NC0003425_Fact Sheet_20190411 (4)

DEPARTEMENT OF ENVIRONMENTAL QUALITY
DIVISION OF WATER RESOURCES
FACT SHEET FOR NPDES PERMIT DEVELOPMENT
NPDES No. NC0003425
Facility Information
Applicant/Facility Name:
Duke Energy Progress/Roxboro Steam Electric Generating Plant
Applicant Address:
1700 Dunnaway Rd., Semora, NC 27343
Facility Address:
1700 Dunnaway Rd., Semora, NC 27343
Permitted Flow
Not limited
Type of Waste:
99.8 % Industrial, 0.2% - domestic
Facility/Permit Status:
Existing/Renewal
County:
Person
Miscellaneous
Receiving Stream:
Hyco Reservoir
Stream Classification:
WS-V, B
Subbasin:
03-02-05
303(d) Listed?:
No
Drainage Area (mi2):
N/A
Primary SIC Code:
4911
Summer 7Q10 (cfs)
0
Regional Office:
RRO
30Q2 (cfs):
0
Quad
Olive Hill
Average Flow (cfs):
0
Permit Writer:
Ser ei Chemikov, Ph.D.
IWC (%):
100%
Date:
04/11/2019
Summary
The Roxboro Steam Electric Plant is an electric generating facility that uses steam turbine generation via
four coal-fired units with a with a combined electric generating output of 2558 MW: Unit No.1 (385 MWe),
Unit No. 2 (670 MWe), Unit No. 3 (707MWe) and Unit No. 4 (700 MWe).
The facility discharges to subbasin 030205 in the Roanoke River Basin. The facility operates five internal
outfalls and two outfalls to Hyco Reservoir. Discharges are mostly industrial, with a very small domestic
flow (internal Outfall 008) piped to the on -site ash pond. Discharges from the ash pond (internal Outfall
002), once -through cooling water and FGD treatment system (internal outfall 010) are discharged to the
Heated Water Discharge Pond (outfall 003). The Heated Water Discharge Pond and Coal Pile Runoff
(outfall 006) both discharge to Hyco Reservoir. The Hyco Reservoir is a 17.6 km2 waterbody constructed
in 1963 by CP&L to serve as a cooling water source. The receiving waterbody is class WS-V; B. The facility
is located in the Lower Piedmont area of the state, the applicable state water quality temperature
standard is 32°C (89.6° F).
This facility is subject to EPA effluent guideline limits per 40 CFR 423 - Steam Electric Power Generating
Point Source Category which were amended November 3, 2015. The facility is also subject to the Cooling
Water Intake Structures Rules (40 CFR 125) effective October 14, 2014. The intake flow is > 125 MGD.
Duke requested the addition of three new outfalls on the permit; two to reflect the future treatment
systems for the low volume wastes as the ash basin will be closed and one for the overflow from the east
ash basin extension and stormwater runoff.
Description of existing outfalls:
Outfall 003 - Heated Water Discharge Pond to Hyco Reservoir. This pond combines all internal outfalls
(002, 005, 008, 009, 010) before discharging to Hyco Reservoir. In addition, once -through cooling water
from condensers for units 1, 2, and 3, once -through cooling water from heat exchangers, seepage from ash
pond, and stormwater runoff from plant drainage areas are discharged to the discharge pond.

NPDES PERMIT FACT SHEET
Page 2
Roxboro Steam Electric Plant
NPDES No. NC00003425
Outfall 006 - Coal Pile Runoff discharges directly to Hyco Reservoir. Coal pile runoff wastewaters
include runoff from the coal pile, limestone pile and gypsum pile, truck wheel wash area and coal
handling areas. Treatment is accomplished by neutralization, sedimentation and equalization. This is an
episodic discharge.
Internal Outfall 002 - Ash Pond discharging to the heated water discharge pond. The ash pond receives
wastewater from the following source:
• Bottom ash transport waters
• Silo wash water
• Ash landfill leachate and runoff (this landfill receives CCR from Mayo and Roxboro
plants)
• Dry -ash handling system wash water
• Blowdown from Unit 4 cooling tower
• Coal mill rejects and pyrites
• Sewage treatment plant effluent
• Low volume waste consisting of boiler blowdown, equipment maintenance cleaning
wastewaters, RO reject wastewater and floor drains. Low volume wastes are treated by
neutralization.
• Emergency overflow from FGD system blowdown.
Internal Outfall 005 - Cooling tower blowdown from Unit 4.
Internal Outfall 008 - Treated domestic wastewater. The treatment system consists of a screen,
communitor, surge tank, aeration tank, clarifier, chlorine contact chamber and sludge holding tank. A
new package plant will be installed to replace the existing plant.
Internal Outfall 009 - Chemical metal cleaning waste. Wastewaters from cleaning of the boilers is
generated every five to eight years. Every three to five years wastewaters are generated from cleaning the
heat exchangers. The wastewaters generated can be treated by evaporation or by neutralization and
precipitation.
Internal Outfall 010 - Flue Gas Desulfurization (FGD) treatment system discharging to the discharge
canal. The scrubber system removes SOx by mixing flue gas with a limestone slurry. The blowdown from
the scrubber is discharged to a gypsum settling pond system then to a bioreactor which utilizes
microorganisms to reduce soluble contaminants to insoluble forms (under anaerobic conditions) that then
precipitate from solution. Wastewater is discharged to the ash pond effluent channel. An emergency
overflow from the FGD system blowdown discharges to the ash pond.
Proposed Outfalls:
Outfall 001- Stormwater and the oveflow from the east ash basin extension. The east ash basin was
closed and subsequently a landfill was built over the old basin. A portion of the basin remained as an
open pond. It has come to the attention of the Division that there are some coal combustion residuals
within the pond. The Division has requested that Duke removes the residuals. In addition to the pond
overflow this outfall discharges stormwater runoff.
Internal Outfalls 012A, 012B and 012C - Low volume waste and other wastewaters. Duke will build two
basin treatment systems to treat wastewaters that now go to the ash basin. The basins will discharge to
the heated discharge pond and an emergency overflow from one of the basins will discharge to Hyco
Lake (012C).
2

