NC0039586_Fact Sheet_20210903 (2)

DEQ / DWR
FACT SHEET FOR NPDES PERMIT DEVELOPMENT
NPDES Permit No. NC0039586
Facility Information
Applicant/Facility Name
Duke Energy Progress/Harris Nuclear Plant and Harris Energy
and Environmental Center
Applicant Address
5413 Shearon Harris Rd., New Hill, NC 27562
Facility Address
5413 Shearon Harris Rd., New Hill, NC 27562
Permitted Flow (MGD)
Outfall 006 — not limited
Outfall 007 — 0.02 MGD
Type of Waste
Industrial and domestic
Facility Class
Class II
County
Wake
Facility Status
Renewal
Regional Office
Raleigh
Stream Characteristics
Receiving Stream
Harris Reservoir
Stream Classification
WS-V
Drainage basin
Cape Fear
Subbasin
03-06-07
Drainage Area (sq. mi.)
NA
Use Support
Supporting
Summer 7Q10 (cfs)
NA
303(d) Listed
No
Winter 7Q10 (cfs)
NA
State Grid
New Hill
30Q2 (cfs)
NA
USGS Topo Quad
E23SW
Average Flow (cfs)
NA
Permit Writer
Sergei
Chernikov, Ph.D.
IWC (%)
NA
Date
3/25/2021
Summary:
Duke Energy Progress owns and operates the Harris Nuclear Plant (HNP), a 930 MW generating unit
and associated facilities. The facility has two outfalls to Harris Reservoir, Outfalls 006 and 007. Outfall
006 is the combined discharge of five internal outfalls (001 through 005). Outfall 007 is the outfall for
the treatment system at the Harris Energy and Environmental Center, which includes facilities that
provide support services (laboratories and training classrooms). HNP operates employs an open air
recirculating closed cycle cooling water system drawing make-up water from Harris Reservoir.
Outfalls Description:
Internal Outfall 001— Cooling tower blowdown. The system uses a natural draft cooling tower system
discharging an average of 4.6 MGD.
Internal Outfall 002 — Sewage Treatment facility for treatment of industrial and domestic wastewaters
from the HNP. The treatment system was upgraded to accommodate additional staff during outages
and maintenance activities. The total capacity of the new treatment system is 0.065 MGD. The effect
of this increase in the total discharged flow will be minimal as the additional wastewaters represent
only 1.3 % of total flow discharged through outfall 006.
Internal Outfall 003 — Metal Cleaning Wastes. Cleaning of equipment with chemicals is rarely
conducted. The wastewater generated in the process would be treated in the waste neutralization basin
and settling basin.
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Internal Outfall 004 — Low volume wastes. Low volume wastes are generated from the following
processes: demineralize water treatment system, floor drains, non -radioactive oily wastes, containment
drains, steam generator and auxiliary boiler draining, condensate polishers, miscellaneous drains and
leaks from condenser, steam generator and secondary components, auxiliary boiler system blowdown,
and other miscellaneous waste streams. Low volume wastes are treated by neutralization, sedimentation
and separation. The wastes may be treated by oil/water separator if needed.
Internal Outfall 005 — Radwaste treatment system. Treatment for potential radioactive liquids. The
waste streams are collected in tanks and sampled prior to selecting treatment. Radwaste is treated by a
Modular Fluidized Transfer Demineralization System. Radiological treatment process and components
are modified as necessary to achieve desired treatment in compliance with the Nuclear Regulatory
regulations. If not radioactive, the wastes are routed to the low volume waste treatment system.
Outfall 006 — Combined outfall to Harris Reservoir. Outfalls 001, 002, 003, 004, and 005 are combined
in a common pipe discharging 40 feet below the surface.
Outfall 007 — Harris Energy and Environmental Center (HEEC) WWTP. Wastewaters generated at the
HEEC include domestic wastes, laboratory wastes, cooling tower blowdown from A/C system, and
stormwater.
