NC0001422_Modification_20200121

DUKE L V. Sutton Energy Complex
801 Sutton Steam Plant Rd
`, ENERGY® Wilmington, NC 28401
PROGR i. - o:910 341 4750
f 910 341 4790
January 21,2020 RECEIVED
JAN 2 7 2020
Ms.Julie Grzyb
NC Division of Water Resources NCDEQ/DWR/NPDES
1617 Mail Service Center
Raleigh,NC 27699-1617
Subject: Duke Energy Progress, LLC.
L.V. Sutton Energy Complex NPDES Permit NC0001422
NPDES Permit Modification Request
Dear Ms. Grzyb:
This letter and the attached materials are provided in support of Duke Energy Progress, LLC's(Duke
Energy)request to modify the L.V. Sutton NPDES permit. Duke Energy requests the following
modifications be made to the permit to reflect updated operating conditions and/or align the terms with
other Duke Energy permits for similar activities:
1. Duke Energy requests modified permit limits at outfall 001 based on the enclosed CORMIX
model demonstration undertaken in accordance with permit condition A(22).
Condition A (22) of the subject permit provides that"The permittee may elect to conduct
a water quality model of the dilution factor for Outfall 001. Contingent upon EPA
approval of the Lower Cape Fear Modeling and its results, the Reasonable Potential
Analysis will be conducted again and the permit limits will be based on the new flow
numbers established by the model."
Duke Energy contracted Geosyntec to develop a water quality model of the dilution
factor for Outfall 001 for revising the WQBELs. Geosyntec completed the development
of a mixing zone model to simulate the dilution of constituents of concern in the Cape
Fear River due to discharge from Outfall 001. Duke Energy presented a draft report to
document the data, model inputs, assumptions, and results for both the EFDC model and
the CORMIX model to NCDEQ during a meeting on October 10, 2018. The final
CORMIX dilution model is included with this submittal as Attachment 1.
2. Duke Energy requests extension of the compliance schedule for copper at outfall 008 to
perform water effects ratio(WER)study
Condition A(29) of the subject permit provides a compliance schedule for copper and
nickel at outfall 008. Duke Energy requests an additional 2 years for compliance with
copper at outfall 008. The required copper and nickel evaluation study plan was
submitted to DEQ in July of 2018, as well as two required progress reports describing the
findings of the evaluation study.

L.V. Sutton Electric Plant NPDES Permit NC0001422
NPDES Modification Request
The evaluation and progress reports failed to find any current source of copper from the
plant. However,the former coal generating unit which operated at the Sutton Plant from
the 1950s until 2013 utilized condenser tubes made in part from copper. These tubes were
in contact with the recirculated cooling water and were the primary source of copper in
the wastewater. The natural gas combined cycle plant, brought online with the retirement
of the coal units, uses titanium condenser tubes. It is likely that existing copper in the
cooling pond is due to legacy coal operations making short term reductions challenging.
Duke Energy is undertaking a WER study in accordance with a plan to be approved by
the Divisions Aquatic Toxicity Unit. This demonstration is anticipated to be successful
but will likely take beyond the existing compliance date of October 1, 2020.
The nickel permit limit at outfall 001 was based on two data points that were above the
water quality standard. Since the permit effective date, nickel has been non-detect or
below the water quality standard. Duke Energy believes compliance with the nickel limit
should not be an issue.
3. Duke Energy requests the addition of wastewater flows from LOLA excavation to outfall
001.
The excavation of CCR materials in the lay of land area(LOLA) area is currently
underway. As this area is excavated, groundwater and ash contact water are filling the
area left void by the excavation. This area is currently segregated from other areas via
sheet pile walls. Duke Energy requests that future wastewater discharge from the LOLA
be added as a contributory source to outfall 001. The characteristics of the wastewater
from this area would be consistent with historic ash pond dewatering discharges from the
1984 and 1971 basins. A map identifying the location of the LOLA area is included at
Attachment 2.
4. Duke Energy requests toxicity monitoring return to a quarterly frequency at outfall 001.
Since the permit effective date, the L.V. Sutton Energy complex has conducted acute
toxicity testing monthly. The testing has shown no significant acute mortality at a
concentration of 90% in all 26 samples. Quarterly toxicity testing would more than
sufficient to determine any aggregate toxic effect on aquatic organisms from the outfall
001 discharge.
5. Duke Energy requests the language in the footnote related to the use of physical-chemical
treatment at outfall 001 be aligned with other Duke Energy permits language.
6. Duke Energy requests removal of internal outfalls 005,006,007,and 009.
Duke Energy requests removal of NPDES permit coverage from internal outfalls 005, 006,
007, and 009. Flows from these outfalls are composed of wastewater from the combined and
simple cycle units and some stormwater runoff. The flows themselves do not consist of a
categorical flow that must meet certain limits prior to commingling. Additionally,the flows

