; DP 1998, 1999, 2000, 2001, 2002, 2003, 2004). Epilimnetic and metalimnetic DO 2-5

values during the spring and summer of 2004 were typically slightly lower than measured at similar depths in 2003, especially in the background zone, although exceptions to this were observed in both zones. In both the mixing and background zones, August, 2004 DO concentrations in the waters above 10m were considerably higher than measured in 2003 even though temperatures were warmer. Hypolimnetic DO values measured during this period were also either equal to or slightly greater than measured in 2003 in both the mixing and background zones. All dissolved oxygen values recorded in 2004 were within the historical range (DPC 1985, 1987, 1988a, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997; DP 1998, 1999, 2000, 2001, 2002, 2003, 2004).

Considerable differences were observed between 2004 and 2003 fall DO values in both the mixing and background zone, especially in the metalimnion and hypolimnion during the months of September, October and November (Figures 2-6 and 2-7). These interannual differences in autumn DO levels are common in Catawba River reservoirs and can be explained by the effects of variable weather patterns on water column cooling and mixing.

Warmer air temperatures would delay water column cooling (Figure 2-3, 2-4) which, in turn, would delay the onset of convective mixing of the water column and the resultant reaeration of the metalimnion and hypolimnion. Conversely, cooler air temperatures would promote the rate and magnitude of this process resulting in higher DO values earlier in the year. The 2004 autumn DO data indicate that fall reaeration proceeded faster and was more complete throughout the water column than observed in the corresponding months in 2003.

Consequently, DO levels in these months in 2004 were higher than observed in 2003.

Interannual differences in DO patterns are common not only within the Catawba River Basin, but throughout Southeastern reservoirs, and can reflect yearly differences in hydrologic, meteorologic, and limnologic forcing variables (Cole and Hannon 1985; Petts, 1984).

The seasonal pattern of DO in 2004 at the discharge location was similar to that measured historically, with the highest values observed during the winter and lowest observed in the summer and early fall (Figure 2-5). The lowest DO concentration measured at the discharge location in 2004 (5.55 mg/L) occurred in July and August, and was 1.45 mg/L higher than measured in August 2003 (4.1 mg/L) and similar to DO levels measured in August 2002 (5.4 mg/L), and August 2001 (5.5 mg/L).

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Reservoir-wide Temperature and Dissolved Oxygen The monthly reservoir-wide temperature and DO data for 2004 are presented in Figures 2-8 and 2-9. These data are similar to that observed in previous years and are characteristic of cooling impoundments and hydropower reservoirs in the Southeast (Cole and Hannon, 1985; Hannon et. al., 1979; Petts, 1984). For a detailed discussion on the seasonal and spatial dynamics of temperature and dissolved oxygen during both the cooling and heating periods in Lake Norman, the reader is referred to earlier reports (DPC 1992, 1993, 1994, 1995, 1996).

The seasonal heat content of both the entire water column and the hypolimnion for Lake Norman in 2004 are presented in Figure 2-1 Oa; additional information on the thermal regime in the reservoir for the years 2003 and 2004 is found in Table 2-3. Annual minimum heat content for the entire water column in 2004 (7.92 Kcal/cm 2 ; 8.0 0 C) occurred in early February, whereas the maximum heat content (29.72 Kcal/cm 2 ; 28.99 0 C) occurred in early July. Heat content of the hypolimnion exhibited a somewhat different temporal trend as that observed for the entire water column. Annual minimum hypolimnetic heat content occurred in early February and measured 4.40 Kcal/cm2 (7.0 0 C), whereas the maximum occurred in mid-September and measured 16.18 Kcal/cm 2 (23.6 0 C). Heating of both the entire water column and the hypolimnion occurred at approximately a linear rate from minimum to maximum heat content. The mean heating rate of the entire water column equaled 0.118 Kcal/cm 2 /day and 0.054 Kcal/cm 2 /day for the hypolimnion. The 2004 heat content and heating rate data were similar to that observed in previous years (DPC 1985, 1987, 1988a, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997; DP 1998, 1999, 2000, 2001, 2002, 2003, 2004).

