NCS000575_Draft Fact Sheet_2020083

DENR/DEMLR
FACT SHEET FOR NPDES STORMWATER PERMIT MODIFICATION
NPDES No. NCS000575
Facility Information
Applicant/Facility Name:
Asheville Steam Electric Plant
Applicant Address:
200 CP&L Drive, Arden, North Carolina 28704
Facility Address:
200 CP&L Drive, Arden, North Carolina 28704
Permitted Flow:
N/A Stormwater Discharges Only)
Industrial Activities:
Primary SIC Code: 4911- Electric Services
Permit Status:
New NPDES Stormwater Permit
County:
Buncombe Count
Miscellaneous
Receiving Stream:
Lake Julian and
French Broad
River
Regional Office:
Asheville
Stream Classification:
C and B
Respectively
State Grid / USGS Quad:
303 d Listed?
H , statewide
Permit Writer:
Matthew Gwinn
Subbasin:
04-03-02
Date:
Facility Location: Lat. 35° 28' 01" N Long. 82' 32' 13" W
BACKGROUND
Duke Energy's Asheville coal fired steam electric plant was retired in January of 2020. Coal
combustion residual (CCR) from the original steam electric plant was collected in an ash basin
constructed in conjunction with the original steam electric plant in 1964. The original coal fired
steam electric plant has been replaced by a new natural gas burning combined cycle station. In
addition to the new combined cycle station, Duke Energy is building a new CCR landfill for disposal
of CCR from the original 64-ash basin. Duke Energy has submitted a modification request
that includes the proposed addition of four new Stormwater outfalls., !two of these outfalls SW-9
and SW0101 will receive discharge from areas associate with the combined cycle station, while the
other two outfalls (SW011 and SW012) will receive discharge from the access roads for the new
CCR landfill.
PROPOSED ADDITIONAL OUTFALLS AND MONITORING REQUIREMENTS
The Division considered potential pollutants from past and present industrial activities (coal-fired
electric generation, plant decommissioning, and future ash removal) and data submitted in the
modification request received on January 29, 2020. The analytical monitoring requirements under
the current permit include priority pollutant metals, TSS, total rainfall, boron, and pH.
Parameters are based on potential pollutants in the drainage area, sampling results, and in some
cases, dependent upon future activities (e.g., ash removal through the drainage area). Below is a
table of the proposed monitoring for each outfall at the 4Y-er�Asheville Steam Electric Plant
site. All outfalls ultimately discharge to the Lake Julian and an unnamed tributary to Powell Creek.
Ni"I: ES Stor M�,,, to Permit NCYM05749

Stormwater Discharge Outfall (SDO) Monitoring
SW-9 and SW01 0
New Combined Cycle Station
Total Suspended Solids (TSS)
FREOUENCY: Semi-annual monitoring
BASIS: Potential pollutant from drainage areas and BMP
effectiveness indicator.
pH
FREQUENCY, Semi-annual monitoring
BASIS: Pollutant indicator.
Stormwater Discharge Outfall (SDO) Monitoring
SWO11 and SWO12
New Coal Combustion Residual Landfill
Total Suspended Solids (TSS)
FREOUENCY: Semi-annual monitoring (quarterly during coal or
CCR transport).
BASIS: Potential pollutant from drainage areas and BMP
effectiveness indicator. Quarterly during coal or CCR transport to
ensure proper handling during transport.
Priority Pollutant Metals Ag, As,
FREQUENCY: Semi-annual monitoring (quarterly during coal or
Be, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Se,
CCR transport)
TI, and Zn.
BASIS: Pollutant indicator for coal combustion residual (CCR)
constituents.
Boron
FREOUENCY: -Semi-annual monitoring (quarterly during coal or
CCR transport)
BASIS: Coal combustion residual (CCR) constituent / coal tracer.
Polychlorinated biphenyl
FREOUENCY: Semi-annual monitoring: may be discontinued
compounds (PCBs)
after the first year (two samples) if not detected.
BASIS: PCBs persist in the environment if ever released. BMP
effectiveness indicator for decommissioning activities associated
with the original coal burning steam electric station.
Non -Polar Oil & Grease by
FREOUENCY: Semi-annual monitoring (quarterly during coal or
EPA Method 1664 (SGT-HEM)
CCR transport)
BASIS: Potential pollutant from lubricants associate with CCR
transport vehicles.
pH
FREOUENCY: Semi-annual monitoring (quarterly during coal or
CCR transport)
BASIS: Pollutant indicator and important to interpreting toxicity
potential of metals.
STORMWATER BENCHMARKS AND TIERED RESPONSE
Rather than limits, North Carolina NPDES Stormwater permits contain benchmark concentrations.
Stormwater benchmarks are numerical action levels for stormwater monitoring. Benchmarks are
not effluent limits, and benchmark exceedances are not permit violations. Benchmarks
provide facilities a tool for assessing the significance of pollutants in stormwater discharges and the
effectiveness of best management practices (BMPs). Benchmark concentrations are intended as
guidelines for the facility's development and implementation of the Stormwater Pollution
Prevention Plan (SPPP).
Benchmark exceedances require the permittee to increase monitoring, increase management
actions, increase record keeping, and/or install stormwater BMPs in a tiered program. The permit
establishes a tiered approach to specify actions the permittee must take in response to analytical
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MIDES Storm� atcr Permit NCYM057549
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results above benchmark concentrations (Part II, Section B., following Table 10). The tiered
structure of the permit provides the permittee and NCDEMLR wide flexibility to address issues that
may arise with one or more parameters and/or outfalls.
