NC0004774_Fact Sheet_20180917

DEQ/DWR
FACT SHEET FOR NPDES PERMIT DEVELOPMENT
NPDES No. NC0004774
I. PROPOSED PERMIT ACTION
Duke Energy Carolina, LLC, (hereafter, "Duke Energy' or "Duke Energy') has applied for renewal
of permit NC0004774 for its Buck Combined Cycle Station (formerly, the Buck Steam Station). The
Division of Water Resources has reviewed the application and additional information submitted by
Duke Energy and has made a tentative determination to reissue the permit with modifications.
This Fact Sheet describes the Buck facility; its wastestreams and receiving streams; recent and
planned changes in the facility; its compliance history; the proposed terms and conditions of the
permit and the rationale for those; and the schedule and process for public participation in the
Divisions final decision on the permit.
II. SUMMARY
Duke Energy owns and operates the Buck Combined Cycle Station (BCCS), a steam electric power
generating facility in Rowan County near Spencer, North Carolina. For permitting purposes, the
facility includes the Buck Steam Station (BSS), now retired; the 620 MW Combustion Turbine
Combined Cycle (CTCC) plant; and the associated system of coal ash and waste settling ponds. The
combined site is approximately 640 acres (1 sq. mi.) in size. The facility is currently authorized to
discharge process wastes, comingled stormwater, and other wastewaters to the Yadkin River and its
tributaries at multiple points, subject to the terms and conditions of NPDES permit NC0004774.
Duke Energy has also applied to the Division of Energy, Mining, and Land Resources (DEMLR) for
two NPDES stormwater permits. The permits will govern the discharge of stormwaters that are not
intermixed with wastewaters. Each will apply to a different part of the site: NCS000578 for the
former Buck Steam Station (site restoration) and NCS000554 for the Buck CTCC (active operations).
DEMLR plans to issue the permits in coordination with reissuance of this wastewater permit.
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
Page 1
FACILITY INFORMATION
Permittee:
Duke Energy Carolinas, LLC
Permittee Address:
526 S. Church Street, Mail Code EC3XP, Charlotte, NC
28202
Facility Name:
Buck Combined Cycle Station (formerly Buck Steam Station)
Facility Address:
1385 Dukeville Road, Salisbury, NC 28146
Facility County: Rowan
Facility Type:
Industrial — Steam Electric Power Generation
SIC Code(s): 4911
Permitted Flow:
Not Limited
Facility Status: Existing
Waste Type:
Industrial
WWTP Grade: PC -1
WATERBODY INFORMATION ADDITIONAL INFORMATION
Waterbody Name:
Yadkin River Regional Office:
Mooresville
Classification:
WS -V USGS Topo Quad:
E17NW
Subbasin:
03-07-06 Permit Action:
Renewal
HUC8:
03040102 Permit Writer:
Mike Templeton
Drainage Area (miz):
3,452 Date:
September 17, 2018 — Final Permit
Summer 7Q10 (cfs):
Winter 7Q10 (cfs):
Average Flow (cfs):
Listed:
IWC (%):
1,030
1,480
4,960
Not for POCs
0.1%, 0.3%, 0.7%, & 100%
I. PROPOSED PERMIT ACTION
Duke Energy Carolina, LLC, (hereafter, "Duke Energy' or "Duke Energy') has applied for renewal
of permit NC0004774 for its Buck Combined Cycle Station (formerly, the Buck Steam Station). The
Division of Water Resources has reviewed the application and additional information submitted by
Duke Energy and has made a tentative determination to reissue the permit with modifications.
This Fact Sheet describes the Buck facility; its wastestreams and receiving streams; recent and
planned changes in the facility; its compliance history; the proposed terms and conditions of the
permit and the rationale for those; and the schedule and process for public participation in the
Divisions final decision on the permit.
II. SUMMARY
Duke Energy owns and operates the Buck Combined Cycle Station (BCCS), a steam electric power
generating facility in Rowan County near Spencer, North Carolina. For permitting purposes, the
facility includes the Buck Steam Station (BSS), now retired; the 620 MW Combustion Turbine
Combined Cycle (CTCC) plant; and the associated system of coal ash and waste settling ponds. The
combined site is approximately 640 acres (1 sq. mi.) in size. The facility is currently authorized to
discharge process wastes, comingled stormwater, and other wastewaters to the Yadkin River and its
tributaries at multiple points, subject to the terms and conditions of NPDES permit NC0004774.
Duke Energy has also applied to the Division of Energy, Mining, and Land Resources (DEMLR) for
two NPDES stormwater permits. The permits will govern the discharge of stormwaters that are not
intermixed with wastewaters. Each will apply to a different part of the site: NCS000578 for the
former Buck Steam Station (site restoration) and NCS000554 for the Buck CTCC (active operations).
DEMLR plans to issue the permits in coordination with reissuance of this wastewater permit.
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
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The Buck Tie Station, a large substation facility, is a separate operation located between the BSS and
CTCC. The Tie Station does not discharge wastes to surface waters and is not subject to NPDES
permit requirements.
Permit NC0004774 was last issued in December 2011 and expired August 31, 2016. On February 26,
2016, prior to expiration, Duke Energy applied for permit renewal. In accordance with NPDES
regulations, the permit was administratively extended and remains in effect until the Division takes
final action on the application, that is, until it issues a new permit or denies the application.
The current permit authorizes the discharge of once -through noncontact cooling waters to the
mainstem of the Yadkin River/ High Rock Lake and the discharge of process and other wastes from
the ash pond system to a side cove of the lake and, on an emergency basis, to the mainstem of the
river.
Duke Energy's facilities, operations, and waste management needs at the Buck site have changed
substantially since the permit was last issued. The last coal-fired units have been retired, and all
power is now generated at the CTCC plant. Duke Energy is required to decant and dewater the ash
ponds and dispose of the accumulated ash, and it will discharge treated wastes from those
operations. Wastewater outfall configurations will evolve as these changes take place. Duke Energy
must also address the discharge from two "constructed seeps" at the ash ponds. The draft permit
includes extensive modifications to address these changes, as described in this fact sheet.
III. RECEIVING WATERS
The Buck Combined Cycle Station is located adjacent to the Yadkin River in the upper reaches of
High Rock Lake. The side channels of the lake to the east and west of the site behave as impounded
waters, except at low water levels. The mainstem of the river (segment 12-(108)b), though part of the
lake, is still generally riverine in nature. All receiving waters are classified WS -V, and their
designated uses include aquatic life propagation, maintenance of biological integrity (including
fishing and fish), wildlife, secondary recreation, and industrial water supplies. This portion of the
Yadkin River is considered lower piedmont waters (15A NCAC 02B .0202, Definitions).
Stream Flows. High Rock Dam was constructed and High Rock Lake impounded in 1927. The dam
and reservoir are the uppermost of six hydroelectric projects on the river. These have been owned
and operated by Alcoa Power Generating Inc. (APGI) under FERC licenses 2197 (Yadkin Project)
and 2206 (Yadkin -Pee Dee River Project). In 2017, Cube Hydro Partners, LLC, acquired four of the
projects, including High Rock.
Flow through the system is managed collectively to ensure sufficient flows throughout; however, no
minimum flow is specified for the High Rock project. Under normal conditions, water levels at the
dam fluctuate as much as 10 feet on a seasonal basis.
The statistical stream flows for this reach of the river are listed on page 1 of this fact sheet. The flows
were determined by the USGS in the 1980s based on historical data. The USGS has not updated the
stream flows since that time due to the complexity and uncertainty of the effects of hydropower
operations in the Yadkin -Pee Dee River system.
Water Quality Assessment. The Division's 2014 Integrated Report indicated that High Rock Lake in
the vicinity of the Buck site met state criteria for water temperature, dissolved oxygen, and pH. The
lake did not meet criteria for chlorophyll a, turbidity, mercury (fish consumption advisory), and
PCBs (fish consumption advisory).
Chlorophyll a. The majority of the lake exhibits symptoms of nutrient over -enrichment. The
Division and affected stakeholders have worked to develop a TMDL to address these impacts.
More recently, a Scientific Advisory Committee was established by the Division and is
developing protective nutrient criteria for the lake.
TurbidLty violations are common throughout the High Rock Lake watershed. Turbidity is a
measure of clarity in water and often increases due to excessive sediment loading in the stream.
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
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Soil erosion is the most common source of sediment loads and turbidity. Some erosion occurs
naturally, though human activities can accelerate the process considerably. The Buck facility is
not a significant source of sediments or turbidity in the lake.
Mercury is found naturally at low levels in rock, soil and water throughout North Carolina and
is also released into the air when fossil fuels (or other materials) are burned. Measurable levels of
mercury have been found in certain fish species in waters across the state. On April 2, 2008, the
NC DHHS issued a statewide fish consumption advisory for mercury. In response, the Division
listed all surface waters as impaired for mercury in fish tissue. In 2012, the Division prepared a
TMDL and implementation strategy to address the issue, and the U.S. EPA approved both.
PCBs have long been used as coolants and lubricants in transformers, capacitors, and other
electrical equipment. The manufacture of PCBs was stopped in the U.S. in 1977 because of
evidence of environmental and human health impacts. On March 13, 2013, the NC DHHS issued
a fish consumption advisory for catfish larger than 18 inches caught in reservoirs in the Yadkin -
Pee Dee River system, including High Rock Lake. The advisory noted that the limit on catfish
consumption in the mercury advisory would also be protective of potential health effects from
PCBs in those fish. The Buck facility is not a significant source of PCBs.
The Buck facility is not considered to be a significant contributor to these impairments in the lake.
Fish Tissue Sampling. Under the current permit, Duke Energy is required to analyze fish tissue
samples from the mainstem of the Yadkin River once per permit cycle to monitor for accumulation
of arsenic, selenium, and mercury. Accumulation has not been observed in the samples collected.
Biological Monitoring. By agreement with the Division, Duke Energy conducts annual biological
and chemical monitoring to evaluate the possible impacts of its thermal discharges upon the
macroinvertebrate and fish community in in the Yadkin River near Buck Steam Station. The latest
BIP (balanced and indigenous population) report was submitted to DWR in November of 2011. The
report concluded that the indigenous macroinvertebrate community in the river varied with the
extreme high- and low -flow years in the study period (2003-2008) but remained within the historic
range of densities; and that the river continues to have a balanced and indigenous fish community.
IV. PERMITTED FACILITY
A. History of Buck Power Generating Facilities
The Buck Steam Station (BSS) began operations with two coal-fired steam -electric generation units in
1926. The units were rated at 35 MW each. Units 3 and 4 (80 and 40 MW) were added in the early
1940s, and Units 5 and 6 (135 MW each) were added it 1953. To meet peak demands, three 31 MW
natural gas/ fuel oil -fired combustion turbine units, Units 7C, 8C, and 9C, were added in 1970. See
Figure 1.
Units MW
1,2 35
3,4 80
5,6 135
7C, 8C, 9C 35
CTCC 620
Figure 1 - Operating Lives of Generating Units - Buck Station
1920s I 1930s I 1940s I 1950s I 1960s I 1970s I 1980s I 1990s I 2000s I 2010s
Duke Energy retired Units 1 and 2 in the 1970s and Units 3 and 4 in May 2011. Duke Energy
constructed the Buck Combustion Turbine Combined Cycle (CTCC) plant, a 620 MW, natural gas-
fired, steam electric power generating facility, and the new plant began operating commercially in
late 2011. BSS Units 7C, 8C, and 9C were then retired in October 2012. Units 5 and 6, the last of the
coal-fired units, were retired in April 2013.
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
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The CTCC plant is now the sole power -generating unit at the Buck site. The plant utilizes two
combustion turbine generators, two heat recovery steam generators (boilers), and one steam turbine
generator (known as a 2 X 1 configuration) to produce electricity.
The plant employs wet cooling towers for steam generator condenser cooling. Evaporative losses
from these cooling towers are estimated at 3,273 gpm (4.7 MGD). Water in the cooling tower system
is typically recycled 5 times before blowdown is sent to the CTCC wastewater sump. Make-up water
is withdrawn from the river and treated prior to use; and other CTCC wastestreams, including
chiller system blowdown, are reused as make-up waters. The design average blowdown rate from
the system is 400 gpm. Wastes from treatment of cooling tower make-up water (23 gpm), service
waters and floor drains (5 gpm), and potable water treatment wastes (2 gpm) are also discharged to
the wastewater sump. The CTCC plant generates an estimated total 430 gpm (0.62 MGD) of
wastewater. These flows are pumped from the wastewater sump to Cell 1 of the ash basin system.
B. Coal Ash Basins/ Settling Ponds
Duke Energy maintains an ash basin system consisting of three cells and associated earthen dikes,
discharge structures, and canals. The cells are designated as Cell 1 - Additional Primary Pond, Cell 2
- Primary Pond, and Cell 3 - Secondary Pond. The original ash pond began operation in 1957. The
pond was later divided to form Ponds 2 and 3 (approximately 81 acres). Ash from the coal
combustion process was sluiced to Cell 2. Cell 1 was the last cell constructed, in 1982, to provide
additional storage (approximately 90 acres). Coal ash was then routed to Cell 1 until the end of coal-
fired operations. Wastes flow from Cell 1 to Cell 2 to Cell 3 and discharge from Cell 3 to a cove of
High Rock Lake at Outfall 002. These wastes are described below.
C. Wastestreams and Outfalls - Current Permit
The current permit authorizes the following discharges and discharge locations:
Table 1. Existing Process Outfalls
OUTFALL
EFFLUENT
LATITUDE
LONGITUDE
RECEIVING WATER
CLASS
001
Once -through non -contact cooling water
35.713890
-80.375280
Yadkin River/
High Rock Lake
WS -V
004
Screenings from raw water intake
35.713890
-80.375560
Yadkin River/
High Rock Lake
WS -V
Process wastewaters, treated domestic
UT Yadkin River/ cove
002
wastes, contaminated groundwater, and
35.712220
-80.364170
of High Rock Lake
WS -V
comingled stormwater
002A
Emergency overflow from Yard Sump
35.713890
-80.373060
Yadkin River
WS -V
Outfall 001. When the permit was last issued, in early 2011, coal-fired units 3, 4, 5, and 6 and gas-
fired units 7C, 8C, and 9C were operational. The gas-fired CTCC came online before the end of 2011.
At the time, most of the water pumped from the river was used for once -through non -contact
cooling in the Condenser Cooling Water (CCW) system and returned to the river at Outfall 001. The
CCW system's design flow was 395 MGD; the average reported flow from 2011 through March 2013
was 177 MGD. The system ceased operation in 2013 with the retirement of the last coal-fired units.
The current permit establishes temperature limits for the discharge. Consistent with Sections 301
and 316(a) of the Clean Water Act, the permit sets a mixing zone that extends to High Rock Lake
Dam within which the state's surface water quality standard for temperature is modified so long as
Duke Energy can demonstrate that the river still maintains balanced and indigenous populations of
fish and macroinvertebrate species.
Intake Screen Backwash. The facility withdraws water from the Yadkin River at the BSS
powerhouse. In addition to providing cooling capacity in the CCW system, the water was and is
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
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used to meet other cooling needs and to provide process make-up waters and sanitary (potable)
waters. The raw water is screened to prevent vegetative and other debris and any fish in the vicinity
from being drawn into the plant. Historically, the intake screens have required periodic backwashes
(design flow of 0.225 MGD) to clear them of debris, and the screenings are returned to the river. A
new system was installed in 2017 that uses bursts of air to clear the screens. It still returns screenings
to the river but without the associated flow.
This release of screenings is deemed permitted under 15A NCAC 02H .0106(f)(2) so long as no water
quality standards are contravened. Thus, the current permit does not set specific limitations or
monitoring requirements for the discharge.
Silt accumulation around the intake has been periodically dredged. The spoils were conveyed to the
ash ponds for settling and were discharged subject to the requirements for Outfall 002. The new
system reaches the river from above, and dredging is not expected to be needed.
Outfall 002. When the permit was issued in 2011, the BSS process wastestreams consisted primarily
of coal pile runoff, fly and bottom ash, ash transport water, low-volume wastes (including water
treatment wastes, wet scrubber air pollution control waters, laboratory and sampling streams, and
boiler/ condenser/ cooling tower blowdowns), and metal cleaning wastes. Other flows included
domestic wastewater (0.002 MGD), petroleum -contaminated groundwater, and stormwater runoff
from the plant site (0.364 MGD). Coal pile runoff and coal ash were conveyed directly to Cell 1 of the
ash basin system, and most other wastes were pumped to Cell 2 from the BSS Yard Sump adjacent to
the powerhouse.
Settled wastes from the ash basins was and is discharged at Outfall 002. The estimated average
design flow was 4.4 MGD; the average actual flow reported from 2011 through March 2013 was 1.6
MGD. The discharge is subject to limitations for oil & grease, total suspended solids, pH, iron,
copper, and chronic toxicity.
With the startup of the CTCC in 2011, new wastes flows were generated that were similar in nature
to those generated at the BSS gas-fired units. Key among them are blowdown from the condenser
cooling towers and from the chiller and closed -cycle cooling towers; blowdowns from the heat
recovery steam generators (HRSG) and from auxiliary boilers; residuals from the settling, filtration,
reverse osmosis, demineralization, and ultrafiltration processes used to produce potable and process
makeup water for the plant. The design flow for these waste flows is 430 gpm, or 0.62 MGD. All
CTCC flows drain to the Plant Sump and are pumped to Cell 1 of the ash basin system. Sanitary
sewage is now treated and disposed separately in an on-site system permitted by Rowan County.
Sanitary sewage is now treated and disposed separately in an on-site system permitted by Rowan
County.
Metal cleaning wastes generated in the course of regular maintenance at the CTCC are directed to a
blind sump. These wastes are collected for offsite disposal and are not discharged to surface waters.
With the retirement of the last BSS units in 2013, the historic process wastes (including coal pile
runoff and coal ash wastes) and the withdrawals of river water for cooling and process makeup
waters were eliminated or greatly reduced:
• Outfall 001. Withdrawals for the Condenser Cooling Water system (once -through, non -
contact) were eliminated entirely.
• Outfall 002. The coal yard and other BSS facilities have been or are being removed, and most
wastes have been eliminated. The BSS powerhouse is scheduled to be demolished in 2018,
and the last waste flows (raw water treatment wastes, stormwater from the BSS site, and
groundwater flows) will be eliminated in that process.
These changes in the production facilities have vastly reduced process and cooling water flows and
the potential for impacts on surface waters. In 2011-2012, while the last coal-fired units were still
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
Page 5