Receiving Stream:
The discharge is to Harris Reservoir, classified WS-V in the Cape Fear River Basin, HUC
030300040102. Harris Reservoir is not listed as impaired in the draft 2016 303(d) list.
316(b):
The permittee submitted report required to comply with the Cooling Water Intake Structure Rule per
40 CFR 125.95.
The facility uses one of the seven impingement BTA (Best Technology Available) alternatives
identified in the rule - closed -cycle cooling with a natural draft cooling tower. Hence, the Division
concludes that this system is consistent with a closed -cycle recirculating system defined in 40 CFR
125.92(c) and meets the BTA standards for Impingement Mortality defined in 40 CFR 125.94(c)(1).
The report determined that the cooling system employed by the plant achieved a calculated flow
reduction of 91% based on design flow and 365 days per year operation. Furthermore, using actual
flows during the 2016-2018 period, the withdrawal reduction is 97.0%. Additional evaluation of the
facility based on the factors in 40 CFR 122.25(f) indicates that the existing closed -cycle cooling
provides benefits to entrainment relative to once -through cooling. The report also states that "The
entrainment at the facility is low and is not expected to involve federally protected species or their
designated critical habitat. Potential impacts to fish and shellfish population at the plant is also
extremely unlikely due to the operation of the intake." Therefore, the Division designated the existing
closed -cycle cooling as BTA for Entrainment.
Permit Requirements:
Internal Outfall 001— Cooling tower blowdown.
The permittee requested that the requirements for total chromium and total zinc be moved to outfall
006. Limits for both parameters are required by Federal Effluent Guidelines and must be applied at the
discharge point of the blowdown before comingling with other wastewaters. The limits will not be
modified. Table 1 lists the Effluent Limitations Guidelines (ELG) applicable to this outfall.
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ELGs Outfall 001
Pollutant
Daily Maximum
Monthly Average
ELG
Free Available
Chlorine
0.5 mg/L
0.2 mg/L
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)
126 pollutants
No detectable amounts
40 CFR 423.13 (d) (1)
pH
6 to 9 S.U.
40 CFR 423.12 (b) (1)
Monitoring Requirements/Proposed Changes Outfall 001
Parameter
Monitoring
requirements/Limits*
Changes
Flow
Monitor
No changes
15A NCAC 2B.0500
Free Available
chlorine
0.2 mg/L MA
0.5 mg/L DM
No changes
40 CFR 423.13 (d) (1)
Total Residual
Chlorine
Monitor
No changes
40 CFR 423.13 (d) (2)
Time of TRC
discharge
120 min
No changes
40 CFR 423.13 (d) (2)
Total chromium
0.2 mg/L MA
0.5 mg/L DM
No changes
40 CFR 423.13 (d) (1)
Total zinc
1 mg/L MA
1 mg/L DM
No changes
40 CFR 423.13 (d) (1)
pH
6 to 9 S.U.
No changes
40 CFR 423.12 (b) (1)
MA — Monthly Average, DM — Daily Maximum
Internal Outfall 002 — HNP domestic treatment system.
The permittee requested to eliminate the ammonia monitoring requirements and apply it at outfall 006.
Ammonia is monitored at the discharge point from domestic WWTPs to ensure proper operation and
treatment. The ammonia requirements will remain at outfall 002.
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Monitoring Requirements/Proposed Changes Outfall 002
Parameter
Monitoring
requirements/Limits
Changes
t as'
Flow
0.065 MGD
No changes
New treatment system was
installed.
TSS
30 mg/L monthly aver
45 mg/L daily max
No changes
Domestic wastewater, 15A
2B .0400
BOD
30 mg/L monthly aver
45 mg/L daily max
No changes
Domestic wastewater, 15A
2B .0400
Fecal Coliform
200/100 mL monthly
average
400/100 mL daily max
No changes
15A 2B .0200
Ammonia
Monitor
No changes
DWR Policy
Total Residual
chlorine
Monitor
No changes
DWR Policy
Internal Outfall 003 — Metal cleaning wastes
This outfall is subject to the ELG in the following Table.
