NC0004987_Request for Reduced 316 (b)_20241022

4' DUKE Marshall Steam Station
8320 East Highway 150
ENERGY Terrell NC 28682
RECEIVED
October 17, 2024 OCT 2 2 2024
Sergei Chernikov, Ph.D.
North Carolina Department of Environmental Quality NCDEQ/DWR/NPDES
Division of Water Resources
Industrial NPDES Permitting Unit
1617 Mail Service Center
Raleigh NC 27699-1617
Re: Request for Reduced 316(b) Information with Next NPDES Permit Renewal Application
Duke Energy Carolinas, Marshall Steam Station, NPDES Permit NC0004987
Dear Dr. Chernikov:
In conformity with 40 CFR 125.95(c), after initial submission of the 40 CFR 122.21(r) permit application
studies, a facility may request to reduce the information required with subsequent permit renewal
applications if conditions at the facility and in the waterbody remain substantially unchanged since the
previous application.
In response, Duke Energy Carolinas(Duke Energy) requests that the North Carolina Department of
Environmental Quality (NCDEQ)authorize a limited 316(b) information submittal for the Marshall Steam
Station's next NPDES permit renewal application. The Marshall Steam Station (Marshall) continues to
comply with the 316(b) Rule with operational and technology features to reduce cooling water intake
structure impingement and entrainment.
To support this request, Duke Energy provides the following information to demonstrate that facility and
waterbody conditions are substantially unchanged, and that the previously submitted 316(b)
information remains representative of the current source water, intake structure,cooling water system,
operating conditions, and that the applicable additional technology evaluation remains valid. To
facilitate NCDEQ's review, this request is structured to address the relevant requirements at 40 CFR
122.21(r)for existing facilities with cooling water intake structures.
Facility Overview and Initial Submission of 316(b) Information
Marshall currently is comprised of four coal-fired units with a total generating capacity of approximately
2,058 megawatts (MW). Marshall uses once through cooling (OTC)for cooling the condenser discharge
water and other auxiliary heat exchangers. Water withdrawn from Lake Norman is the cooling water
source and is also used for service water or other needs at the station.
Duke Energy submitted the most recent NPDES permit renewal application for Marshall to NCDEQ on
March 29, 2021. That application included the facility's initial submission of the 316(b) information
required by 40 CFR 122.21(r). The information requirements applicable to Marshall are found in
subsections (r)(2)through (r)(13). In response, NCDEQ determined that the facility's cooling water
intake structure location, design, construction, and capacity reflect the Best Technology Available (BTA)

t DUKE Marshall Steam Station
8320 East Highway 150
ENERGY® Terrell NC 28682
for minimizing the adverse environmental impacts associated with impingement or entrainment of
aquatic organisms. (NPDES Permit NC0004987, Part I,A.24.) There have been no changes to the
facility's configuration or operation since the initial submittal of 316(b) information that would impact
impingement or entrainment.
Source Water Physical Data—40 CFR 122.21(r)(2)
Lake Norman is part of the Catawba-Wateree system that is managed by Duke Energy and regulated by
the Federal Energy Regulatory Commission (FERC Project 2232). The Catawba River begins in western
North Carolina near Morganton and flows into South Carolina where it joins Big Wateree Creek to form
the Wateree River. The Catawba-Wateree project is comprised of 12 hydroelectric stations and 11
reservoirs and spans over 225 river miles. The Catawba-Wateree Project reservoirs have nearly 80,000
surface acres of water and approximately 255 billion gallons of usable storage.
Lake Norman is the largest reservoir in North Carolina with approximately 32,339 surface acres. Lake
Norman was created by the construction of the Cowans Ford Dam during 1963 for hydroelectric
generation and to provide cooling water for Marshall and the McGuire Nuclear Station. Selected Lake
Norman characteristics are provided in the table below.
Parameter Metric
Watershed Drainage 1,790 square miles
Surface Area 32,339 acres
Full Pool Elevation 760 feet
Maximum Depth 110 feet
Mean Depth 33.5 feet
Average Discharge 3,085 cubic feet per second (cfs)
Retention Time 239 days
Marshall is located in Catawba County, North Carolina, approximately 40 miles northwest of Charlotte
on the northwestern shore of Lake Norman. Land near Marshall is somewhat rural and residential;
however, Catawba County is experiencing positive population growth and is part of the Charlotte-
Concord Combined Statistical Area (Metrolina).
Marshall withdraws water from Lake Norman utilizing a curtain wall structure with a 15-foot high
opening along the reservoir bottom (approximately 77 feet below full pool elevation). A study
performed during 2016 demonstrated that the curtain wall is a highly effective technology to reduce
impingement and entrainment. The curtain wall structure is summarized in section (r)(5) of this
document and the curtain wall study is summarized in section (r)(7) of this document.
There have been no changes to the source waterbody or cooling water intake structure since the
facility's initial 316(b) submission, and that information remains representative of facility and waterbody
conditions.