operating, the cooling water flows at Outfall 001 averaged 177 MGD, and process and other flows at
Outfall 002 totaled less than 2 MGD (design 4.4 MGD). Since the retirement of those units in April
2013, flows have averaged less than 0.5 MGD. See Figure 2.
In the course of these changes, the terms and conditions of the wastewater permit have continued to
satisfy both technology-based and water quality -based standards.
Outfall 002A. The BSS Yard Sump discharges to the Yadkin River in rare instances when flows to
the sump exceed its pumping capacity. Monitoring is required and a pH limit applies if the
discharge lasts more than one hour.
Two overflows occurred in this permit term, one each in 2011 and 2013. Each lasted less than one
hour and released less than 45,000 gallons to the river.
Figure 2 - Flow Reductions - Buck Station
D. Compliance History
Duke Energy's discharge monitoring reports indicate the facility has met all permit limits during the
previous permit cycle, as summarized in Table 2, below.
Table 2. DMR Summary, 2011-2016
OUTFALL
PARAMETER LIMIT
Mo Avg/ Daily Max
COMPLIANCE
PERIOD
PERIOD
AVG
PEAK MO AVG/
DAILY MAX
001
Temperature 95, F/ -
Jan 2011 — Mar 2013
72.61F
95°F/ 101°F
002
0&G 11.0 / 15.0 mg/L
Jan 2011 — Jun 2016
<5 mg/L
<5 / <5 mg/L
TSS 23.0 / 74.0 mg/L
6.6 mg/L
22.5 / 30 mg/L
Cu 1.0 / 1.0 mg/L
<0.005 mg/L
0.006 / 0.006 mg/L
Fe 1.0 / 1.0 mg/L
0.26 mg/L
0.6 / 0.6 mg/L
pH 6-9 s.u.
N/A
6.5 min., 8.9 max.
WET (7 -day Static) P/F
Mar 2011— Jun 2016
Passed all
WET (Chronic) P/F
Mar 2011 — Sep
2011
Passed all
002A
Flow
Jan 2011 — Jun 2016
0.044 MG (4/11), 0.03 MG (3/13)
pH 6-9 s.u.
Monitoring is only required if
discharge exceeds 1 hour duration.
No monitoring reported.
TSS
Fecal coliform
Iron
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
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V. REGULATORY DRIVERS
Effluent limitations and other special conditions in the existing and proposed permits must adhere
to and satisfy applicable rules and regulations. The following are essential in developing this permit:
A. Federal Effluent Guidelines
The Buck Combined Cycle Station (like the Buck Steam Station before it) is subject to federal
Effluent Limitations Guidelines (ELGs) for the Steam Electric Power Generation Point Source
Category, 40 CFR Part 423. The U.S. EPA published revisions to the ELGs on November 3, 2015
to improve control of pollutants found in the following wastestreams: flue -gas desulfurization
(FGD) wastewater, fly ash transport water, bottom ash transport water, combustion residual
leachate from landfills and surface impoundments, nonchemical metal cleaning wastes, and
wastewater from flue gas mercury control (FGMC) systems and gasification systems. The BCCS
does not employ FGD.
These regulations form the basis for developing technology-based effluent limitations (TBELs)
for the facility (see TBELs in Section VI.B, below).
B. State Water Quality Standards
Many of the parameters detected in the facility discharges are subject to NC surface water
quality standards. These standards are the basis for developing water quality -based effluent
limitations (WQBELs) for the facility (see WQBELs in Section VI.C, below).
C. Coal Ash Management Act; Related Agreement
Duke Energy is subject to requirements of the 2014 Coal Ash Management Act (S.L. 2014-122)
and subsequent revisions. The Act requires comprehensive changes in how Duke Energy
manages its coal-fired stations and coal ash storage facilities. Among other things, it requires
Duke Energy to (1) evaluate and remediate the coal ash basins at its North Carolina facilities and
close the ash basins at the Buck facility by August 1, 2019, and (2) identify and properly manage
wastewater seeps from the ash basins at those facilities.
D. Clean Water Act 316(a) Variance
Section 316(a) of the Clean Water Act provides that a thermal discharge may be granted a
variance from stream standards for temperature if the permittee can demonstrate that the
discharge will still ensure "the protection and propagation of a balanced, indigenous population
of shellfish, fish, and wildlife in and on that body of water." The criteria for establishing such a
variance are set forth in 40 CFR Part 125, Subpart H.
The Division has granted a temperature variance for operation of the Buck Steam Station since
the mid-1970s. The thermal mixing zone originally extended to the High Rock Lake Dam.
E. Clean Water Act 316(b) Raw Water Intake Regulations
Section 316(b) of the Clean Water Act requires that cooling water intake structures minimize the
adverse environmental impact of their operation. The requirements for intake structures at
existing facilities are set forth in 40 CFR Part 125, Subpart J, last revised on August 14, 2014, and
40 CFR 401.14. Existing facilities with a design intake flow of 2 MGD or greater must meet Best
Technology Available (BTA) standards for impingement and entrainment mortalities. 40 CFR
125.95(a)(2) requires permittees, at permit renewal or other approved date, to submit
information to verify that its intake structure satisfies the BTA standards.
Closed -cycle recirculating cooling systems are one of the pre -approved compliance alternatives
for impingement and entrainment, see §125.94(c)(1). The CTCC plant employs such a system
and, therefore, satisfies the requirements for an interim BTA. The Director has made a tentative
determination to approve the CWIS, contingent upon Duke's submittal and the Director's
acceptance of the additional information required by 40 CFR 122.21(r).
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
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VI. RATIONALE FOR EFFLUENT LIMITATIONS AND MONITORING REQUIREMENTS
Duke Energy's facilities, operations, and waste management needs at the Buck site have changed
substantially since the permit was last issued. New regulatory requirements, legal agreements and
other developments have placed additional demands on Duke Energy and the Buck facilities.
In response to these demands, Duke Energy proposes to:
• Continue operation of the CTCC plant;
• Complete the decommissioning of the Buck Steam Station and restoration of the BSS site;
• Undertake remediation of the ash basin system: decanting, dewatering, and reburning of the
ash ("beneficiation') for use in concrete manufacturing;
• Manage discharges from two ash basin constructed seeps;
• Modify its waste treatment operations as necessary; and
• Modify its outfall configuration and install additional outfalls to accommodate these
activities.
The draft permit includes significant modifications to accommodate these changes, as described in
this section.
A. Proposed Wastestreams and Outfalls
The sources and types of waste discharges will increase and, for permitting purposes, can be
categorized as those coming from steam electric power operations, coal ash pond remediation, and
two ash pond constructed seeps. Table 3 lists the existing and planned outfalls for discharges from
power generation and ash pond remediation. Table 4 notes the location of the constructed seep
outfalls.
Table 3. Proposed Process Outfalls
OUTFALL
EFFLUENT
LATITUDE
LONGITUDE
RECEIVING
CLASS
WATER
Steam Electric Operations
Initial BSS/ CTCC Operations
Yadkin
002
Process and sanitary (water treatment),
35.71222o
-80.36417o
River/ cove of
Rivvee
WS -V
contaminated groundwater, and comingled
High Rock Lake
stormwater
Interim CTCC Operations
UT Yadkin
002
Process and sanitary (water treatment)
35.712220
-80.364170
River/ cove of
WS -V
wastewaters
High Rock Lake
001A/
CTCC Operations
35.713840
-80.375390
Yadkin River/
006
Process and sanitary (water treatment)
35.714160
-80.374130
HRL (mainstem)
WS -V
(proposed)
wastewaters
002A
Emergency overflow from Yard Sump
35.713890
-80.373060
Yadkin River/
WS -V
HRL (mainstem)
004
Raw water intake screenings
35.713840
-80.375560
Yadkin River/
WS -V
High Rock Lake
Ash Basin Remediation
Ash Pond Decanting/ Dewatering
UT Yadkin
002
35.712220
-80.364170
River/ cove of
WS -V
Treated waters from ash basin remediation
High Rock Lake
007
Ash Pond Decanting/ Dewatering
Yadkin River/
(proposed)
Treated waters from ash basin remediation
35.71545°
-80.36522°
HRL (mainstem)
WS -V
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Duke Energy — Buck Combined Cycle Station — NC0004774
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1. Steam Electric Operations
Outfall 002. Sanitary (water treatment) and other wastes will continue to be generated in
small amounts at the BSS until its demolition, scheduled for 2018. CTCC operations will
continue to generate process and sanitary wastes typical of steam electric power generating
facilities. These wastes will continue to be collected at the BSS Yard Sump and the CTCC
Plant Wastewater Sump, respectively, and pumped to the ash basins for settling and
discharge at Outfall 002.
Domestic wastewater is now directed to an on-site waste system permitted by Rowan
County and will no longer be subject to this NPDES permit.
When the NPDES stormwater permits for the facility are issued, Duke Energy will proceed
with demolition of the remaining BSS structures and remediation of that portion of the Buck
site. In general, work will begin on the western end of the site and proceed toward the
eastern end. All sources of wastes to the BSS Yard Sump - and the Yard Sump itself - will be
eliminated in this effort. Restoration of the BSS site will eliminate the discharge of
contaminated stormwater to the ponds.
Outfalls 001A/ 006. Once the BSS wastes are eliminated and this wastewater permit is
issued, Duke Energy will redirect all flows from the CTCC Wastewater Sump to the Yadkin
River in accordance with the new permit. The CTCC wastes may initially discharge at the
existing Outfall 001 (renumbered 001A). Outfall 001A will be removed in the course of the
BSS demolition, and Duke Energy will then divert flows to a new Outfall 006 for those waste
flows, to be located in the same vicinity, adjacent to the Buck boat ramp and dock.
2. Ash Basin Remediation
• Outfall 002/ 007 - Decant Phase. When the CTCC waste flows have been redirected to
Outfall 001A/ 006, Duke Energy will begin remediation of the ash ponds. First, free waters
in the ponds will be decanted, treated (as necessary), and discharged, either at the existing
Outfall 002 or at a new Outfall 007 to be constructed to the Yadkin River mainstem north of
Outfall 002.
• Outfall 002/ 007 - Dewatering Phase. When free waters are removed to a depth of 3 feet,
remediation will enter the dewatering phase. The remaining free water and the interstitial
waters within the ash deposits will be removed, treated (as necessary), and discharged at
Outfall 002 or 007.
(Duke Energy has not yet indicated whether it will remove the ash pond impoundments once
the ash is removed, nor the nature of any flows that would continue to discharge from the site at
that time. Thus, the permit does not address discharges from the ponds beyond the dewatering
phase, and the permit requirements for that phase would apply to any such discharge.)
3. Ash Basin Constructed Seep Discharges
Process for Seep Identification and Permitting. In 2014, Duke Energy developed and
implemented a Plan for Identification of New Discharges for the Buck property, as required under
the CAMA. The Plan specifies that Duke Energy will inspect the site on a regular basis and,
when a seep is identified, ensure that any discharge is properly addressed.
Duke Energy identified and sampled 17 potential seeps from the ash basin system, and seven
more potential seeps and Areas of Wetness were identified later, for a total of 24 sampling
points. Duke Energy and DEQ now propose to regulate constructed seeps in the NPDES permit
and to enter into a Special Order of Compliance (SOC) that will govern discharges from other
seeps.
Of the seeps identified thus far, S-11 and S-17 are the only engineered seeps, and they will be
regulated as Outfalls 111 and 117 under this permit; see Table 4. The remaining points are
proposed to be regulated under the SOC, once it is established.
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
Page 9

