NC0088048_Fact Sheet_20230620

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FACT SHEET FOR EXPEDITED PERMIT RENEWALS

This form must be completed by Permit Writers for all expedited permits which do not require
full Fact Sheets. My be administratively renewed with minor changes but may include more
complex issues (Special Conditions, 303(d) listed water, toxicity testing, instream monitoring,
compliance concerns).
Basic Information for Expedited Permit Renewals
Permit Writer/Date Joe R. Corporon, P.G. / 20Jun2023
Permit Number / Facility Grade NC0055048 / WPCS - PCNC
Facility Name Crabtree Bane LLC - Stonegate MHP WTP
Facility Contact Emily Bane, Manager
[[e-mail]]
Basin Name / Hydrological Unit Neuse River Basin / 03-04-01
Receiving Stream UT to Rhodes Creek
Stream Classification in Permit WS-IV; NSW
Does permit need Daily Max NH3 limits? No
Does permit need TRC limits/language? Already included
Does permit have WET testing? No
Does permit have Special Conditions? Updated eDMR condition
Does permit have instream monitoring? No
Is the stream impaired (on 303(d) list)? No
Any obvious compliance concerns? Maybe. Uses bleach to disinfect resulting in
sporadic TRC limit violations
Any permit mods since last permit? No
Current expiration date January 31, 2023
New expiration date January 31, 2028
Comments received on Draft Permit?
Greensand Filter - Stonegate MHP operates a small greensand WTP for local MHP use only (backwash
averages 0.00231 MGD). DWR developed the permit considering the Neuse River Nutrient Monitoring
Strategy. This Permittee is currently not eligible for NCG59 because TN/TP monitoring is required and is
unavailable in NCG59’s greensand monitoring table. No WET test or stream monitoring required.
System Chemicals Used by the Permittee:
• Potassium permanganate (Total Manganese monitoring required)
• No zinc used
• No fluoride used
• Disinfects w/ chlorine bleach
For Renewal (Per WTP Policy for Greensand):
1. Kept Total Manganese, Monitor & Report (WS-IV; NSW)
2. Discontinued Turbidity (stream not impaired for Turbidity)
3. Kept TN/TP per Neuse Management Strategy
4. WET testing not required of greensand – no change recommended
5. RPA not conducted / not warranted
6. Updated eDMR text
Compliance History: BIMS records show [no significant compliance issues]:
• Summer 2022 monitoring “frequency” violations for pH, Flow, TRC, and TSS
leading to NOVs (explained by permittee as [staff] medical emergency).
• Spring of 2021 shows four (4) TRC violations to 706% over limit resulting
in enforcement [Permittee disinfects w/ chlorine bleach].
• Fall of 2020 records Frequency violations and limit exceedances for Total
Manganese and Total Hardness, both proceeding to enforcement.
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PROPOSED SCHEDULE FOR PERMIT ISSUANCE
Draft Permit to Public Notice: June 27, 2023
[Tentative] Permit Scheduled to Issue: August 4, 2023
[Tentative] Effective date September 1, 2023
NPDES Division Contact

If you have questions on any of the above information or in the attached permit, please email Joe
R. Corporon, P.G. [[e-mail]].

NAME: DATE: 20JUN2023

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/l
(Dissolved)
Chronic FW,
µg/l
(Dissolved)
Acute SW, µg/l
(Dissolved)
Chronic SW,
µg/l
(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/l for human health protection; cyanide at 5
µg/L and fluoride at 1.8 mg/L for aquatic life protection).
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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/l
Cadmium, Acute WER*{1.136672-[ln hardness](0.041838)} ∙ e^{0.9151 [ln hardness]-3.1485}
Cadmium, Acute Trout waters WER*{1.136672-[ln hardness](0.041838)} ∙ e^{0.9151[ln hardness]-3.6236}
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}
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}
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 hardness]-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 an 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
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• 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/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 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
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] [ss(1+a)] [10-6] }

Where:
ss = in-stream suspended solids concentration [mg/l], 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.

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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 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.
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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)] Ave 216 mg/L ~
Average Upstream Hardness (mg/L)
[Total as, CaCO3 or (Ca+Mg)] ~ ~
7Q10 summer (cfs) 0.0 Zero-flow conditions
[7Q10 and 30Q2 = 0.0 cfs
1Q10 (cfs) 0.0 Zero-flow conditions
[7Q10 and 30Q2 = 0.0 cfs
Permitted Flow (MGD) Not limited per
WTP Policy Average wasteflow 0.00231 MGD