NC0004961_fact sheet - 2020_20210215

DENR/DWR
FACT SHEET FOR NPDES PERMIT DEVELOPMENT
PERMIT RENEWAL
NPDES No. NC0004961
Facility Information
Applicant/Facility Name:
Duke Energy Carolinas, LLC — Riverbend Steam Station
Applicant Address:
P.O. Box 1006, Charlotte, North Carolina 28201
Facility Address:
175 Steam Plant Road; Mount Holly, North Carolina 28120
Permitted Flow
No limit
Type of Waste:
100% industrial
Prim. SIC Code: 4911 — Electric Services
Facility/Permit Status:
Class I/Active; Renewal
County:
Gaston County
Miscellaneous
Receiving Stream:
Catawba River
(Mt. Island Lake)
Regional Office:
Mooresville
Stream Classification:
WS-IV and B-CA
State Grid / USGS Quad:
F15Sw
303(d) Listed?
No
Permit Writer:
Sergei Chernikov,
Ph.D.
Subbasin:
03-08-33
Date:
September 17, 2020
Drainage Area (mi2):
1800
711111W
002A: Lat. 35° 21' 55.44" N Long. 80° 58' 10.92" W
Summer 7Q10 (cfs)
80
Winter 7Q10 (cfs):
30Q2 (cfs)
Average Flow (cfs):
2700
IWC (%) for Outfall 002A:
0.25
SUMMARY
Duke Energy's Riverbend Steam Station was a coal fired steam electric plant in Gaston County,
the electricity generation was discontinued on 04/1/2013. Demolition of the coal-fired plant is
complete. The coal ash has been removed from both ash basins, ash stack, and cinder pit on March
16, 2019.
After decommissioning of both ash ponds, the vast majority of seeps ceased discharges. These
seeps will be removed from the permit. S-2, S-7, and S-8 are surface water features that were
included as outfalls (outfalls 102, 107, and 108) in the latest NPDES permit, but following
excavation of the coal ash impoundment, they were found to be streams. If remediation of
these streams is necessary, it will be addressed through the corrective action plan for the
former impoundment or other administrative process.
Outfall 002A is being repurposed from yard drain sump overflow to remediated groundwater
discharge. The rest of the outfalls are being eliminated from the permit.
This facility discharges to the Mountain Island Lake (Catawba River) in sub -basin 03-08-33. The
receiving stream is not listed as impaired.
REASONABLE POTENTIAL ANALYSIS (RPA)
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
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facility from outfall 002A. For the purposes of the RPA, the background concentrations for all
parameters were assumed to be below detections 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."
Calculations included: As, Be, Cd, Chlorides, Total Cr, Cr (VI), Cu, F, Pb, Hg, Mo, Ni, Se, Ag,
Zn, Tl, Nitrate/nitrite, Al, and Sb (please see attached). The renewal application listed 0.04 MGD
as a projected flow. The analysis indicates no reasonable potential to violate the surface water
quality standards or EPA criteria.
CWA SECTION 316(B)
Since the facility discontinued electricity generation in 2013 and does not use cooling water, it
will not be the subject to the Section 316(b) of Clean Water Act.
INSTREAM MONITORING-OuTFALL 002
The facility historically had 7 monitoring station, 2 located upstream and 5 located downstream.
It is recommended that the monitoring will continue.
The permit also required semi-annual upstream and downstream monitoring of the ash pond
discharge. Upstream site (Station B) is approximately 2 miles upstream of the discharge and
downstream location (Station C) is approximately 0.5 miles downstream of the discharge. These
monitoring stations have been established through the BIP monitoring program, which was
required to maintain 316(a) temperature variance. The monitored parameters are: As, Cd, Cr, Cu,
Hg, Pb, Se, Zn, and Total Dissolved Solids (TDS). The majority of the results are below
detection level (As, Cd, Cr, Pb, Se, Hg, Zn) the rest of the results are below water quality
standards (Cu and TDS). Only Cu demonstrated an increase at the downstream monitoring
location. These results are consistent with the previous monitoring results.
