NC0024392_Report_20230309 (2)

Lake Norman Maintenance Monitoring
Program 2021 Summary
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McGuire Nuclear Station
Lake Norman, Huntersville, North Carolina
NPDES Permit # NCO024392
Duke Energy Water Resources
Huntersville, INC
February 2023
DUKE
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Lake Norman Maintenance Monitoring Program 2021 Summary
McGuire Nuclear Station
Table of Contents
ExecutiveSummary....................................................................................................................................... 1
1 Introduction........................................................................................................................................
2
1.1 Physical Description and Background......................................................................................................2
1.2 316(a) Demonstration Studies.................................................................................................................2
1.3 Station Operations and Thermal Characteristics.....................................................................................3
2 Methods..............................................................................................................................................
8
2.1 Water Quality...........................................................................................................................................8
3 Results and Discussion......................................................................................................................
10
3.1 Water quality.........................................................................................................................................10
3.1.1 Water Temperature and Dissolved Oxygen Profiles................................................................10
3.1.2 General Physicochemistry.......................................................................................................12
3.1.3 Lake Productivity and Trophic Status......................................................................................14
4 References.........................................................................................................................................16
Tables
Table 1-1. Net capacity factors, expressed in percent (%), and monthly average discharge canal water
temperatures for MNS during 2021........................................................................................................................3
Table 2-1. Physicochemical limnology parameters collected during winter and summer in Lake Norman during
2021 (P = profile, S = surface grab, PZ = photic zone composite)...........................................................................9
Table 2-2. Analytical methods and reporting limits for parameters monitored in Lake Norman in 2021...........10
Table 3-1. Summary of surface water quality results in Lake Norman during 2021 monitoring. When values
were less than reporting limit, table presents reporting limits for means and ranges........................................13
Figures
Figure 1-1. Mean monthly air temperatures recorded at MNS during current study period compared to 1989-
2020 average...........................................................................................................................................................4
Figure 1-2. Total annual precipitation recorded at MNS compared to 1990-2020 average (horizontal line) ....... 5
Figure 1-3. Total monthly precipitation recorded at MNS during current study period compared to 1990-2020
monthlyaverages....................................................................................................................................................5
Figure 1-4. Sampling locations and zones for 2021 Lake Norman monitoring.......................................................7
Figure 3-1. Temperature and dissolved oxygen contour plots of Lake Norman main channel locations during
February (top) and August (bottom) 2021...........................................................................................................11
Figure 3-2. Trophic status of four zones of Lake Norman during August 2021 based on different productivity
parameters............................................................................................................................................................15
Appendices
Appendix A. Box and whisker plots depicting historical (1990-2020) analytical data compared to 2021.

Executive Summary
Duke Energy continued surface water monitoring in Lake Norman during 2021, as required by McGuire
Nuclear Station's National Pollutant Discharge Elimination System wastewater discharge permit (No.
NC0024392). Monitoring was performed in accordance with a study plan approved by the North
Carolina Department of Environmental Quality. This report presents operational and environmental data
collected during the 2021 monitoring year and compares the information with historical data. The
primary objective of this monitoring was to assess the impact of the thermal discharge from MNS in
combination with the thermal discharge of Marshall Steam Station (MSS) on the aquatic biological
community populations in Lake Norman.
Duke Energy has two permitted thermal discharges to Lake Norman, one from MNS near Cowans Ford
Dam and one mid -lake at MSS. To evaluate the impacts of the thermal discharges on Lake Norman, two
distinct thermally influenced zones (Zones A and C) were delineated. Zone A represented the area
influenced by the MNS discharge, and Zone C represented the area influenced by the MSS discharge.
Zones B and D represented background conditions that were not thermally influenced for comparison to
zones A and C, respectively.
Lake Norman was mesotrophic (to slightly eutrophic) in 2021 based on lakewide summer chlorophyll a
concentrations and trophic state index. This 2021 lakewide classification is generally consistent with
historical summer conditions (typically mesotrophic) but is higher than the lakewide quarterly mean
based oligo-mesotrophic classification determined prior to 2019. Similar to 2020, high rainfall and
associated nutrient inputs during the winter, late spring and early summer contribute to higher
chlorophyll a concentrations from increased productivity of phytoplankton in 2021. No patterns in the
lake physicochemistry or chlorophyll a were observed in association with the thermal discharge of MNS
or MSS that would adversely affect a balanced indigenous community (BIC).