NPDES PERMIT FACT SHEET Roxboro Steam Electric Plant
Page 3 NPDES No. NC00003425
CWA 316 (W
The permittee shall comply with the Cooling Water Intake Structure Rule per 40 CFR 125.95. The Division
approved the facility request for an alternative schedule in accordance with 40 CFR 125.95(a)(2). The
permittee shall submit all the materials required by the Rule by May 31, 2023. This is an accelerated
schedule that includes:1 year for the development of the sampling plan and obtaining approval from the
Division, 2 years of sampling to adequately characterize seasonal variation, and 1 year for the report
development. Based on the results of the studies, the Division may require an implementation of the
additional measures to reduce impingement and entrainment of the aquatic organisms.
The facility's total intake is designed for approximately 1,114 MGD. Units No.1 and 2 use condensers as
cooling devices. Units No. 3 and 4 use cooling towers as cooling devices. Units 1 and 2 operate in a once -
through cooling mode year round. Unit 3 operates in a once -through cooling mode part of the year
(October 15th - April 30th) and during summer months (May 1st - October 14th) condenser cooling water
is routed to once -though mechanical draft cooling tower. Unit 4 is equipped with closed -cycle
evaporative cooling towers that operate year-round. The CWIS for Unit 4 (CWIS 4) is located on the north
bank of the heated water discharge pond, adjacent to the Unit 4 closed -cycle cooling tower. As a result,
there is no net increase in cooling water withdrawal for the Unit 4 cooling tower make-up water.
The CWIS for Units 1-3 (CWIS 1) is located at the intake forebay immediately east of the Unit 1 turbine -
generator. Cooling water for Units 1-3 is withdrawn through eight bays in CWIS 1 via a 1.7-mile intake
canal located east north-east of the plant. The intake canal directs water to an intake pond which is
connected to the CWIS 1 intake forebay area via a submerged culvert. Unit 1 consists of two intake bays
equipped with one circulating water pump per bay. Units 2 and 3 each consist of three intake bays
equipped with one circulating water pump per bay. Each of the eight intake bays for CWIS 1 is equipped
with trash racks and coarse -mesh (3/8-inch mesh size) vertical traveling screens with a debris spray wash
system and debris collection trough.
Duke Energy provided the following justification as Basis for Designation Belews Station as a Closed
Cycle Recirculation System:
A "closed -cycle recirculating system' is defined at 40 CFR 125.92 (c). The definition addresses
facilities with CCRS that withdraw from waters of the United States where the impoundment was
constructed for the purpose of providing cooling water for the facility:
"Closed -cycle recirculating system also includes a system with impoundments
of waters of the U.S. where the impoundment was constructed prior to October
14, 2014 and created for the purpose of serving as part of the cooling water
system as documented in the project purpose statement for any required Clean
Water Act section 404 permit obtained to construct the impoundment. In the
case of an impoundment whose construction pre -dated the CWA requirement
to obtain a section 404 permit, documentation of the project's purpose must be
demonstrated to the satisfaction of the Director. This documentation could be
some other license or permit obtained to lawfully construct the impoundment
for the purposes of a cooling water system, or other such evidence as the
Director finds necessary." 40 CFR 125.92 (c)(2).
Impoundments are further defined and discussed as a closed -cycle cooling system in the rule's
preamble, stating that:
"Impoundments are surface waterbodies that serve as both a source of cooling water
and a heat sink. As with cooling towers, impoundments rely on evaporative cooling
to dissipate the waste heat; a facility withdraws water from one part of the
impoundment and then discharges the heated effluent back to the impoundment,

NPDES PERMIT FACT SHEET
Page 4
Roxboro Steam Electric Plant
NPDES No. NC00003425
usually in another location to allow the heated water time to cool. Depending on
local hydrology, impoundments may also require makeup water from another
waterbody. Impoundments can be man-made or natural, and can be offset from
other water bodies or as part of a "run of the river" system (the latter are sometimes
referred to as cooling lakes)." 79 Fed. Reg. 48,334 (August 15, 2014)
The system at Roxboro meets the criteria for classification as a CCRS. Roxboro withdraws cooling
water from Hyco Lake which was constructed in a water of the United States for the purpose of
providing cooling water for the Carolina Power & Light Company (now Duke Progress, LLC)
Roxboro Steam Electric Plant prior to the Clean Water Act 404 permitting program. The Carolina
Power & Light Company received authorization for the creation of Hyco Lake in April 1964 for the
Roxboro facility. Numerous documents issued by the State contain several statements and
commensurate justification that the purpose of Hyco Lake was to be "operated ... to reduce
pollution [via condenser cooling water recirculation] in the Hyco River" and is a "cooling pond":
• State of North Carolina Department of Water and Air Resources Permit 522 issued May 4,
1964
• Carolina Power & Light Company, North Carolina State Stream Sanitation Committee
"Application for Approval of Plans" dated April 13,1964
• North Carolina Board of Water and Air Resources Permit 522 Certification dated October
1,1971
• North Carolina Environmental Management Commission Permit 2523 issued July 22,1974
The permit issued by the State of North Carolina Department of Water and Air Resources (the
predecessor Agency to the North Carolina Department of Environmental Quality) authorized
"...operation of a 3,800 acre cooling lake for a design flow of 2,400,000,000 G.P.D., and the
discharge of the effluent into the Hyco River, a tributary in the Roanoke River Basin". The dam
was completed in 1964 and Hyco Lake reached full pool elevation in 1965.
As also required by the definition, make-up water withdrawals attributable to the cooling portion
of the Roxboro cooling system have been minimized. The source of all makeup water is the
approximately 300 square mile Hyco Lake watershed. No other sources of makeup water are
currently available and none are planned.
In addition to minimizing withdrawals for make up water to Hyco Lake, Roxboro also minimizes
cooling water withdrawals from Hyco Lake in multiple ways. First, Unit 4 operates on
recirculating cooling towers that require only small volumes of makeup waters. Those make up
waters are taken from internal process areas consisting of Unit 1-3 cooling water discharge and the
ash basin discharge flows. Second, the cooling water system for Units 1-3 has several design
features that increase their efficiency, including (a) directing deeper, cooler water to the intake as
needed to maintain efficiency by using cooler water from deeper in the reservoir; (b) routing of
cooling water discharges as far as possible upstream from the cooling water intake (subject to
constraints imposed by the Department for thermal impact reasons); and (c) utilization on Unit 3
of a helper cooling tower seasonally which reduces the thermal discharge load to the lake and
allows for more efficient cooling during the summer months. Third, as reflected in the company's
Integrated Resources Plans, filed with the North Carolina Utilities Commission, Roxboro has
operated since 2016 as an "Intermediate" rather than "Baseload" generation source. The reduction
in operating time has resulted in a reduction of average daily withdrawals from greater than 800
MGD when the plant operated as Baseload to 592 MGD in 2018, as reported in the station's annual
water withdrawal reports.
rd