�' DUKE Marshall Steam Station
8320 East Highway 150
ENERGY® Terrell NC 28682
Cooling Water Intake Structure Data—40 CFR 122.21(r)(3)
Marshall is an intermediate (load following)generating station that provides a critical supply of
electricity for the Duke Energy system. It withdraws service and cooling water through a cooling water
intake structure (CWIS) located approximately 1.3 miles from the curtain wall. The CWIS includes bar
racks,fixed panel mesh screens, and pumps.
The Marshall CWIS is divided into four sections, one for each of the four generating units and has a total
of 16 intake bays with three each dedicated to Units 1 and 2 and five each dedicated to Units 3 and 4.
Each 11.2 foot wide bay is equipped with steel vertical bar racks with 2.5 inch spacing to prevent large
debris from contacting the fixed mesh screens.
The fixed mesh screens have 3/8 inch mesh openings and are cleaned as indicated by water level
or as dictated byplant sensors operations.
A total of ten pumps are located at the CWIS with two each dedicated for Units 1 and 2 and three each
dedicated for Units 3 and 4 as listed in the following table. A piping restriction limits the Marshall CWIS
Design Intake Flow(DIF)to 1,463 MGD when all CWIS pumps are operating.
Generating Unit Pump Name Pump Capacity(MGD)
1 1A 181.4
1B 181.4
2 2A 181.4
2B 181.4
3 3A 216.0
3B 216.0
3C 216.0
4 4A 216.0
4B 216.0
4C 216.0
Service water to support the Marshall generating units is withdrawn after the CWIS pumps; therefore,
service water flows are not considered with the DIF, average intake flow(AIF), or the calculated through
screen velocity (TSV). The following table provides the annual average intake flow during the 2019-2023
period.
Annual Average Intake Flow
Year (MGD)
2019 887.7
2020 770.9
2021 883.3
2022 956.9
2023 970.3

�' DUKE Marshall Steam Station
8320 East Highway 150
ENERGY® Terrell NC 28682
The average intake flow(AIF) during the 2019-2023 period was calculated to be 893.8 MGD which
represents about a 39 percent reduction from the DIF. For comparison, the prior 316(b) report
determined the 2014-2019 AIF was 914 MGD.
There have been no changes to the cooling water intake structure since the facility's initial
316(b) submission, and that information remains representative of facility conditions.
Source Water Baseline Biological Characterization Data—40 CFR 122.21(r)(4)
There is an extensive amount of fish population data available for Lake Norman. Duke Energy and the
North Carolina Wildlife Resources Commission routinely conduct surveys to evaluate Lake Norman
aquatic populations. These studies indicate a diverse and abundant fish community is present upstream
and downstream of Marshall.
There are no endangered or threatened species that could be impacted by the Marshall CWIS.
There have been no significant changes to the source waterbody's aquatic community since the initial
316(b) submission, and that information remains representative of water body conditions.
Cooling Water System Data—40 CFR 122.21(r)(5)
Withdrawal from Lake Norman is used to support cooling and other water needs at Marshall. The DIF is
1,463 MGD and the AIF is 893.8 MGD. Each unit at Marshall has one main condenser with the Unit 1
and 2 condenser rated for 239 MGD each and the Unit 3 and 4 condenser rated for 457.9 MGD each.
CWIS pumps are operated as needed to support plant operations. Typically, fewer CWIS pumps are
operated during the colder winter months or during unit outages. CWIS pumps operated about 61
percent during the 2019-2023 period based on the 2019-2023 AIF compared to the DIF.
Based on the current NPDES flow diagram, approximately 95 percent of the water withdrawn is used for
cooling purposes and about five percent is utilized for other plant needs. There is no reuse of cooling
water at Marshall.
TSV at Marshall varies based on the number of operating CWIS pumps. However, at full pool elevation
and all CWIS pumps operating,the calculated TSV is 0.85 feet per second (fps) for Unit 1 and 2 and 1.07
fps for Unit 3 and 4.
The configuration of the Marshall CWIS provides substantial reductions of impingement and
entrainment. Utilization of a curtain wall structure at the entrance to the intake cove results in only the
lower 15 feet of the Lake Norman water column subject to withdrawal. Average ichthyoplankton
densities inside of the curtain wall (e.g.the entrance to the intake cove)were demonstrated to be about
98 percent less than those on the outside of the curtain wall (towards the main Lake Norman
waterbody). The flow reduction of about 39 percent between the DIF and AIF results in lower
corresponding proportional impingement and entrainment rates.