Lake Norman Maintenance Monitoring Program 2021 Summary
McGuire Nuclear Station
1 Introduction
1.1 Physical Description and Background
McGuire Nuclear Station (MNS) consists of two units that were completed in 1981 and 1984 with a total
station net capacity of 2,466 MW. The station is in Mecklenburg County, near Huntersville, North
Carolina on the southern shore of Lake Norman. The lake, which was formed in 1963 by the construction
of Cowans Ford Dam on the Catawba River, was built primarily as a source of non -contact condenser
cooling water (CCW) for steam electric stations and for hydroelectric power generation. In addition to
MNS, two other electric generating stations are located on Lake Norman: 332 MW Cowans Ford
Hydroelectric Station located 0.9 km west of MNS and 2,180 MW Marshall Steam Station (MSS) located
18 km north of MNS. Lake Norman is the largest impoundment in North Carolina with a surface area of
13,087 ha at full pond elevation 231.6 m above mean sea level. The lake has a shoreline length of
approximately 971 km, a mean depth of 10.4 m, and a maximum depth of 33.5 m. The drainage area is
roughly 4,636 km2 with a mean annual outflow of 75.6 m3/s at the dam and an approximate mean
retention time of 207 days.
The CCW system of MNS utilizes a once -through flow pattern where raw water from Lake Norman is
pumped over condensers to cool MNS system components and then discharged back to the lake. The
discharge of this heated water, referred to as "thermal discharge", requires a Clean Water Act (CWA)
316(a) thermal variance, which is regulated through a National Pollutant Discharge Elimination System
(NPDES) permit maintained by MNS (No. NC0024392). The NPDES permit for MNS effective during the
year covered in this report was issued on June 1, 2016 and has monthly average thermal discharge limits
at Outfall 001 (CCW discharge) of 35 °C (95 °F) during October —June and 37.2 °C (99 °F) during July —
September. Similarly, the thermal discharge of the CCW system of MSS also requires a CWA 316(a)
thermal variance. This variance is regulated through a NPDES permit maintained by MSS (No.
NC0004987) and has monthly average thermal discharge limits of 33.3 °C (92 °F) during November —June
and 34.4 °C (94 °F) during July —October. These temperature limits are expected to be protective of
biological communities in the receiving waterbody (i.e., Lake Norman).
Assessment of the potential effects of thermal discharges on biological communities is a key component
of a thermal discharge variance. Section A. (6) of the current MNS NPDES permit requires a Lake Norman
monitoring program approved by the North Carolina Department of Environmental Quality (NCDEQ)
Division of Water Resources that addresses the CWA 316(a) thermal discharge variance provision for
Outfall 001. The approved study plan in place during 2021 is MNS' 2020 Lake Norman §316(a) Study Plan
(Duke Energy 2019b), which was re -approved as the Comprehensive Lake Norman §316(a) Study Plan
(Duke Energy 2020) for both MNS and MSS. In addition, Section A. (16) of the current MNS NPDES
permit requires continuance of the Lake Norman Aquatic Environment Maintenance Monitoring
Program (MMP), including annual submittal of results. The MMP follows the same design as the
approved 316(a) study plan.
1.2 316(a) Demonstration Studies
The original MNS 316(a) demonstration study concluded, and the NCDEQ concurred, that MNS
operations and thermal discharge limit (35°C monthly average for the year) were compatible with the
maintenance of a balanced indigenous community (BIC) in Lake Norman (Duke Power Company 1985).
Shortly after, a permit modification was requested and subsequently granted that increased the thermal
discharge limit during July —September to 37.2 'C. Along with this increased thermal discharge limit,
2

Lake Norman Maintenance Monitoring Program 2021 Summary
McGuire Nuclear Station
Duke Energy was required to submit an annual report to ensure the biotic community in Lake Norman
was meeting the definition of a BIC under this new thermal limit. The MMP was conducted in
accordance with specifications outlined in 40 CFR 125 Subpart H, the USEPA draft 316(a) Guidance
Manual (USEPA 1977), and stakeholder input. These reports were submitted annually since 1988 in lieu
of 316(a) demonstration reports, and like the initial demonstration report, the MMP reports concluded
the permitted thermal limits ensured a BIC in Lake Norman. As required in the MNS 2016 NPDES permit,
a revised monitoring plan (Duke Energy 2017) was prepared to address USEPA, NCDEQ and North
Carolina Wildlife Resources Commission comments and subsequently approved (NCDEQ 2017). An
updated 316(a) demonstration report was submitted in 2019 that supported the same conclusions as
previous reports (Duke Energy 2019a). As a result, the Lake Norman monitoring plan was further revised
in 2019 and 2020 to reduce the frequency of data collection, and these changes were approved by
NCDEQ (NCDEQ 2020a and 2020b).
This MMP report provides a review of MNS operations, thermal characteristics, and the monitoring
components associated with the study year as prescribed by the approved study plan. Monitoring data
are presented in the context of two thermal discharge facilities (MNS and MSS) on Lake Norman.
1.3 Station Operations and Thermal Characteristics
Station capacity factors, along with cooling water temperatures, have a direct effect on the resulting
thermal discharge into the lake. When maintenance is performed, capacity is reduced, whereas gains in
unit efficiency at MNS can result in higher than 100% capacity. In 2021, the average annual unit capacity
was 100.0% for Unit 1 and 90.1% for Unit 2 (Table 1-1).
The NPDES thermal compliance discharge limit for MNS, expressed as a monthly average, was 35.0 °C
(95 °F) for October 1-June 30 and 37.2 °C (99 °F) for July 1-September 31. Thermal discharge limits were
met throughout 2021, and no derates (reductions in station capacity) were required to maintain
compliance with discharge temperatures. The maximum monthly average of 37.0 °C (98.7 °F) was
reported in August (Table 1-1).
Table 1-1. Net capacity factors, expressed in percent (%), and monthly average discharge canal water
temperatures for MNS during 2021.
Unit 1
Net capacity factor
Unit 2
Station
Monthly average temperature
°C °F
January
100.0
100.0
100.0
21.5
70.7
February
100.0
85.8
92.9
20.1
68.2
March
99.9
99.8
99.9
22.7
72.8
April
99.9
100.0
100.0
25.7
78.3
May
99.9
100.0
100.0
29.1
84.5
June
100.0
100.0
100.0
33.0
91.4
July
100.0
100.0
100.0
36.2
97.2
August
100.0
100.0
100.0
37.0
98.7
September
99.9
33.1
66.5
35.5
95.9
October
100.0
62.7
81.4
31.6
88.9
November
100.0
100.0
100.0
28.2
82.7
December
100.0
100.0
100.0
24.6
76.3
Average
100.0
90.1
95.0
28.8
83.8
3

