NC0000752_Fact Sheet_20230120

NC0000752
Fact Sheet
NPDES Permit No. NC0000752
Permit Writer/Email Contact Sergei Chernikov, [e-mail]:
Date: October 3, 2022
Division/Branch: NC Division of Water Resources/NPDES Complex Permitting
Fact Sheet Template: Version 09Jan2017
Permitting Action:
❑X Renewal
❑ Renewal with Expansion
❑ New Discharge
❑ Modification (Fact Sheet should be tailored to mod request)
Note: A complete application should include the following:
• For New Dischargers, EPA Form 2A or 2D requirements, Engineering Alternatives Analysis, Fee
• For Existing Dischargers (POTW), EPA Form 2A, 3 effluent pollutant scans, 4 2nd species WET
tests.
• For Existing Dischargers (Non-POTW), EPA Form 2C with correct analytical requirements based
on industry category.
Complete applicable sections below. If not applicable, enter NA.
1. Basic Facility Information
Facility Information
Applicant/Facility Name:
WestRock Paper, LLC /Roanoke Rapids Mill
Applicant Address:
North Roanoke Avenue, Roanoke Rapids, NC 27870
Facility Address:
North Roanoke Avenue, Roanoke Rapids, NC 27870
Permitted Flow:
28.0 MGD
Facility Type/Waste:
MAJOR Industrial
Facility Class:
Class 4
Treatment Units:
• Mechanical bar screen
• Primary clarifier
• Emergency holding pond
• Sludge lagoon
• Aeration basin
• Three stabilization ponds
Pretreatment Program (Y/N)
N/A
County:
Halifax
Region
Raleigh
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NC0000752
Briefly describe the proposed permitting action and facility background: West Rock Paper, LLC operates
an unbleached (Cluster Rule is not applicable) paper mill in Roanoke Rapids producing high quality
unbleached Kraft paper and paperboard. The mill is integrated including power generation, chemical
recovery, pulp production and final paper and paperboard manufacturing. The site operates a WWTP to
treat the wastewaters generated during the process. The facility is permitted to discharge 28.0 MGD of
process water through Outfall 001 and non -contact cooling water from the evaporator cooling tower through
Outfall 002.
Process wastewaters are conveyed to the WWTP through a concrete lined open channel. The WWTP
consists of a bar screen, 200 ft diameter primary clarifier, 28 million gallon emergency pond, 21.5 acre
aeration pond with 31 aerators, four stabilization ponds with a total of 370 acres, an effluent defoamer
addition system, for solids treatment sludge neutralization tank, two rotary screen thickeners, two screw
presses and a sludge lagoon. The emergency pond is used to divert process flow in the event they have a
power failure, mechanical problems or high strength waste. The water from the emergency pond is pumped
back to the influent channel at a controlled rate. Condensate collected from the process areas is piped
directly to the influent of the aeration basin. Sludge is landfilled on site under permit WQ0000436.
2. Receiving Waterbody Information:
Receiving Waterbody Information
Outfalls/Receiving Stream(s):
Outfall 001/002- Roanoke River
Stream Segment:
23-(26)
Stream Classification:
C
Drainage Area (mi2):
8,384
Summer 7Q10 (cfs)
1,120
Winter 7Q10 (cfs):
30Q2 (cfs):
1,120
Average Flow (cfs):
2400
IWC (% effluent):
3.73
303(d) listed/parameter:
No
Subject to TMDL/parameter:
Statewide Mercury TMDL
Subbasin/HUC:
Roanoke; 030208
USGS Topo Quad:
B28NW/Roanoke Rapids
3. Effluent Data Summary
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NC0000752
Effluent data is summarized below for the period 2015-2020.
Table. Effluent Data Summary — Outfall 001
Parameter
Units
Average
Max
Min
Permit
Limit
Flow
MGD
18.9
26.7
28.0 MA
BOD
lb/day
1,796
4,087
6,852 MA
NH3N
mg/L
2.8
TSS
lb/day
2,774
7,431
15,576 MA
pH
SU
8.0
6.9
6.0-9.0
Temperature
°C
30.6
14.0
MA -Monthly Average, WA -Weekly Average, DM -Daily Maximum
4. Instream Data Summary
Instream monitoring may be required in certain situations, for example: 1) to verify model predictions
when model results for instream DO are within 1 mg/1 of instream standard at full permitted flow; 2) to
verify model predictions for outfall diffuser; 3) to provide data for future TMDL; 4) based on other
instream concerns. Instream monitoring may be conducted by the Permittee, and there are also
Monitoring Coalitions established in several basins that conduct instream sampling for the Permittee (in
which case instream monitoring is waived in the permit as long as coalition membership is maintained).