NPDES PERMIT FACT SHEET
Page 5
Roxboro Steam Electric Plant
NPDES No. NC00003425
The Division concurs with the justification provided by Duke on a provisional basis. Based on 40
CFR 125.92 (c) the Director has determined that operating and maintaining the existing closed -
cycle recirculating system meets the requirements for a provisional BTA. The final determination
will be made upon review of the materials submitted by the permittee. This determination is
consistent with the EPA Region IV decision regarding Robinson station and Belews station, and
the EPA Region III decision regarding North Anna station.
Temperature Mixing Zone - Outfall 003
The facility is located in the Lower Piedmont area of the state, the applicable state water quality
temperature standard is 32°C (89.6° F). The authorized temperature mixing zone for outfall 003 includes
the North Hyco Arm downstream of NC Hwy 57, the main body of Hyco Reservoir downstream of the
confluence of the Cobbs Creek Arm and the North Hyco Arm and the entire after bay lake. USGS data at
the after bay monitoring station (USGS Station 02077303) was reviewed for the period of January 2011 to
April 2016. Data shows that the temperature water quality standard was not exceeded for this period.
Maximum temperature recorded was 30.5°C.
Instream Monitoring
The permit requires monitoring of Hyco Reservoir in accordance to the Biological Monitoring Program as
approved by the Division. Based on the Divisions review of the reports the fish community is
comparable to other piedmont reservoirs and no problems were noted. The draft permit includes
instream monitoring for total arsenic, total selenium, total mercury, total chromium, dissolved lead,
dissolved cadmium, dissolved copper, dissolved zinc, total bromide, total hardness (as CaCO3), turbidity,
and total dissolved solids (TDS). The draft permit also includes annual fish tissue monitoring.
DATA REVIEW�I'ERMIT REQUIREMENTS
Internal Outfall 002 - Ash Pond
This outfall is subject to the Effluent Limitations Guidelines (ELG) in Table 1.
Table 1. ELG Outfall 002 (Prior to November 1, 2018)
Pollutant
Daily Maximum
Monthly Average
ELG
TSS
100 m /L
30 m /L
40 CFR 423.12 (b) (4)
Oil & Grease
20 m / L
15 m /L
40 CFR 423.12 (b) (4)
The current permit requires monitoring for flow and total selenium, limits for Oil & Grease and TSS. A
summary of DMR data for the period of January 2011 to January 2016 is included in Table 2. There have
been no violations of permit limits or conditions.
Table 2. DMR Summary Outfall 002
Parameter
Average
Maximum
Minimum
Flow
10.8 MGD
48.3 MGD
3.1 MGD
TSS
5 mg/ L
21 mg/ L
< 2.5 mg/ L
Total Selenium
14.6 µg/L
68.8 µg/L
< 10 µg/L
O&G
<5mg/L
13.5mg/1
<5mg/L
Table 3. Monitoring Requirements/Proposed Changes Outfall 002
Parameter'y
Monitoring requirements Changes Basis
Flow
Monitor No changes 15A NCAC 2B.0505
TSS
30 mg/L monthly aver No changes 40 CFR 423.12(b)(4)
100 mg/L daily max

NPDES PERMIT FACT SHEET
Page 6
Roxboro Steam Electric Plant
NPDES No. NC00003425
Oil & Grease
15 mg/L monthly aver
No Changes
40 CFR 423.12(b)(4)
20 mg/L daily max
Total Selenium
Monthly monitoring
No changes
Pollutant of concern
Turbidity, pH
No requirement
Monitor
Pollutant of concern for
dewatering/ decanting
Schedule of Compliance Fly Ash/Bottom Ash:
As per 40 CFR 423.13 (k) (1) (i) bottom ash transport water shall not be discharged, compliance with this
section shall be as soon as possible beginning on November 1, 2020, but no later than December 31, 2023.
Duke utilizes wet bottom ash transport system. Duke is proposing to install a remote mechanical drag
chain system. Design of the system is expected to be completed in 8 months, followed by procurement in
12 months. Construction is expected to be completed in 13 months. Duke proposes a 16 month window
to optimize the system at full load and additional 6 months for potential permitting delays.
Consideration was given to the fact that Duke will be undertaking design, procurement and installation
activities in multiple facilities simultaneously. Duke will meet the no discharge of bottom ash
requirement by April 30, 2021.
Fly ash transport water is no longer discharged therefore Duke meets the compliance date of November
1, 2018.
Internal Outfall 002 - Dewatering
To meet the requirements of the Coal Ash Management Act of 2014, the facility needs to dewater two ash
ponds by removing the interstitial water and excavate the ash to deposit it in landfills. The facility's
highest discharge rate from the dewatering process will be 2 MGD. The facility submitted data for the
standing surface water in the ash ponds, interstitial water in the ash, and interstitial ash water that was
treated by filters of various sizes. The following pollutants were detected at concentrations higher than
the water quality standards: selenium, arsenic and molybdenum. A new effluent and monitoring sheet is
included in the permit for the ash pond dewatering phase. As this is an internal outfall the water quality
standards are not applied. Monitoring will be required for selenium, arsenic, molybdenum, antimony,
mercury and copper.
Outfall 003 - Heated Water Discharge Pond (Combined outfalls)
DMR/Compliance Review
Data were reviewed for the period of January 2011 to March 2016. There have been no violations of
permit limits or conditions.
Table 4. DMR Summary Outfall 003
Parameter
Average
Maximum
Minimum
Flow (MGD)
840
1130
6.9
TRC
Not discharged
TP (mg/L)
< 0.036
< 0.05
< 0.05
TN (mg/L)
0.68
1.08
0.44
Temperature (°C)
29
41
130C
Total Arsenic (µg/L)
6.2
17.1
< 2.8
pH (SU)
7.34
8
6.38
Toxicity Testing (003):
Current Requirement: Acute P/F at 90%, February, May, August, November.
Proposed Requirement: Acute P/F at 90%, February, May, August, November.
The facility passed 21 tests out of 21 tests performed for the period of January 2011 to January 2016.
J

NPDES PERMIT FACT SHEET Roxboro Steam Electric Plant
Page 7 NPDES No. NC00003425
Reasonable Potential Analysis Outfall 003:
The Division conducted EPA -recommended analyses to determine the reasonable potential for toxicants
to be discharged at levels exceeding water quality standards/EPA criteria by this facility from outfall 003.
For the purposes of the RPA, the background concentrations for all parameters were assumed to be below
detection level. The RPA uses 95% probability level and 95% confidence basis in accordance with the EPA
Guidance entitled "Technical Support Document for Water Quality -based Toxics Control." With the
approval of the Triennial Review (2007-2014) of the NC Water Quality Standards by the Environmental
Management Commission (EMC) in 2014 and US -EPA (with some exceptions) on April 6, 2016, the
NPDES Permitting Unit is required to implement the new dissolved metal standards in all permits public
noticed after April 6, 2016. The RPA included evaluation of dissolved metals' standards, utilizing
measured hardness value of 100 mg/L CaCO3 for hardness -dependent metals.
A reasonable potential analysis was conducted for arsenic, copper, nickel, selenium, strontium, thallium,
chlorides and zinc. Arsenic data used for the RPA was collected between 2011 and 2016. Data for the
remaining parameters was from a special study for the period of March 2010 to August 2011. Based on
this analysis, the following permitting actions are proposed for this permit:
• Monitoring Only. The following parameters will receive a monitor -only requirement since they
did not demonstrate reasonable potential to exceed applicable water quality standards/criteria,
but the maximum predicted concentration was >50% of the allowable concentration: Arsenic,
selenium, chloride.
• No Limit or Monitoring: The following parameters will not receive a limit or monitoring, since
they did not demonstrate reasonable potential to exceed applicable water quality
standards/criteria and the maximum predicted concentration was <50% of the allowable
concentration: copper, nickel, strontium, and zinc.
Mercury Evaluation Outfall 003:
A mercury evaluation was conducted in accordance with the permitting guidance developed for the
implementation of the statewide Mercury TMDL to determine the need for a limit and Mercury
Minimization Plan (MMP). Monitoring for mercury is not required for outfall 003 but mercury data was
collected during a special study during the period of March 2010 to August 2011. The water quality based
effluent limitation (WQBEL) for mercury is 12 ng/l. The technology based effluent limit (TBEL) is 47
ng/l. None of the annual averages exceeds the WQBEL or TBEL, no limit is required. See the attached
mercury evaluation spreadsheet.
Table 5. Mercury Evaluation
2010
2011
# of Samples
20
16
Annual Average, ng/L
3.6
4.4
Maximum Value, n /L
7.63
6.92
TBEL, ng/L
47
WQBEL, ng/L
12.0
Fable 6. Monitoring Requirements/Proposed Changes Outfall 003
Parameter FMonitoring Basis
requirements/Lin
Flow I Monitor No changes 15A NCAC 2B.0505
7

