NC0063321_fact sheet_20220908

FACT SHEET
EXPEDITED RENEWAL - NPDES PERMIT
NCO063321 — WPCS Grade WW-II
Basic Information
Permit Writer/Date
Joe R. Corporon L.G. / NPDES / 01 Se 2022
Permit Number / WPCS Grade
NC0063321 / Grade WW-II
Flow
0.200 MGD
Owner
Tuckasei ee Water and Sewer Authority TWSA
Facility Name
Cashiers #3 WWTP
Facility Contact
Stan B son, Operations Superintendent / 828-586-5189
Type of Waste
100 % domestic
Basin Name/Sub-basin number
Savannah River Basin / 03-13-01
Receiving Stream
Chattoo a River [Segment 3]
Stream Classification in Permit
B; Trout; ORW [no changes fromprevious]
Does permit need Daily Max NH3 limits?
No need - has MA & WA summer and winter
Does permit need TRC limits/language?
Has limit 22 L revised the TRC footnote for renewal
Does permit have WET testing?
No - per guidance document 2016
[re laced by NH3 limits and monitoring]
Does permit have Special Conditions?
Yes — collection -system additions require MOD see A. (2.).
Does permit have instream monitoring?
YES — Temp, Fecal, DO ORW waters
Is the stream impaired on 303 d list)?
No
Any obvious compliance concerns?
No
Any permit MODS since lastpermit?
No
Request for Renewal
Received 251762022
Current expiration date
August 31, 2022
New expiration date
August 31, 2027
Comments received on Draft Permit?
Revised Ammonia limits: "Winter no greater than 2x Summer"
er 15A NCAC 213.0404(c).
Renewal Strategy -- Flow is 100% domestic to receiving stream classified B; Trout; ORW. In lieu of WET
testing, the Permittee monitors Ammonia w/ limits (summer and winter). Parameters of Concern (POCs)
reported within permit limits [no violations since 16Oct2017 [BOD5]. TWSA has made no treatment system
alterations since last renewal (2017) - no permit changes recommended. DWR updated eDMR text; continued
reminder to Permittee in cover letter of ORW stream classification.
Data Review /Compliance Review -- BIMS effluent data from Jan2018 through Feb2022 (see XL Summaries).
BOD5, TSS, and Ammonia (NH3 as N) compliance good; monitoring effluent for Ammonia and instream
continues considering delicate stream class. Compliance issues limited to one NOV for BOD5 in Oct2017 (no
CPAs).
Flow Summary by Year
Highest Reported
Average Flow
Maximum
Number of
Year
Monthly Average
in MGD
Flow in MGD
Discharges
Flow
2018
0.091
0.216
366
—
2019
0.083
0.184
364
—
2020
0.094
0.213
366
—
2021
0.090
0.267
365
—
2022
0.070
0.204
59
0.113 MGD

WLA for NH3 Allowable = Summer 2.3 mg/L; Winter = 4.9 mg/L: (Effluent NH3 Database: Jan2018-
Jan2022) Ave = 1.21 mg/L; Max = 24.6 mg/L; Min = 0.5 mg/L
Ammonia Nitro en((NH3 as N) - Correction of Previous Limits: By Rule, Ammonia winter limits may not
exceed two (2) times the summer limits (15A NCAC 2B .0206). Therefore, the previous winter limits MA 4.8
mg/L and WA 14.4 mg/L are hereby lowered to 4.4 mg/L MA and 13.2 WA equal to two (2) times the summer
limits [see Table A. (1.)].
Renewal / Comments on DRAFT / Staff Report — ARO's last Staff Report is dated 29Aug2018. A previous
report submitted by a concerned citizen, Bill Floyd, described receiving stream "impacts" he felt threatened the
ORW classification (undocumented). Previous report with photos was added to the file, 2017.
PROPOSED SCHEDULE OF ISSUANCE
Draft Permit to Public Notice:
Permit Scheduled to Issue:
Effective Date
NPDES DIVISION CONTACT
28Jun2022 (est.)
IOSep2022 (est.)
01Oct2022 (est.)
If you have questions about any of the above information, or on the attached permit, please email Joe
R. Corporon, P.G. [e-mail]].
NAME:
DATE: O 1 SEP2022
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 2. NC Dissolved Metals Water Quality Standards/Aquatic Life Protection
Parameter
Acute FW, µg/l
(Dissolved)
Chronic FW, µg/1
(Dissolved)
Acute SW, µg/l
(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 2 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 3. 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, /1
Cadmium, Acute
WER*{1.136672-[ln hardness] (0.041838)} e^10.9151 [ln hardness]-3.1485)
Cadmium, Acute Trout waters
WER*{1.136672-[ln hardness] (0.04183 8)) e^{0.9151[ln hardness] -3.623 6)
Cadmium, Chronic
WER*{1.101672-[ln hardness] (0.041838)} a^{0.7998[ln hardness] -4.445 1)
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)) • eAll .273[In hardness]-1.460}
Lead, Chronic
WER*{1.46203-[ln hardness](0.145712)) • eAll .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}
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/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 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 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) x (s7Q10, cfs *Avg. Upstream Hardness, mom)
(Permitted Flow, cfs + s7Q 10, 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 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 amass balance equation to determine the total allowable concentration (permit limits)
for each pollutant using the following equation:
Ca = (s7010 + Owl (Cwas) — (s7010) (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 s7Q 10)
s7Q 10 = 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 s7Q 10 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.
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:
Table 4
Parameter
Value
Comments(Data Source
Average Effluent Hardness (mg/L)
N/A
No metals monitored
[Total as, CaCO3 or (Ca+Mg)]
Average Upstream Hardness (mg/L)
N/A
[Total as, CaCO3 or (Ca+Mg)]
7Q10 summer (cfs)
N/A
1Q10 (cfs)
N/A
Permitted Flow (MGD)
N/A
0.200