ELGs Outfall 003
Pollutant
Daily Maximum
Monthly Average
ELG
Total Copper
1 mg/L
1 mg/L
40 CFR 423.13 (e)
Total Iron
1 mg/L
1 mg/L
40 CFR 423.13 (e)
pH
6 to 9 S.U.
40 CFR 423.12 (b) (1)
This outfall did not discharge during the past permit cycle. No changes are proposed for Outfall 003.
Internal Outfall 004 — Low volume wastes
This outfall is subject to the following ELGs.
ELGs Outfall 004
Pollutant
Daily Maximum
Monthly Average
ELG
TSS
100 mg/L
30 mg/L
40 CFR 423.12 (b) (3)
Oil and Grease
20 mg/L
15 mg/L
40 CFR 423.12 (b) (3)
pH
6 to 9 S.U.
40 CFR 423.12 (b) (1)
Monitoring Requirements/Proposed Changes Outfall 004
Parameter
Monitoring
requirements/Limits
Changes
Basis
Flow
1.5 MGD
No changes
15A NCAC 02B .0500
pH
6 to 9 S.U.
No changes
40 CFR 423.12 (b) (1)
TSS
30 mg/L MA
100 mg/L DM
No changes
40 CFR 423.12 (b) (3)
Oil and grease
15 mg/L MA
20 mg/L DM
No changes
40 CFR 423.12 (b) (3)
Internal Outfall 005 — Radwaste treatment system (low volume wastes)
This outfall is subject to the following ELGs.
ELGs for Outfall 005
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Pollutant
Daily Maximum
Monthly Average
ELG
=
TSS
100 mg/L
30 mg/L
40 CFR 423.12 (b) (3)
Oil and Grease
20 mg/L
15 mg/L
40 CFR 423.12 (b) (3)
pH
6 to 9 S.U.
40 CFR 423.12 (b) (1)
Monitoring Requirements/Proposed Changes Outfall 005
Parameter
Monitoring
requirements/Limits
Changes
Basis
i
Flow
Monitor
No changes
15A NCAC 02B .0505
pH
6 to 9 S.U.
No changes
40 CFR 423.12 (b) (1)
TSS
30 mg/L MA
100 mg/L DM
No changes
40 CFR 423.12 (b) (3)
Oil and grease
15 mg/L MA
20 mg/L DM
No changes
40 CFR 423.12 (b) (3)
Outfall 006— Combined outfall (Outfalls 001, 002, 003, 004, and 005)
This outfall has an approved mixing zone for temperature. The mixing zone comprises 200 acres around
the point of discharge. 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).
Water Effect Ratio Study
Special Condition A. (9) of the HNP permit requires the facility to achieve compliance with the final
effluent limits for zinc and copper at outfall 006 as specified in in the effluent limitations and
monitoring requirements for Special Condition A. (6) by September 30, 2021. As part of that
compliance schedule, Duke also had to develop a corrective action plan (CAP) with annual
benchmarks in the years leading up to September 30, 2021. The CAP identified anti -corrosion
chemicals as the main contributor to elevated zinc levels in the effluent. After changing processes and
discontinuing the use of zinc based corrosion inhibitors, zinc levels have dropped dramatically and
compliance with the final effluent limits has been achieved. Sources of copper were also evaluated in
the CAP. No copper compounds are added to the process and the source of copper was determined to
be the concentration of copper levels in the lake (-1 µg /L) from evaporation in the cooling water
with minor contributions from leaching from existing equipment.