It is required that the monitoring at the stations B and C will continue until discharges from the
station are ceased. It is also required that the facility uses low level method 1631E for all Hg
analysis.
FISH TISSUE MONITORING-OuTFALL 002
The permit required fish tissue monitoring for As, Se, and Hg near the ash pond discharge once
every 5 years. This frequency is consistent with EPA guidance. Sunfish and bass tissues were
analyzed for these trace elements. The results were below action levels for Se and Hg (10.0 µg/g
— Se, 0.40 µg/g — Hg, NC) and screening value for As (1.20 — µg/g, EPA). These results are
consistent with the previous monitoring results.
TOXICITY TESTING- Outfall 002:
Current Requirement: 24hr Chronic P/F @ 2.7%
Recommended Requirement: 24hr Chronic P/F @ 0.25%
Monitoring Schedule: January, April, July, October
This facility has passed all chronic toxicity tests during the previous permit cycle, please see
attached. The change in the instream waste concentration was made based on the significant
decrease in the discharge volume.
For the purposes of the permitting, the long term average flow was used in conjunction with the
7Q10 summer flow to calculate the percent effluent concentrations to be used for WET.
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Although the calculated IWC for this discharge is 0.1%, the decision was made to use 0.25% to
allow for flow fluctuation.
COMPLIANCE SUMMARY
There were no violations of effluent standards contained in the permit during the previous permit
term, please see attached.
PERMIT LIMITS DEVELOPMENT
• The pH limits in the permit are based on the North Carolina water quality standards (15A
NCAC 2B .0200).
• The limits for Oil and Grease and Total Suspended Solids (Outfall 002 and Outfall 002A)
are based on the Best Professional Judgment and are lower than prescribed in the 40 CFR
423
• The Whole Effluent Toxicity limit is based on the requirements of 15A NCAC 2B .0500.
PROPOSED CHANGES:
• The following Outfalls have been eliminated from the permit because the flow has ceased
after the ash ponds have been decommissioned and ash removed: 001, 002, 011, 101, 103,
104, 105, 106, 109, 110, 111, and 112.
• There are additional Outfalls that have been eliminated from the permit: 102, 107, and 108.
The seeps that have been assigned these Outfall numbers are still flowing, but following
excavation of the coal ash impoundment, they were found to be streams. If remediation of
these streams is necessary, it will be addressed through the corrective action plan for the
former impoundment or other administrative process.
• Outfall 002A has been repurposed for the discharge of the treated groundwater.
• Appendix A has been repurposed from Plan for Identification of New Discharges to the
Compliance Boundary Map to be consistent with other Duke permits.
• Chronic toxicity requirements have been transferred from Outfall 002 to Outfall 002A.
• Groundwater Monitoring Well Construction and Sampling special condition has been
removed from the permit to be consistent with other Duke permits.
• Ash Closure Plan special condition has been removed from the permit due to the
completion of the coal ash excavation.
• Priority Pollutant Analysis condition has been removed from the permit since Outfall 002
is closed.
• Chronic Toxicity Monitoring frequency was reduced from Monthly to Quarterly due to the
completion of the coal ash excavation.
• Ash Settling Basin special condition has been removed from the permit due to the
completion of the coal ash excavation and decommissioning of the coal ash basins.
• Total Copper and Total Iron Monitoring has been removed from the permit since the
facility has been decommissioned and no longer subject to 40 CFR 423.
• The type of sampling for Outfall 002A has been changed from Grab to Composite based
on the requirements of 15A NCAC 2B .0500.
• Monitoring for Arsenic, Selenium, and Mercury have been added to Outfall 002A based
on the permitting policy for coal-fired power plants.
• The Applicable State Law special condition has been removed from the permit due to the
removal of all coal ash from the site.
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PROPOSED SCHEDULE:
Draft Permit to Public Notice:
Permit Scheduled to Issue:
December 22, 2020 (est.)
February 15, 2021 (est.)
STATE CONTACT:
If you have any questions on any of the above information or on the attached permit, please contact
Sergei Chernikov at [phone] or [e-mail]
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