Lake Norman Maintenance Monitoring Program 2021 Summary
McGuire Nuclear Station
Meteorological forces can exert significant influences, both directly and indirectly, on the physical,
chemical, and biological characteristics of aquatic ecosystems, and documentation of local and regional
meteorology can often provide insight into the spatial and temporal dynamics in these characteristics
(Wetzel 2001). Two important meteorological parameters are air temperature and precipitation. Data
for these two variables were obtained from a meteorological monitoring site established near MNS and
were utilized to document localized temporal meteorological trends.
Air temperatures influence variability in a waterbody's thermal regime via seasonal water column
heating and cooling. Air temperatures during 2021 were generally near average compared to data
collected since 1990. Only October (2.2 °C above) and December (4.6 °C above) had monthly air
temperatures greater than 2.0 °C outside of the average (Figure 1-1).
30
25
& 20
o
m
L
15
L
Q
E
H 10
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Figure 1-1. Mean monthly air temperatures recorded at MNS during current study period compared to 1989-
2020 average.
Precipitation affects hydrologic characteristics in aquatic ecosystems by controlling water volume, inflow
rates, and water column mixing. This hydrodynamic influence can be additionally magnified or modified
by reservoir outflow characteristics, resulting in variations in spatial and temporal water quality and
biological regimes. In addition to influencing hydrologic and hydraulic characteristics, precipitation can
impact water quality by direct chemical loading associated with atmospheric chemistry or indirectly via
constituent loading associated with watershed runoff. The rainfall total of 97.7 cm recorded in 2021 was
below average (Figure 1-2). However, monthly precipitation totals were variable and ranged from 6.6
cm below average in April and November to 7.3 cm above average in July (Figure 1-3). These rainfall
patterns directly affected the hydrologic inflow and discharge of the reservoir.
4

Lake Norman Maintenance Monitoring Program 2021 Summary
McGuire Nuclear Station
180
160
140
a 60
40
20
0
00 O1 orx 00 O� 00 Oa OA O<° 04 y0 yL yb ti0 ti� y0
0 0 ti� 0 0 -P do ,yo ,yo -0 do do do yo ti0 ti0
Figure 1-2. Total annual precipitation recorded at MNS compared to 1990-2020 average (horizontal line).
18
16
14
12
U
0 10
.6
.a 8
�U
L
d 6
4
2
0
0 1990-2020 Avg
f 2021
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Figure 1-3. Total monthly precipitation recorded at MINIS during current study period compared to 1990-2020
monthly averages.
The thermal influence of MNS and MSS on Lake Norman was originally determined through thermal
infrared surveys and temperature modeling (Duke Power Company 1985). Thermal plume maps were
developed in 198S from an airborne thermal infrared survey as part of the original 316(a)
5

Lake Norman Maintenance Monitoring Program 2021 Summary
McGuire Nuclear Station
demonstration, in 1991 as part of the MNS NPDES permit renewal efforts, and again in 2017 using a
calibrated hydrodynamic model (Duke Power Company 1985; Duke Power Company 1991; Duke Energy
2019a). The updated maps indicated that recent meteorology and station operations had not
substantially altered the original 1985 delineation.
For purposes of this report and the assessment of the Lake Norman biological communities, zones of
study were established based on the thermal plume delineations. Monitoring locations (depicted in
Figure 1-4) were associated with the MNS and MSS discharges and the following lake zones:
• Zone A - lower portion of Lake Norman influenced by the thermal discharge from MNS.
• Zone B - non -thermally influenced reference area upstream of the thermal discharge from MNS
and downstream of the thermal discharge from MSS.
• Zone C - middle portion of Lake Norman influenced by the thermal discharge from MSS.
• Zone D - non -thermally influenced reference area upstream of the MSS thermal discharge.
6

Lake Norman Maintenance Monitoring Program 2021 Summary
McGuire Nuclear Station
N
O Water Quality Monitoring Location
0 ElectrofishingTransect
■ Duke Energy Facility 0 O 0
0 0
Zone D
0 0
MARSHALL
STEAM
STATION
■
0 0
0 NctiS o0 Zone
0
Zone D ° c
0 0 00 0
ter`
0
O 0" 0
a
0 O
IVC,16
O
0 Zone B
00 O 0
0 0
° 0 0
0
0 Zone A
° NC-73
Lake Norman 0
North Carolina t OLL�-
0 2.5 5 0
�. ENE ■
COWANS FORD
HYDRO STATION MCGUIRE NUCLEAR Kil meters STATION
Figure 1-4. Sampling locations and zones for 2021 Lake Norman monitoring.
7