To achieve compliance with copper limits, Duke conducted a water -effects ratio (WER) study for
copper in 2019 (Corrective Action Plan for Copper and Zinc for Harris Nuclear Plant NPDES Permit -
Year 3 Activities Report, August 19, 2019). Dissolved copper standards in 15A NCAC 2B allows for
the use of a WER when deriving hardness -based dissolved copper standards. The WER study
proposed a WER = 5 for use in the standards calculation. However, the WER study was conducted at
100% effluent with an average effluent hardness of 43.8 mg/L. The Division requested, per EPA
guidance for WER evaluations in lakes, to do a mixing zone analysis (MZA) in conjunction with
another WER study which incorporates effluent mixed with site water at a ratio to be determined by
the near -field dilution from the mixing zone in order to derive a WER that reflects mixing of the
effluent with the receiving water. This would factor in all the variables beyond hardness that affect
copper toxicity (e.g. dissolved organic carbon, pH, cations/anions that form copper complexes, etc.)
inherent in the combined effluent and receiving water.
Duke completed the MZA using CORMIX simulations in 2020 (Corrective Action Plan for Copper
and Zinc for Harris Nuclear Plant NPDES Permit- Year 4 Activities Report, August 19, 2020). The
MZA evaluated four seasonal conditions, with the summer season determined to be the most limiting
condition due to the presence of the summer thermocline which affects the buoyant thermal
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discharge. Duke submitted a revised report in February 2021 along with a permit modification
application requesting the incorporation of the MZA in calculating copper and zinc limits and
withdrawal of the WER study. The CORMIX study proposes a dilution of 15.3:1 at a radial distance
of 177 ft and plume width of 278 ft. This value is the dilution found by applying the EPA criteria for
sizing acute mixing zones found in EPA's Technical Support Document for Water -quality Based
Toxics Control (TSD) section 4.3.2.
Summary of Proposed Copper Limits from the WER and CORMIX studies.
Proposed Limits Cu
Hardness (mg/L)
Monthly Average (µg/L)
Daily Maximum (µg/L)
WER
43.6
63.6
88.8
CORMIX
26.2
166.1
166.1
Discussion & Suggestions
While the acute mixing zone size in the MZA is correctly sized according to the most limiting criteria
from the TSD, the TSD also cautions about applying mixing zones when the effluent may attract biota
and specifically mentions temperature as a possible attractive force. In the MZA, the summer
condition is most limiting (with respect to dilution) because of the summer thermocline inhibiting the
buoyancy of the discharge, resulting in plume contact with a thermal stratified layer. Temperature
profiles of the lake showed no stratified layer during colder seasons. There is concern that a large
acute mixing zone as proposed may attract biota, especially in the winter months. The MZA is still
useful for understanding plume dynamics, future WER studies, and potential 316(a) variances.
When a WER is granted, a study must be performed every permit cycle to maintain the WER for the
next permit. Because a WER is site specific, this value may change permit to permit to reflect
changes in the effluent and receiving water characteristics as well as updates to methodology. Given
that the existing WER study is based on effluent characteristics only, several options are provided for
the current permit modification request and compliance schedule.
The Division proposes to use the calculated WER study value to derive limits for the
renewal/modification and require the WER study for the next permit cycle to incorporate site water
per EPA guidance and the Division's prior request.
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Renewal -- NPDES NC0039586
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Monitoring Requirements/Proposed Changes Outfall 006
Parameter
Monitoring
requirements/Limits
Changes
Basis
Hydrazine
60 µg/L during regular
operations
2.0 mg/L during period
following wet lay-up
during extended outage,
maximum of 48 hours.
No changes
Protection of water quality
Temperature
Monitor
No changes
Approved mixing zone
pH
6 to 9 SU
No changes
15A 2B .0200
Total Copper
7.9 µg/L Monthly
average
10.5 µg/L Daily
maximum
Change limits
63.6 µg/L Monthly
average
88.8 µg/L Daily
maximum
New limits are based on the
WER study results. There
is no RP for these limits.
Total Zinc
126 µg/L Monthly
average
126 µg/L Daily
maximum
Remove limits
No reasonable potential to
exceed the water quality
standards.