Table 4. Constructed Seeps
POTENTIAL OUTFALL
RECEIVING
SAMPLING POINT ID LATITUDE LONGITUDE EFFLUENT
NUMBER
CHANNEL
STREAM
S-11 35.707126 -80.374034 - 111
UT Yadkin R.
5-17 35.7058 -80.3753 - 117
UT Yadkin R.
B. Basis of Effluent Limitations
Limits are generally classified as one of two types:
• Technology-based effluent limitations (TBELs) are applicable waste treatment performance
standards (if any) and apply regardless of the discharge's impacts to the receiving waters.
• Water quality -based effluent limits (WQBELs) ensure that a discharge does not cause or
contribute to an exceedance of applicable surface water quality standards and criteria.
WQBELs represent the maximum allowable effluent concentration that will not cause an
exceedance under specific low -flow conditions.
A discharge may be subject to one or both types of limit for any given parameter of concern.
1. TBELs
a. Process Wastewaters
Process waste discharges from the Buck facility are subject to technology-based effluent
limitations established in the Effluent Limitations Guidelines (ELGs) for Steam Electric
Power Generating Point Source Category, 40 CFR Part 423.
40 CFR 423.12 and 423.13 set BPT and BAT performance standards, respectively, applicable
to discharges from the Buck facilities. The requirements are summarized below:
The following Buck process waste flows are subject to the Steam Electric ELGs. Although the
coal-fired operations have ceased, the technology-based limits that applied to most waste
sources will continue to apply to the pond discharges until the residuals from past
operations ('legacy' sources) are removed. Metal cleaning wastes are no longer discharged to
the ash basin system and are not treated as legacy sources.
Initial BSS/CTCC Operations - Outfall 002:
• Cooling tower blowdown (CTCC);
• Low volume waste sources (CTCC, legacy BSS @ powerhouse, ash ponds); and
• Coal pile runoff, ash transport waters, ash leachate (legacy BSS @ ponds).
Interim CTCC Operations - Outfalls OOIAIO06:
• Cooling tower blowdown (CTCC);
• Low volume waste sources (CTCC, legacy BSS @ ponds); and
• Coal pile runoff, ash transport waters, ash leachate (legacy BSS @ ponds).
CTCC Operations - Outfalls OOIAIO06:
• Cooling tower blowdown (CTCC); and
• Low-volume wastes (CTCC).
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
Page 10

40 CFR 423.12
BPT STANDARDS FOR EXISTING FACILITIES
(a) (Explanatory)
(b) (1) pH: 6-9 at all times
(2) No discharge of PCBs
(3) Low volume waste sources:
(4) Fly & bottom ash transport waters:
(11) Combustion residual (ash) leachate:
(5) Metal cleaning wastes:
BPT Effluent Limits
Daily Max Mo. Average
(mg/L) (mg/L)
TSS
100.0 30.0
O&G
20.0 15.0
(5) Metal cleaning wastes:
(8) Free available chlorine and total chlorine: restrictions
on duration of discharges (1 unit max, 2 hr/day max)
(9) Coal pile runoff
BPT Effluent Limits
Daily Max Mo. Average
(mg/ L)
(mg/L)
TSS 50.0 1 -
(10) Coal pile runoff — storm overflow waiver
(12) Concentration limits allowed
(13) Combined wastestreams
40 CFR 423.13
BAT STANDARDS FOR EXISTING FACILITIES
(a) No discharge of PCBs
(b) (1) Once -through cooling water (>:25 MW capacity)
BAT Effluent Limits
Daily Max Mo. Average
(mg/L) (mg/L)
rot
al residual 0.2
rine
(2) Restrictions on chlorine discharges (2 hr/day max)
(c) (<25 MW capacity — Not Applicable)
(d) (1) Cooling tower blowdown:
BPT Effluent Limits
Daily Max
Mo. Average
1.0 1.0
Total Iron
(mg/L)
(mg/L)
TSS
100.0
30.0
O&G
20.0
15.0
Total Copper
1.0
1.0
Total Iron
1.0
1.0
Once -through cooling water:
Cooling tower blowdown:
0.2
Total Cr
BPT Effluent Limits
Daily Max
Mo. Average
1.00
(mg/L)
(mg/L)
Fee available
0.5
0.2
lorine
(8) Free available chlorine and total chlorine: restrictions
on duration of discharges (1 unit max, 2 hr/day max)
(9) Coal pile runoff
BPT Effluent Limits
Daily Max Mo. Average
(mg/ L)
(mg/L)
TSS 50.0 1 -
(10) Coal pile runoff — storm overflow waiver
(12) Concentration limits allowed
(13) Combined wastestreams
40 CFR 423.13
BAT STANDARDS FOR EXISTING FACILITIES
(a) No discharge of PCBs
(b) (1) Once -through cooling water (>:25 MW capacity)
BAT Effluent Limits
Daily Max Mo. Average
(mg/L) (mg/L)
rot
al residual 0.2
rine
(2) Restrictions on chlorine discharges (2 hr/day max)
(c) (<25 MW capacity — Not Applicable)
(d) (1) Cooling tower blowdown:
(2) Restrictions on chlorine discharges (1 unit max, 2
hr/day max)
(3) Alternative to monitoring priority pollutants
(e) Chemical metal cleaning wastes:
BAT Effluent Limits
Daily Max
Mo. Average
1.0 1.0
Total Iron
(mg/L)
(mg/L)
Free available
0.5
0.2
chlorine
126 priority
No detectable amount
pollutants*
except:
0.2
0.2
Total Cr
Total Zn
1.00
1.00
(2) Restrictions on chlorine discharges (1 unit max, 2
hr/day max)
(3) Alternative to monitoring priority pollutants
(e) Chemical metal cleaning wastes:
(f) -(k) (Not Applicable)
(1) Combustion residual (ash) leachate:
BAT Effluent Limits
Daily Max Mo. Average
(mg/L) (mg/L)
TSS 100.0 30.0
(m) Concentration limits allowed
(n) Combined wastestreams
* Contained in chemicals for cooling tower maintenance.
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
Page 11
BAT Effluent Limits
Daily Max Mo. Average
(mg/L) (mg/L)
Total Copper
1.0 1.0
Total Iron
1.0 1.0
(f) -(k) (Not Applicable)
(1) Combustion residual (ash) leachate:
BAT Effluent Limits
Daily Max Mo. Average
(mg/L) (mg/L)
TSS 100.0 30.0
(m) Concentration limits allowed
(n) Combined wastestreams
* Contained in chemicals for cooling tower maintenance.
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
Page 11

b. Ash Basin Remediation
Discharges from the ash pond during remediation will be subject to the Steam Electric ELGs
at least until completion of remediation:
Ash Pond Decanting/Dewatering - Outfalls 002/007:
• Low volume waste sources (legacy BSS & CTCC); and
• Coal pile runoff, ash transport waters, ash leachate (legacy BSS).
c. Ash Basin Constructed Seeps
Discharges from the constructed seeps will also be subject to the Steam Electric ELGs:
Ash Basin Constructed Seeps - Outfalls 111 & 117:
• Cooling tower blowdown (CTCC);
• Low volume waste sources (CTCC, legacy BSS @ powerhouse, ash ponds); and
• Coal pile runoff, ash transport waters, ash leachate (legacy BSS @ ponds).
d. Domestic Wastewater
Domestic wastewater is now directed to an on-site waste system permitted by Rowan
County and will no longer be subject to this NPDES permit.
2. WQBELs - Reasonable Potential Analysis (RPA)
Purpose and Methodology. The need for water quality -based effluent limits (WQBELs) was
evaluated for each discharge of process wastes, ash remediation waters, and ash basin seepage
using the Divisions Reasonable Potential Analysis (RPA) methodology. The RPA used here is a
statistical means of evaluating whether toxicants discharged by a facility have a reasonable
potential to cause an exceedance of water quality standards or EPA -recommended criteria in the
receiving stream. The Divisions methodology is approved by the U.S. EPA and is consistent
with the EPA's Technical Support Document for Water Quality -based Toxics Control, or "TSD".
The RPA evaluates actual effluent data for each waste discharge and estimates the maximum
concentration for each pollutant of concern that will not be exceeded in 95% of future samples,
with 95% confidence. It also calculates for each parameter the maximum allowable effluent
concentration, which is the highest discharge concentration that, at design discharge flow and
statistical low flows in the receiving stream, will not exceed the surface water quality standard
or criterion in the stream. If the maximum predicted effluent concentration of a pollutant is
greater than the maximum allowable concentration, the discharge is said to show a reasonable
potential to cause an exceedance of that standard or criterion. When that is the case, an effluent
limit is warranted and is included in the permit.
The Division compiled effluent data for discharges at the Buck site and conducted RPAs for each
toxicant of concern at each outfall. A minimum of 12 samples is preferred for RPAs. In most
cases, fewer than ten samples were available for the Buck discharges; often a single result. In
these cases, the RPA calculations conservatively account for the resulting uncertainties. Still,
additional monitoring is needed to support a more rigorous evaluation of the discharges' likely
impacts on water quality.
For the purposes of these RPAs, instream background concentrations for all toxicant parameters
were assumed to be below detection levels. Standards for hardness -dependent metals were
calculated assuming a default hardness value of 25 mg/L as CaCO3-
Flow Values. The following assumptions were used to set stream flow values for the RPAs.
Discharges to Yadkin River Mainstem. The mainstem of the Yadkin River adjacent to the
Buck site is generally riverine in nature and provides mixing and dilution to discharges. For
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
Page 12