Lake Norman Maintenance Monitoring Program 2021 Summary
McGuire Nuclear Station
2 Methods
Methods employed for the 2021 MMP followed the approved Lake Norman §316(a) study plan (Duke
Energy 2019b and 2020). Accordingly, semiannual water quality parameters were monitored in 2021.
2.1 Water Quality
Surface water physicochemical data were used to characterize the environmental conditions of Lake
Norman. These data were collected to help provide an understanding of the basic productivity of the
reservoir ecosystem and potential chronic or acute changes in aquatic communities. These data were
also evaluated in consideration of cumulative influences with the thermal discharges on a BIC.
Water quality monitoring performed in Lake Norman during 2021 was collected semi-annually during
winter and summer. Chlorophyll a was collected in the summer 2021. Monitoring components are
outlined in Table 2-1. Field parameters (temperature, dissolved oxygen [DO], pH, and specific
conductivity) were measured at each location with a multi -parameter data sonde such as Hydrolab (OTT
Hydromet, Loveland, Colorado) or Aqua TROLL (In -Situ, Inc., Fort Collins, Colorado). Measurements
started at the lake surface (0.3 m) and continued at one -meter intervals to 10 m, then two -meter
intervals to the lake bottom. Pre- and post -calibration procedures associated with operation of the data
sondes were documented in both electronic and hard -copy format. Data were captured and stored
electronically and converted to spreadsheet format following data validation.
Water samples for laboratory analysis were collected by various means depending on the sample depth
and analyte. Surface (0.3 m) samples were collected via peristaltic pump or direct dip, and photic zone
(defined as 2 times measured Secchi depth) samples were collected with an integrated depth sampler.
Samples were collected in high -density polyethylene (HDPE) or polyethylene terephthalate (PET) sample
bottles. Dissolved -fraction samples were field -filtered with a 0.45-µm in -line disposable filter and a
peristaltic pump. Filter capsules were pre -rinsed by running >_500 mL of sample water through the filter
prior to discharging into the sample bottles. Sample bottles were pre -acidified where applicable. Water
samples were stored on ice in a sample cooler and in the dark immediately following collection to
minimize the potential for physical, chemical, and microbial transformation.
Laboratory analytical methods, reporting limits, and sample preservation techniques are included in
Table 2-2. Laboratory water chemistry analyses were performed by a state -certified laboratory, primarily
the Duke Energy Analytical Laboratory located in Huntersville, NC (North Carolina Division of Water
Resources [NCDWR] Certification #248). Other contract laboratories utilized during the study period
were confirmed to have current NCDWR laboratory certifications for the parameters being analyzed.
Standard chain of custody procedures and documentation were followed throughout these analyses.
Data were subjected to various numerical and graphical techniques to evaluate spatial and temporal
trends within the lake, interrelationships among constituents, and the potential effect on lake biota.
Trophic state index (TSI; Carlson 1977), which assesses the overall productivity of the lake, was one
metric evaluated. TSI values for phosphorus, Secchi depth, and chlorophyll a were calculated to
standardize these select physiochemical variables for comparison. TSI values range on a scale of 0 to 100
and were considered in relation to the intended use of the waterbody and BIC support.
Data were evaluated using seasonal comparisons among zones and historical comparisons within zones
(Appendix A). For the purposes of this report, historical water quality and analytical data included the
8

Lake Norman Maintenance Monitoring Program 2021 Summary
McGuire Nuclear Station
years 1990-2020. The availability of large zones that were not thermally influenced immediately
upstream (zones B and D) allowed for comparisons with the thermally influenced zones (A and C) to
assess potential impacts. Data within each zone were also compared to lake -wide values for context.
Analytical results reported to be equal to or less than the method reporting limit were evaluated at the
reporting limit for numerical and statistical assessments.
Table 2-1. Physicochemical parameters collected during winter and summer in Lake Norman during 2021 (P =
profile, S = surface grab, PZ = photic zone composite).
Parameter
Monitoring
Temperature
P
Dissolved oxygen
P
Specific conductivity
P
pH
P
Calcium
S
Magnesium
S
Chloride
S
Sulfate
S
Hardness (Calculated)
S
Copper
S
Zinc
S
Turbidity
S
Secchi
S
Total phosphorus
PZ
Ammonia nitrogen
PZ
Nitrate + nitrite nitrogen
PZ
Total Kjeldahl nitrogen
PZ
Chlorophyll a(l)
PZ
(1) Chlorophyll a collected in summer only
9

Lake Norman Maintenance Monitoring Program 2021 Summary
McGuire Nuclear Station
Table 2-2. Analytical methods and reporting limits for parameters monitored in Lake Norman in 2021.
Parameter Method (EPA/ASTM/SM) Preservation Reporting Limit
Temperature
Thermistor, SM 2550 B-2010
N/A
0.1 °C
Oxygen, Dissolved
Luminescent (LDO) cell, ASTM D888-09-C
N/A
0.1 mg/L
Conductivity, Specific
Thermistor, SM 2510 B-2011
N/A
1 µS/cm3
PH
SM 4500H B-2011
N/A
0.1 unit
Calcium
ICP, EPA 200.7
HNO3 to pH <2
0.05 mg/L
Magnesium
Atomic Emission/ICP, EPA 200.7
HNO3 to pH <2
0.01-0.02 mg/L
Chloride
Ion Chromatography, EPA 300.0
N/A
0.1 mg/L
Sulfate
Ion Chromatography, EPA 300.0
<_6 °C
0.1 mg/L
Total Hardness
Calculation, SM 2340B
N/A
N/A
Copper, Total
ICP Mass Spectroscopy, EPA 200.8
<_6° C; HNO3 to pH <2
1.0-2.0 µg/L
Zinc, Total
ICP Mass Spectroscopy, EPA 200.8
<_6° C; HNO3 to pH <2
5 µg/L
Turbidity
Turbidimetric, EPA 180.1
<_6° C
0.05 NTU
Secchi
Hutchinson (1975)
N/A
N/A
Phosphorus, Total
Colorimetric, EPA 365.1
<_6° C; H2SO4 to pH <2
0.01-0.05 mg/L
Ammonia
Colorimetric, EPA 350.1
<_6° C; H2SO4 to pH <2
0.10 mg/L
Nitrate + Nitrite
Colorimetric, EPA 353.2
<_6° C; H2SO4 to pH <2
0.02 mg/L
Total Kjeldahl Nitrogen
Colorimetric, EPA 351.2
<_6° C; H2SO4 to pH <2
0.10 mg/L
Chlorophyll a
SM 1020OH-2011
<_6° C; darkness
2 µg/L
3 Results and Discussion
3.1 Water quality
3.1.1 Water Temperature and Dissolved Oxygen Profiles
Historical thermal data for Lake Norman have shown temporal and spatial variations in water
temperatures. In addition to the thermal influences from MNS and MSS, these variations were largely
governed by atmospheric conditions and physical characteristics of the lake (e.g., water depth, clarity,
inflow and outflow rates). General patterns of well -mixed winter conditions and highly stratified
summer conditions emerge each year due to the monomictic nature of the reservoir. Lake Norman
followed similar thermal stratification and destratification regimes for the months surveyed during the
2021 monitoring period.
Influence of thermal plumes from MNS and MSS were primarily localized in 2021, consistent with
historical data and previous thermal analyses (Duke Power Company 1985; Duke Energy 2017; Appendix
A). The mean surface water temperature measured at the end of the MNS discharge canal was 26.1 T.
The mean water temperature in Zone A was 21.5 °C and was similar to that in Zone C (21.8 °C). These
temperatures were warmer than the mean temperatures in reference zones B and D (19.2 °C and 18.8
°C, respectively). Temperature profile data documented warmer discharge water near the surface, with
cooler water below. Thermal discharge plumes were discrete and did not extend throughout the water
10