Metals benchmarks are calculated to mimic acute water quality standards and with the guidance of
NC's Division of Water Resources (DWR). Acute standards Drotect aquatic life from negative
imraacts of short-term exraosure to higher levels of chemicals where the discharge enters a
waterbodv. 'I"he Stormwaterer �* Pro r ai�n achuses acute standards
because of the ephemeral nature of rainfall events.
NC DWR follows established federal procedures for calculating acute standards when developing
the benchmarks„ t l tin the acute c* � etals benchmarks normally reflect one half
of the calculated Final Acute Value (the "1/z FAV"). EPA estimates the FAV by a conducting -a
statistical analysis of Dublished peer -reviewed acute toxicity data. The FAV is designed to protect
95 percent of the species in the most sensitive genera that has been tested and aDplying a safety
factor of two to protect water quality. In most cases, translation into total recoverable values is
based on an assumed hardness of 25 mg/1 and a total suspended solids (TSS) concentration of 10
mg/1.
The Division may evaluate monitoring results to determine if a smaller suite of parameters for
some outfalls is adequate to characterize potential pollution or BMP effectiveness. For example,
one or more metals or other parameters may serve as an adequate tracer for the presence of ash
pollution during disturbance or ash removal in specific drainage areas at this site. For parameters
that do not have a stormwater benchmark, the Division may develop a benchmark value if
appropriate toxicity data become available or if rising trends in concentrations suggest a persistent
source. A summary of the benchmarks in the draft permit, and their basis, is below:
Parameter
Benchmark
Basis
Antimony Sb , m L Total
0.09
Acute Aquatic Criterion, 1/2 FAV
Arsenic (As), m L Total
0.34
Acute Aquatic Criterion, 1/2 FAV
Beryllium Be , m L Total
0.065
Acute Aquatic Criterion, 1/2 FAV
Cadmium Cd , m L Total
0.003
Acute Aquatic Criterion, 1/2 FAV
1/2 FAV, based on (Cr III + Cr VI) acute thresholds
Chromium (Cr), mg/L (Total)
0.9
and assumption that industrial activities here are
not a source of hexavalent chromium.
Copper (Cu), m L Total
0.010
Acute Aquatic Criterion, 1/2 FAV
Lead (Pb), m L Total
0.075
Acute Aquatic Criterion, 1/2 FAV
Monitoring only, CCR/Coal Constituent. Hg
influenced by regional transport and wet
Mercury (Hg), ng/L (Total)
N/A
deposition. Values above 12 ng/L (NC WQ
standard) should be noted on the DMR but do not
trigger Tier Responses.
Nickel (Ni), m /L (Total)
0.335
Acute Aquatic Criterion, 1/2 FAV
Polychlorinated biphenyl
Detected
NC Water Quality Standards vs. present Arochlors
compounds (PCBs), µg/L
quantitation levels (higher than standard)
1/2 FAV, NC -specific, based on 1986 Study on Se
Selenium (Se), mg/L (Total)
0.056
impacts in North Carolina
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MIDES Stor M�,atcr Permit NCYM057549
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Parameter
Benchmark
Basis
Acute Aquatic Criterion, 1/2 FAV. (The Division
Silver (Ag), mg/L (Total)
0.0003
notes this value is below the practical quantitation
level (PQL) of 1 µg/L of EPA Method 200.8)
Monitoring only, GGWCC
Boron (B), mg/L
N/A
R/Coal Constituent. Narrative National
Monitoring Only, CCR/Coal constituent.
Thallium (TI), mg/L (Total)
N/A
National Recommended Human Health Criterion.
Zinc Zn , m L Total
0.126
Acute Aquatic Criterion, 1/2 FAV
Total Suspended Solids (TSS),
National Urban Runoff Program (NURP) Study,
mg/L
100
1983
Non -Polar Oil & Grease, EPA
Review of other state's daily maximum benchmark
Method 1664 (SGT-HEM),
15
concentration for this more targeted 0&G; NC WQ
mg/L
Standard that does not allow oil sheen in waters.
pH
6-9
NC Water Quality Standard (Range)
MERCURY MONITORING REQUIREMENTS
The proposed permit requires mercury to be measured in stormwater samples by EPA Method
1631E, which can detect levels as low as 0.5 ng/l. This requirement is consistent with recent
federal rule -making that requires NPDES permittees to monitor discharges with sufficiently
sensitive test procedures approved under 40 CFR §136. Modifications to 40 CFR §122.44(i) require
a method that has a minimum level (ML) at or below the effluent limit (not applicable here), or the
lowest minimum level (ML) of EPA approved analytical methods for the measured parameter.
Based on results, Method 1631E will be required to quantify levels in these discharges. NC DEMLR
understands that this method is more costly and requires a more intensive sampling protocol than
most other parameters, and that fish tissue sampling will be provided during the permit cycle.
Therefore, no benchmark applies that would trigger tiered response actions. Proposed permit
provisions also allow the permittee to use field blank and/or method blank concentrations to adjust
reported mercury levels as long as documented is submitted with the Data Monitoring Report
(DMR).
PROPOSED SCHEDULE FOR PERMIT ISSUANCE:
Draft Permit to Public Notice:
Permit Scheduled to Issue:
STATE CONTACT:
If you have any questions about any of the above information or the attached permit, please contact
Mdie Rand ll att Gwinn at [phone] or [e-mail]
act Ylect
Ni"I:ES Stor :,�atcrPcrmit NCYM057549