L. V. Sutton Electric Plant NPDES Permit NC0001422
NPDES Modification Request
contribute to the aggregate discharge at outfall 008 to Sutton lake have the same permit limits
as all of the internal outfalls. The discharge of these outfalls is to the effluent channel and
then to Sutton Lake via outfall 008. The monitoring requirements for outfall 008 are
protective of surface water quality and adequate to characterize the discharge to Sutton Lake
from these minor internal sources. A map of the outfall locations is included as Attachment
3.
7. Remove NPDES coverage for ash basin outfalls 002 and 004.
Duke Energy requests the removal of NPDES permit coverage from outfalls 002 and 004.
These outfalls are from the now excavated 1971 and 1984 ash basins. The basins no
longer have an outfall structure or mechanism to discharge to Sutton Lake,with the 1984
basin being dry. Duke Energy proposes, upon approval of this modification,to discharge
the remaining wastewater in the 1971 basin via outfall 001.
Thank you for your consideration of the above-requested items. If there are any questions, please contact
either:
• Ms. Lori Tollie, Environmental Specialist, at(336)854-4916 or email Lori.Tollie@duke-
energy.com, or
• Mr. Kent Tyndall, Environmental Professional for the L. V. Sutton Energy Complex Plant;phone
[phone] or e-mail [e-mail].
I certify, under penalty of law, that this document and all attachments were prepared under my
direction or supervision in accordance with a system designed to assure that qualified personnel
properly gather and evaluate the information submitted. Based on my inquiry of the person or
persons who manage the system, or those persons directly responsible for gathering the
information, the information submitted is, to the best of my knowledge and belief true, accurate,
and complete. I am aware that there are significant penalties for submitting false information,
including the possibility offines and imprisonment for knowing violations.
Sincerely,
on Talbot
Station Manager
Enclosures

Attachment 1 - CORMIX Model
•
Prepared for:
eirak, DUKE
'-‘,-" v ENERGY®
PROGRESS
Duke Energy Progress, LLC
526 South Church Street
Charlotte, North Carolina 28202
MIXING ZONE ANALYSIS, Addendum
L.V. SUTTON ENERGY COMPLEX
801 Sutton Steam Plant Road
Wilmington, North Carolina
Prepared by:
Geosyntec°
consultants
I totinlrC Cun.oltunts DINE,Pl
Geosyntec Consultants of NC, PC
1300 South Mint Street Suite 300
Charlotte, North Carolina 28203
License No. C-295
Project No. GC6463
January 2020

L.V.Sutton Energy Complex
Mixing Zone Analysis Geosyntec°
consultants
TABLE OF CONTENTS
1. INTRODUCTION 1
2. MIXING ZONE METHODOLOGY 2
2.1 CORMIX Model Inputs 2
2.1.1 Discharge Characterization 2
2.1.2 Outlet Structure Configuration 2
3. MODEL RESULTS 3
3.1 Embayment Model 3
3.2 River Model 3
4. REVISED PERMIT LIMITS 5
LIST OF TABLES
Table 1: Updated Embayment Model Inputs with Effluent Flow of 0.35 MGD 7
Table 2: Updated Embayment Model Inputs with Effluent Flow of 3.5 MGD .7
Table 3: Updated Inputs for CORMIX River Model with Effluent Flow of 0.35 MGD 8
Table 4: Updated Inputs for CORMIX River Model with Effluent Flow of 3.5 MGD .8
Table 5: Current and Revised Effluent Limits for Outfall 001 at L.V. Sutton Energy Complex 9
LIST OF FIGURES
Figure 1: Simulated Dilution of Outfall 001 Effluent in the Embayment for the Maximum
Stratification Scenario with 0.35 MGD Discharge 11
Figure 2: Simulated Dilution of Outfall 001 Effluent in the Embayment for the Maximum
Stratification Scenario with 3.5 MGD Discharge 12
Figure 3: Simulated Dilution of Outfall 001 Effluent in the Lower Cape Fear River for the
Maximum Stratification Scenario with 0.35 MGD Discharge 13
Figure 4: Simulated Dilution of Outfall 001 Effluent in the Lower Cape Fear River for the
Maximum Stratification Scenario with 3.5 MGD Discharge 13
Figure 5: Simulated Dilution of Outfall 001 Effluent in the Lower Cape Fear River for the Three
Scenarios with 0.35 MGD Discharge 14
Figure 6: Simulated Dilution of Outfall 001 Effluent in the Lower Cape Fear River for Maximum
Stratification with 3.5 MGD Discharge 15
GC6462/2020(0114)_SuttonMixingZoneAnalysis 1 January 2020