If applicable, summarize any instream data and what instream monitoring will be proposed for this
permit action: The current permit requires instream monitoring for dissolved oxygen, conductivity, and
temperature. Review of instream data for the past five years indicates that the dissolved oxygen standard
of 5 mg/L was always maintained, and there was very little difference between upstream and downstream
stations. This draft permit maintains the same instream monitoring requirements.
Is this facility a member of a Monitoring Coalition with waived instream monitoring (Y/N): NO
Name of Monitoring Coalition: NA
5. Compliance Summary
Summarize the compliance record with permit effluent limits (past 5 years): The facility reported no limit
violations during the last 5 years.
Summarize the compliance record with aquatic toxicity test limits and any second species test results
(past 5 years): The facility passed 18 of 18 quarterly chronic toxicity tests.
Summarize the results from the most recent compliance inspection: N/A
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6. Water Quality -Based Effluent Limitations (WQBELs) - Outfall 001
Dilution and Mixing Zones
In accordance with 15A NCAC 2B.0206, the following streamflows are used for dilution considerations
for development of WQBELs: 1Q10 streamflow (acute Aquatic Life); 7Q10 streamflow (chronic Aquatic
Life; non -carcinogen HH); 30Q2 streamflow (aesthetics); annual average flow (carcinogen, HH).
If applicable, describe any other dilution factors considered (e.g., based on CORMIX model results): NA
If applicable, describe any mixing zones established in accordance with 15A NCAC 2B. 0204(b): NA
Oxygen -Consuming Waste Limitations
Limitations for oxygen -consuming waste (e.g., BOD) are generally based on water quality modeling to
ensure protection of the instream dissolved oxygen (DO) water quality standard. Secondary TBEL limits
(e.g., BOD= 30 mg/1 for Municipals) may be appropriate if deemed more stringent based on dilution and
model results.
If permit limits are more stringent than TBELs, describe how limits were developed: N/A
Ammonia and Total Residual Chlorine Limitations
Limitations for ammonia are based on protection of aquatic life utilizing an ammonia chronic criterion of
1.0 mg/1 (summer) and 1.8 mg/1 (winter). Acute ammonia limits are derived from chronic criteria,
utilizing a multiplication factor of 3 for Municipals and a multiplication factor of 5 for Non -Municipals.
Limitations for Total Residual Chlorine (TRC) are based on the NC water quality standard for protection
of aquatic life (17 ug/1) and capped at 28 ug/1 (acute impacts). Due to analytical issues, all TRC values
reported below 50 ug/1 are considered compliant with their permit limit.
Describe any proposed changes to ammonia and/or TRC limits for this permit renewal: There are no
proposed changes.
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 Y2 detection limit for "less than" values; and 4) streamflows 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 of
Instream Dissolved Metals Standards, dated June 10, 2016.
A reasonable potential analysis was conducted on effluent toxicant data collected between during the last
5 years. 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: N/A
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NC0000752
• 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: N/A.
• 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: As, Be, Cd, Cr, Total Phenolic Compounds, Cu, F, Pb, Hg, Mo, Ni, Se, Ag, and
Zn.
Attached is a spreadsheet of the RPA results as well as a copy of the Dissolved Metals Implementation
Fact Sheet for freshwater/saltwater to this Fact Sheet.
Toxicity Testing Limitations — Outfall 001
Permit limits and monitoring requirements for Whole Effluent Toxicity (WET) have been established in
accordance with Division guidance (per WET Memo, 8/2/1999). Per WET guidance, all NPDES permits
issued to Major facilities or any facility discharging "complex" wastewater (contains anything other than
domestic waste) will contain appropriate WET limits and monitoring requirements, with several
exceptions. The State has received prior EPA approval to use an Alternative WET Test Procedure in
NPDES permits, using single concentration screening tests, with multiple dilution follow-up upon a test
failure.