NPDES PERMIT FACT SHEET
Page 8
Roxboro Steam Electric Plant
NPDES No. NC00003425
TRC
200 µg/L
Modified limit to
State WQ standards, 15A NCAC
instantaneous max
28 µg/L daily max
2B .0200. The water quality
standard is more stringent than
the effluent guidelines limit.
TP
Monitor
No changes
15A NCAC 2B .0500
TN
Monitor
No changes
15A NCAC 2B .0500
Temperature
Monitor
No changes
Approved Mixing zone
Total Arsenic
Monitor
No changes
Based on results from RPA,
Predicted concentration greater
than 50% of allowable.
Total Selenium
No requirement
Quarterly monitoring
Based on results from RPA,
Predicted concentration greater
than 50% of allowable.
Total Thallium
No requirement
Quarterly monitoring
Pollutant of concern.
Chloride
No requirement
Quarterly monitoring
Based on results from RPA,
Predicted concentration greater
than 50% of allowable.
pH
6 to 9 SU
No changes
State WQ standards, 15A NCAC
2B .0200
Acute toxicity
P/F 90%
No changes
State WQ standards, 15A NCAC
2B .0200
Internal Outfall 005 - Cooling Tower Blowdown from Unit 4
This outfall is subject to the ELGs in Table 7.
Table 7. ELG Outfall 005
Pollutant
Daily Maximum
Monthly Average
ELG
Free Available
Chlorine
0.5 mg/L
0.2 mg/L
40 CFR 423.12 (d) (1)
126 Pollutants
No detectable amounts
40 CFR 423.13 (d) (1)
Total Chromium
0.2 mg/L
0.2 mg/L
40 CFR 423.13 (d) (1)
Total Zinc
1.0 mg/L
1.0 mg/L
40 CFR 423.13 (d) (1)
The permit includes monitoring for flow and Total Residual Chlorine (TRC), limits for Free Available
Chlorine, Total Chromium, Total Zinc and 126 priority pollutants.
Special condition A. (14) in the current permit doesn't allow the discharge of the cooling tower blowdown
to the discharge pond, it has to be discharged to the ash pond. With the modifications planned to the site
and the future closure of the existing ash pond Duke will like to have the option to discharge the
blowdown to the discharge pond. This will continue to be an internal outfall subject to the same limits
under 40 CFR 423. The limits apply before it comingles with any other waste stream so there is no change
in limits or other permit conditions by allowing the cooling tower blowdown to discharge into the
discharge pond.
DMR/Compliance Review:
Data were reviewed for the period of January 2011 to January 2016. There have been no violations of
permit limits or conditions. Flow was the only parameter monitored at this outfall since the facility did
not chlorinate or added chromium or zinc for maintenance activities. Flow is reported as 7.2 MGD on a
daily basis.
N.

NPDES PERMIT FACT SHEET
Page 9
Table 8. Monitoring Requirements/Proposed Changes Outfall 005
Roxboro Steam Electric Plant
NPDES No. NC00003425
Parameter
Monitoring
Requirements/Limits
Changes
Basis
Flow
Monitor
No changes
15A NCAC 2B.0505
Free available
500 µg/L daily max
No changes
40 CFR 423.13 (d)(1)
chlorine
200 µ /L monthlyaverage
Total Residual
Chlorine
Monitoring
No changes
40 CFR 423.13 (d) (2)
Total chromium
200 µg/L daily max
No changes
40 CFR 423.13 (d)(1)
200 µg/L monthly average
Total Zinc
1.0 mg/L daily max
No changes
40 CFR 423.13 (d)(1)
1.0 mg/L monthly average
The 126 priority
pollutants
No detectable amount
No changes
40 CFR 423.13 (d)(1)
Outfall 006 - Coal Pile Runoff
This outfall is subject to the ELG in Table 9.
Table 9. ELG Outfall 006
Pollutant
Daily Maximum
Monthly Average
ELG
TSS
50 mg/ L
40 CFR 423.12 (b) (9)
pH
6 to 9 SU
40 CFR 423.12 (b) (1)
DMR/Compliance Review:
Data were reviewed for the period of January 2008 to March 2013. There have been no violations of
permit limits or conditions.
Table 10. DMR Summary Outfall 006
Parameter
Average
Maximum
Minimum
Flow (MGD)
0.23
0.05
0.002
TSS (mg/L)
2.6
76.6
< 2.5
pH (SU)
7.39
8.9
6.04
Priority Pollutant Scan:
The application included the results of one scan. Selenium was detected above the water quality
standard.
This is an episodic discharge. The pond only discharges under heavy rain events, therefore limits will be
applied as acute limits.
Table 11. Monitoring Requirements/Proposed Changes Outfall 006
Parameter
Monitoring
Changes
requirements/Limits
Flow
Monitor
No changes
15A NCAC 2B .05
TSS
50 mg/L instantaneous
No changes
40 CFR 423.12(b)(9)
max
pH
6 to 9 SU
No changes
40 CFR 423.12 (b) (1)
Total selenium
No requirement
56 µg/L Daily Max
RPA
Acute toxicity
P/F 90%
No changes
State WQ standards, 15A
NCAC 2B .0200
b