L.V Sutton Energy Complex
Mixing Zone Analysis Geosyntec
consultants
1. INTRODUCTION
Geosyntec Consultants of North Carolina, PC (Geosyntec) has prepared this report addendum to
document the updated results of a mixing zone study completed on behalf of Duke Energy
Progress, LLC (DEP). The L.V. Sutton Energy Complex(Sutton or Site) is currently permitted to
discharge into Lower Cape Fear River (LCFR) through Outfall 001 under National Pollutant
Discharge Elimination System(NPDES) Discharge Permit No.NC0001422 (NCDEQ, 2017).
This report serves as an addendum to the original report submitted in February 2019 to address
feedback from the North Carolina Department of Environmental Quality (NCDEQ) to update the
effluent flow from Outfall 001 to 0.35 million gallon per day (MGD) or the current representative
flow from Outfall 001. In addition, the report includes modeling of the revised configuration for
Outfall 001 as a 12"pipe which was constructed in 2019. DEP also requested an additional model
run to account for potential future discharge increase to 3.5 MGD.
The following sections discuss the data review and analysis to develop the Cornell Mixing Zone
Model (CORMIX)model inputs to account for both NCDEQ and DEP requests.
GC6462/2020(0114)_SuttonMixingZoneAnalysis 1 January 2020

L.V.Sutton Energy Complex p
Mixing Zone Analysis Geosyntec
consultants
2. MIXING ZONE METHODOLOGY
Geosyntec conducted a mixing zone study to simulate the dispersion of the discharge plume from
Outfall 001 in the LCFR under three scenarios for the 0.35 MGD discharge including: maximum
stratification,minimum stratification,and off-site design scenarios.The scenarios are described in
detail in the main report (Geosyntec 2019). The most conservative scenario (maximum
stratification) was used to simulate the increased effluent flow of 3.5 MGD.
2.1 CORMIX Model Inputs
Available outfall configuration, receiving water, and discharge characteristics data were used as
inputs to the CORMIX model to simulate dilution of the discharge plume from Outfall 001 into
the LCFR. Outfall 001 discharges into a small embayment which then enters the LCFR(Figure 10
in the main report). As discussed in the main report, CORMIX modeling was completed in two
steps for the embayment model and the river model.
Receiving water characteristics input data were kept consistent with the approach in the main
report. Input data for discharge characteristics and outfall configuration for Outfall 001 was
updated in the embayment model and the river model. Table 1 and Table 2 summarize the input
for the embayment model,while Table 3 and Table 4 summarizes inputs for the river model. The
following sections document the input data updates.
2.1.1 Discharge Characterization
The mixing zone model needs to include the effluent characteristics such as flow rate,temperature,
and concentration to simulate the effluent plume in the river. In this application, the discharge
input parameters were kept consistent with the approach in the main report except effluent flow.
As recommended by the NCDEQ, the average effluent flow of 0.35 MGD between August 2016
and October 2019 was used as an input into the CORMIX model. An additional model run with
3.5 MGD was done using the maximum stratification scenario to account for a future discharge
increase from 1971 Basin. This increased effluent discharge number was based on the discussions
between DEP and NCDEQ staff.
2.1.2 Outlet Structure Configuration
CORMIX requires specification of pipe outfall diameter and its distance from the nearest bank
(shoreline).DEP has completed the separation of Cooling Pond water discharge from Lake Sutton
and the coal combustion residuals (CCR)basin wastewater, as per the requirement in the NPDES
Permit NC0001422 dated December 2015. The CCR basin wastewater now discharges through a
12"pipe directly into the embayment of the LCFR. Outfall 001 was modeled as a 12"pipe located
10 feet away from embayment shoreline. The pipe height above the stream bed for each scenario
was estimated based on the design drawings and the water depth of each scenario (Tables 1 and
2).
GC6462/2020(0114)_SuttonMixingZoneAnalysis 2 January 2020