Lake Norman Maintenance Monitoring Program 2021 Summary
McGuire Nuclear Station
column (Figure 3-1), suggesting available habitat for aquatic communities. A summary of temperature
measurements made from the surface of Lake Norman during 2021 monitoring can be found in Table 3-
1.
Overall, DO concentrations throughout Lake Norman were comparable to historical data (Appendix A).
Surface DO concentrations in 2021 were lower in the thermally influenced zones compared to the
reference zones (Table 3-1), which was largely attributed to temperature differences resulting in lower
oxygen solubility in the thermally influenced zones. The range and variability of surface DO
concentrations were largely driven by water temperature and biological activity (i.e., photosynthetic
release of oxygen by phytoplankton). Cooler water temperatures during the winter resulted in the
highest DO levels observed throughout the lake (Figure 3-1). The lowest surface DO concentration
measured, 0.5 mg/L, was in the MSS discharge canal during August. Water discharged into this canal
originates from the hypolimnion of Lake Norman, which becomes hypoxic in the summer (Figure 3-1),
and travels under a skimmer wall to the station's CCW intake. DO concentrations were above 7.0 mg/L
at other monitoring locations in Zone C, indicating rapid reoxygenation of the hypoxic water as it
reentered the lake.
Additionally, the natural formation of a negative heterograde oxygen curve (NHOC) occurred during the
summer of 2021 as is common for Lake Norman (Duke Energy 2011). Hypolimnetic DO declines
throughout the summer until a state of anoxia exists. This DO "squeeze" is not uncommon in reservoirs
both with and without thermal discharge influence and can result in fish kills. Under certain conditions,
these hypoxia-related fish kills have occurred in Lake Norman (Rice et al. 2013; Duke Energy 2017). In
2021, the NHOC did not result in a notable fish kill that would affect the BIC in Lake Norman. A summary
of DO measurements made in Lake Norman during 2021 monitoring can be found in Table 3-1.
E
L
Q
ar
Temperature Dissolved oxygen
Zones
20
2E.
30
August
3�
10 15 20 2`_. 30
oC
6
10
12
14
16
18
20
22
24
26
28
30
32
Distance from dam (km)
reuruary
August
10 1`_. 20 25 30
mg/L
Figure 3-1. Temperature and dissolved oxygen contour plots of Lake Norman main channel locations during
February (top) and August (bottom) 2021.
11

3.1.2 General Physicochemistry
During 2021, specific conductivity throughout Lake Norman was low, ranging from 43 to 64 µS/cm
(Table 3-1). Measurements were in the bottom 10 percent of the historical range of values in each zone
during each season (Appendix A). Reservoir flow through associated with heavy rainfall events preceding
the monitoring events may have reduced the ionic concentrations of Lake Norman during 2021. Low
conductivity indicated little impact from wastewater sources with potential to affect the BIC.
The temporal and spatial variability of pH in southeastern reservoirs is often correlated to lake
productivity. During 2021, pH in all zones were within typical ranges for Lake Norman and supportive of
aquatic life use in NC (between 6.0 and 9.0; NCDWR 2022). Surface pH ranged from 6.2 to 8.5 with little
difference between thermally influenced zones and the associated reference zones (Table 3-1). Higher
values were recorded at some of the farthest upstream sampling sites where productivity was higher. At
these sites, conditions were more favorable (i.e., elevated nutrients) for phytoplankton growth which
led to the higher pH values during periods of photosynthesis.
The major cations monitored in Lake Norman were calcium and magnesium, and major anions
monitored were chloride and sulfate. During 2021, concentrations of the cations and anions were
generally consistent across zones and seasons (Table 3-1). Cation concentrations were within the
historical range; however, as with specific conductivity, anion concentrations during 2021 were below
the historical medians (Appendix A). Overall, hardness concentrations remained low (<20 mg/L)
throughout the lake and were within the historical ranges in each zone of Lake Norman during 2021
(Table 3-1; Appendix A). There is no evidence that the low hardness has adversely impacted the aquatic
community.
During 2021, copper and zinc concentrations were within historical ranges (Table 3-1). All total zinc
concentrations were below laboratory reporting limits. Total copper concentrations were either below
or just slightly above lab reporting limits across all zones and seasons. These trace metal concentrations,
on their own or in combination with thermal influences, showed low potential for adversely impacting a
BIC in Lake Norman.
Historical turbidity values in Lake Norman have been low with highest turbidity typically reported during
winter and at upstream monitoring locations (Appendix A) where flow velocities and effects from
inflows (e.g., sediments, productivity, detritus) are higher. Turbidity in 2021 followed a similar pattern
with winter values higher than normal due to an extended period of heavy rainfall preceding the
monitoring event. Typically, turbidity in Lake Norman allows for adequate light penetration for
supporting macrophyte and phytoplankton communities and within ranges that would not impact a BIC
in Lake Norman.
12