NPDES PERMIT FACT SHEET
Page 10
Internal Outfall 008 - Domestic WWTP
Table 12. DMR Review Outfall 008
Roxboro Steam Electric Plant
NPDES No. NC00003425
Parameter
Average
Maximum
Minimum
Flow (MGD)
0.007
0.01
0.002
TSS (mg/ 1)
14.7
30
5
pH (SU)
6.8
7.3
6.5
BOD (mg/L)
10.4
28
2.1
NH3N (mg/L)
0.8
1.6
< 0.1
Table 13. Monitoring Requirements/Proposed Changes Outfall 008
Parameter
MonitoringMMI
Changes
Basis
requirements/Limits
Flow
0.015 MGD
0.025 MGD
WWTP was upgraded
TSS
30 mg/L monthly
No changes
NPDES rules for secondary
aver
treatment of domestic
45 m /L daily max
wastewater,15A 2B .0400
pH
6 to 9 SU
No changes
State WQ standards,15A 2B
.0200
BOD
30 mg/L monthly
No changes
NPDES rules for secondary
aver
treatment of domestic
45 m /L daily max
wastewater,15A 2B .0400
Total ammonia
Monitor
No changes
DWQ Policy
Internal Outfall 009 - Chemical cleaning waste
Table 14. Monitoring Requirements/Proposed Changes Outfall 009
Parameter
Monitoring V
requirements/Limits
Changes
Basis
Flow
Monitor
No changes
15A NCAC 213.0505
Total Copper
1.0 mg/L monthly aver
No changes
40 CFR 423.13 (e)
1.0 mg/L daily max
Total Iron
1.0 mg/L monthly aver
No changes
40 CFR 423.13 (e)
1.0 mg/L daily max
TSS
30 mg/L monthly aver
No changes
40 CFR 423.13 (e)
100 mg/L daily max
Oil & Grease
15 mg/L monthly aver
No changes
40 CFR 423.13 (e)
20 mg/L daily max
Internal Outfall 010 - FGD
This outfall is subject to the Effluent Limitations Guidelines (ELG) in Table 15. These are new limitations
promulgated November 3, 2015.
Table 15. ELG Outfall 010
Pollutant
Dail Maximum M7-onthly Average
ELG
pH
6 to 9 SU
40 CFR 423.12 (b) (1)
TSS
100 mg/ L
30 mg/ L
40 CFR 423.12 (b) (11)
Oil and grease
20 m /L
15 m /L
40 CFR 423.12 (b) (11)
Total Arsenic
11 µ /L
8 µ /L
40 CFR 423.13 (g) (1) (i)
Total Mercury
788 ng/L
356 ng/L
40 CFR 423.13 (g) (1) (i)
Total Selenium
23 µg/L
12 µg/L
40 CFR 423.13 (g) (1) (i)
Nitrate/nitrite
17 mg/L
4.4 mg/L
40 CFR 423.13 (g) (1) (i)
10

NPDES PERMIT FACT SHEET
Page 11
Roxboro Steam Electric Plant
NPDES No. NC00003425
The current permit includes monitoring for flow, total beryllium, total mercury, total antimony, total
selenium, total silver and total vanadium. Table 16 includes a summary of DMR data for the period of
January 2011 to January 2016. There have been no violations of permit limits or conditions.
Table 16. DMR Summary Outfall 010
Parameter
Average
Maximum
Minimum
Flow (MGD)
0.84
1.77
0.01
Total Beryllium (µg/L)
3.9
10
< 1
Total Mercury (µg/L)
1.08
9.6
< 1
Total Selenium (µg/L)
102
712
< 50
Total Silver (µg/L)
6
8.4
< 5
Total Antimony (µg/L)
31
70
< 25
Total Vanadium (µg/L)
< 25
< 25
< 5
Table 17. Monitoring Requirements/Proposed Changes Outfall 010
Parameter
Monitoring
requirements/Limits
Changes
Basis
Flow
Monitor
No changes
15A NCAC 2B.0505
Total Beryllium
Monitor
Remove monitoring
Internal outfall, not a
parameter of concern.
Total Vanadium
Monitor
Remove monitoring
Internal outfall, not a
parameter of concern.
Total Antimony
Monitor
Remove monitoring
Internal outfall, not a
parameter of concern.
Total Silver
Monitor
Remove monitoring
Internal outfall, not a
parameter of concern.
Total Arsenic
No monitoring
11 µg/L daily max and
8 µg/L monthly
40 CFR 423.13 (g) (1) (i)
average
Total Selenium
Monitor
23 µg/L daily max and
12 µg/L monthly
40 CFR 423.13 (g) (1) (i)
average
Nitrate/Nitrite
No monitoring
17 mg/L daily max and
4.4 mg/L monthly
40 CFR 423.13 (g) (1) (i)
average
Total Mercury
Monitoring
788 ng/L daily max
and 356 ng/L monthly
40 CFR 423.13 (g) (1) (i)
average.
Schedule of Compliance FGD:
40 CFR 423 establishes compliance dates for the new limitations. Permittee must meet limits as soon as
possible beginning on November 1, 2020 but no later than December 31, 2023.
Duke utilizes a biological treatment system to treat FGD wastewaters. Duke anticipates that it will be
required to install physical/chemical treatment followed by selenium reduction technology to meet the
FGD guidelines. Evaluation of new technologies, design, and siting of the system is expected to take 30
months. The evaluation phase includes evaluation of existing treatment system, flow optimization, siting
of the new system within the plant, selection of technology and permitting. Procurement is expected to be
completed in 20 months, construction and tie-in expected to be completed in 16 months considering that
tie-in has to be done during outages. Startup and optimization under all expected operating conditions is
estimated for 15 months. An additional 6 months is included in the schedule for potential permitting
delays. Duke will meet the FGD ELG by December 31, 2021. As the new treatment system will be placed
11

NPDES PERMIT FACT SHEET Roxboro Steam Electric Plant
Page 12 NPDES No. NC00003425
in operation and the old pond may still discharge until it is decommissioned a new outfall is included in
the permit for the new system.
Proposed Outfalls Requirements:
Outfall 001
RPA: An RPA was conducted for proposed outfall 001. RPA was conducted for total arsenic, cadmium,
chlorides, total chromium, total copper, total lead, total mercury, total molybdenum, total nickel,
selenium, total zinc, antimony, sulfate and total thallium. As a result of the RPA limits are required for
the following parameters: arsenic, fluoride, sulfides and selenium.
Mercury
Mercury data was collected during 2014 and 2015. 2014 data was collected using method 245 which has a
higher detection limit that 1631. Data for 2015 was used to evaluate a need for a limit. The annual average
was 5.2 ng/l, no limit will be implemented.
Table 18. Outfall 001 Proposed Limits/Monitoring:
Parameter
Monitoring requirements/Limits
Basis
Flow
Monitor
15A NCAC 2B.0505
pH
6 to 9 SU
State WQ standards,15A 2B .0200
Total arsenic, total copper, total
Monitor
Coal ash parameters of concern.
antimony, total lead, total zinc,
total barium, total iron, total
manganese, total nickel, total
mercury, and chlorides
Total Selenium
5 µg/L Monthly Average
RPA
56 µg/L Daily Max
Total Arsenic
10 µg/L Monthly Average
RPA
340 µg/L Daily Max
Fluoride
1.8 mg/L Monthly Average
RPA
1.8 mg/L Daily Max
Sulfates
250 mg/L Monthly Average
RPA
250 mg/L Daily Max
TDS, Hardness, Conductivity
Monitor
Parameters of concern
Acute toxicity
Quarterly Limit
State WQ standards,15A NCAC
2B .0200
Low Volume Waste Treatment System:
Two new treatment systems will be installed to treat wastewaters currently delivered to the ash basin.
Low volume wastes, metal cleaning wastes, stormwater, and other miscellaneous wastes that are routed
to the ash basin will be rerouted to new treatment systems. Duke proposes two separate treatment
systems. The new outfalls will be designated as outfall 012A and outfall 012B. The overflow from the
012B basin will be designated as outfall 012C. Duke estimated that design, construction and start up of
the new treatment system will be completed within 30 months of permit issuance.
12