L.V.Sutton Energy Complex
Mixing Zone Analysis Geosyntec
consultants
3. MODEL RESULTS
The embayment model and river model were used to simulate the mixing of the discharge from
Outfall 001 in the embayment and the LCFR respectively. The following sections discuss the
results of the CORMIX model simulations.
3.1 Embayment Model
The first step in the CORMIX modeling simulated the effluent plume discharge directly from
Outfall 001 into the embayment for three scenarios described in the main report using the 0.35
MGD discharge. Among the three scenarios at 0.35 MGD, the maximum stratification scenario
resulted in minimum dilution of the effluent(Table 3). The most critical condition is therefore the
maximum stratification scenario. The description of the results is therefore focused on the
maximum stratification scenario.
A three-dimensional (3-D) representation of the simulated dilution in the embayment for the
maximum stratification scenario using the 0.35 MGD discharge is shown in Figure 1. The plume
is dominated by the momentum of the effluent in the embayment and it attaches to the surface.
The simulated centerline dilution at the edge of embayment located at 30 m, is 12.9. The width of
plume is about 16.08 m.The plume extends up to 0.25 meters(m)below the water surface. Figure
2 shows a 3-D representation of the simulated dilution in the embayment for the maximum
stratification scenario using the 3.5 MGD discharge. The plume is also dominated by the
momentum of the effluent in the embayment and it is attached to the surface. The simulated
centerline dilution at the edge of the embayment (30 m downstream of the outfall) is 14.6. The
width of the plume is about 4.8 m. The plume extends up to 2.4 m below the water surface. The
results of the 0.35 MGD and 3.5 MGD embayment models were used as inputs into the
corresponding river model.
3.2 River Model
The second step in the CORMIX modeling simulated the effluent plume discharge from
embayment into the LCFR for the three scenarios described above.Among the three scenarios,the
maximum stratification resulted in minimum dilution of effluent. A 3-D representation of the
simulated dilution in the LCFR for the maximum stratification scenario using the 0.35 MGD
discharge is shown in Figure 3. The effluent plume from the embayment into the LCFR has very
little momentum and therefore quickly attaches to the river bank. A 3-D representation of the
simulated dilution in the LCFR for the maximum stratification scenario using the 3.5 MGD
discharge is shown in Figure 4. The effluent plume from the embayment into the LCFR for this
scenario also has very little momentum and therefore quickly attaches to the river bank.
Figure 5 presents the simulated dilution of the Outfall 001 effluent at 0.35 MGD under three
scenarios in the LCFR. The simulated dilution at 50 m from Outfall 001 in the LCFR for the
maximum stratification scenario is 104.7.
GC6462/2020(0114)_SuttonMixingZoneAnalysis 3 January 2020

L.V.Sutton Energy Complex
Mixing Zone Analysis Geosyntec
consultants
The river model was also run for the potential future discharge of 3.5 MGD using the maximum
stratification scenario. The simulated dilution at 50 m from Outfall 001 in the LCFR is 115.3
(Figure 6).
The simulated dilution factor was used to calculate revised permit limits for Outfall 001.
GC6462/2020(0114)_SuttonMixingZoneAnalysis 4 January 2020

L.1!Sutton Energy Complex
Mixing Zone Analysis Geosyntec
consultants
4. REVISED PERMIT LIMITS
The permit limits for Outfall 001 were recalculated based on the simulated dilution factor of 115.3
(3.5 MGD) at 50 m from Outfall 001. Table 5 presents the current limits (which assume no
dilution)and revised permit limits based on the most conservative mixing zone scenario.
GC6462/2020(0114)_SuttonMixingZoneAnalysis 5 January 2020

TABLES

Table 1: Updated Embayment Model Inputs with Effluent Flow of 0.35 MGD
Maximum Minimum Offsite
Description Units Source
Stratification Stratification Design
Discharge Geometry: Plume Dimensions
Pipe diameter 12 12 12 in DEP
Above or below water surface Below Below Below m Design drawings
Height of pipe above water
surface 5.7 5.9 6.3 m Design drawings
Distance of pipe from bank 10 10 10 ft Design drawings
Discharge Flow: Plume Discharge from Embayment
Flow rate 0.35 0.35 0.35 MGD NCDEQ request for 0.35
MGD
Table 2: Updated Embayment Model Inputs with Effluent Flow of 3.5 MGD
Description Maximum Units Source
Stratification
Discharge Geometry: Plume Dimensions
Pipe diameter 12 in DEP
Above or below water surface Below m Design drawings
Height of pipe above water
5.7 m Design drawings
surface
Distance of pipe from bank 10 ft Design drawings
Discharge Flow: Plume Discharge from Embayment
Flow rate 3.5 MGD DEP request for 3.5 MGD