Total Suspended
Solids
Monitor
No changes
15A 2B .0200
NH3 as N
Monitor
No changes
15A 2B .0200
Total Arsenic
No monitoring
Add monitoring
Based on RPA. Predicted
result >50% allowable and
limited dataset.
Total Selenium
No monitoring
Add monitoring
Based on RPA. Predicted
result >50% allowable.
Total Nitrogen,
Total Phosphorus
Monitor
No changes
15A NCAC 02B .0508
Flow
No requirement
Monitor
15A NCAC 02B .0505
Outfall 007 — Domestic wastewater plant at HEEC.
The permittee requested the monthly BOD limits of 30 mg/1 monthly average and 45 mg/1 daily
maximum to apply year around limit. The summer limits are more stringent than winter limits to protect
instream DO. Antibacksliding regulations do not allow for less stringent limits that the current permit.
Monitoring Requirements/Proposed Changes Outfall 007
Parameter
Monitoring
requirements/Limits
Changes
Basis
Flow
0.02 MGD
No changes
15A NCAC 02B .05
Total Suspended
Residue
30 mg/L monthly aver
45 mg/L daily max
No changes
Domestic wastewater, 15A
2B .0200
BOD (summer)
15 mg/L monthly aver
22.5 mg/L daily max
30 mg/L monthly aver
45 mg/L daily max
No changes
Water quality limited
BOD (winter)
Fecal Coliform
200/100 mL monthly
average
400/100 mL daily max
No changes
15A 2B .0200
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Ammonia (summer)
4 mg/L monthly aver
20 mg/L daily max
8 mg/L monthly aver
35 mg/L daily max
No changes
Water quality limited
Ammonia (winter)
Total Residual
chlorine
28 µg/L
No changes
15A 2B .0200
DO
5 mg/L
No changes
15A 2B .0200
Total Nitrogen,
Total Phosphorus,
TKN, Nitrate Nitrite.
Monitor
No changes
15A 2B .0500
Compliance Summary:
Summarize the compliance record with permit effluent limits (past 5 years): The facility had the following limit
violations during the last 5 years: two Zinc limits violations, two Oil and Grease limit violations, and one fecal
coliforms limit violations. All violations occurred in 2018 and 2019.
Summarize the compliance record with aquatic toxicity test limits and any second species test results (past 5
years): The facility passed all the WET tests during the last 5 years, please see attached.
Summarize the results from the most recent compliance inspection: The latest compliance inspection was
conducted on 02/27/2020. The inspection report did not identify any deficiencies, except for limit violations.
Reasonable Potential Analysis (RPA) for Toxicants:
If applicable, conduct RPA analysis and complete information below.
The need for toxicant limits is based upon a demonstration of reasonable potential to exceed water quality
standards, a statistical evaluation that is conducted during every permit renewal utilizing the most recent
effluent data for each outfall. The RPA is conducted in accordance with 40 CFR 122.44 (d) (i). The NC RPA
procedure utilizes the following: 1) 95% Confidence Level/95% Probability; 2) assumption of zero background;
3) use of 'A detection limit for "less than" values; and 4) stream flows used for dilution consideration based on
15A NCAC 2B.0206. Effective April 6, 2016, NC began implementation of dissolved metals criteria in the RPA
process in accordance with guidance titled NPDES Implementation oflnstream Dissolved Metals Standards,
dated June 10, 2016.
A reasonable potential analysis was conducted on effluent toxicant data provided by the facility in the permit
application. Pollutants of concern included toxicants with positive detections and associated water quality
standards/criteria. Based on this analysis, the following permitting actions are proposed for this permit:
• Effluent Limit with Monitoring. The following parameters will receive a water quality -
based effluent limit (WQBEL) since they demonstrated a reasonable potential to exceed
applicable water quality standards/criteria.