permitting purposes, the Division used the stream flow values last developed by the USGS
to evaluate limits for these discharges.
Discharges to Yadkin River Side Channels. Outfall 002 discharges to a side cove of High
Rock Lake. Outfall 002 is located approximately 0.7 mile from the mainstem of the river.
While the mainstem is riverine, the cove does not reliably provide mixing or dilution for
discharges.
Discharges to Unnamed Tributaries. The constructed seeps designated as Outfalls 111 and
117 discharge to the same unnamed tributary, which then flows to the side channel along the
west side of the Buck site. It is assumed that these are zero -flow streams and provide no
dilution to the discharge.
Additional assumptions and results of the RPAs for each outfall and discharge are described
below. Detailed results of each RPA are attached to this Fact Sheet.
NOTE: A discharge may be subject to one or both types of limit for any given parameter of
concern. If the discharge is subject to both TBELs and WQBELs for a parameter, the more
stringent limit is applied in the permit. If water quality standards or criteria have been
established for the parameter, the TBEL is compared to the maximum allowable effluent
concentration, and the more stringent value is applied as a limit.
C. Results of RPAs
1. Outfall 002 - Initial BSS/CTCC Operations.
RPAs were conducted for the current discharge from the ash ponds, prior to closure of the BSS
Yard Sump and diversion of CTCC flows to the Yadkin River, and prior to the start of ash pond
decanting. The calculations were conducted with Jan 2012 to Jun 2016 DMR data for metals
monitored under the current permit (arsenic, copper, mercury, and selenium); and with results
from the one-time sampling required for permit renewal (Form 2C results): aluminum,
antimony, beryllium, boron, cadmium, total chromium, iron, lead, magnesium, manganese,
molybdenum, nickel, thallium, and zinc. The waste flow was 0.62 MGD, derived from the
application. Available dilution in the impounded cove was assumed to be zero, a significant
decrease from previous permits.
The results indicate that the discharge shows reasonable potential to cause an exceedance of one
or more standards for arsenic, antimony, trivalent chromium, hexavalent chromium, copper,
nickel and zinc and warrants monitoring for mercury and selenium (maximum predicted
concentration > 1/z maximum allowable concentration). Where acute standards have not been
adopted (antimony), the Daily Maximum limit is set equal to the Monthly Average.
2. Outfall 002 - Interim Outfall - CTCC.
RPAs were conducted using monitoring data for a single sampling event at the CTCC Plant
Sump, provided in Form 2C of the permit application. The parameters included aluminum,
antimony, boron, cadmium, total chromium, copper, fluoride, iron, lead, magnesium,
manganese, mercury, molybdenum, nickel, selenium, thallium, and zinc. While the RPA is
designed to account for the uncertainties of limited data, it will be necessary for Duke Energy to
more thoroughly characterize the discharge in the coming term of the permit. The discharge
flow rate was determined from component wastestream flows found in the application package
and supplemental materials.
The analysis indicates that the discharge shows reasonable potential to cause an exceedance of
one or more standards for aluminum, antimony, chloroform, trivalent chromium, hexavalent
chromium, copper, fluoride, nickel, and zinc. Where acute standards have not been adopted
(antimony, fluoride, chloroform), the Daily Maximum limit is set the same as the Monthly
Average.
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
Page 13

Duke Energy has indicated it does not use chloroform at the facility, and its detection could be
the result of lab contamination. Further analysis is required to verify its presence before a limit is
set.
3. Outfall 001A/ 006 - CTCC Operations.
RPAs were conducted for the discharge of process and sanitary wastes once those flows are
diverted to Outfalls 001A and then 006. The RPAs were based on results from the same sampling
event, reported in Duke Energy's permit application; a waste flow of 0.62 MGD, and a summer
7Q10 flow of 1,030 cfs. Parameters evaluated included aluminum, antimony, arsenic, beryllium,
cadmium, chloroform, total chromium, copper, fluoride, lead, magnesium, manganese, mercury,
nickel, selenium, and zinc.
The analysis indicates that the discharge does not show reasonable potential to violate acute or
chronic aquatic life standards in the river for the pollutants of concern.
Temperature limits and variance conditions from the previous permit are carried forward to
apply to CTCC discharges, once those flows are diverted from the ash ponds to the Yadkin
River.
4. Outfalls 002/007 - Ash Pond Decanting.
RPAs were conducted for the potential discharge from the ash ponds during the decanting
phase. These RPAs were conducted for aluminum, antimony, boron, cadmium, total chromium,
copper, fluoride, iron, lead, magnesium, manganese, molybdenum, nickel, selenium, thallium,
vanadium, and zinc. They used the results from samples of standing water ("free water')
collected from the ash basins on January 9, 2015; to introduce a margin of safety, the maximum
reported values from Cell 3 were used.
Discharge flow was based on estimated discharge from treatment units installed for this purpose
-1,200 gpm (1.728 MGD). The 7Q10 flow used for Outfall 002 (impounded waters) was zero;
and for Outfall 007, 1,030 cfs.
The analysis indicates reasonable potential for several parameters to exceed surface water
quality standards or EPA criteria at Outfall 002: total dissolved solids (TDS), arsenic, chlorides,
copper, antimony, lead, nickel, and selenium. Chromium warrants further monitoring.
The analysis indicates no reasonable potential to exceed surface water quality standards or EPA
criteria if the flow is diverted to Outfall 007.
5. Outfalls 002/007 - Ash Pond Dewatering,
RPAs were conducted for the potential discharge from the ash ponds during the dewatering
phase. These RPAs were conducted for aluminum, antimony, boron, cadmium, total chromium,
copper, fluoride, iron, lead, magnesium, manganese, molybdenum, nickel, selenium, thallium,
vanadium, and zinc. They used the results from samples of interstitial waters (those waters
within the ash deposits) collected from the ash basins on January 9, 2015; to introduce a margin
of safety, the maximum reported values from unfiltered samples were used.
Discharge flow was based on estimated discharge from treatment units installed for this purpose
- 500 gpm (0.72 MGD). The 7Q10 flow used for Outfall 002 (impounded waters) was zero; and
for Outfall 007, 1,030 cfs.
The analysis for Outfall 002 indicates reasonable potential for the same parameters as in the
decanting phase, with the addition of thallium. Again, chromium warrants further monitoring.
The analysis for Outfall 007 indicates no reasonable potential to exceed surface water quality
standards or EPA criteria.
6. Outfalls 111 and 117 - Ash Basin Constructed Seep Management
RPAs were conducted for flows from the constructed seeps using available data from sampling
conducted since 2013. The parameters evaluated in these RPAs were total dissolved solids,
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
Page 14

chlorides, aluminum, antimony, arsenic, boron, cadmium, total chromium, copper, iron, lead,
manganese, mercury, molybdenum, nickel, selenium, thallium, and zinc.
The maximum reported flows for seep S-11 were multiplied by a factor of 10 to account for
uncertainties in the flow rates. No flows had been recorded for seep S-17, so the S-11 flow was
used for those RPAs as well. For permitting purposes, the constructed seeps were assumed to
discharge to zero -flow waters.
The analyses indicate that Outfalls 111 and 117 both show reasonable potential for TDS, and
Outfall 117 also shows reasonable potential for aluminum.
D. WQBELs - Mercury Evaluations
Mercury levels in the process discharges and seepage flows were also evaluated in accordance with
the Divisions Permitting Guidelines for Statewide Mercury TMDL. According to the Guidelines, annual
average mercury concentrations are compared to the 12.0 ng/L water quality standard, and
maximum values are compared to a treatment performance standard of 47.0 ng/L. If either standard
is exceeded, it is applied as the corresponding effluent limitation in the permit: annual average or
daily maximum. The results for the Buck facility are as follows.
1. Process Outfall Evaluations
Outfall 002 - Initial BSS/CTCC Operations. Duke Energy monitors mercury at Outfall 002 on a
quarterly basis. Results from March 2012 through June 2016 are summarized in Table 3.
Table 3. Mercury Results — Outfall 002
YEAR
2012
2013
2014
2015
2016
Annual Average Concentration (ng/L)
0.58
0.59
0.81
0.71
2.3
Maximum Sampling Result (ng/L)
0.83
0.74
1.3
0.88
1.77
Number of Samples
4
4
5
4
3
With an IWC of 100%, the allowable mercury concentration for this outfall is equal to the surface
water quality standard of 12 ng/L. All annual average mercury concentrations are below the
allowable level, and all maximum sampling results are below the TBEL of 47.0 ng/L. Thus, per
the Guidelines, mercury limits are not warranted at this outfall.
Outfall 002 - Interim Outfall - CTCC. Duke Energy has only reported one sampling event at the
CTCC Plant Sump. Given an IWC of 100%, the allowable mercury concentration is again 12
ng/L. The one sample result, reported on the Form 2C in Duke Energy's permit application, was
13 ng/L, greater than the allowable level. Thus, a mercury limit is warranted at this outfall.
Outfall 001A/ 006 - CTCC. Duke Energy plans to divert the CTCC discharge to the Yadkin
River once the steam station is decommissioned. This will result in an IWC of 0.1 % and an
allowable mercury concentration 1,000 times greater than the standard. As a result, the mercury
limit for this discharge will no longer be warranted.
2. Ash Pond Decanting and Dewatering Outfall Evaluations
On January 9, 2015, Duke Energy sampled the free-standing and interstitial waters in its ash
basin system. The mercury results for each set of waters were evaluated as above; the maximum
values in each case were used in order to conservatively test the impacts that could result from
discharging these without treatment to the receiving water.
Outfall 002/ 007 (DecantingPhasel. The maximum value reported for the free-standing waters
was 6.96 ng/L. This is less than the allowable concentration of 12 ng/L. Thus, no mercury limit
is required.
Outfall 002/ 007 (Dewatering Phasel. The maximum value reported for the interstitial waters
was 6.7 ng/L. Again, this is less than the allowable concentration of 12 ng/L, and no mercury
limit is required.
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
Page 15

3. Ash Basin Constructed See -os Evaluation
From September 2014 to October 2017, Duke Energy sampled the constructed seeps
approximately four times each for an array of parameters, including mercury. The mercury
results were evaluated as above; and the maximum value was used as a conservative test.
The constructed seeps discharge to an unnamed tributary to the side channel of the lake on the
west side of the Buck site. The maximum reported value was 3.3 ng/L, and no mercury limit is
warranted for either discharge.
E. Toxicity Testing
Whole effluent toxicity monitoring and limits are established according to the Divisions long-
standing toxicity policy. The following is a summary of current and proposed toxicity requirements
for each outfall.
1. Outfall 002 (Initial BSS/CTCC Operations, Interim CTCC Operations)
Current: Chronic P/F @ 0.7% using Ceriodaphnia dubia; quarterly, during the months of March,
June, September, and December.
Recommended: Chronic P/F @ 90% using Ceriodaphnia dubia; quarterly, during the months of
March, June, September, and December; effective six months after the effective date of the
permit.
During the current permit cycle, the facility passed all (19 out of 19) toxicity tests at the 0.7%
waste concentration. In order to reflect the limited dilution available at this outfall and to
conform to the Divisions policy for discharges to impounded waters, the draft permit requires
the same quarterly Chronic P/F test using Ceriodaphnia dubia but at a waste concentration of
90%.
2. Outfall 001A/006 (CTCC Operations)
Current: None - new discharge.
Recommended: Chronic P/F @ 0.1% using Ceriodaphnia dubia; quarterly, during the months of
March, June, September, and December.
When the process and sanitary flows are diverted to the new outfall structures, the toxicity test
will change to reflect the dilution available at the new location(s). In other respects, the
requirement remains the same as at Outfall 002.
3. Outfall 002 (Decanting and Dewatering of Ash Ponds)
Current: None - new discharge.
Recommended: Chronic P/F @ 90% using Ceriodaphnia dubia; monthly test for both phases.
The same chronic test will be required during decanting and dewatering of the ash ponds.
Testing is required on a monthly basis due to the potential variability of the discharge
characteristics during the course of the remediation project.
4. Outfall 007 (Decanting and Dewatering of Ash Ponds)
Current: None - new discharge.
Recommended: Chronic P/F @ 0.3% (decant phase) and 0.1% (dewatering phase) using
Ceriodaphnia dubia; monthly test for both phases.
Testing will continue at a monthly frequency when and if the discharge is relocated to a new
Outfall 007at the river. The other requirements for the test are the same as those at Outfall 002.
5. Outfalls 111 and 117 (Constructed Seeps)
Current: None - newly permitted discharge.
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
Page 16

Recommended: The Division is not proposing toxicity limits or monitoring for the constructed
seeps at this time. The characteristics are generally similar to ash pond discharges, which already
have toxicity limits. The discharge is also less contaminated - and likely less toxic - than the
decanting/ dewatering discharges, which will receive toxicity limits. Thus, WET tests here
would be of little value.
F. Summary of Proposed Effluent Limitations and Monitoring Requirements
Part I of the permit is organized into four sections:
A. Steam Electric Operations
B. Ash Basin Remediation
C. Ash Basin Constructed Seeps Management
These sections are primarily effluent limits pages for the various outfalls and operating phases at the
facility.
The following tables summarize the proposed effluent limits and other requirements, as described
above, for each discharge and each phase of operations (Sections A. -B.). Then follows a brief
description of the special conditions in Section C.
F1. Steam Electric Operations (Section A of Permit).
1. Outfall 001- Once -Through Non -Contact Cooling Water.
This operation is no longer active, and the outfall is deleted from the permit. Thermal limits, the
316(a) temperature variance, and other relevant conditions are applied to process discharges at other
outfalls.
(go to next page)
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
Page 17