Table 3: Updated Inputs for CORMIX River Model with Effluent Flow of 0.35 MGD
Description Maximum Minimum Offsite Units Source
Stratification Stratification Design
Discharge Geometry: Plume Dimensions
Plume width 8.97 12.44 12.56 m Embayment model
Depth of discharge channel 0.44 2.95 3.05 m Embayment model
Discharge Flow: Plume Discharge from Embayment
Flow rate 7.33 70.93 74.14 MGD Calculated equivalent
mixing flow
Predicted discharge
Concentration 7.78 0.835 0.80 % excess at the edge of
embayment
Table 4: Updated Inputs for CORMIX River Model with Effluent Flow of 3.5 MGD
Description Maximum Units Source
Stratification
Discharge Geometry: Plume Dimensions
Plume width 4.78 m Embayment model
Depth of discharge channel 2.39 m Embayment model
Discharge Flow: Plume Discharge from Embayment
Flow rate 8.33 MGD Calculated equivalent
mixing flow
Predicted discharge
Concentration 6.83 % excess at the edge of
embayment

Table 5: Current and Revised Effluent Limits for Outfall 001 at L.V. Sutton Energy
Complex
Revised Limit
Current Limits
(3.5 MGD)
Parameter
Monthly Daily Monthly Daily
Limit Limit Limit Limit
Total Mercury(ug/L) 47 47 5,421 5,421
Total Arsenic(ug/L) 10 50 1,153 5,767
Total Selenium(ug/L) 5 56 577 6,459
Total Iron(mg//L) 1 1 115 115
Total Lead(ug/L) 25 33.8 2,884 3,898
Total Cadmium(ug/L) 2 15 231 1,730

SJ?If1DIJ

Dilution S
1.0 2.2 5.0 )l.2 25.0 56.0 125.2 280.0
r u
10'lz
-2
-4 x
5
0
Figure 1: Simulated Dilution of Outfall 001 Effluent in the Embayment for the Maximum
Stratification Scenario with 0.35 MGD Discharge

Dilution S
1 0 1 3 2.2 3 3 4 9 74 11 0 rd..) 24.3 30.3 54.0 ea5 120 0
2 Nc
\-2 X
-3�
2
Figure 2: Simulated Dilution of Outfall 001 Effluent in the Embayment for the Maximum
Stratification Scenario with 3.5 MGD Discharge

Dilution S
5 1.0 1.3 1.8 2.3 3.1 4.1 5.4 7.1 9.5 12.5 16.6 22.0
MEW -11111=11111111111111
5 44 1j, �
111111111111.
01111101111
UA
-20
to
Figure 3: Simulated Dilution of Outfall 001 Effluent in the Lower Cape Fear River for the
Maximum Stratification Scenario with 0.35 MGD Discharge
Dilution S
1.0 1.4 2.1 3.0 4.3 6.2 8.9 12.8 18.4 26.5 38.2 55.0
UMW """Milli
1
-5
Figure 4: Simulated Dilution of Outfall 001 Effluent in the Lower Cape Fear River for the
Maximum Stratification Scenario with 3.5 MGD Discharge

700 ;
r ..
600
r
500
r r
0 400 .`%ra
- -
LL
0
300
o i
200
5 = 104.7
30 35 40 45 50 55 60 65 70 75 80
Distance Downstream(m)
Max Stratification — — —Min Stratification Off Site Design
Figure 5: Simulated Dilution of Outfall 001 Effluent in the Lower Cape Fear River for the
Three Scenarios with 0.35 MGD Discharge

200
180
160
140 { .�
S = 115.3 "00"
120
rts
LL
c 100
0
80
60 •
40 /
20 !
0 E.*a
30 35 40 45 50 55 60 65 70 75 80
Distance Downstream(m)
Figure 6: Simulated Dilution of Outfall 001 Effluent in the Lower Cape Fear River for
Maximum Stratification with 3.5 MGD Discharge

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L.V. Sutton Electric Plant NPDES Permit NC0001422
NPDES Modification Request
Attachment 3
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NORTH CAROLtIA Attachment 3- Site Map
L.V. Sutton Energy Complex
New Hanover County