�•N DUKE Marshall Steam Station
8320 East Highway 150
ENERGY® Terrell NC 28682
There have been no changes to the cooling water intake structure since the facility's initial 316(b)
submission, and that information remains representative of facility conditions.
Chosen Method(s) of Compliance with Impingement Mortality Standard—40 CFR 122.21(r)(6)
Marshall currently complies with the 316(b) impingement standards as follows:
• Operation of a curtain wall structure that reduces entrainment about 98 percent
• Flow reduction of 39 percent based on the DIF compared to the 2019-2023 AIF flow
Based on these technology and operation measures, entrainment and impingement at Marshall is
markedly reduced.
There have been no changes to the impingement compliance technologies or cooling water system
operations since the facility's initial 316(b)submission, and that information remains representative of
facility conditions.
Entrainment Performance Studies—40 CFR 122.21(r)(7)
An extensive study was performed to quantitatively determine the efficacy of the Marshall curtain wall
structure during March through October 2016. The objectives of this study were to evaluate potential
selectivity of the curtain wall on species and life stages and to quantify the entrainment benefit of the
curtain wall.
The Marshall curtain wall withdraws from the Lake Norman water column at depths from 60 feet below
the surface (at full pool elevation) and an additional 15 feet to the bottom of Lake Norman. At these
depths, fish eggs and larvae are not as abundant as compared to those present closer to the water
surface.
Samples were obtained on both sides of the curtain wall. The 2016 studies demonstrated that the
Marshall curtain wall effectively reduced entrainment by more than 95 percent.
A study was conducted at the Duke Energy Oconee Nuclear Station located in Senaca, South Carolina,
which also has a curtain wall structure similar to that utilized at Marshall. This study demonstrated a 90
percent entrainment reduction during the peak entrainment period and substantially more during other
months.
No changes have occurred with the Marshall curtain wall structure since the facility's initial 316(b)
submittal, and that information remains representative of current conditions.

Marshall Steam Station
�•' DUKE 8320 East Highway 150
ENERGY® Terrell NC 28682
Operational Status—40 CFR 122.21(r)(8)
Marshall consists of four coal-fired units with a total capacity of 2,058 MW. Since submission of the
facility's initial 316(b) reports required by the 2014 316(b) Rule,there have been no significant changes
in plant operations. Per Duke Energy's 2023 North Carolina Carbon Reduction Plan Supplement
preferred path, Units 1 and 2 at Marshall are projected to be replaced by January 1, 2029 with simple
cycle combustion turbines that require no cooling water. Units 3 and 4 are projected to retire by
January 1, 2032 and be replaced with a highly efficient combined cycle unit(s). However, legislative or
other operational requirements may result in changes to the projected retirement dates. Note that the
Carbon Reduction Plan and Integrated Resource Plan is for planning purposes and is not a definitive
determination by Duke Energy Carolinas, nor is it indicative of the location or date of any necessary
replacement generation.
During 2019-2023,the average facility net capacity factor was 35.7 percent. During this period,
individual monthly net capacity factors ranged from zero to 80.5 percent. The most recent five-year
(2019-2023) average net capacity factor is similar to that provided in the previous reports submitted in
2021. Note that the provided capacity factors are not necessarily indicative of future generation.
Entrainment Characterization Study—40 CFR 122.21(r)(9)
Marshall most recently conducted a two-year extensive entrainment characterization study during
March-October 2016 and March-October 2017. Entrainment samples were collected twice/month
during this period. During each sample event,four samples were obtained at approximate six-hour
intervals to evaluate diurnal entrainment. Approximately 100 cubic meters(m3)of volume was
obtained during each sample. Eggs and larvae were filtered through a 300 µm net and preserved for
laboratory processing. Size and other morphological characteristics were determined at the laboratory.
All activities were conducted in accordance with the project Standard Operating Procedures and Quality
Assurance documents.
The following table provides a summary of the 2016-2017 Marshall entrainment sampling.
[due to document formatting, table provided on following page]