2. Outfall 002 - Initial BSS/CTCC Operations.
This condition will govern process discharges from the ash ponds until Duke re-routes those flows
to a new discharge at Outfall 001A or 006.
Effluent limitations and monitoring requirements are as follows:
PARAMETER
LIMITATIONS AND MONITORING
CHANGE
BASIS
Monthly
Average
Daily
Maximum
Frequency/
Type
Flow (MGD)
Weekly / Logs
None
15A NCAC 02B .0505
pH
>_ 6.0 and <_ 9.0 standard units
Weekly / Grab
None
40 CFR 423.12(b)(1)
Total Nitrogen, mg/L
Monthly / Grab
None
15A NCAC 02B .0508
Total Phosphorus, mg/L
Monthly / Grab
None
15A NCAC 02B .0508
Total Suspended Solids
23.0 mg/L
74.0 mg/L
Quarterly / Grab
None
40 CFR 423.12(b)(3)
Oil and Grease
11.0 mg/L
15.0 mg/L
Quarterly / Grab
None
40 CFR 423.12(b)(3)
Total Hardness, mg/L as CaCO3
Quarterly / Grab
New monitoring
Parameter of concern
Total Arsenic (ef.. [>6 mos.])
10.0 pg/L
340 pg/L
Quarterly / Grab
New limit
RPA, 15A NCAC 02B .0200
Total Selenium, pg/L
Quarterly / Grab
None
Parameter of concern
Total Mercury, ng/L
Quarterly / Grab
None
Parameter of concern
Total Antimony
(effective [>6 mos.])
5.6 pg/L
5.6 pg/L
Quarterly / Grab
New limit
RPA, 15A NCAC 02B .0200
Total Chromium, ug/L
200 pg/L
200 pg/L
Quarterly / Grab
New limit
40 CFR 423.13(d)
Trivalent Chromium
(effective [>6 mos.])
flu ,
905 pg/L
Quarterly / Calc'd
New limit
15A NCAC 02B .0200
Hexavalent Chromium
(effective [>6mos])
11.0 pg/L
16.0 pg/L
Quarterly /Grab
New limit
15A NCAC 02B .0200
Total Copper (eff. [>6 mos.])
7.9 pg/L
10.5 pg/L
Quarterly / Grab
New limit
15A NCAC 02B .0200
Total Nickel (eff. [>6 mos.])
25.0 lag/L
335 pg/L
Quarterly / Grab
New limit
RPA, 15A NCAC 02B .0200
Total Zinc (eff. [>6 mos.])
126 lag/L
126 pg/L
Quarterly / Grab
New limit
15A NCAC 02B .0200
Chronic Toxicity (1st 6 mos)
(effective [>6 mos])
P/F @ 0.7%
P/F @ 90%
Quarterly /Grab
None
New limit
15A NCAC 02B .0208
The 126 priority pollutants
except Total Chromium and
Total Zinc
No detectable amount
Annually / Grab
New limits
40 CFR 423.13(d)
* IWC means Instream Waste Concentration
Flow. Daily flows are determined weekly based on operating logs for the ash ponds.
pH. The instantaneous limit for pH is based on the Effluent Limitations Guidelines (ELGs) for
Steam Electric Power Generation facilities.
Nutrients. Nutrient monitoring is as required in 15A NCAC 02B.0508.
Oil & Grease, TSS. The ELGs include limits for Oil & Grease and TSS. The limits in this permit were
previously tightened to account for mixing of regulated and unregulated wastestreams. The flow
balance has changed since that time. Updating the adjustment could result in relaxed limits. The
facility has consistently met the limits, so the existing limits are continued.
The EPA has objected to the footnote in the existing permit allowing a net/gross adjustment to the
TSS limit, and the footnote has been deleted.
Hardness monitoring is necessary to determining applicable standards for hardness -dependent
metals.
Copper, Zinc. The ELGs set technology-based limits (TBELs) for total copper and total zinc at 1.0
mg/L Monthly Average and Daily Maximum. The discharge does not show reasonable potential to
exceed the dissolved metal water quality standards for either metal; however, discharging at the 1.0
Fact Sheet - NPDES Permit Renewal
Duke Energy - Buck Combined Cycle Station - NC0004774
Page 18

mg/L total metal limits could cause an exceedance in either case. Thus, the permit sets water
quality -based limits (WQBELs) for total copper and total zinc. (See Compliance Schedule, below.)
Iron. No requirements. The state no longer has an iron standard, and the ELG limits (1.0 mg/L)
apply only when metal cleaning wastes (none here) are discharged.
Chromium. The ELGs set limits for total chromium at 0.2 mg/L. The discharge does not show
reasonable potential to exceed either the previous surface water standard for total chromium or the
current standards for dissolved trivalent and hexavalent chromium (one data point, less than PQL).
However, as with copper and zinc, discharging at the TBEL concentrations (total metals) could cause
an exceedance of applicable dissolved metals standards in the receiving stream. Thus, the permit
includes TBELs for total chromium and WQBELs for hexavalent and trivalent chromium.
Selenium and Mercury do not show reasonable potential but are pollutants of concern and will
continue to be monitored to provide additional data for the next RPAs.
Arsenic, Antimony, and Nickel exhibit reasonable potential to cause exceedances of surface water
standards, and the maximum allowable effluent concentrations for each are applied as limits. If
there is no acute standard, the Daily Maximum limit is set equal to the Monthly Average limit. These
WQBELs become effective six months after the effective date of the permit
The 126 Priority Pollutants. The ELGs prohibit discharge of these pollutants except for chromium
and zinc, for which they set TBELs (see above). The regulations also provide that the monitoring
requirement can be waived at the Director's discretion if calculations demonstrate that the pollutants
will be at low enough concentrations so as to not be detected in the discharge. This condition
includes language to that effect.
Chronic Toxicity is limited and testing is required on a quarterly basis per the Division's whole
effluent toxicity protocol. The initial IWC will be 0.7%, as in the current permit; this will increase to
90% six months after the effective date of the permit to reflect the limited dilution in the cove.
Chlorine. Detention times in the ash ponds are relatively long and allow for dissipation of chlorine
prior to discharge. Therefore, neither ELG limits nor monitoring requirements for chlorine are
included in the permit.
Monitoring frequencies are similar to those in the current permit, which take into account the
detention times in the ash ponds; except that flow and pH monitoring is increased to weekly to be
more consistent with minimum frequencies at other NPDES facilities.
Compliance Schedule -Metals and Chronic Toxicity.
The permit allows Duke Energy six months to comply with the new limits for metals and chronic
toxicity (or to divert flows to the river via Outfall 001A or 006). For those metals with applicable
TBELs, the TBELs will apply for the first six months of the permit term and replaced by the WQBELs
beginning with the seventh month.
Additional Provisions.
• Authorized waste flows are specified, and it is noted that, per NCGS § 130A -309.210(c), the
discharge of stormwater from the facilities to the ash ponds on or after December 31, 2018, is
prohibited.
• The discharge of metal cleaning wastes is prohibited as is the discharge of floating solids or
visible foam in other than trace amounts.
• The Permittee must notify the Division prior to eliminating the BSS waste flows, a change that
triggers new effluent limitations and monitoring requirements for the discharge.
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
Page 19

3. 0utfall 002 - CTCC Operations.
This condition will govern process discharges from the ash ponds after Duke has eliminated waste
flows from the Steam Station and until it re-routes the CTCC plant flows to either Outfall 001A or
0utfall 006.
Upon elimination of the BSS flows, effluent limitations and monitoring requirements are as follows:
PARAMETER
LIMITATIONS AND MONITORING
Monthly Daily Frequency/
Average Maximum Type
CHANGE
BASIS
Flow (MGD)
Weekly / Logs
None
15A NCAC 02B .0505
pH
>_ 6.0 and 5 9.0 standard units
Weekly / Grab
None
40 CFR 423.12(b)(1)
Total Nitrogen, mg/L
Monthly / Grab
None
15A NCAC 02B .0508
Total Phosphorus, mg/L
Monthly / Grab
None
15A NCAC 02B .0508
Total Suspended Solids
23.0 mg/L
74.0 mg/L
Monthly / Grab
None
40 CFR 423.12(b)(3)
Oil and Grease
11.0 mg/L
15.0 mg/L
Monthly / Grab
None
40 CFR 423.12(b)(3)
Total Hardness, mg/L as CaCO3
Monthly / Grab
New monitoring
Parameter of concern
Total Arsenic, lag/L
Monthly / Grab
None
RPA, 15A NCAC 02B .0200
Total Selenium, lag/L
Monthly / Grab
None
RPA, 15A NCAC 02B .0200
Total Mercury (eff. [>6 mos.])
12.0 ng/L (annual average) 4
Monthly / Grab
None
Hg Evaluation
Total Aluminum (>6 mos.)
6.5 mg/L
6.5 mg/L
Monthly / Grab
New limit
RPA, 15A NCAC 02B .0200
Total Antimony (>6 mos.)
5.6 lag/L
5.6 lag/L
Monthly / Grab
New limit
RPA, 15A NCAC 02B .0200
Total Chromium
200 lag/L
200 lag/L
Monthly / Grab
New limit
40 CFR 423.13(d)
Trivalent Chromium
(effective [>6 mos.])
118 lag/L
905 lag/L
Monthly / Calc'd
New limit
15A NCAC 02B .0200
Hexavalent Chromium (effective
[>6 mos.])
11.0 lag/L
16.0 lag/L
Monthly / Grab
New limit
15A NCAC 02B .0200
Total Copper (eff. [>6mos])
7.9 lag/L
10.5 lag/L
Quarterly / Grab
New limit
15A NCAC 02B .0200
Total Nickel (>6mos)
25.0 lag/L
335 lag/L
Monthly / Grab
New limit
RPA, 15A NCAC 02B .0200
Total Zinc (eff. [>6mos.])
126 lag/L
126 lag/L
Quarterly / Grab
New limit
15A NCAC 02B .0200
Total Fluoride (>6mos.)
1.8 mg/L
1.8 mg/L
Monthly / Grab
New limit
RPA, 15A NCAC 02B .0200
Chloroform, lag/L
Quarterly / Grab
New monitoring
RPA, 02B .0200**
Chronic Toxicity (1st6mos)
(effective[>6mos J)
P/F @ 0.7%
P/F @ 90%
Quarterly /Grab
None
New limit
15A NCAC 02B .0200
The 126 priority pollutants
except Total Chromium and
Total Zinc
No detectable amount
Annually / Grab
New limits
40 CFR 423.13(d)
* IWC means Instream Waste Concentration
** Maximum predicted concentration > 1/2 Maximum allowable concentration
The final permit will specify the expiration and effective dates for these limits.
Limits were evaluated based on a single sample whose results were reported in a Form 2C in the
permit application. Most requirements are similar to or the same as those for the initial 0utfall 002
effluent page, above. Key differences are as follows:
Arsenic shows no reasonable potential. It remains a parameter of concern, and monitoring is
required.
Copper, Hexavalent Chromium, Aluminum, Antimony, Nickel, Zinc, and Fluoride. The discharge
shows reasonable potential for these parameters, and WQBELs are included in the permit. See
Compliance Schedule, below.
Mercury. The only sample was analyzed for mercury and, because it exceeded the 12.0 ng/L
standard (13.0 ng/L), an annual limit is applied.
Fact Sheet - NPDES Permit Renewal
Duke Energy - Buck Combined Cycle Station - NC0004774
Page 20

Chloroform was detected in this sample, but the result is unexpected and the source is unknown.
The permit requires additional monitoring to check for its presence; if the initial analysis is less than
the PQL (non -detect), monitoring is waived for the duration of the permit term.
Compliance Schedule - Metals and Chronic Toxicity. The permit allows Duke Energy six months
from the effective date of the permit to comply with the new limits for metals and chronic toxicity
(or to divert flows to the river via Outfall 001A or 006). In the meantime, the existing limits apply.
This is a continuation, not an extension, of the six month compliance period in Condition A.(1.).
Monitoring. Monitoring frequencies for most parameters are increased to monthly due to the
addition of new WQBELs. This increase also applies to parameters that have been monitored less
frequently because of the long holding times in the ash ponds.
Additional Provisions.
• Authorized waste flows are specified, and it is again noted that, per NCGS § 130A -309.210(c), the
discharge of stormwater from the facilities to the ash ponds on or after December 31, 2018, is
prohibited.
• Given the limited characterization of this discharge, the Permittee must sample at least once
more and submit a completed Form 2C application with the results within 180 days in order to
identify or verify the parameters of concern.
• Regular monitoring of this particular combination of waste flows will provide additional data
for future RPAs for key parameters. Monitoring frequencies for most of the limited parameters
are increased to monthly.
• The Permittee must notify the Division prior to diverting the sump discharge to Outfall 001A or
006, in order to trigger new effluent limitations and monitoring requirements for the discharge.
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
Page 21

