NC0063614_Fact Sheet_20230418

FACT SHEET FOR PERMIT RENEWAL
NPDES Permit Number NCO063614
Table 1 --Basic Information for Minor [<1.00 MGD] Permit Renewal
Permit Writer/Date Joe R. Corporon,P.G. 18A r2023
Permittee/Facility Name AQUA of NC,INC. /Wildwood Green WWTP
Facility Class WWTP WPCS Grade II
Amanda Berger,Director of Environmental Compliance
Facility Contact 919-773-0406 [[e-mail]]
202 Mackenan Court, Cary,NC 27511
Basin Name/Hydrological Unit Neuse River Basin /03-04-01
Receiving Stream UT To Upper Barton Creek(Lower Falls Lake)
Stream Classification in Permit WS-IV;NSW
Does permit need Daily Max NH3 limits? No—limits exist as MA/DM,summer and winter
Does permit need TRC limits/language? UV disinfection(TRC backup -monitor"only if'used
Does permit have WET testing? Yes—TGP3E Chronic Ceriodaphnia—changed Table only
"Monitor and Report"to"Limited" see below
Does permit have Special Conditions? Nitrogen allocation(Neuse River);
Does permit have instream monitoring? Yes DO and Temperature]
Is the stream impaired on 303(d)list No
Any obvious compliance concerns? No
Any permit mods since lastpermit? No
Current expiration date January31,2023
New expiration date January 31,2028
Comments received on Draft Permit?
Facility Summary
AQUA North Carolina Inc. —Wildwood Green WWTP (WPCS Class-II) discharges Upper Barton
Creek(tributary to Lower Falls Lake), stream Class WS-IV; NSW. This facility treats 100%-domestic
wastes supporting a current local population (estimated) of 1892 people.
Evaluation of Current Monitoring - established per guidance in 2B .0508.
• Previous Whole Effluent Toxicity(WET); 2018 Table A. (L) [TGP3B] previously indicates
"Monitor and Report"but Condition A. (5.) says "Limited." Table in error; adjusted table only.
• Ammonia(NH3 as N) limits (27Aug1990) set at summer 9.0 mg/L MA and 35.0 mg/L DM,
and winter 18.0 mg/L MA and 35.0 mg/L [IWC= 72%; receiving-stream flows are in BIMS;
• TN and TP continued 2/Month with limits—no changes recommended.
• TN and TP Annual Averages with limits (per Neuse TMDL)—no changes recommended.
• Noted tech correction letter for TN (23F62018), "limits effective 0lJan2019;"
• Since last renewal, Quarterly Average monitoring expired 31Dec2018.
Flow Summary:
Table 2—Annual Flows (total samples 814); permitted at 0.016 MGD
[*2023 excludes"outlier"reported 31Ju12022 as 147.66175 MGD].
Year Ave Minimum Maximum N
2021 0.034 0.004 0.125 365
2022 0.028 0.003 0.123 365
2023* 0.027 0.005 0.054 59
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Table 3 -- Compliance Summary-BIMS Databases Jan2021 to Feb2023
Parameter Average Max Min Count Action/Limit
Flow(MGD) 0.031 0.125 0.003 789 Limited-0.100 MGD
Flow(mgal/month) 0.916 1.229 0.596 25 Monitor and Report
BOD 5-day 2.199 mg/L 5.5 mg/L 2 mg/L 112 11.0 mg/L-16.5 mg/L summer/
22 mg/L-33 mg/L winter
TSS 2.736 mg/L 14 mg/L 2.5 mg/L 112 30/45 mg/L
Fecal(per#100 1.21 22 1 112 200MA/40ODM
Ammonia 0.278 mg/L 4.9 mg/L 0.0098 mg/L 112 9.0 mg/L-35.0 mg/L summer/
18/0 mg/L-35.0 mg/L winter
Total Kjeldahl Nitrogen 0.99 mg/L 4.2 mg/L 0.37 mg/L 53 Monitor and Report
TKN C0625
Nitrite CO 6301 6.23 mg/L 24 mg/L 0.18 m /L 53 Monitor and Report
Dissolved Oxygen 8.73 mg/L 236.2 mg/L 7.5 mg/L 218 Daily Ave not<6.0 mg/L
Total Residual Chlorine - - - - Backup-"Only if'used
H Standard Units 7.51 8.4 7.0 124 Monitor&Report
Total Nitrogen 7.22 mg/L 24.82 mg/L 4.85 m /L 53 Limit 8.0 mg/L
Total Phosphorus 1.29 mg/L 6.3 mg/L 0.25 mg/L 54 Limit 1.0 mg/L
Total Nitrogen[Load] 55.3 lb/mon 124.5 lb/mon 21.0 lb/mon 25 Monitor&Report
Total Phosphorus [Load] 10.0 lbs/yr 28.9 lbs/yr 3.0 lbs/yr 10 Monitor&Report
Whole Effluent Toxicity - 6 TGP3B-all PASS [Annual]
Renewal Summary:
• updated facility description and permit text.
• corrected Outfall location on facility map [updated BIMS]
• resorted effluent table by Measurement Frequency [see A. (1.)]
• considered Neuse River TMDL requirements for TN/TP-no changes recommended.
PROPOSED SCHEDULE FOR PERMIT ISSUANCE
Draft Permit to Public Notice: April 18, 2023
[Tentative] Permit Scheduled to Issue: May 19, 2023
[Tentative] Effective date July 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: 18APx2023
If
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J �

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 Chronic FW, µg/l Acute SW, µg/l Chronic SW, µg/l
(Dissolved) (Dissolved) (Dissolved) (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 213.0200 (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).
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, /l
Cadmium,Acute WER*{1.136672-[1n hardness](0.041838)} •e^{0.9151 [In hardness]-3.14851
Cadmium,Acute Trout waters WER*{1.136672-[ln hardness](0.04183 8)) •e^{0.9151[ln hardness]-3.623 61
Cadmium,Chronic WER*{1.l0l672-[1n hardness](0.04183 8)) •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[In 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 All.273[ln hardness]-1.460}
Lead,Chronic WER*{1.46203-[ln hardness](0.145712)} • e^{1.273[In 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)
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Zinc,Chronic WER*0.986 •e^{0.8473[ln hardness]+0.8841
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/WOBELs 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
1 Q 10 using the formula 1 Q 10=0.843 (s7Q 10,cfs)0.993
• Effluent hardness and upstream hardness, site-specific data is preferred
• 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 IQ 10 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.
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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 = I
Ctotal 1 + 1 [KEG.] [ss(1+a)] 10_6] 1
Where:
ss= in-stream suspended solids concentration [mg/1], 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 oroaram under a
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 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=(s7Q 10+Qw) (Cwgs)^(s7Q 10) (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:
1 Q 10=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.
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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)
Average Effluent Hardness(mg/L) Not Applicable.
[Total as, CaCO3 or(Ca+Mg)] No metals monitoring
Average Upstream Hardness(mg/L) Not Applicable.
[Total as, CaCO3 or(Ca+Mg)] No metals monitoring
7Q 10 summer(cfs) No Data in BIMS
1 Q 10 (cfs) No Data in BIMS
Permitted Flow(MGD) 0.016
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