NPDES PERMIT FACT SHEET Roxboro Steam Electric Plant
Page 13 NPDES No. NC00003425
Internal Outfall 012A - treatment system for the landfill stormwater, treated extracted groundwater,
contact and non -contact storm water and discharging to the discharge pond.
Table 19. Outfall 012A Pro osed Limits/Monitorin :
Parameter
Monitoring
Basis
re uirements/Limits
Flow
Monitor
15A NCAC 2B.0505
Total Suspended Solids
30 mg/L Monthly Average
40 CFR 423.12 (b)(3)
100 m /L Daily Max
Oil & Grease
15 mg/L Monthly Average
40 CFR 423.12 (b)(3)
20 mg/L Daily max
Total arsenic, total selenium, total
Monitor during ash basin
Parameters of concern
mercury, total molybdenum, total
closure
antimony, total copper
Internal Outfall 012B - treatment system for plant low volume wastes, FGD treatment system effluent,
domestic waste treatment system, anhydrous ammonia emergency discharge, metal cleaning wastes,
stormwater runoff, and cooling tower blowdown. The discharge from outfall 012B will go to the discharge
canal.
Table 20. Outfall 012B Proposed Limits/Monitoring:
Parameter
Monitoring requirements/Limits
Basis
Flow
Monitor
15A NCAC 213.0505
Total Suspended Solids
30 mg/L Monthly Average
100 mg/L Daily Max
40 CFR 423.12 (b)(3)
Oil & Grease
15 mg/L Monthly Average
20 mg/L Daily max
40 CFR 423.12 (b)(3)
Ammonia
Monitor
Monitor during emergency discharge
of anhydrous ammonia
Emergency Outfall 012C - This is the emergency overflow from the low volume waste treatment system
(Outfall 01213)
Table 21. Outfall 012C Proposed Limits/Monitoring:
Parameter
Monitoring
re uirements/Limits
Basis
Flow
Monitor
15A NCAC 213.0505
Total Suspended Solids
30 mg/L Monthly Average
100 mg/L Daily Max
40 CFR 423.12 (b)(3)
Oil & Grease
15 mg/L Monthly Average
20 m /L Daily max
40 CFR 423.12 (b)(3)
Ammonia
1.0 mg/L Monthly average
5.0 mg/L Daily max
Monitor during emergency
discharge of anhydrous ammonia
Arsenic
Monitor
Parameter of concern
Mercury
Monitor
Parameter of concern
Selenium
Monitor
Parameter of concern
Nitrate/ nitrite
Monitor
Parameter of concern
Copper
Monitor
Parameter of concern
Iron
Monitor
Parameter of concern
13

NPDES PERMIT FACT SHEET
Page 14
Public Notice/Public Hearing
Roxboro Steam Electric Plant
NPDES No. NC00003425
The first draft of this permit was public noticed on August 30, 2016. A public hearing was held on October
4, 2016. A second public notice was done on January 21, 2017 since the first notice went to a newspaper out
of the area.
Summary of permit modifications:
• A separate effluent page for the dewatering of the ash ponds (Outfall 002) was added to the
permit.
• Outfall 001 was reinstated to monitor discharge of seeps and stormwater.
• A new internal outfall (Outfall 011) was added to the permit to monitor the discharge from the
proposed FGD treatment system.
• Special Condition A. (14) that prohibited the discharge of cooling tower blowdown from outfall
005 to the discharge canal was eliminated from the permit.
• A special condition was added to describe Section 316(b) requirements for submittal of applicable
information.
• A special condition was added to the permit to require an Ash Pond Closure Plan.
• A Special Condition was added to the permit to require compliance with Senate Bill 729 (Coal
Ash Management Act).
• Attachment 1 entitled "Groundwater Monitoring Plan' was added to the permit.
• Attachment 2 entitled "Plan for Identification of New Discharges" was added to the permit.
Summary of modifications to October 2016 permit:
• Condition A. (1) Effluent Limitations and Monitoring Requirements for seeps - monitoring
requirements were updated to include the same list of parameters monitored for seeps in other
Duke permits.
• Condition A. (2) Effluent Limitations and Monitoring Requirements for the ash basin -
monitoring was added for arsenic, molybdenum, and chromium. In addition, a statement was
added with the requirement to use physical/chemical treatment during dewatering.
• Condition A. (2) & A. (3) Effluent Limitations and Monitoring Requirements for the ash basin -
Statement regarding no discharge of fly ash was modified to read that no discharge of fly ash is
allowed. The statement pertaining to the schedule of compliance with the ELG for zero
discharge of bottom ash was corrected to read April 30, 2021 instead of November 1, 2018.
• Condition A. (10) & A. (11) Effluent Limitations and Monitoring Requirements for the FGD -
footnote 3 was corrected to read December 31, 2023.
• Turbidity sampling was eliminated from internal outfall 002. Turbidity monitoring is included
at outfall 003.
• Supplement to cover sheet was modified to include flows that were not listed and add
proposed outfalls and outfalls.
• Condition A. (6) Effluent Limitations and Monitoring Requirements outfall 006:
o Oil and Grease limits were added since it receives truck wash waters.
o The RPA was revised and limits for total selenium were added.
• Condition A. (4) Effluent Limitations and Monitoring Requirements for outfall 003:
o Footnote 4 was modified to include a statement regarding the addition of temperature
limits if the facility is not in compliance with the temperature water quality standard.
o Reporting of the temperature at the afterbay station was added to the monitoring
requirements for outfall 003, reporting of temperature at 4C, 4D was eliminated.
o The RPA was revised and limits for thallium were added.
• Condition A. (17)- temperature reporting requirements were modified.
14