4. Outfall 001A - CTCC Operations.
This condition will govern the discharge of CTCC plant flows to Outfall 001A.
Effluent limitations and monitoring requirements are as follows:
PARAMETER
LIMITATIONS AND MONITORING
Monthly Daily Frequency/ Type
Average Maximum
CHANGE
BASIS
Flow (MGD)
Daily / Logs
New
15A NCAC 02B .0505
pH
>_ 6.0 and :5 9.0 standard units
Daily / Grab
New
40 CFR 423.12(b)(1)
Temperature (Effluent)
35°C (95°F)
Daily / Grab
New
15A NCAC 02B .0200
Temperature Rise (Effl — Intake)
Daily / Grab
New
15A NCAC 02B .0208
Total Nitrogen, mg/L
Monthly / Grab
New
15A NCAC 02B .0500
Total Phosphorus, mg/L
Monthly / Grab
New
15A NCAC 02B .0500
Total Suspended Solids
23.0 mg/L
74.0 mg/L
2/Month / Grab
New
40 CFR 423.12(b)(3)
Oil and Grease
11.0 mg/L
15.0 mg/L
2/Month / Grab
New
40 CFR 423.12(b)(3)
Total Residual Chlorine
28.0 pg/L
2/Month / Grab
New
40 CFR 423.12(b)(3)
Free Available Chlorine
200 pg/L
500 pg/L
2/Month / Grab
New
40 CFR 423.13(d)(1)
Total Hardness, mg/L as CaCO3
2/Month / Grab
New
Parameter of concern
Total Arsenic
Quarterly / Grab
New
POC — No RP**
Total Selenium, pg/L
Quarterly / Grab
New
POC — No RP**
Total Mercury, ng/L
Quarterly / Grab
New
POC — No RP**
Total Aluminum
Quarterly / Grab
New
POC — No RP**
Total Antimony
Quarterly / Grab
New
POC — No RP**
Total Chromium
200 pg/L
200 pg/L
2/Month / Grab
None
40 CFR 423.13(d)
Total Copper
Quarterly / Grab
New
40 CFR 423.13(e)
Total Nickel
Quarterly / Grab
New
POC — No RP**
Total Zinc
1,000 pg/L
1,000 pg/L
2/Month / Grab
None
15A NCAC 02B .0200
Total Fluoride
Quarterly / Grab
New
POC — No RP**
Chloroform, pg/L
Quarterly / Grab
New
POC — No RP**
Chronic Toxicity
P/F at 0.1% IWC*
Quarterly / Grab
New
15A NCAC 02B .0200
The 126 priority pollutants
except CrT and ZnT
No detectable amount
Annually / Grab
New
40 CFR 423.13(d)
* IWC means Instream Waste Concentration
** Parameter of concern, did not show reasonable potential bases on limited data set.
Most requirements are similar to or the same as those for the initial and interim Outfall 002 effluent
pages, above. Differences are described below:
Temperature. This condition includes the same 35°C effluent limit and temperature rise limits as
before and, in paragraphs below the limits table, other provisions of the thermal variance.
With retirement of the BSS coal-fired units, heated discharges are less than 1% of past flows and
thermal loads. It is not clear that a variance or mixing zone is needed any longer. Duke Energy has
requested continuation of its 316(a) temperature variance for this permit cycle so that it can evaluate
the need. A special condition in Section C of the permit provides that, if Duke Energy plans to
request continuation of the variance in the next cycle, it must perform a thermal mixing study to
justify the variance and determine the extent of the thermal mixing zone.
Copper, Chromium, Zinc, Oil & Grease, TSS, and pH. Limits are based on the ELGs. None of the
metals exhibited reasonable potential. Included option for reducing pH frequency if first 3 months'
results indicate lower frequency will adequately characterize the discharge.
Other Metals, Fluoride. These parameters are not subject to ELGs and, due to the greater dilution in
the river, none exhibited reasonable potential. Thus, no water quality -based limits are warranted.
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
Page 22

Chlorine. TBELs for free available chlorine are included per the ELGs. A WQBEL of 28.0 pg/L for
total residual chlorine is included, along with the standard footnote regarding the 50 pg/ L
compliance threshold.
Chloroform. In case the chloroform sample from the previous condition has not been collected when
this condition takes effect, the condition and the original compliance date are carried forward.
Monitoring. Direct discharge to the river (rather than to the ash ponds) warrants more frequent
monitoring for most parameters, even though the IWC is greatly reduced. The Permittee can request
reduced frequencies when sufficient data indicate a consistently high level of compliance with the
new limits.
Additional Provisions.
• The permit requires a new pollutant scan and Form 2C application within 180 days of
discharge at the new outfall, unless a scan has already been performed to satisfy the
previous conditions.
• Concurrent discharge from 001A and 006 is only allowed to the extent necessary to bring the
new outfall online.
Duke Energy must notify the Division prior to diverting the sump discharge to a new Outfall
006.
5. Outfall 006 - CTCC Operations.
Requirements for Outfall 006 are the same as for Outfall 001A. Both discharge to the same receiving
stream and have the same low IWC.
6. Outfall 002A - Emergency Yard Sump Overflow.
Effluent limitations and monitoring requirements are as follows:
PARAMETER
LIMITATIONS AND MONITORING
CHANGE BASIS
Monthly
Average
Daily Frequency/ Type
Maximum
Flow (MGD)
Episodic / Estimate
None 15A NCAC 0213 .0505
pH
>_ 6.0 and <- 9.0 standard units Episodic / Grab
None 40 CFR 423.12(b)(1)
Total Suspended Solids, mg/L
Episodic / Grab
None Parameter of concern
Monitoring is required if overflow event exceeds one hour in duration.
Fecal coliform has been removed, since domestic wastes now go to a permitted septic tank system.
This discharge will be eliminated with the removal of the Yard Sump, as soon as 2018.
7. Intake Screen Backwash.
The existing special condition is incorrect (or at least misleading) in saying that the discharge "is
permitted without limitations or monitoring requirements." The language is modified to be clearly
consistent with the rule language.
8. Internal Outfall 008 - Beneficiation Plant.
The Coal Ash Beneficiation Plant is under design at this writing. Analyses of wastes from a similar
site were provided but do not necessarily represent the wastes to be generated at the Buck site.
Wastes are expected to be limited to truck wash waters. Flows are estimated at less than 5,000 gpd
and could be zero if the system operates as a closed loop. The aim of this condition is get a measure
Fact Sheet - NPDES Permit Renewal
Duke Energy - Buck Combined Cycle Station - NC0004774
Page 23

of the actual flow and characteristics of the wastestream once the plant is operational. The parameter
list includes typical parameters of concern at other coal ash -related outfalls at the facility.
Monitoring requirements are as follows:
PARAMETER
LIMITATIONS AND MONITORING
Monthly Daily Frequency/
Average Maximum Type
CHANGE
BASIS
Flow, MGD
Daily/ Estimate
(first year)
New monitoring
15A NCAC 02B .0505
pH
Once/ Grab
New monitoring
15A NCAC 02B .0505
Total Suspended Solids
Once/ Grab
New monitoring
15A NCAC 02B .0505
Oil and Grease
Once/ Grab
New monitoring
15A NCAC 02B .0505
Total Dissolved Solids, mg/L
Once/ Grab
New monitoring
15A NCAC 02B .0505
Chlorides, mg/L
Once/ Grab
New monitoring
15A NCAC 02B .0505
Fluoride, mg/L
Once/ Grab
New monitoring
15A NCAC 02B .0505
Nitrate/nitrite as N, mg/L
Once/ Grab
New monitoring
15A NCAC 02B .0505
Sulfates, mg/L
Once/ Grab
New monitoring
15A NCAC 02B .0505
Total Hardness, mg/L as CaCO3
Once/ Grab
New monitoring
15A NCAC 02B .0505
Total Arsenic, lag/L3
Once/ Grab
New monitoring
15A NCAC 02B .0505
Total Selenium, pg/L3
Once/ Grab
New monitoring
15A NCAC 02B .0505
Total Copper
Once/ Grab
New monitoring
15A NCAC 02B .0505
Total Lead, mg/L3
Once/ Grab
New monitoring
15A NCAC 02B .0505
Total Nickel, lag/L 3
Once/ Grab
New monitoring
15A NCAC 0213.0
Total Thallium, lag/L3
Once/ Grab
New monitoring
15A NCAC 02B .0505
Total Zinc, mg/L3
Once/ Grab
New monitoring
15A NCAC 02B .0505
Additional Provisions.
• The Permittee is required to notify the Division of the plant's startup.
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
Page 24

Section B. Ash Basin Remediation, Constructed Seeps
1. Outfall 002 - Ash Pond Decanting.
Effluent limitations and monitoring requirements are as follows:
PARAMETER
LIMITATIONS AND MONITORING
Monthly Daily Frequency/ Type
Average Maximum
CHANGE
BASIS
Flow (MGD)
Weekly / Logs
New
15A NCAC 02B .0505
pH
>_ 6.0 and 5 9.0 standard units
Weekly / Grab
New
40 CFR 423.12(b)(1)
Total Nitrogen, mg/L
Monthly / Grab
New
15A NCAC 02B .0500
Total Phosphorus, mg/L
Monthly / Grab
New
15A NCAC 02B .0500
Total Suspended Solids, mg/L
23.0 mg/L
74.0 mg/L
Monthly / Grab
New
40 CFR 423.12(b)(3)
Oil and Grease
11.0 mg/L
15.0 mg/L
Monthly / Grab
New
40 CFR 423.12(b)(3)
Total Dissolved Solids
500 mg/L
500 mg/L
Monthly / Grab
New
RPA, 15A NCAC 02B .0200
Turbidity, NTU
Monthly / Grab
New
15A NCAC 02B .0200
Chlorides
250 mg/L
250 mg/L
Monthly / Grab
New
RPA
Total Hardness, mg/L as CaCO3
Monthly / Grab
New
Parameter of concern
Total Arsenic
10.0 lag/L
340 pg/L
Weekly / Grab
New
RPA, 15A NCAC 02B .0200
Total Selenium
5.0 pg/L
56.0 pg/L
Weekly / Grab
New
RPA, 15A NCAC 02B .0200
Total Mercury, ng/L
Weekly / Grab
New
TMDL
Total Antimony
5.6 lag/L
5.6 pg/L
Monthly / Grab
New
RPA, 15A NCAC 02B .0200
Total Chromium, ug/L
Monthly / Grab
New
POC - No RP**
Hexavalent Chromium, ug/L
Monthly / Grab
New
POC - No RP**
Trivalent Chromium, ug/L
Monthly / Grab
New
POC - No RP**
Total Copper
7.9 lag/L
10.5 lag/L
Monthly / Grab
New
RPA, 40 CFR 423.13(e)
Total Lead
2.9 lag/L
75.0 lag/L
Monthly / Grab
New
RPA, 15A NCAC 02B .0200
Total Nickel
25.0 lag/L
335 lag/L
Monthly / Grab
New
RPA, 15A NCAC 02B .0200
Total Thallium, lag/L
Monthly / Grab
New
POC - No RP
Chronic Toxicity
P/F at 90% IWC*
Quarterly / Grab
New
15A NCAC 02B .0200
* IWC means Instream Waste Concentration
** Parameter of concern; did not show reasonable potential but max predicted concentration > 1/2 max allowable concentration.
Effluent limitations are a combination of TBELs and WQBELs, as described in a previous section.
Parameters of concern were identified based on applicable ELGs or waste characterization of the ash
pond waters.
Flow. Average daily flows are determined weekly based on operating logs for the ash ponds.
pH. The instantaneous limit for pH is based on the Effluent Limitations Guidelines (ELGs) and
surface water quality standard.
Oil & Grease, TSS. The limits at Outfall 002 for process discharges are retained for the pond
remediation efforts.
Copper, Arsenic, Selenium, Antimony, Lead, Nickel, Chlorides, and TDS exhibit reasonable
potential, and the permit includes limits for each. If there is no acute standard, the Monthly Average
limit value is applied to the Daily Maximum limit as well. Limits can be either TBELs or WQBELs,
whichever is more stringent for a particular parameter.
Iron. The ELGs set limits for iron at 1.0 mg/L. The state no longer has an iron standard, so the ELG
limits apply.
Total Chromium was detected in the ash pond free water. The results do not require a limit but do
warrant additional monitoring to determine whether hexavalent or trivalent chromium are
parameters of interest.
Mercury and Thallium are parameters of interest and will be monitored.
Fact Sheet - NPDES Permit Renewal
Duke Energy - Buck Combined Cycle Station - NC0004774
Page 25

Monitoring frequencies for all parameters except flow and pH are set at monthly for decant
discharges; flow and pH are set at weekly.
Nutrient monitoring is as required in 15A 02B .0508.
Hardness monitoring is necessary for determining applicable standards for hardness -dependent
metals.
Additional Provisions.
• The permit does not include a limit for discharge flow. However, the level of water in the
ash pond shall not be lowered more than 1 foot per week without prior approval of the DEQ
Dam Safety Program (DEMLR).
• The condition specifies use of a floating suction pump pipe for decanting, per EPA.
• When the water level is less than three feet above the ash, these decanting requirements end,
and dewatering requirements become effective. (Though not specifically stated here, the
Division has said that the facility cannot return to these decanting requirements once
dewatering begins.)
• Continuous pH and TSS monitoring is required when decanting is performed, with
automatic shutdown if average TSS exceeds half of Daily Maximum limit or if the 15 -minute
composite pH is outside the range of 6.1-8.9 s.u.
• The discharge is not allowed to exceed the 25 NTU surface water standard (for lakes and
reservoirs not designated as Trout waters, 15A NCAC 02B .0211(3)(k)) nor cause an increase
in turbidity in the river.
• The discharge of floating solids or visible foam in other than trace amounts is prohibited.
• The Permittee must notify the Division prior to commencement of ash dewatering or
diversion of ash pond discharges to the proposed Outfall 007.
• The Permittee must cease discharge and notify the Division if the monthly average As, Se,
Hg, Sb, Cu, Pb, Ni, or Tl discharge reaches 85% of the maximum allowable effluent
concentration (from the RPAs).
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
Page 26