Table 3-1. Summary of surface water quality results in Lake Norman during 2021 monitoring. When values were less than reporting limit, table presents reporting
limits for means and ranges.
NC Surface MNS Discharge canal Zone A Zone B MSS Discharge canal Zone C Zone D
water
standard','
Mean Range Mean Range Mean Range Mean Range Mean Range Mean Range
Temperature (°C)
<- 32 °C
26.1
15.2-37
21.5
9.8-33.1
19.2
8.0-30.3
21.9
12.7-31.1
18.8
7.8-29.8
18.9
6.8-31.1
Dissolved Oxygen (mg/L)
>:4.0 mg/L
8.2
5.7-10.7
8.7
6.8-10.6
9.5
7.6-11.2
5.9
0.5-11.2
9.7
7.2-11.6
10.6
7.6-12.6
Specific conductivity
N/A
49
45-52
47
43-52
48
43-51
56
47-64
51
50-53
50
46-53
(µS/cm)
pH
6.0-9.0
6.8
6.7-6.9
7.0
7.0-7.1
7.3
7.0-7.8
6.6
6.2-6.9
7.1
6.9-7.7
7.3
6.9-8.5
Calcium (mg/L)
N/A
3.08
2.99-3.16
2.98
2.91-3.03
3.15
2.89-3.99
4.33
3.80-4.88
3.45
2.79-4.08
3.21
2.55-3.80
Magnesium (mg/L)
N/A
1.58
1.55-1.61
1.57
1.48-1.66
1.60
1.50-1.68
1.93
1.92-.94
1.68
1.61-1.77
1.61
1.46-1.73
Chloride (mg/L
230 mg/L
3.6
3.4-3.8
3.6
3.3-3.8
3.7
3.3-4.1
5.2
4.6-5.7
4.2
3.9-4.3
3.2
3.1-4.2
Sulfate (mg/L)
250 mg/L
2.6
2.4-2.8
2.6
2.4-2.8
2.6
2.4-2.9
3.7
2.88-4.6
2.7
2.4-2.9
2.4
1.9-2.9
Hardness (mg/L)
100 mg/L
14.2
14.1-14.2
13.9
13.4-14.4
14.5
13.4-16.9
18.8
17.4-20.1
15.6
13.7-17.0
14.7
13.0-16.4
Copper, total (µg/L)
N/A
1.74
1.62-1.86
1.64
1.35-1.78
1.43
1.18-1.83
2.57
2.49-2.64
1.56
1.14-2.04
1.51
<1- <2
Zinc, total (µg/L)
N/A
<5.00
<5.00
<5.00
<5.00
<5.00
<5.00
<5.00
<5.00
<5.00
<5.00
<5.00
<5.00
Turbidity (NTU)
25 NTU
3.4
1.5-5.4
3.2
1.2-5.3
3.4
1.4-5.1
10
2.8-18
4.9
1.9-9.9
8.3
2.1-24
Secchi depth (m)
N/A
2.2
1.4-3.0
2.2
1.6-3.0
2.2
1.3-2.9
1.2
0.4-2.0
1.7
1.1-2.7
1.4
0.4-2.4
0.015-
0.015-
0.047-
0.021-
0.019-
Total phosphorus (mg/L)
N/A
0.033
0.032
0.016-0.048
0.034
0.049
0.039
0.045
<0.050
<0.050
<0.050
<0.050
0.058
Ammonia nitrogen (mg/L)
N/A
<0.10
<0.10
<0.10
<0.10
<0.10
<0.10
0.12
<0.10-0.14
<0.10
<0.10
<0.10
<0.10
Nitrite+ nitrate nitrogen
0.01mg/L
0.24
0.14-0.34
0.21
0.099-0.32
0.20
0.048-0.36
0.31
0.24-0.38
0.24
0.049-0.38
0.20
0.02-0.41
(mg/L)
Total Kjeldhal nitrogen
N/A
0.14
0.12-0.16
0.16
<0.10-0.26
0.15
<0.1-0.21
0.21
0.20-0.21
0.16
0.10-0.34
0.20
0.12-0.32
(mg/L)
Chlorophyll a (µg/L)
4.5
4.5
6.1
5.7-6.6
6.3
5.9-6.7
3.1
3.1
9.3
7.8-11.0
15.7
10.3-22.6
NC 02B Water Quality Standards for Surface Waters; water supply (WS) criteria.
z EPA National Recommended Water Quality Criteria for Aquatic Life used when NC Standard is not available
13