The seasonal oxygen content and percent saturation of the whole water column, and the hypolimnion, are depicted for 2004 in Figure 2-lOb. Additional oxygen data can be found in Table 2-4 which presents the 2004 AHOD for Lake Norman and similar estimates for 18 Tennessee Valley Authority (TVA) reservoirs. Reservoir oxygen content was greatest in mid-winter when DO content measured 10.9 mg/L for both the whole water column and the hypolimnion. Percent saturation values at this time approached 98 % for the entire water column and 94 % for the hypolimnion. Beginning in early spring, oxygen content began to decline precipitously in both the whole water column and the hypolimnion, and continued to decline linearly until reaching a minimum in mid summer. Minimum summer volume-weighted DO values for the entire water column measured 4.6 mg/L (60 % saturation),

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whereas the minimum for the hypolimnion was 0.3 mg/L (3.8 % saturation). The mean rate of DO decline in the hypolimnion over the stratified period, i.e., the AHOD, was 0.046 mg/cm 2 /day (0.058 mg/L/day) (Figure 2-lOb), and is similar to that measured in 2003 (DP 2004).

Hutchinson (1938, 1957) proposed that the decrease of DO in the hypolimnion of a waterbody should be related to the productivity of the trophogenic zone. Mortimer (1941) adopted a similar perspective and proposed the following criteria for AHODs associated with various trophic states; oligotrophic - < 0.025 mg/cm 2 /day, mesotrophic - 0.026 mg/cm 2 /day to 0.054 mg/cm 2 /day, and eutrophic - 2 0.055 mg/cm 2 /day. Employing these limits, Lake Norman should be classified as mesotrophic based on the calculated AHOD value of 0.046 mg/cm2 /day for 2004. The oxygen based mesotrophic classification agrees well with the mesotrophic classification based on chlorophyll a levels (Chapter 3). The 2004 AHOD value is also similar to that found in other Southeastern reservoirs of comparable depth, chlorophyll a status, and secchi depth (Table 2-4).

Striped Bass Habitat Suitable pelagic habitat for adult striped bass, defined as that layer of water with temperatures < 26 'C and DO levels 2 2.0 mg/L, was found lake-wide from mid September 2003 through early July 2004. Beginning in mid June 2004, habitat reduction proceeded rapidly throughout the reservoir both as a result of deepening of the 26 'C isotherm and metalimnetic and hypolimnetic deoxygenation (Figure 2-11). Habitat reduction was most severe from mid July through early September when no suitable habitat was observed in the reservoir except for a small, but variable, zone of refuge in the upper, riverine portion of the reservoir, near the confluence of Lyles Creek with Lake Norman. Habitat measured in the upper reaches of the reservoir appeared to be influenced by both inflow from Lyles Creek and discharges from Lookout Shoals Hydroelectric facility, which were somewhat cooler than ambient conditions in Lake Norman. Upon entering Lake Norman, this water apparently mixes and then proceeds as a subsurface underflow as it migrates downriver (Ford 1985).

A secondary temporary refuge was also observed in the hypolimnion near the dam during this period, but this lasted only until late July when dissolved oxygen was reduced to < 2.0 mg/l by microbial demands. The reservoir was completely devoid of habitat for adult striped bass from 27 July to 9 August, or about two weeks. These habitat conditions were 2-8

marginally better than observed in most previous years, including 2003 which exhibited complete habitat elimination for a period of about 30-35 days.

Physicochemical habitat was observed to have expanded appreciably by mid September, primarily as a result of epilimnion cooling and deepening, and in response to changing meteorological conditions. The temporal and spatial pattern of striped bass habitat expansion and reduction observed in 2004 was generally similar to that previously reported in Lake Norman, and many other Southeastern reservoirs (Coutant 1985, Matthews et al. 1985, DPC 1992, 1993, 1994, 1995, 1996, 1997, DP 1998, 1999, 2000, 2001, 2002, 2003, 2004).

However, despite overall similarities in the pattern, rate, and extent of habitat depletion in 2004 versus previous years, a significant die-off of striped bass (2610 fish) was observed in 2004. A detailed account of this phenomenon is found in Chapter 5.

Turbidity and Specific Conductance Surface turbidity values were generally low at the MNS discharge, mixing zone, and mid-lake background locations during 2004, ranging from 1.0 to 3.4 NTU's (Table 2-5). Bottom turbidity values were also relatively low over the study period, ranging from 0.9 to 7.5 NTU's (Table 2-5). Turbidity values observed in 2004, as a whole, were slightly lower than measured in 2003 (Table 2-5), but well within the historical range (DPC 1985, 1987, 1988a, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997; DP 1998, 1999, 2000, 2001, 2002, 2003, 2004).