• 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: Selenium, Arsenic, Zinc, Copper. Limit for Copper was not implemented
becauyse predicted Copper concentration of 63.5 µg/L is less than the WER based limit of
63.6 µg/L.
• 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: Beryllium, Cadmium, Total Phenolic Compounds, Total Chromium, Cyanide,
Fluoride, Lead, Mercury, and Nickel.
Attached are the RPA results and a copy of the guidance entitled "NPDES Implementation of lnstream
Dissolved Metals Standards — Freshwater Standards."
Additional Changes to Permit:
1. Special Condition A. (9) was edited to reflect completion of the Water Effect Ratio (WER) study.
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Renewal -- NPDES NC0039586
Page 8

PROPOSED SCHEDULE OF ISSUANCE
Draft Permit to Public Notice: July 13, 2021
Permit Scheduled to Issue: September 5, 2021
NPDES UNIT CONTACT
If you have questions regarding any of the above information or on the attached permit, please contact
Sergei Chernikov at [phone].
CHANGES IN THE FINAL PERMIT
1). Monitoring for Total Zinc was removed from the permit to correct an error (Outfall 006).
2). The language in Special Condition A. (17) was updated to eliminate inconsistency with the Fact
Sheet.
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Renewal -- NPDES NC0039586
Page 9

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, µg/1
(Dissolved)
Acute SW, µg/1
(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 2B.0200 (e.g., arsenic at 10 µg/1 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, µg/1
Cadmium, Acute
WER* {1.136672-[In 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-[In hardness](0.041838)} • e^{0.7998[ln hardness] -
4.4451 }
Chromium III, Acute
WER*0.316 • e^{0.8190[ln hardness]+3.7256}
Chromium III, Chronic
WER*0.860 • e^{0.8190[ln hardness]+0.6848}
Copper, Acute
WER*0.960 • e^{0.9422[ln hardness]-1.700}
Copper, Chronic
WER*0.960 • e^{0.8545[ln hardness]-1.702}
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Lead, Acute
WER* {1.46203- [In hardness] (0.145712) } • e^ {1.273 [In hardness] -
1.460}
Lead, Chronic
WER* {1.46203- [In hardness] (0.145712) } • e^ {1.273 [In hardness] -
4.705 }
Nickel, Acute
WER*0.998 • e^{0.8460[in hardness]+2.255}
Nickel, Chronic
WER*0.997 • e^{0.8460[in hardness]+0.0584}
Silver, Acute
WER*0.85 • e^{1.72[ln hardness]-6.59}
Silver, Chronic
Not applicable
Zinc, Acute
WER*0.978 • e^{0.8473[ln hardness]+0.884}
Zinc, Chronic
WER*0.986 • e^{0.8473[ln hardness]+0.884}
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/WQBELs 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:
• Critical low flow of the receiving stream, 7Q10 (the spreadsheet automatically
calculates the 1Q10 using the formula 1Q10 = 0.843 (s7Q10, cfs) 0.993
• Effluent hardness and upstream hardness, site -specific data is preferred
• Permitted flow
• Receiving stream classification
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Renewal -- NPDES NC0039586
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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/L) + (s7Q10, cfs *Avg. Upstream Hardness, mg/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.
4. The
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 1 + { [Kpo] [sso+a)I [10-6] }
Where:
ss = in -stream suspended solids concentration [mg/11, 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 sheet labeled DPCs.
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
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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 + Qw) (Cwqs) — (s7Q10) (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* Olg/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
6. 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)
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Average Effluent Hardness
(mg/L)
[Total as, CaCO3 or (Ca+Mg)]
25.0
Default value
Average Upstream Hardness
(mg/L)
[Total as, CaCO3 or (Ca+Mg)]
25.0
Default value
7Q10 summer (cfs)
17.14
CORMIX model, 8:ldilution
1Q10 (cfs)
14.16
RPA calculation
Permitted Flow (MGD)
1.58
Design flow of treatment system
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