2. Outfall 002 - Ash Pond Dewatering.
Effluent limitations and monitoring requirements are as follows:
PARAMETER
LIMITATIONS AND MONITORING
Monthly Daily
Average Maximum Frequency/ Type
CHANGE
BASIS
Flow (MGD)
Daily / Grab
New
15A NCAC 02B .0505
pH
>_ 6.0 and 5 9.0 standard units
Daily / Grab
New
40 CFR 423.12(b)(1)
Total Nitrogen, mg/L
Weekly / Grab
New
15A NCAC 02B .0500
Total Phosphorus, mg/L
Weekly / Grab
New
15A NCAC 02B .0500
Total Suspended Solids, mg/L
23.0 mg/L
74.0 mg /L
Weekly / Grab
New
40 CFR 423.12(b)(3)
Oil and Grease
11.0 mg/L
15.0 mg /L
Weekly / Grab
New
40 CFR 423.12(b)(3)
Total Dissolved Solids
500 mg/L
500 mg /L
Weekly / Grab
New
RPA, 15A NCAC 02B .0200
Turbidity, NTU
Weekly / Grab
New
15A NCAC 02B .0200
Chlorides
250 mg/L
250 mg /L
Weekly / Grab
New
RPA, 15A NCAC 02B .0200
Total Hardness, mg/L as CaCO3
Weekly / Grab
New
Parameter of concern
Total Arsenic
10.0 pg/L
340 pg /L
Weekly / Grab
New
RPA, 15A NCAC 02B .0200
Total Selenium
5.0 pg/L
56 pg /L
Weekly / Grab
New
RPA, 15A NCAC 02B .0200
Total Mercury, ng/L
Weekly / Grab
New
TMDL
Total Antimony
5.6 lag/L
5.6 lag /L
Weekly / Grab
New
RPA, 15A NCAC 02B .0200
Total Chromium, ug/L
Weekly / Grab
New
POC - No RP**
Hexavalent Chromium, ug/L
Weekly / Grab
New
POC - No RP**
Trivalent Chromium, ug/L
Weekly / Grab
New
POC - No RP**
Total Copper
7.9 lag/L
10.5 lag /L
Weekly / Grab
New
RPA, 40 CFR 423.13(e)
Total Lead
2.9 lag/L
75 lag /L
Weekly / Grab
New
RPA, 15A NCAC 02B .0200
Total Nickel
25 lag/L
335 lag /L
Weekly / Grab
New
RPA, 15A NCAC 02B .0200
Total Thallium, lag/L
0.4 lag/L
0.4 lag /L
Weekly / Grab
New
RPA, 15A NCAC 02B .0200
Chronic Toxicity
P/F at 90% IWC*
Monthly / Grab
New
15A NCAC 02B .0200
* IWC means Instream Waste Concentration
** Parameter of concern; did not show reasonable potential but max predicted concentration > 1/2 max allowable concentration.
Requirements for dewatering operations are the same as or similar to those for decanting, with the
following exceptions:
Thallium exhibits reasonable potential, and limits are included in the permit.
Monitoring frequency for all parameters is increased from monthly to weekly.
Additional Provisions.
• Once dewatering begins, the ash basin remediation remains subject to those requirements
and cannot revert to the decanting requirements.
• The Permittee must notify the Division prior to diversion of ash pond discharges to the
proposed Outfall 007.
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Duke Energy - Buck Combined Cycle Station - NC0004774
Page 27

3. Outfall 007 - Ash Pond Decanting.
Effluent limitations and monitoring requirements are as follows:
PARAMETER
LIMITATIONS AND MONITORING
Monthly Daily
Average Maximum Frequency/ Type
CHANGE
BASIS
Flow
1.73 MGD
Weekly / Logs
New
15A NCAC 02B .0505
pH
>_ 6.0 and 5 9.0 standard units
Weekly / Grab
New
40 CFR 423.12(b)(1)
Total Nitrogen, mg/L
Monthly / Grab
New
15A NCAC 02B .0500
Total Phosphorus, mg/L
Monthly / Grab
New
15A NCAC 02B .0500
Total Suspended Solids, mg/L
23.0 mg/L 74.0 mg /L
Monthly / Grab
New
40 CFR 423.12(b)(3)
Oil and Grease
11.0 mg/L 15.0 mg /L
Monthly / Grab
New
40 CFR 423.12(b)(3)
Total Dissolved Solids, mg/L
Monthly / Grab
New
POC — No RP**
Turbidity, NTU
Monthly / Grab
New
Parameter of concern
Chlorides, mg/L
Monthly / Grab
New
POC — No RP**
Total Hardness, mg/L as CaCO3
Monthly / Grab
New
Parameter of concern
Total Arsenic
Weekly / Grab
New
POC — No RP**
Total Selenium
Weekly / Grab
New
POC — No RP**
Total Mercury, ng/L
Weekly / Grab
New
TMDL
Total Antimony, lag/L
Monthly / Grab
New
POC — No RP**
Total Chromium, ug/L
Monthly / Grab
New
POC — No RP**
Total Copper, lag/L
Monthly / Grab
New
POC — No RP**
Total Lead, lag/L
Monthly / Grab
New
POC — No RP**
Total Nickel, lag/L
Monthly / Grab
New
POC — No RP**
Total Thallium, lag/L
Monthly / Grab
New
POC — No RP**
Chronic Toxicity
P/F at 0.3% IWC*
Quarterly / Grab
New
15A NCAC 02B .0200
* IWC means Instream Waste Concentration
** Parameter of concern, did not show reasonable potential.
Requirements for discharges of decanting wastes at Outfall 007 are the same as at Outfall 002 with
the following exceptions:
Flow. The flow limit is based on the 1,200 gpm design pumping rate provided by Duke.
Limits. Available dilution increases dramatically at the new outfall; thus, all limits applied to this
discharge, with the exception of chronic toxicity, are TBELs.
Additional Provisions.
• This condition is not intended to authorize concurrent discharge from Outfalls 002 and 007
except to the extent necessary to bring the new outfall online.
• Once dewatering begins, the ash basin remediation remains subject to those requirements
and cannot revert to the decanting requirements.
• As in Outfall 002 requirements for decanting, the Permittee must cease discharge and notify
the Division if the monthly average As, Se, Hg, Sb, Cu, Pb, Ni, or Tl discharge reaches 85% of
the maximum allowable effluent concentration (from the RPAs).
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Duke Energy — Buck Combined Cycle Station — NC0004774
Page 28

4. Outfall 007 - Ash Pond Dewatering.
Effluent limitations and monitoring requirements are as follows:
PARAMETER
LIMITATIONS AND MONITORING
Monthly Daily Frequency/ Type
Average Maximum
CHANGE
BASIS
Flow
0.72 MGD
Daily / Grab
New
15A NCAC 02B .0505
pH
>_ 6.0 and <- 9.0 standard units
Daily / Grab
New
40 CFR 423.12(b)(1)
Total Nitrogen, mg/L
Weekly / Grab
New
15A NCAC 02B .0500
Total Phosphorus, mg/L
Weekly / Grab
New
15A NCAC 02B .0500
Total Suspended Solids, mg/L
23.0 mg/L 74.0 mg /L
Weekly / Grab
New
40 CFR 423.12(b)(3)
Oil and Grease
11.0 mg/L 15.0 mg /L
Weekly / Grab
New
40 CFR 423.12(b)(3)
Total Dissolved Solids, mg/L
Weekly / Grab
New
POC - No RP**
Turbidity, NTU
Weekly / Grab
New
Parameter of concern
Chlorides, mg/L
Weekly / Grab
New
POC - No RP**
Total Hardness, mg/L as CaCO3
Weekly / Grab
New
Parameter of concern
Total Arsenic
Weekly / Grab
New
POC - No RP**
Total Selenium
Weekly / Grab
New
POC - No RP**
Total Mercury, ng/L
Weekly / Grab
New
TMDL
Total Antimony, lag/L
Weekly / Grab
New
POC - No RP**
Total Chromium, ug/L
Weekly / Grab
New
POC - No RP**
Total Copper, lag/L
Weekly / Grab
New
POC - No RP**
Total Lead, lag/L
Weekly / Grab
New
POC - No RP**
Total Nickel, lag/L
Weekly / Grab
New
POC - No RP**
Total Thallium, lag/L
Weekly / Grab
New
POC - No RP**
Chronic Toxicity
P/F at 0.1% IWC*
Monthly / Grab
New
15A NCAC 02B .0200
* IWC means Instream Waste Concentration
** Parameter of concern, did not show reasonable potential.
As with Outfall 007 -Decanting, all limits applied to this discharge, with the exception of chronic
toxicity, are TBELs.
Flow. The flow limit is based on the 500 gpm design pumping rate provided by Duke.
Additional provisions applicable to this discharge are similar to or the same as those for Outfall 002 -
Dewatering or Outfall 007 -Decanting.
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Duke Energy - Buck Combined Cycle Station - NC0004774
Page 29

5. Outfalls 111 & 117 - Ash Pond Constructed
Parameters of concern and monitoring requirements for the constructed seep discharges are as
agreed upon by EPA Region 4, Duke Energy, and DEQ, based on characterization of seeps collected
from Duke Energy's 14 North Carolina coal ash facilities. Effluent limitations are a combination of
TBELs and WQBELs, as described in previous sections.
Effluent limitations and monitoring requirements for Outfalls 111 and 117 are as follows:
PARAMETER
LIMITATIONS AND MONITORING
Monthly Daily Frequency/ Type
Average Maximum
CHANGE
BASIS
Flow (MGD)
1/Mo-1/Qtr /
Estimate
New
15A NCAC 02B .0505
pH
>_ 6.0 and :5 9.0 standard units
1/Mo-1/Qtr / Grab
New
40 CFR 423.12(b)(1)
Temperature, °C
1/Mo-1/Qtr / Grab
New
Parameter of concern
Total Suspended Solids, mg/L
30.0 mg/L 100.0 mg/L
1/Mo-1/Qtr / Grab
New
40 CFR 423.12(b)(3)
Oil and Grease
15.0 mg/L 20.0 mg/L
1/Mo-1/Qtr / Grab
New
40 CFR 423.12(b)(3)
Total Dissolved Solids, mg/L
1/Mo-1/Qtr / Grab
New
POC — No RP*
Conductivity, pmho/cm
1/Mo-1/Qtr / Grab
New
Parameter of concern
Chlorides, mg/L
1/Mo-1/Qtr / Grab
New
Parameter of concern
Fluoride, mg/L
1/Mo-1/Qtr / Grab
New
Parameter of concern
Nitrate/nitrite as N, mg/L
1/Mo-1/Qtr / Grab
New
Parameter of concern
Sulfates, mg/L
1/Mo-1/Qtr / Grab
New
Parameter of concern
Total Hardness, mg/L as CaCO3
1/Mo-1/Qtr / Grab
New
Parameter of concern
Total Arsenic
1/Mo-1/Qtr / Grab
New
POC — No RP*
Total Selenium
1/Mo-1/Qtr / Grab
New
POC — No RP*
Total Mercury, ng/L
1/Mo-1/Qtr / Grab
New
TMDL
Total Aluminum (117 on/y)
6.5 mg/L 6.5 mg/L
1/Mo-1/Qtr / Grab
New
RPA, 15A NCAC 02B .0200
Total Barium, mg/L
1/Mo-1/Qtr / Grab
New
POC — No RP*
Total Cadmium, lag/L
1/Mo-1/Qtr / Grab
New
POC — No RP*
Total Chromium, lag/L
1/Mo-1/Qtr / Grab
New
POC — No RP*
Total Copper
1/Mo-1/Qtr / Grab
New
POC — No RP*
Total Lead, lag/L
1/Mo-1/Qtr / Grab
New
POC — No RP*
Total Manganese, mg/L
1/Mo-1/Qtr / Grab
New
POC — No RP*
Total Nickel, lag/L
1/Mo-1/Qtr / Grab
New
POC — No RP*
Total Thallium, lag/L
1/Mo-1/Qtr / Grab
New
POC — No RP*
Total Zinc, lag/L
1/Mo-1/Qtr / Grab
New
POC — No RP*
* Parameter of concern; did not show reasonable potential but max predicted concentration > 1/2 max allowable concentration.
Flow. Daily flows are to be estimated using appropriate methods.
pH, Oil & Grease, TSS, Coj2per, and Iron. The limits for these parameters are based on the ELGs.
Other Metals. The discharge does not exhibit reasonable potential for the remaining metals. Because
these remain parameters of concern, the permit requires regular monitoring for those listed.
Monitoringfor or all parameters will be conducted on a monthly basis for the first year and quarterly
thereafter.
G. RATIONALE FOR OTHER SPECIAL CONDITIONS
The following is a summary of changes (or lack thereof) made to the special conditions found in
Section C. Most are the result of on-going negotiations regarding the management and disposal of
coal ash at Duke Energy's facilities in North Carolina.
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1. Special Conditions Retained
These existing special conditions remain in the permit with minimal changes. Some have been
combined with other conditions by topic but are listed separately here:
Chemical Discharges (combined with similar)
Best Management Practices Plan (combined with Chemical Discharges condition)
Polychlorinated Biphenyl Compounds (combined with Chemical Discharges condition)
Metal Cleaning Waste (combined with Chemical Discharges condition)
Biocide Condition
Intake Screen Backwash (relocated to Section A, with revisions)
Floating Materials (relocated to Discharges of Other Materials)
Waivers
Ash Pond Closure (combined with Ash Pond Operations condition)
Ash Pond (Capacity) (combined with Ash Pond Operations condition)
Structural Integrity of Ash Pond Dam (combined with Ash Pond Operations condition)
2. S12ecial Conditions Revised
a. Definitions. By agreement, the ELG definitions in the existing permit have been abbreviated.
b. Chronic Toxicity. Chronic toxicity limits continue to apply at Outfall 002, but the IWC is
corrected to 90%, because the river channel has now closed to form a cove and provides no
dilution.
Similar limits will apply at new Outfalls 001A, 006, and 007. All three discharge to the
mainstem of the river and have an IWC of 0.1%.
The IWCs for Outfalls 002 and 007 apply for all discharges, that is, process discharges and
discharges from decanting and dewatering of the ash ponds.
c. Instream Monitoring - Toxicants. The permit requires monthly instream monitoring (4,000
ft. upstream and approximately 2,500 feet and 10,000 ft. downstream of the Outfall 002) for
total arsenic, total selenium, total mercury, total chromium, dissolved lead, dissolved
cadmium, dissolved copper, dissolved zinc, total bromide, total hardness, temperature,
turbidity, and total dissolved solids (TDS). It provides that sampling locations may be
modified with the written approval of the Division in order to provide representative
results.
Rationale for use of total vs. dissolved metals:
• Mercury and selenium water quality standards are still expressed as total metals.
• Total Arsenic - aquatic life standards are expressed as dissolved metals, but the 10 pg/L
standard for Water Supply and Human Health waters is the total form and is, therefore,
more stringent and the controlling standard.
• Total Chromium - the PQL for total chromium is 5 pg/L. If instream samples are < 10 or
< 5 pg/L, they indicate compliance with Cr3+ and Cr6+. If the instream total chromium
value exceeds the allowable Cr3+ concentration, instream testing should be modified to
include dissolved Cr3+ sampling.
• Dissolved lead, cadmium, copper, zinc - the instream standards are dissolved, and the
dissolved metal results and concurrent total hardness results allow for direct comparison
to the instream standard.
d. CWA Section 3160 Temperature Variance - Thermal/ Mixing Study. The Division has
granted a temperature variance for operation of the Buck Steam Station since the mid-1970s.
Duke Energy has requested that the temperature variance be continued in this permit term.
With the variance, the Division approved a thermal mixing zone extending to the High Rock
Lake Dam. Duke Energy monitors temperature at multiple depths at the dam and uses the
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
Page 31