Specific conductance in Lake Norman in 2004 ranged from 50 to 100 umho/cm, and was generally similar to that observed in 2003 (Table 2-5), and historically (DPC 1985, 1987, 1988a, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997; DP 1998, 1999, 2000, 2001, 2002, 2003, 2004). Lake-wide, mean conductance values in 2004 were similar to those measured in 2003, but were about 10 umhos/cm lower than observed in 2002. Differences were most pronounced in the surface waters during the summer with mean conductance values averaging almost 20 umhos/cm (about 30 %) less in 2004 and 2003 than 2002. These differences appear to have been related to interannual variability in watershed precipitation totals (Figures 2-2a & 2-2b) and the corresponding influence on reservoir water level (Figure 2-12) and volume, as well as inflow and outflow rates. Precipitation totals for the Lake Norman watershed, as recorded at MNS, were considerably less in 2002 than 2003 and 2004.

Reduced levels of precipitation inputs within the watershed would be expected to result in less sub-surface and overland runoff to adjacent streams and lakes. Reduced stream inflows 2-9

and lake levels would, in turn, concentrate chemical constituents within the water column.

Conversely, increases in stream inflows and lake levels would be expected to result in an initial increase in some constituents as material is transported from the terrestrial environment to the adjacent aquatic ecosystem, followed by a decrease in constituent concentration due to dilution associated with additional increases in water volume and corresponding movement through the system (Gray 1970, Kazmann 1988).

Specific conductance values in surface and bottom waters in 2004 were generally similar throughout the year except during the period of intense thermal stratification, i.e., August through November when an increase in bottom conductance values was observed. These increases in bottom conductance values appeared to be related primarily to the release of soluble iron and manganese from the lake bottom under anoxic conditions (Table 2-5). This phenomenon is common in both natural lakes and reservoirs that exhibit extensive hypolimnetic oxygen depletion (Hutchinson 1957, Wetzel 1975).

pH and Alkalinity During 2004, pH and alkalinity values were similar among MNS discharge, mixing and background zones (Table 2-5). Values of pH were also generally similar to values measured in 2003 (Table 2-5), and historically (DPC 1985, 1987, 1988a, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997; DP 1998, 1999, 2000, 2001, 2002, 2003, 2004). Alkalinity values were also similar between years. Individual pH values in 2004 ranged from 6.1 to 8.0, whereas alkalinity ranged from 12.5 to 36 mg/L, expressed as CaCO 3 .

Maior Cations and Anions The concentrations of major ionic species in the MNS discharge, mixing, and mid-lake background zones are provided in Table 2-5. Lake-wide, the major cations were sodium, calcium, magnesium, and potassium, whereas the major anions were bicarbonate, sulfate, and chloride. The overall ionic composition of Lake Norman during 2004 was generally similar to that reported for 2003 (Table 2-5) and previously (DPC 1985, 1987, 1988a, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997; DP 1998, 1999, 2000, 2001, 2002, 2003, 2004).

Concentrations of several constituents, most notably calcium and potassium, and to a lesser extent chloride, magnesium, and sodium, were however, consistently less in 2004 than 2003, but these differences were not statistically significant and values were within historical ranges.

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Nutrients Nutrient concentrations in the discharge, mixing, and mid-lake background zones of Lake Norman for 2004 and 2003 are provided in Table 2-5. Overall, nutrient concentrations in 2004 were well within historical ranges (DPC 1985, 1987, 1988a, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997; DP 1998, 1999, 2000, 2001, 2002, 2003, 2004). Nitrogen and phosphorus levels in 2004 were low and generally similar to those measured in 2003 (DP 2004). Total phosphorus and ortho-phosphorus concentrations were typically measured at or below the analytical reporting limits for these constituents, i.e., 10 ug/L and 5 ug/L, respectively. For total phosphorus, only three of the forty samples analyzed exceeded a concentration greater than 10 ug/L, and the highest concentration measured was 12 ug/L.

For ortho-phosphorus eight of forty samples exceeded 5 ug/L, and the highest concentration measured was 13 ug/L in the bottom waters of the mixing zone in November. Nutrients were generally higher in the upper portions of the reservoir compared to the lower sections, but the differences were slight and not statistically significant (p< 0.05). Spatial variability in various chemical constituents, especially nutrient concentrations, is common in long, deep reservoirs (Soballe et al. 1992).