3.1.3 Lake Productivity and Trophic Status
During 2021, water clarity, as measured by Secchi depth, in Lake Norman indicated sufficient light
penetration for macrophyte and phytoplankton growth and chlorophyll a production. Water clarity
during winter of 2021 were within historical ranges but shallower than the historical median, most likely
due to turbidity from above average rainfall in the watershed during that period. The range of secchi
depths measured during summer 2021 (2.0 m in Zone D to 2.9 m in Zone A), were also within historical
ranges but generally deeper than the historical median. As shown in Figure 3-2, summer secchi depths
indicated a lakewide mesotrophic classification (TSI 47; Carlson 1977), consistent with historical summer
conditions for Lake Norman.
Total phosphorus and nitrogen (i.e., ammonia, nitrate -nitrite, and total Kjeldahl nitrogen [TKN])
concentrations in Lake Norman followed similar patterns of historical seasonal ranges observed in all
zones of the lake (Table 3-1; Appendix A). Although the concentrations of total phosphorus have
generally been lowest in summer and highest in winter, results for summer 2021 were analyzed at a
higher detection limit (0.02 mg/L) than the reporting limit (0.01 mg/L) for the winter 2021 and
historically. Total phosphorus concentrations during the summer of 2021 were less than reporting limit
of 0.05 mg/L; therefore, temporal and spatial trends for the summer results could not be determined.
However, total phosphorus concentrations during winter 2021 decreased from upstream to
downstream (Appendix A) which has been documented previously in Lake Norman and other reservoirs
(Duke Energy 2021b; Yurk & Ney 1989).
Seasonally, TKN concentrations were slightly lower during the summer. Spatially, concentrations of TKN
were similar lake -wide within each season. Although ammonia concentrations continue to be low
(mostly less than the detection limit), the laboratory detection limit currently available does not afford
spatial or temporal comparisons for this parameter. During 2021, the nitrogen to phosphorus ratio for
the year was a moderate 15:1, whereas during the summer the N:P ratio (4:1) was low. Although this
moderate to low ratio may indicate a possible nitrogen limiting condition forming seasonally for Lake
Norman, the elevated reporting limits for ammonia and total phosphorus may skew the ratio and not
serve to provide an accurate conclusion for this metric. Previous reports have found a high N:P ratio
(Duke Energy 2021a), which is common in freshwater lakes (USEPA 1978; Schindler et al. 2008). Trends
in the data will continue to be monitored to identify possible shifts away from conditions favorable for
edible phytoplankton communities (rather than nitrogen -fixing blue-green algae).
Chlorophyll a concentrations in Lake Norman were generally within ranges of those reported in previous
years (Appendix A). Concentrations increased from downstream to upstream, and individual
concentrations ranged from 5.7 µg/L in Zone A to 22.6 µg/L in Zone D (Table 3-1; Appendix A). During
2021, 80 percent of the individual chlorophyll a concentrations indicated mesotrophic conditions (zones
A, B and C) and the remaining twenty percent indicated eutrophic conditions (Zone D). The lakewide TSI
of 52 suggests a eutrophic classification (Carlson 1977) during 2021; however, as shown in Figure 3-2,
this classification is weighted by the upstream, Zone D, chlorophyll a concentrations. The most
upstream concentrations in Zone D were greater than the 90th percentile of the historical range. All
samples collected since 1990, including all zones in 2021, had concentrations considered suitable for
aquatic life use in North Carolina (< 40 µg/L, NCDWR 2022). Overall, summer chlorophyll a
concentrations indicated mesotrophic to slightly eutrophic reservoir conditions in Lake Norman. No
trend in chlorophyll a concentration has been observed between thermally influenced zones and their
reference zones, suggesting little impact on Lake Norman from MNS or MSS operations.
14

Lake Norman Maintenance Monitoring Program 2021 Summary
McGuire Nuclear Station
Like 2020, the semiannual data collected in 2021 have not necessarily suggested a trend towards
eutrophication. Historical quarterly monitoring often indicated inconsistent variability of the trophic
state through the year with spring, summer and fall conditions ranging from oligotrophic to slightly
eutrophic. Nevertheless, above normal rainfall in portions of 2020 and 2021 led to higher nutrient loads
from the watershed. Higher productivity in the reservoir may have short-term positive effects on the
fish community including increased recruitment, growth, and survival.
70
Eutrophic (50-70)
60
Ln
N
co
50
LF) F�
Mesotrophic (40-50)
40
gligotrophic (¢40)
30
Zone A Zone B Zone C Zone D
—N— Secchi
tTP
f chl-a
Figure 3-2. Trophic status of four zones of Lake Norman during August 2021 based on different productivity
parameters.
1s