Describe proposed toxicity test requirement: This is a Major Facility, and a chronic WET limit at 3.7%
effluent will continue.
Mercury Statewide TMDL Evaluation— Outfall 001
There is a statewide TMDL for mercury approved by EPA in 2012. The TMDL target was to comply
with EPA's mercury fish tissue criteria (0.3 mg/kg) for human health protection. The TMDL established a
wasteload allocation for point sources of 37 kg/year (81 lb/year), and is applicable to municipals and
industrial facilities with known mercury discharges. Given the small contribution of mercury from point
sources (-2% of total load), the TMDL emphasizes mercury minimization plans (MMPs) for point source
control. Municipal facilities > 2 MGD and discharging quantifiable levels of mercury (>1 ng/1) will
receive an MMP requirement. Industrials are evaluated on a case -by -case basis, depending if mercury is a
pollutant of concern. Effluent limits may also be added if annual average effluent concentrations exceed
the WQBEL value (based on the NC WQS of 12 ng/1) and/or if any individual value exceeds a TBEL
value of 47 ng/1
Describe proposed permit actions based on mercury evaluation: The facility provided only one mercury
result of <150.0 ng/L and the allowable limit is 321.7 ng/L. Since no annual average mercury
concentration exceeded the WQBEL, and no individual mercury sample exceeded the TBEL, no mercury
limit is required.
Other TMDL/Nutrient Management Strategy Considerations
If applicable, describe any other TMDLs/Nutrient Management Strategies and their implementation
within this permit: N/A
Other WQBEL Considerations
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NC0000752
If applicable, describe any other parameters of concern evaluated for WQBELs: NA
If applicable, describe any special actions (HQW or ORW) this receiving stream and classification shall
comply with in order to protect the designated waterbody: N/A
If applicable, describe any compliance schedules proposed for this permit renewal in accordance with
15A NCAC 2H.0107(c)(2)(B), 40CFR 122.47, and EPA May 2007 Memo: N/A
If applicable, describe any water quality standards variances proposed in accordance with NCGS 143-
215.3(e) and 15A NCAC 2B. 0226 for this permit renewal: NA
7. Technology -Based Effluent Limitations (TBELs)
Industrials (if not applicable, delete and skip to next Section)
Describe what this facility produces: producing high quality unbleached Kraft paper and paperboard.
List the federal effluent limitations guideline (ELG) for this facility: §40 CFR 430.32 and §40 CFR
430.34.
If the ELG is based on production or flow, document how the average production/flow value was
calculated: This ELG is based on production. The annual average production (tons/day) for the past 5
years was reported as 1,458 tons/day.
For ELG limits, document the calculations used to develop TBEL limits: The limits in the Table below are
based on production of 1,458 tons/day and the effluent guidelines in §40 CFR 430.32 and §40 CFR
410.34.
Monitoring for pentachlorophenol and trichlorophenol is not required if the facility doesn't use
chlorophenolic-containing biocides.
Table. TBEL Development per 40 CFR 430.32/BPT and 40 CFR 430.34/BAT
Pollutant
Daily Maximum
BPT/BAT
(lb/1000 lb)
Daily Maximum
Limit
(lb /d)
Monthly Average
BPT/BAT
(lb/1000 lb)
Monthly Average
Limit
(lb/d)
BOD5
5.6
18,289
2.8
9,145
TSS
12
39,191
6
19,596
Pentachloro
phenol
0.00058
1.89
Trichlorophe
nol
0.00053
1.73
If any limits are based on best professional judgement (BPJ), describe development: NA
Document any TBELs that are more stringent than WQBELs: NA
Document any TBELs that are less stringent than previous permit:
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Proposed TBELs for BOD are slightly higher than in the previous permit due to the increases in
production. In 1995, DWQ developed a field -calibrated, steady-state model for dissolved oxygen in
approximately 74 miles of the Roanoke River, which extends from NC 48 bridge at Roanoke Rapids to
the Wildlife Resources Commission boat ramp at Hamilton. At existing permitted loads during low flow
conditions, the predicted minimum dissolved oxygen level is approximately 6.0 mg/L. The instream
monitoring indicates that the predictions are correct and slight increase in the BOD should not result in
the contravention of the instream DO standard of 5.0 mg/L. The DWR will continue to evaluate DO
concentrations in this portion of the Roanoke River.