Nitrite-nitrate concentrations were consistently lower at all locations in 2004 compared to 2003 (Table 2-5), but similar to historical values (DPC 1985, 1987, 1988a, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997; DP 1998, 1999, 2000, 2001, 2002, 2003, 2004). The lower values measured in 2004 compared to 2003 were probably related primarily to interannual differences in precipitation inputs (Figure 2-2a). Nitrate-nitrite concentrations in atmospheric precipitation in this portion of North America typically range from about 600 to 1000 ug/L; consequently, rainfall serves as a significant source of nitrogen to aquatic ecosystems in the Southeast both in the form of direct and indirect inputs (Langmuir 1997).

Metals Metal concentrations in the discharge, mixing, and mid lake background zones of Lake Norman for 2004 were similar to those measured in 2003 (Table 2-5) and historically (DPC 1985, 1987, 1988a, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997; DP 1998, 1999, 2000, 2001, 2002, 2003, 2004). Iron concentrations in surface and bottom waters were generally low (< 0.2 mg/L) during 2004, the lone exception being a 0.63 mg/L value measured in the bottom waters at Location 5 in August. Nowhere in the reservoir in 2004 did iron concentrations exceed NC's water quality standard (NCDENR 2004) for this 2-11

constituent (1.0 mg/L), which is unusual. Typically, iron concentrations increase in the bottom waters during the late summer, and early fall, in response to changing redox conditions (see below). It's unclear why this phenomenon was not as prevalent in 2004 as in previous years.

Similarly, manganese concentrations in the surface and bottom waters were generally low (<

100 ug/L) in 2004, except during the summer and fall when bottom waters were anoxic (Table 2-5). This phenomenon, i.e., the release of manganese (and iron) from bottom sediments in response to low redox conditions (low oxygen levels), is common in stratified waterbodies (Stumm and Morgan 1970, Wetzel 1975). Manganese concentrations in the bottom waters rose above NC's water quality standard (NCDENR 2004) for this constituent, i.e., 200 ug/L, at various locations throughout the lake in summer and fall in 2004, and is characteristic of historical conditions (DPC 1985, 1987, 1988a, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997; DP 1998, 1999, 2000, 2001, 2002, 2003, 2004).

Concentrations of other metals in 2004 were typically low, and often below the analytical reporting limit for the specific constituent (Table 2-5). All values for cadmium, lead and zinc were reported as either equal to or below each constituent's reporting limit, and no NC water quality standard was exceeded. All copper concentrations were less than 3 ug/L, and well below the NC standard of 7 ug/L (NCDENR 2004).

FUTURE STUDIES No changes are planned for the Water Chemistry portion of the Lake Norman maintenance-monitoring program.

SUMMARY

Annual precipitation in the vicinity of MNS in 2004 totaled 44.6 inches or 17.1 inches less than observed in 2003, but similar to the long-term precipitation average for this area (46.3 inches). Air temperatures in 2004 were generally warmer than measured in 2003, as well as the long-term mean. The most pronounced differences occurred in May when 2004 temperatures averaged 3.5 0 C warmer than 2003, and 2.6 'C warmer than the long-term average.

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Temporal and spatial trends in water temperature and DO in 2004 were similar to those observed historically, and all data were within the range of previously measured values.

Water temperatures in 2004 were generally warmer than observed in 2003 in both the mixing and background zones. Winter temperatures averaged about 0.3 'C warmer throughout the water column in 2004 versus 2003. Summer temperatures averaged about 2 to 3 'C warmer in 2004 versus 2003, with the primary differences observed in the upper 10 m of the water column. Minimal differences in hypolimnetic (below 20 m) temperatures were observed between 2004 and 2003 during the summer; the lone exception was in September when the lower waters were warmer than observed in 2003, especially in the background zone. These thermal differences can be explained by differential cooling of the water column in 2004 versus 2003, in response to lower air temperatures in the preceding month of August.

Interannual differences in water temperatures, especially in the surface waters, typically paralleled differences exhibited in air temperatures between 2004 and 2003.

Winter and early spring DO values in 2004 were generally equal to or slightly lower, in both the background and mixing zones, than measured in 2003, except in January in the background zone which exhibited slightly higher oxygen concentrations in 2004 versus 2003.

The interannual differences in DO values measured during this period appeared to be related predominantly to the warmer water column temperatures in 2004 versus 2003.

Spring and summer DO values in 2004 were highly variable throughout the water column in both the mixing and background zones ranging from highs of 6 to 8 mg/L in surface waters to lows of 0 to 2 mg/L in bottom waters. This pattern is similar to that observed in 2003 and earlier years. Epilimnetic and metalimnetic DO values during the spring and summer of 2004 were typically slightly lower than measured at similar depths in 2003, especially in the background zone, although exceptions to this were observed in August in both zones.