Lake Norman Maintenance Monitoring Program 2021 Summary
McGuire Nuclear Station
4 References
Carlson, RE. 1977. Atrophic state index for lakes. Limnology and Oceanography 22:361-369.
Carlson, RE. 1991. Expanding the trophic state concept to identify non -nutrient limited lakes and
reservoirs. Pages 59-71 in Enhancing the States Management Programs. North American Lake
Management Society, Madison, Wisconsin.
Duke Energy. 2011. Lake Norman maintenance monitoring program: 2010 summary. Duke Energy
Corporation. Charlotte, NC.
Duke Energy. 2017. Lake Norman maintenance monitoring program: 2016 summary. Duke Energy
Corporation. Charlotte, NC.
Duke Energy. 2017. McGuire Nuclear Station 2018 Lake Norman 316(a) Study Plan. Duke Energy
Corporation. Charlotte, NC.
Duke Energy. 2019a. CWA §316(a) balanced and indigenous population study report (2016-2018),
McGuire Nuclear Station. Duke Energy Corporation. Charlotte, NC.
Duke Energy. 2019b. 2020 Lake Norman §316(a) Study Plan, McGuire Nuclear Station. Duke Energy
Corporation. Charlotte, NC.
Duke Energy. 2020. Lake Norman Comprehensive §316(a) Study Plan, Marshall Steam Station and
McGuire Nuclear Station. Duke Energy Corporation. Charlotte, NC.
Duke Energy. 2021a. CWA §316(a) Balanced and indigenous community study report (2014-2020),
Marshall Steam Station. Duke Energy Corporation. Charlotte, NC.
Duke Energy. 2021b. Lake Norman maintenance monitoring program: 2019 summary. Duke Energy
Corporation. Charlotte, NC.
Duke Power Company. 1985. McGuire Nuclear Station 316(a) demonstration. Duke Power Company.
Charlotte, NC.
Duke Power Company. 1991. Plumemap: an airborne thermal survey, February 9, 1991. Duke Power
Company. Charlotte, NC.
Hutchinson, GE. 1975. A Treatise on Limnology. John Wiley and Sons, New York.
NCDEQ. 2017. Review of Progress Energy, McGuire Nuclear Station (NPDES Permit NC0024392): "2019
Lake Norman Study Plant". Water Sciences Section. Raleigh, NC.
NCDEQ. 2020a. Review of Duke Energy Progress McGuire Nuclear Station (Lake Norman) 316 (a) 2020
Study Plan (NC0024392). Water Sciences Section. Raleigh, NC.
NCDEQ. 2020b. Review of Duke Energy Marshall Steam Station: Lake Norman (Amended)
Comprehensive 316(a) Study Plan (NC0004987). Water Sciences Section. Raleigh, NC.
16

Lake Norman Maintenance Monitoring Program 2021 Summary
McGuire Nuclear Station
NCDWR. 2022. Title 15A of the North Carolina Administrative Code (NCAC) subchapter 02B, sections
.0100 through .0300 (effective date: September 1, 2022). Environmental Management
Commission. Raleigh, NC.
Rice, JA, JS Thompson, JA Sykes, and CT Waters. 2013. The role of metalimnetic hypoxia in striped bass
summer kills: consequences and management implications. Pages 121-145 in JS Bulak, CC
Coutant, and JA Rice, editors. Biology and management of inland striped bass and hybrid striped
bass. American Fisheries Society, Symposium 80, Bethesda, Maryland.
Schindler, DW, RE Hecky, DL Findlay, MP Stainton, BR Parker, MJ Paterson, KG Beaty, M Lyng, SEM
Kasian. 2008. Eutrophication of lakes cannot be controlled by reducing nitrogen input: results of
a 37-year whole -ecosystem experiment. Proceedings of the National Academy of Sciences of the
United States of America, 105:11254-11258.
USEPA. 1977. Interagency 316(a) Technical Guidance Manual and Guide for Thermal Effects Sections of
Nuclear Facilities Environmental Impact Statements. Office of Water Enforcement, Permits
Division, Industrial Permits Branch. Washington, DC.
USEPA. 1978. A compendium of lake and reservoir data collected by the national eutrophication survey
in Eastern, North-Central, and Southeastern United States. Working Paper No. 475.
Wetzel, RG. 2001. Limnology: Lake and River Ecosystems, Third Edition. Academic Press. San Diego,
California.
Yurk, JJ, and JJ Ney. 1989. Phosphorus -fish community biomass relationships in southern Appalachian
reservoirs: can lakes be too clean for fish? Lake and Reservoir Management 5:89-90.
17

Appendices

Appendix A. Box and whisker plots depicting historical
(1990-2020) analytical data compared to 2021.
PLOT KEY:
O Historical data
2021 data
Horizontal line represents median
Boxes show 2Vand 75' percentiles
Whiskers show 1Q'h and 91h percentiles
A-1
0
4
C Q
A B C ❑
Zones

40
30
m 20
w
CL
h
10
0
100
80
N
560
7
chi 40
w
41
C
C0 20
0
Winter Summer
T
H.
A B C ❑ A B C ❑
Winter Summer
A B C ❑ A B C ❑
14
12
-i,10
(V 8
F
0
6
CA
O 4
2
0
9.5
9.0
8.5
s.o
C
T5
Q
7.0
6.5
6.0
5.5
A-2
Winter Summer
A S C D A B C C
Winter Summer
A B C ❑ A B C ❑

a
6
m
�4
.0
cc
U
2
a
1a
s
Es
0 4
U
2
0
Winter Summer
A B C D A B C D
Winter Summer
I
IaI
❑
,
•
,
■
n
n
u
�
- ��
Fi
-
A B C D A S C D
2.5
2.0
E 1.5
N
d
�1.0
N
0.5
0.0
s
s
N 4
2
A-3
Winter Summer
A S C D A S C D
Winter Summer
A B C ❑ A B C ❑

30
25
0
0
20
15
5
Winter Summer
U
6
9
A B C ❑ A B C ❑
Winter Summer
6
5
J4
N
Q3
0
U
W
t—F 2
1
0
44
4 1 I I I I i I 4
A B C D A B C D
A-4
Winter Summer
A B C ❑ A B C ❑
Winter Summer
A B C D A B C D

6
5
E4
L
R
-03
L
U
GO2
1
0
0.30
0.25
J 020
rn
E
c
0
0.10
0.05
0.00
0.8
0.6
rn
0.4
z
Y
0.2
0,0
Winter Summer
A B C D A B C ❑
Winter Summer
B C D A B C
Winter Summer
B C D A B C
N
0.02
Winter Summer
0
° 0 0 0
O
O
A B G ❑ A B G ❑
Winter Summer
0.5
0.4 T
J
rn
0.3
m
IA
� 0.2
.t'
2
40
30
ZL
d
A-5
B C D A B 0
Summer
P
O
T
G
q � Ell 1
A 6 G P