NPDES PERMIT FACT SHEET
Page 15
Roxboro Steam Electric Plant
NPDES No. NC00003425
• A. (8) Effluent Limitations and Monitoring Requirements for outfall 008 - monitoring
requirements were modified to require quarterly monitoring for one year after the new plant
start operations, annual monitoring is required after one year of quarterly monitoring.
• Two new internal outfalls (Outfall 012A and 012B) were added to the permit for the two
proposed retention basins for the treatment of low volume wastes that are now sent to the ash
basin. Duke will build two separate wastewater treatment systems to handle the wastes that go
to the ash pond. These ponds will be in different locations in the site and will require each a
separate outfall into the effluent channel.
• Outfall 012C was added to the permit for the emergency overflow of the proposed lined
retention basin discharging through outfall 012B.
• A table including a list of all the seeps locations was added to Condition A. (14).
Modifications to January 2017 draft permit:
• Seeps special condition was eliminated. Seeps will be addresses through Special Order by
Consent EMC SOC WQ S18-005.
• The groundwater monitoring well construction and sampling condition was eliminated from the
permit.
• A footnote was added to outfalls 001 and 003 that requires that the discharge from the
decanting/dewatering operations is discontinued if any of the identified pollutants reaches 85%
of the allowable concentrations.
• Requirements for Outfall 001 were modified. The outfall location was established at the LIT to
Hyco Lake. Monitoring was increased to weekly during the removal of the ash from the east ash
basin extension.
• RPA for outfall 003 was revised using updated thallium criteria. As a result of the RPA no limit
for thallium is necessary.
• Monitoring frequency for arsenic, selenium and mercury at outfall 003 was increased to weekly
during dewatering.
• The note for outfall 002 that contained the requirement to use physical -chemical treatment during
decanting and dewatering was modified. The installation of physical/chemical treatment is not
required unless necessary to meet the water quality standards.
• Outfall 006 requirements were modified to reflect the nature of the discharge. This pond
discharge is episodic, it only discharges if there is a heavy rain event, therefore limits were
implemented as daily maximums.
• pH limits were eliminated from internal outfalls.
• The flow page for 0.15 MGD for the domestic treatment system (outfall 008) was eliminated since
the WWTP was upgraded to 0.25 MGD.
• Monitoring for arsenic, mercury, antimony, copper, molybdenum and selenium were added to
Outfall 012A due to the contribution from ash basin closure flows and treated groundwater.
• The schedule of compliance to meet FGD ELG limits was modified to December 31, 2021.
• The Groundwater Monitoring Well Construction and Sampling condition was eliminated.
• Special condition A. (28) Compliance Boundary was added to the permit. Groundwater
compliance boundary maps were added to the permit as Attachment A and B. Attachment A
describes the current compliance boundary and Attachment B describes the compliance
boundary once the ash is removed from the East Ash Basin Extension.
• Special condition for instream sampling was modified to require monthly sampling, to add
sulfides to the list of monitored parameters and to specify the sampling location.
• Fish tissue monitoring special condition was modified to clarify requirements.
• For clarification the identification of outfall 003 was modified to heated water discharge pond.
• The special condition for 316(b) requirements was modified to include a schedule to submit the
required information in 122.21(r) by May 31, 2022.
15

NPDES PERMIT FACT SHEET Roxboro Steam Electric Plant
Page 16 NPDES No. NC00003425
STATE CONTACT
If you have any questions on any of the above information or on the attached permit, please contact -
Sergei Chernikov at [phone].
Changes in the Final Permit:
• Monitoring for Fecal Coliforms and BOD were eliminated from Outfall 012B and Outfall 012C to
correct an error, these parameters are monitored at Outfall 008 (domestic package plant).
16

NPDES PERMIT FACT SHEET Roxboro Steam Electric Plant
Page 17 NPDES No. NC00003425
NPDES Implementation of Instream Dissolved Metals Standards - Freshwater Standards
The NC 2007-2015 Water Quality Standard (WQS) Triennial Review was approved by the NC
Environmental Management Commission (EMC) on November 13, 2014. The US EPA
subsequently approved the WQS revisions on April 6, 2016, with some exceptions. Therefore, metal
limits in draft permits out to public notice after April 6, 2016 must be calculated to protect the new
standards - as approved.
Table 1. NC Dissolved Metals Water Quality Standards/Aquatic Life Protection
Parameter
Acute FW, µg/1
(Dissolved)
Chronic FW,
µ9/1
(Dissolved)
Acute SW, µg/l
(Dissolved)
Chronic SW,
µg/1
(Dissolved)
Arsenic
340
150
69
36
Beryllium
65
6.5
---
---
Cadmium
Calculation
Calculation
40
8.8
Chromium III
Calculation
Calculation
---
---
Chromium VI
16
11
1100
50
Copper
Calculation
Calculation
4.8
3.1
Lead
Calculation
Calculation
210
8.1
Nickel
Calculation
Calculation
74
8.2
Silver
Calculation
0.06
1.9
0.1
Zinc
Calculation
Calculation
90
81
Table 1 Notes:
1. FW= Freshwater, SW= Saltwater
2. Calculation = Hardness dependent standard
3. Only the aquatic life standards listed above are expressed in dissolved form. Aquatic life
standards for Mercury and selenium are still expressed as Total Recoverable Metals due to
bioaccumulative concerns (as are all human health standards for all metals). It is still
necessary to evaluate total recoverable aquatic life and human health standards listed in 15A
NCAC 213.0200 (e.g., arsenic at 10 µg/l for human health protection; cyanide at 5 µg/L and
fluoride at 1.8 mg/L for aquatic life protection).
Table 2. Dissolved Freshwater Standards for Hardness -Dependent Metals
The Water Effects Ratio (WER) is equal to one unless determined otherwise under
15A NCAC 02B .0211 Subparagraph (11) (d)
Metal
NC Dissolved Standard, [tg/1
Cadmium, Acute
WER*{1.136672-[ln hardness](0.041838)} e^{0.9151 [In hardness]-
3.1485}
Cadmium, Acute Trout
waters
WER*{1.136672-[ln hardness](0.041838)} e^{0.9151[ln hardness] -
3.62361
Cadmium, Chronic
WER*{1.101672-[ln hardness](0.041838)} e^{0.7998[ln hardness]-
4.4451 }
Chromium III, Acute
WER*0.316 • e^{0.8190[ln hardness]+3.7256}
17

NPDES PERMIT FACT SHEET
Page 18
Roxboro Steam Electric Plant
NPDES No. NC00003425
Chromium III, Chronic
WER*0.860 e^{0.8190[ln hardness]+0.68481
Copper, Acute
WER*0.960 e^{0.9422[ln hardness]-1.7001
Copper, Chronic
WER*0.960 e^{0.8545[ln hardness]-1.7021
Lead, Acute
WER* { 1.46203- [ln hardness] (0.145712)1 • e^ { 1.273 [ln hardness] -
1.4601
Lead, Chronic
WER* { 1.46203- [ln hardness] (0.145712)1 • e^ { 1.273 [ln hardness] -
4.7051
Nickel, Acute
WER*0.998 e^{0.8460[ln hardness]+2.2551
Nickel, Chronic
WER*0.997 e^{0.8460[ln hardness]+0.05841
Silver, Acute
WER*0.85 • e^{1.72[ln hardness]-6.591
Silver, Chronic
Not applicable
Zinc, Acute
WER*0.978 e^{0.8473[ln hardness]+0.8841
Zinc, Chronic
WER*0.986 e^{0.8473[ln hardness]+0.8841
General Information on the Reasonable Potential Analysis (RPA)
The RPA process itself did not change as the result of the new metals standards. However,
application of the dissolved and hardness -dependent standards requires additional consideration in
order to establish the numeric standard for each metal of concern of each individual discharge.
The hardness -based standards require some knowledge of the effluent and instream (upstream)
hardness and so must be calculated case -by -case for each discharge.
Metals limits must be expressed as `total recoverable' metals in accordance with 40 CFR 122.45(c).
The discharge -specific standards must be converted to the equivalent total values for use in the RPA
calculations. We will generally rely on default translator values developed for each metal (more on
that below), but it is also possible to consider case -specific translators developed in accordance with
established methodology.
RPA Permitting- Guidance/WOBELs for Hardness -Dependent Metals - Freshwater
The RPA is designed to predict the maximum likely effluent concentrations for each metal of
concern, based on recent effluent data, and calculate the allowable effluent concentrations, based on
applicable standards and the critical low -flow values for the receiving stream.
If the maximum predicted value is greater than the maximum allowed value (chronic or acute), the
discharge has reasonable potential to exceed the standard, which warrants a permit limit in most
cases. If monitoring for a particular pollutant indicates that the pollutant is not present (i.e.
consistently below detection level), then the Division may remove the monitoring requirement in the
reissued permit.
1. To perform a RPA on the Freshwater hardness -dependent metals the Permit Writer
compiles the following information:

NPDES PERMIT FACT SHEET Roxboro Steam Electric Plant
Page 19 NPDES No. NC00003425
• Critical low flow of the receiving stream, 7Q10 (the spreadsheet automatically
calculates the 1Q10 using the formula 1Q10 = 0.843 (s7Q10, cfs) 0.99'
• Effluent hardness and upstream hardness, site -specific data is preferred
• Permitted flow
• Receiving stream classification
2. In order to establish the numeric standard for each hardness -dependent metal of concern
and for each individual discharge, the Permit Writer must first determine what effluent and
instream (upstream) hardness values to use in the equations.
The permit writer reviews DMR's, Effluent Pollutant Scans, and Toxicity Test results for any
hardness data and contacts the Permittee to see if any additional data is available for
instream hardness values, upstream of the discharge.
If no hardness data is available, the permit writer may choose to do an initial evaluation
using a default hardness of 25 mg/L (CaCO3 or (Ca + Mg)). Minimum and maximum limits
on the hardness value used for water quality calculations are 25 mg/L and 400 mg/L,
respectively.
If the use of a default hardness value results in a hardness -dependent metal showing
reasonable potential, the permit writer contacts the Permittee and requests 5 site -specific
effluent and upstream hardness samples over a period of one week. The RPA is rerun using
the new data.
The overall hardness value used in the water quality calculations is calculated as follows:
Combined Hardness (chronic)
_ (Permitted Flow, cfs *Avg. Effluent Hardness, mg/" + (s7Q10, cfs *Avg. Upstream Hardness,
m L
(Permitted Flow, cfs + s7Q10, cfs)
The Combined Hardness for acute is the same but the calculation uses the 1Q10 flow.
3. The permit writer converts the numeric standard for each metal of concern to a total
recoverable metal, using the EPA Default Partition Coefficients (DPCs) or site -specific
translators, if any have been developed using federally approved methodology.
19

NPDES PERMIT FACT SHEET
Page 20
4. The
Roxboro Steam Electric Plant
NPDES No. NC00003425
EPA default partition coefficients or the "Fraction Dissolved" converts the
value for dissolved metal at laboratory conditions to total recoverable metal
at in -stream ambient conditions. This factor is calculated using the linear
partition coefficients found in The Metals Translator: Guidance for
Calculating a Total Recoverable Permit Limit from a Dissolved Criterion
(EPA 823-B-96-007, June 1996) and the equation:
_Cdiss — 1
Ctotal I + 1 [Kpo] [ss(l+a)] [10-6] }
Where:
ss = in -stream suspended solids concentration [mg/1], minimum of 10 mg/L
used, and
Kpo and a = constants that express the equilibrium relationship between
dissolved and adsorbed forms of metals. A list of constants used for each
hardness -dependent metal can also be found in the RPA program under a
numeric standard for each metal of concern is divided by the default partition coefficient (or
site -specific translator) to obtain a Total Recoverable Metal at ambient conditions.
In some cases, where an EPA default partition coefficient translator does not exist (ie.
silver), the dissolved numeric standard for each metal of concern is divided by the EPA
conversion factor to obtain a Total Recoverable Metal at ambient conditions. This method
presumes that the metal is dissolved to the same extent as it was during EPA's criteria
development for metals. For more information on conversion factors see the June, 1996
EPA Translator Guidance Document.
5. The RPA spreadsheet uses a mass balance equation to determine the total allowable
concentration (permit limits) for each pollutant using the following equation:
Ca = (s7Q10 + w) (C)ygs) — (s7 Q1W (Cb)
Qw
Where: Ca = allowable effluent concentration (µg/L or mg/L)
Cwqs = NC Water Quality Standard or federal criteria (µg/L or mg/L)
Cb = background concentration: assume zero for all toxicants except NH3* (µg/L or
mg/L)
Qw = permitted effluent flow (cfs, match s7Q10)
s7Q10 = summer low flow used to protect aquatic life from chronic toxicity and human
health through the consumption of water, fish, and shellfish from noncarcinogens (cfs)
* Discussions are on -going with EPA on how best to address background
concentrations
Flows other than s7Q10 may be incorporated as applicable:
1Q10 = used in the equation to protect aquatic life from acute toxicity
QA = used in the equation to protect human health through the consumption of
water, fish, and shellfish from carcinogens
30Q2 = used in the equation to protect aesthetic quality
20

NPDES PERMIT FACT SHEET
Page 21
Roxboro Steam Electric Plant
NPDES No. NC00003425
G. The permit writer enters the most recent 2-3 years of effluent data for each pollutant of
concern. Data entered must have been taken within four and one-half years prior to the
date of the permit application (40 CFR 122.21). The RPA spreadsheet estimates the 95th
percentile upper concentration of each pollutant. The Predicted Max concentrations are
compared to the Total allowable concentrations to determine if a permit limit is
necessary. If the predicted max exceeds the acute or chronic Total allowable
concentrations, the discharge is considered to show reasonable potential to violate the
water quality standard, and a permit limit (Total allowable concentration) is included in
the permit in accordance with the U.S. EPA Technical Support Document for Water
Quality -Based Toxics Control published in 1991.
7. When appropriate, permit writers develop facility specific compliance schedules in
accordance with the EPA Headquarters Memo dated May 10, 2007 from James Hanlon to
Alexis Strauss on 40 CFR 122.47 Compliance Schedule Requirements.
8. The Total Chromium NC WQS was removed and replaced with trivalent chromium and
hexavalent chromium Water Quality Standards. As a cost savings measure, total chromium
data results may be used as a conservative surrogate in cases where there are no analytical
results based on chromium III or VI. In these cases, the projected maximum concentration
(95th %) for total chromium will be compared against water quality standards for chromium
III and chromium VI.
9. Effluent hardness sampling and instream hardness sampling, upstream of the discharge, are
inserted into all permits with facilities monitoring for hardness -dependent metals to ensure
the accuracy of the permit limits and to build a more robust hardness dataset.
10. Hardness and flow values used in the Reasonable Potential Analysis for this permit included:
Parameter
Value
Comments (Data Source)
Average Effluent Hardness (mg/L)
[Total as, CaCO3 or Ca+M ]
25.0
Default value
Average Upstream Hardness
(mg/L)
[Total as, CaCO3 or (Ca+Mg)]
25.0
Default value
7Q10 summer cfs
0
Lake or Tidal
1Q10 cfs
0
Lake or Tidal
Permitted Flow (MGD)
2.1
For dewatering
21