Summer hypolimnetic DO values were also either equal to or slightly greater than measured in 2003 in both the mixing and background zones. All DO values recorded in 2004 were within historical ranges.

Reservoir-wide isotherm and isopleth information for 2004, coupled with heat content and hypolimnetic oxygen data, illustrated that Lake Norman exhibited thermal and oxygen dynamics characteristic of historical conditions and similar to other Southeastern reservoirs of comparable size, depth, flow conditions, and trophic status. Availability of suitable pelagic habitat for adult striped bass in Lake Norman in 2004 was generally similar in distribution and amount to historical conditions observed annually since 1983. Despite 2-13

similarities in habitat conditions to previous years, the largest striped bass die-off ever observed in the reservoir (2599 fish) occurred in the summer of 2004.

All chemical parameters measured in 2004 were within the concentration ranges previously reported for the lake during both preoperational and operational years of MNS. Specific conductance values in 2004 were slightly lower than measured in 2003, a high-water year, as were concentrations of nitrite-nitrate nitrogen, calcium and potassium, and to a lesser extent, chloride, magnesium and sodium. Ammonia, ortho-phosphorus, and total phosphorus values were low in 2004 and similar to 2003.

Concentrations of metals in 2004 were also low, and often below the analytical reporting limits. Values for cadmium, lead and zinc were reported as either equal to or below the reporting limit. Copper concentrations were generally less then 3 ug/L, and well below the NC standard of 7 ug/L.

Manganese and iron concentrations in the surface and bottom waters were generally low in 2004, except during the summer and fall when bottom waters became anoxic, and the release of soluble forms of these metals into the water column was observed. In contrast to previous years, at no time during 2004 did iron concentrations exceed NC's water quality standard (1.0 mg/L). Manganese levels, however, did exceed the State standard (200 ug/L) in the bottom waters throughout the lake in the summer and fall, and are characteristic of historical conditions.

LITERATURE CITED American Public Health Association (APHA). 1995. Standard Methods for the Examination of Water and Wastewater. I 9th Edition. APHA, Washington, DC.

Coutant, C. C. 1985. Striped Bass, Temperature, and Dissolved Oxygen: a Speculative Hypothesis for Environmental Risk. Trans. Amer. Fisher. Soc. 114:31-61.

Cole, T. M. and H. H. Hannon. 1985. Dissolved Oxygen Dynamics. In: Reservoir Limnology: Ecological Perspectives. K. W. Thornton, B. L. Kimmel and F. E. Payne editors. John Wiley & Sons. NY.

Duke Energy Company. 2004. McGuire Nuclear Station. Updated Final Safety Analysis Report. Duke Energy Company, Charlotte, NC.

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Duke Power Company. 1985. McGuire Nuclear Station, 316(a) Demonstration. Duke Power Company, Charlotte, NC.

Duke Power Company. 1987. Lake Norman Maintenance Monitoring Program: 1986 Summary. Duke Power Company, Charlotte, NC.

Duke Power Company. 1988. Lake Norman Maintenance Monitoring Program: 1987 Summary. Duke Power Company, Charlotte, NC.

Duke Power Company. 1989. Lake Norman Maintenance Monitoring Program: 1988 Summary. Duke Power Company, Charlotte, NC.

Duke Power Company. 1990. Lake Norman Maintenance Monitoring Program: 1989 Summary. Duke Power Company, Charlotte, NC.

Duke Power Company. 1991. Lake Norman Maintenance Monitoring Program: 1990 Summary. Duke Power Company, Charlotte, NC.

Duke Power Company. 1992. Lake Norman Maintenance Monitoring Program: 1991 Summary. Duke Power Company, Charlotte, NC.

Duke Power Company. 1993. Lake Norman Maintenance Monitoring Program: 1992 Summary. Duke Power Company, Charlotte, NC.

Duke Power Company. 1994. Lake Norman Maintenance Monitoring Program: 1993 Summary. Duke Power Company, Charlotte, NC.

Duke Power Company. 1995. Lake Norman Maintenance Monitoring Program: 1994 Summary. Duke Power Company, Charlotte, NC.

Duke Power Company. 1996. Lake Norman Maintenance Monitoring Program: 1995 Summary. Duke Power Company, Charlotte, NC.

Duke Power Company. 1997. Lake Norman Maintenance Monitoring Program: 1996 Summary. Duke Power Company, Charlotte, NC.

Duke Power. 1998. Lake Norman Maintenance Monitoring Program: 1997 Summary.