average to determine compliance with temperature limits. Historically, the facility has met
the requirements of the 316(a) variance.
By agreement with the Division, Duke Energy conducts biological monitoring each permit
cycle to evaluate the possible impacts of its discharges upon the macroinvertebrate and fish
community in the Yadkin River near Buck Steam Station. The latest BIP (balanced and
indigenous population) report was submitted to DWR in November of 2011. The report
concluded that the indigenous macroinvertebrate community in the river varied with the
extreme high- and low -flow years in the study period (2003-2008) but remained within the
historic range of densities; and that the river has a balanced and indigenous fish community.
Retirement of the Buck Steam Station in 2013 eliminated the cooling water flows for which
the variance and mixing zone were originally approved. The CTCC discharges a lesser
thermal load in its cooling tower blowdowns: approximately 1 % of the previous flow rate, at
significantly lower temperatures. The difference in impacts to the river have yet not been
evaluated, and it is not clear whether the variance and mixing zone are necessary.
The Division proposes to grant the variance request for this permit term. In order to continue
the variance in the next permit term, Duke Energy must conduct a thermal/ mixing study at
the facility. The study would evaluate the thermal impacts of its discharges, determine the
extent of the mixing zone, and determine whether a variance is still necessary for the
discharge. The permit calls for Duke Energy to develop and submit a study plan to the
Division and to submit the findings of the study no later than 31/2 years after the effective
date of the permit.
e. CWA Section 316(b) - Intake Structure Requirements. Duke Energy must comply with the
revised Cooling Water Intake Structure (CWIS) Rule, 40 CFR 125.95. For the purposes of
applying the rule, the Actual Intake and Design Intake Flows for this facility are both greater
than 2 MGD and less than 125 MGD, and the CTCC plant's 10 -cell cooling tower unit
qualifies as a closed -cell recirculating system as defined in 40 CFR 125.92(c).
The CWIS rule requires that permittees satisfy Best Technology Available (BTA) standards to
minimize adverse environmental impacts at their cooling water intakes. Based on Duke's
2016 renewal application, the Director has tentatively determined that operation of the
existing closed -cycle recirculating system meets the BTA standard to minimize impingement
and entrainment mortalities. To receive final approval, Duke must provide additional
information as required in 40 CFR 122.21(r) to the Director's satisfaction. The permit allows
31/2 years for this submittal (that is, one year prior to its renewal application), consistent with
the requirements for other Duke facilities. Fish Tissue Monitoring Near Ash Pond Discharge.
Monitoring is required once during the permit term, and results are to be submitted with the
next application for renewal.
g. Emergency Overflow - Ash Pond. DEQ's Dam Safety Program (in DEMLR) has issued an
order requiring Duke Energy to install an emergency overflow structure at the final ash
pond (Cell 3). Duke Energy requested that the permit include specific authorization for the
overflow structure, as well as any necessary effluent limitations. The Supplement to Cover
Page in the permit will note the addition of the structure. Because limits would be waived in
the event of a 10 -year 24-hour design storm, and monitoring is already conducted at Outfall
002, the permit does not specify limits or require additional monitoring for any overflows
from the ponds.
3. Special Conditions Added
Several new conditions have been added or existing conditions modified in most or all Duke
Energy permits as the result of deliberations among EPA Region 4, Duke Energy, and DEQ.
The first four conditions are existing and new requirements that are collected in Section C rather
than being repeated multiple times throughout the permit.
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Duke Energy — Buck Combined Cycle Station — NC0004774
Page 32

a. Notifications and Submittals. Provides standard Division addresses.
b. Chemical Discharges. Combines several existing special conditions regarding toxic/
hazardous chemicals.
c. Discharges of Other Materials. A combination of existing and new general requirements.
d. Effluent Sampling Locations. Specifies general location for any effluent sampling point.
e. Waste Treatment Modifications. The current application mentions a new waste holding
pond but provides no details as to how it will be configured or operated. This condition
requires the Permittee to provide that information prior to startup and to do the same for
any future treatment changes.
f. Flow Monitoring and Reporting. Combines two new conditions regarding flow.
g. Electronic Reporting Requirements. Adds standard language pertaining to the new federal
requirements for electronic reporting.
h. Applicable State Law. The permit cites the Coal Ash Management Act of 2014, noting that it
can only be enforced by the state.
i. Ash Pond Closure Agreement. Negotiated language regarding ash pond closure is added.
j. Groundwater Compliance Boundary. Adds standard language pertaining to said boundary.
k. Attachment 1- Groundwater Compliance Boundary Map. The attachment is a map of the
groundwater compliance boundary for the Buck site.
4. S12ecial Conditions Deleted
a. Chemical Metal Cleaning Wastes. Metal cleaning wastes from the BSS have been eliminated,
and the CTCC collects its wastes in a blind sump for disposal off-site.
b. Toxicity Reopener. This condition duplicates language already found in the chronic toxicity
limit condition.
c. Monitoring Frequencies. This condition is no longer necessary.
d. Groundwater Monitoring Well Construction and Sampling. The negotiated approach for
addressing groundwater requirements has been revised and this condition is no longer
necessary. Attachment 1 has been added as part of the new approach.
VII. SUMMARY OF BASES FOR AND MODIFICATIONS OF PERMIT
The permit includes extensive additions, deletions, and revisions to reflect actual and anticipated
changes in the facility operations, outfall configuration, ash pond remediation, seep management,
and the associated waste discharges. The permit incorporates conditions agreed upon by EPA
Region 4, Duke Energy, and DEQ.
Part I of the permit has been divided into three sections to improve its organization, and a table of
contents has been added to aid navigation through the document. Sections A contains effluent limits
and other requirements for the steam electric discharges. Section B contains requirements for the ash
basin remediation discharges and for two constructed seep discharges. Section C contains other
special conditions applicable to activities in any or all of the first two sections.
A. Bases for Effluent Limitations
• Effluent limitations in the permit are based on applicable water quality standards and
federal treatment performance standards.
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Duke Energy — Buck Combined Cycle Station — NC0004774
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• The temperature limits (Outfalls 001A, 006) are based on the North Carolina water quality
standards (15A NCAC 2B .0200) and the current 316(a) Thermal Variance.
• The limits for Oil and Grease and Total Suspended Solids (all outfalls) were established in
accordance with the effluent guidelines for steam electric facilities, 40 CFR Part 423.
• The pH limits in the permit (all outfalls) are based on the North Carolina water quality
standards (15A NCAC 2B .0200), in addition to 40 CFR Part 423 for Outfalls 002, 001A, 006.
• The turbidity limits in the permit (Outfalls 002 and 007, Decanting and Dewatering) are
based on the North Carolina water quality standards (15A NCAC 2B.0200).
• The Whole Effluent Toxicity limit (Outfalls 002, 001A, 006, and 007) is based on the
requirements of 15A NCAC 2B.0500.
• The limits for metals in the permit (Outfall 001A, 006, 002/ 007 [Decanting & Dewatering],
111, and 117) are based on the North Carolina water quality standards (15A NCAC 2B .0200),
except that the 1.0 mg/L limits for copper, iron, and zinc and the 0.2 mg/L limits for
chromium are based on 40 CFR Part 423.
• The limits for Hg at Outfall 002 are based on the Divisions Permitting Guidelines for Statewide
Mercury TMDL.
B. Key Modifications
• Deletion of Outfall 001, previously used for once -through cooling waters but now inactive.
• Addition of new water quality -based effluent limitations for ash pond discharges to Outfall
002 to reflect lack of consistent flows in this portion of the river channel; limits will become
effective six months after the effective date of the permit.
• Addition of new effluent limitations and monitoring requirements for:
• proposed Outfalls 001A and 006 for the diversion of all waste discharges from the CTCC
to the Yadkin River mainstem;
• Outfall 002 for the discharge of decanting and dewatering wastes from the ash basins to
the existing outfall;
• proposed Outfall 007 for the diversion of decanting and dewatering waste discharges to
the Yadkin River mainstem; and
• discharge from ash basin constructed seeps, designated as Outfalls 111 and 117.
• Updating of conditions regarding Clean Water Act 316(a) (temperature) variance and 316(b)
(intake structure) requirements.
• Removal of the Special Condition for Metal Cleaning Wastes, which are no longer
discharged.
• Addition of new water quality -based limits based on the dissolved metals standards,
including hardness -dependent standards.
• Addition of Total Hardness monitoring at Outfalls 002, 001A, 006, and 007 to implement new
dissolved metals standards.
• Addition of an Applicable State Law special condition to acknowledge the Coal Ash
Management Act and Senate Bill 729.
• Addition of a new condition to reflect the EPA's final NPDES Electronic Reporting Rule,
which became effective December 21, 2015.
• Addition of the Groundwater Compliance Boundary map for the site (Attachment 1).
Proposed Schedule for Permit Issuance:
Draft Permit to Public Notice: May 13, 2018
Public Hearing: June 13, 2018
Fact Sheet — NPDES Permit Renewal
Duke Energy — Buck Combined Cycle Station — NC0004774
Page 34

Close of Comment Period: June 20, 2018
Permit Scheduled to Issue: August, 2018
State Contact:
If you have any questions on any of the above information or the attached permits, please contact
Mike Templeton at [phone].
Public Hearing and Response to Comments
The Division held a public hearing at 6 p.m., June 13, 2018, at the Rowan County Cooperative
Extension in Salisbury. Jon Risgaard served as hearing officer. The purpose of the hearing was to
gather public comments regarding three draft NPDES permits for the Duke Energy Carolinas, LLC,
Buck facilities in Salisbury,:
• Buck Steam Station, NCS000578;
• Buck Combustion Turbine Combined Cycle (CTCC) Station, NCS000554; and
• Buck Combined Cycle Station, NC0004774.
The hearing was required under the Coal Ash Management Act of 2014 (NCGS 130A-306.200 et
seq.). Public notice of the hearing was published in the Salisbury Post on May 13, 2018, and posted
on the DEQ website at https: / /bit.ly/2KSG7rm. Oral and written comments were received at the
hearing, and additional written comments were received during the comment period, which ended
on June 20, 2018.
Information concerning the hearing, including comments received, the Division's response to
comments, and resulting changes in the permit and fact sheet, can be found in the Hearing Officer's
report.
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Duke Energy — Buck Combined Cycle Station — NC0004774
Page 35