(' DUKE Marshall Steam Station
8320 East Highway 150
ENERGY® Terrell NC 28682
Percent of Total
Common Name 2016 2017
Clupeid Group (note 1) 42 56
Shad Group (note 2) 24 <1
Alewife (note 3) 14 <1
Threadfin Shad (note 3) 10 0
Unidentified Fish 6 8
White Perch 2 23
Darter Species 2 1
Gizzard Shad (note 3) 1 0
Carp and Minnow Family 0 5
Yellow Perch 0 3
Sunfish Species 0 1
Common Carp 0 1
TOTAL 100 100
note 1: Alewife, Gizzard Shad,Threadfin Shad. The 316(b) Rule considers these to be fragile fish.
note 2: Gizzard Shad,Threadfin Shad. The 316(b) Rule considers these to be fragile fish.
note 3:The 316(b) Rule considers these to be fragile fish.
Based on this study, entrainment was greatest during the April—June period with the majority of
organisms collected represented by species considered to be fragile by the Rule (such as Alewife,
Gizzard Shad, and Threadfin Shad).
Using the DIF flow, it was estimated that approximately 40.4 million ichthyoplankton were entrained
during 2016 and 60.2 million during 2017. Based on actual cooling water withdrawals(e.g.AIF flow),
approximately 24.1 million ichthyoplankton were entrained during 2016 and 31.6 million during 2017.
As there have been no physical or operational CWIS changes at Marshall and no observed changes in the
Lake Norman aquatic community,the 2016-2017 entrainment study remains representative of current
Marshall conditions.
Comprehensive Technical Feasibility and Cost Evaluation Study—40 CFR 122.21(r)(10)
An investigation of potentially applicable additional entrainment and impingement technology measures
was conducted for Marshall. Of note,the measures currently employed (curtain wall and operational
measures) reduce entrainment to that comparable to closed cycle cooling. After the initial review was
completed,the candidate technologies for further evaluation were closed cycle cooling conversion using
mechanical draft cooling towers and installation of fine mesh screen with 0.75 millimeter(mm) mesh.
These two technologies were completely evaluated and included draft engineering, tentative
construction schedules, and preliminary capital and annual operating costs. The following table
provides a summary of the closed cycle cooling and fine mesh screen technologies.

Marshall Steam Station
fits DUKE 8320 East Highway 150
ENERGY® Terrell NC 28682
Characteristic Mechanical Draft 0.75 mm Mesh
Cooling Towers Traveling Screens
Capital Cost, 2020$ $470,900,000 $52,100,000
Annual Operating Cost, 2020$ $7,290,000 $1,040,000
Annual Social Costs, 2020$ $83,770,000 $5,010,000
Time to Implement,years 6.75 8.00
We fully acknowledge that the costs to implement and operate the two potential candidate
technologies have increased since the 2021 study report submittal and the prior planned retirement
date (2034) has changed for all four units. Although the numeric costs to implement the two potential
candidate technologies have increased since the 2021 study report submittal, the overall conclusion
remains that any additional technologies would be wholly disproportionate to any benefit.
Furthermore, implementation of additional candidate technologies prior to the planned the estimated
unit retirement dates could not reasonably be accomplished at Marshall. Therefore, repeating this
(r)(10) study would provide limited, if any, additional information for NCDEQ consideration.
Benefits Valuation Study—40 CFR 122.21(r)(11)
The two candidate technologies in the (r)(10) report were subject to a benefits valuation analysis that
included monetization and stock size quantified benefits. Of note, the existing technology and
operational measure at Marshall reduce entrainment to that commensurate with using cooling towers.
The study determined the following annualized benefits with the two additional technologies evaluated.
Annual Value based on Annual Value based on
Technology 2016 Entrainment, 2020$ 2017 Entrainment, 2020$
100%flow reduction $56 $581
Mechanical Draft Cooling Towers $45 $456
0.75 mm Fine Mesh Traveling Screens $2 $89
The submitted evaluation further determined that the Mechanical Draft Cooling scenario would have a
net benefit of-$586,350,000 (net negative benefit) while the 0.75 mm Fine Mesh Screen scenario would
have a net benefit of-$45,890,000(net negative benefit). The cost to benefit ratio for these two
technologies were determined to be 29,318:1 for mechanical draft cooling towers and 1,531:1 for fine
mesh traveling screens.
Although the numeric benefits and costs to implement the two potential candidate technologies have
increased since the 2021 study report submittal,the overall conclusion remains that any additional
technologies would be wholly disproportionate to any benefit. Furthermore, implementation of
additional candidate technologies prior to the planned the estimated unit retirement dates could not
reasonably be accomplished at Marshall. Therefore, repeating this (r)(11) study would provide limited,
if any, additional information for NCDEQ consideration.