Proposed TBELs for TSS, pentachlorophenol, and trichlorophenol are also increasing due to the increase
in production.
8. Antidegradation Review (New/Expanding Discharge):
The objective of an antidegradation review is to ensure that a new or increased pollutant loading will not
degrade water quality. Permitting actions for new or expanding discharges require an antidegradation
review in accordance with 15A NCAC 2B.0201. Each applicant for a new/expanding NPDES permit
must document an effort to consider non -discharge alternatives per 15A NCAC 2H.0105( c)(2). In all
cases, existing instream water uses and the level of water quality necessary to protect the existing use is
maintained and protected.
If applicable, describe the results of the antidegradation review, including the Engineering Alternatives
Analysis (EAA) and any water quality modeling results: NA
9. Antibacksliding Review:
Sections 402(o)(2) and 303(d)(4) of the CWA and federal regulations at 40 CFR 122.44(1) prohibit
backsliding of effluent limitations in NPDES permits. These provisions require effluent limitations in a
reissued permit to be as stringent as those in the previous permit, with some exceptions where limitations
may be relaxed (e.g., based on new information, increases in production may warrant less stringent TBEL
limits, or WQBELs may be less stringent based on updated RPA or dilution).
Are any effluent limitations less stringent than previous permit (YES/NO): Yes
If YES, confirm that antibacksliding provisions are not violated: The antibacksliding provisions are not
violated since the new limits are based on the 40 CFR 430 Subpart C requirements for the new
production value and they are not expected to negatively impact the instream DO concentrations.
10. Monitoring Requirements
Monitoring frequencies for NPDES permitting are established in accordance with the following
regulations and guidance: 1) State Regulation for Surface Water Monitoring, 15A NCAC 2B.0500; 2)
NPDES Guidance, Monitoring Frequency for Toxic Substances (7/15/2010 Memo); 3) NPDES Guidance,
Reduced Monitoring Frequencies for Facilities with Superior Compliance (10/22/2012 Memo); 4) Best
Professional Judgement (BPJ). Per US EPA (Interim Guidance, 1996), monitoring requirements are not
considered effluent limitations under Section 402(o) of the Clean Water Act, and therefore anti -
backsliding prohibitions would not be triggered by reductions in monitoring frequencies.
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NC0000752
For instream monitoring, refer to Section 4.
11. Electronic Reporting Requirements
The US EPA NPDES Electronic Reporting Rule was finalized on December 21, 2015. Effective
December 21, 2016, NPDES regulated facilities are required to submit Discharge Monitoring Reports
(DMRs) electronically. Effective December 21, 2020, NPDES regulated facilities will be required to
submit additional NPDES reports electronically. This permit contains the requirements for electronic
reporting, consistent with Federal requirements.
12.Summary of Proposed Permitting Actions:
Table. Current Permit Conditions and Proposed Changes
Parameter
Current Permit
Proposed Change
Basis for Condition/Change
Flow — Outfall 001
Outfall 002
MA 28.0 MGD
Unlimited
No change
No change
15A NCAC 2B .0505
BOD5-Outfall 001
DM 17,361 mg/L
MA 8,680 mg/L
DM 18,289 mg/L
MA 9,145 mg/L
TBEL. Based on increased
production per 40 CFR 430 Subpart
C.
NH3-N-Outfall
001
Monitor only
No change
WQBEL. Based on protection of
State WQ criteria. 15A NCAC
2B.0200
TSS-Outfall 001
DM 37,202 mg/L
MA 18,601 mg/L
DM 39,191 mg/L
MA 19,596 mg/L
TBEL. Based on increased
production per 40 CFR 430 Subpart
C.
Pentachlorophenol
-Outfall 001
DM 1.8 lb/day
DM 1.89 lb/day
TBEL. Based on increased
production per 40 CFR 430 Subpart
C.
Trichlorophenol-
Outfall 001
DM 1.64 lb/day
DM 1.73 lb/day
TBEL. Based on increased
production per 40 CFR 430 Subpart
C.