(' DUKE Marshall Steam Station
8320 East Highway 150
ENERGY® Terrell NC 28682
Non-Water Quality Environmental and Other Impacts—40 CFR 122.21(r)(12)
Other aspects associated with implementation of two candidate technologies, mechanical draft cooling
towers and fine mesh traveling screens,were fully evaluated. These factors included energy
consumption, additional air pollutants, noise, safety(such as icing), impact on facility reliability, and
water consumption. The following table provides a summary of this report.
Mechanical Draft 0.75 mm Fine Mesh
Factor
Cooling Towers Traveling Screens
Implementation,years 6.75 8.00
Unit outage, months (each) 4 2
Capital cost, 2020$ $470,900,000 $51,200,000
Annual operating cost, 2020$ $7,290,000 $1,040,000
Annual energy use, MWhr 179,945 3,313
Unit outage replacement power, MWhr 2,981,496 1,490,748
Annual air pollutant increase,tons PM2.5 = 1.7 none
PM10= 3.3
Noise impact Moderate Minor
Increased pump
Station reliability impact 88 hours/year derate headloss and screen
maintenance
Consumptive water use Between 92 161%more Minor
than current
Although the monetary impacts of these additional factors for the two potential candidate technologies
have slightly changed since the 2021 study report submittal,the overall conclusion remains that any
additional technologies would be wholly disproportionate to any benefit. Furthermore, implementation
of additional candidate technologies prior to the planned unit retirement dates could not reasonably be
accomplished at Marshall. Therefore, repeating this (r)(12) study would provide limited, if any,
additional information for NCDEQ consideration.
External Peer Review—40 CFR 122.21(r)(13)
The Marshall (r)(10), (11), and (12) reports were thoroughly evaluated by the following external peer
reviewers, including their employment at the time of the 2021 Marshall 316(b) report submittal:
• Paul Jakus, PhD—Professor and Applied Economics Department Head at Utah State University.
Dr.Jakus reviewed the economics components of the (r)(10) and (r)(11) reports.
• John Maulbetsch, PhD—owner and principal of Maulbetsch Consulting. Dr. Maulbetsch
reviewed the closed cycle cooling components of the (r)(10) reports.
• Joe Raulli, PE—Technical Director at O'Brien and Gere. Mr. Raulli reviewed the fine mesh and
alternate water components of the (r)(10) report and the entire (r)(12) report.
• Jame Rice, PhD—Department of Applied Ecology at North Carolina University Professor
Emeritus. Dr. Rice reviewed the biological components of the (r)(11) reports.

r
�� DUKE Marshall Steam Station
8320 East Highway 150
ENERGY® Terrell NC 28682
Each of the external peer reviewers provided additional comments or questions which were fully
resolved prior to submittal of the 2021 Marshall 316(b) study reports. These external peer reviewers
improved the draft reports with additional detail, clarification,or validation to facilitate the Agency
review.
The peer review was conducted independently by an individual with no contributions or control of the
draft reports provided to the external peer reviewers.
With respect to implementation of additional technologies or operational measures at Marshall, any
benefits would be wholly disproportionate to the costs. Therefore, repeating the external peer review
would provide limited, if any, additional information for NCDEQ consideration.
Summary
The initial 316(b) reports as required by the rule for existing facilities in 40 CFR 122.21(r)for the Duke
Energy Carolinas Marshall Steam Station,were submitted to NCDEQ on March 29, 2021, with the most
recent NPDES permit renewal application.These comprehensive reports provided detailed information
about the facility's cooling water system, source waterbody, and evaluation of additional technologies
beyond those already implemented. Since that initial 316(b) submittal, conditions at the facility and in
the waterbody remain substantially unchanged, and the previously submitted information remains j
representative of current source water, intake structure, cooling water system, operating conditions, 1
and potentially applicable additional technologies costs and benefits.The NPDES permit for Marshall
expires on April 30, 2027.
Conducting a replicate 316(b) study report for the Marshall Steam Station would be an expensive and
time-consuming process. As there have been no changes to the configuration or operation of Marshall's
cooling water system or intake structure, and the facility already employs technologies and operational
measures to minimize the adverse environmental impacts associated with impingement or entrainment
of aquatic organisms, Duke Energy respectfully requests that NCDEQ authorize a reduced 316(b)
information submittal for the next NPDES permit renewal. In lieu of recreating the full reports required
by 40 CFR 122.21(r), we request that NCDEQ allow the facility to certify that no operational or
technology changes have occurred that would impact the Marshall Steam Station cooling water system
or intake structure with respect to the 316(b) Rule for existing facilities.
If you have any questions about this request, please contact Mr. Don Safrit at 919-546-6146 or
[e-mail].
Sincerely,
Jeffrey Flanagan
General Manager III

DUKE Marshall Steam Station
8320 East Highway 150
l' ENERGY® Terrell NC 28682
Cc: Scott LaSala
Don Safrit
Michael Smallwood
Julie Stahl