DO-Outfall 001
Monitor only - effluent
and instream
No change
WQBEL. State WQ standard, 15A
NCAC 2B .0200 and 15A NCAC 2B
.0500
pH-Outfall 001
and Outfall 002
6.0 — 9.0 SU
No change
WQBEL. State WQ standard, 15A
NCAC 2B .0200
pH-Outfall 002
Monitor only, effluent
and instream
No change
WQBEL. State WQ standard, 15A
NCAC 2B .0500
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Total Nitrogen-
Outfall 001
Monitor only
No change
State WQ standard, 15A NCAC 2B
.0500
Total Phosphorus-
Outfall 001
Monitor only
No change
State WQ standard, 15A NCAC 2B
.0500
Conductivity-
Outfall 001
Monitor only - effluent
and instream
No change
State WQ standard, 15A NCAC 2B
.0200 and 15A NCAC 2B .0500
Toxicity Test —
Outfall 001
Chronic limit, 3.7%
effluent
No change
WQBEL. No toxics in toxic
amounts. 15A NCAC 2B.0200 and
15A NCAC 2B.0500
Temperature-
Outfall 001 and
Outfall 002
Monitor only
No change
State WQ standard, 15A NCAC 2B
.0500
Temperature-
Outfall 001
Monitor only, effluent
and instream
No change
State WQ standard, 15A NCAC 2B
.0200 and 15A NCAC 2B .0500
Total Copper-
Outfall 001
DM 227.36 pg/L
MA 211.25 pg/L
Remove the limits
WQBEL. State WQ standard, 15A
NCAC 2B .0200. Based on the RPA
results.
Total Hardness
Effluent and upstream
monitoring
No change
Needed for implementing new state
WQ standards, 15A NCAC 2B
.0200.
Electronic
Reporting- Outfall
001 and Outfall
002
Electronic Reporting
Special Condition
No change
In accordance with EPA Electronic
Reporting Rule 2015.
MGD — Million gallons per day, MA - Monthly Average, WA — Weekly Average, DM — Daily Max
13. Public Notice Schedule:
Permit to Public Notice: 10/18/2022
Per 15A NCAC 2H .0109 & .0111, The Division will receive comments for a period of 30 days following
the publication date of the public notice. Any request for a public hearing shall be submitted to the
Director within the 30 days comment period indicating the interest of the party filing such request and the
reasons why a hearing is warranted.
14. Fact Sheet Addendum (if applicable):
Were there any changes made since the Draft Permit was public noticed (Yes/No): Yes, please see
Section 16.
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If Yes, list changes and their basis below: NA
15. Fact Sheet Attachments (if applicable):
• RPA Spreadsheet Summary
• Dissolved Metals Implementation/Freshwater or Saltwater
• ELG calculations
16. Changes in the Final Permit.
• The new PFAS Special Condition was added to the permit to implement EPA's PFAS Guidance
and in response to the public comments.
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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-[ln hardness](0.041838)} - e^{0.9151 [ln hardness]-
3.1485}
Cadmium, Acute
waters
Trout
WER*{1.136672-[ln hardness](0.041838)} - e^{0.9151[1n hardness] -
3.62361
Cadmium, Chronic
WER*{1.101672-[ln hardness](0.041838)} - e^{0.7998[In hardness]-
4.4451 }
Chromium III, Acute
WER*0.316 - e^{0.8190[ln hardness]+3.7256}
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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[In hardness]-1.702}
Lead, Acute
WER* { 1.46203-[ln hardness](0.145712)} • e^ {1.273 [ln hardness]-1.460}
Lead, Chronic
WER* { 1.46203-[ln hardness](0.145712)} • e^ {1.273 [ln hardness1-4.705 }
Nickel, Acute
WER*0.998 • e^{0.8460[ln hardness]+2.255}
Nickel, Chronic
WER*0.997 • e^{0.8460[ln 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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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.
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 =
Ctotal
Where:
1
1 + { [KPo] Iss(1+a)] [10 6l 1
ss = in -stream suspended solids concentration [mg/1], minimum of 10 mg/L used,
and
4. The 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.
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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 + 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* (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
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
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N C0000752
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+Mg)]
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
1 Q 10 (cfs)
0
Lake or Tidal
Permitted Flow (MGD)
2.1
For dewatering
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