NC0020443_Fact Sheet_20220705

DEQ / DWR / NPDES
EXPEDITED FACT SHEET - NPDES PERMIT RENEWAL
NPDES Permit NC0020443
Joe Corporon, P.G., Compliance & Expedited Permitting Unit 05Ju12022
Facility Information
Applicant/Facility Name
Town of Columbia
Columbia Wastewater Treatment Plant (WWTP)
Applicant Address
P.O. Box 361, Columbia, NC 27925
Facility Address
604 N. Road Street Extension (NCSR 1219)
Facility Contact
Rhett White, Town Manager [[e-mail].]
Permitted Flow (MGD)
0.600 MGD
Type of Waste
100% Domestic Wastewater Discharge
Facility Class
WW-2
County
Tyrrell
Permit Status
Renewal
Regional Office
WaRO
Stream Characteristics
Receiving Stream
Scuppernong River
Stream Classification
SC
Stream Segment
[30-14-4-9]
Drainage basin
Pasquotank
Summer 7Q10 (cfs)
Tidal
Subbasin
03-01-53
Winter 7Q10 (cfs)
Tidal
Use Support
ND
30Q2 (cfs)
Tidal
303(d) Listed
No
Average Flow (cfs)
Tidal
State Grid
D33NE
IWC (%)
100%
USGS Topo Quad
Columbia West, NC
Facility History -- Town of Columbia WWTP (Columbia) is a minor municipal (flow < 1 MGD)
WWTP, WPCS Grade 2 treating 100% domestic waste with a design capacity of 0.600 MGD. The
Permittee has made no significant changes in the system since last renewal, an upgrade in 2010
from 0.300 MGD to 0.600 MGD [ATC No. 020443A01]; see below, Treatment System
Configuration.
Compliance — The attached Violations Summary is sorted by year (newest to oldest). The latest violations
occurred in Dec2021. Occasional NOVs issued for enterococci and TSS (2021), and TSS, BOD-5 (2020).
Whole Effluent Toxicity (WET) testing is currently not required — no changes recommended.
The Permittee Requests Changes for Renewal -- The Permittee's application requests DWR to
reduce monitoring frequencies (3/Week) for BOD-5, TSS, Ammonia Nitrogen (NH3 as N), and
Enterococci (see App., Analysis of Testing Results for the Past Three Years. However, BIMS
databases suggest limit violations for these parameters (see attached Compliance Summary).
Therefore, no changes recommended.
Renewal Summary — Updated facility description and map; updated table and footnotes [section A. (1.)];
updated text for Electronic Reporting.
Receiving -Stream —Columbia discharges via Outfall 001 into the Scuppernong River [Stream Segment
30-14-4-9]. This segment is not listed as impaired in the 2018 North Carolina 303(d) report.
Implementation of 2012 Statewide Mercury TMDL — Initially, Columbia's permit required Quarterly
monitor for Mercury in keeping with a statewide Mercury strategy. In response to the Columbia's request
(05Jan2015), the Division reduced monitoring from Quarterly to Annually (03Mar2015), and in 2017,
again modified monitoring to once (1) per permit cycle [see A. (1.), footnote 7]. No changes
recommended for this renewal.
Fact Sheet - Renewal Sep2020
NPDES Permit NC0020443
Page 1 of 7

Treatment System Configuration:
• influent flow meter
• a mechanical bar screen with manual bar screen bypass
• aerated grit removal system
• two (2) each 325,000-gallon oxidation ditches [w/ return -activated sludge]
• four (4) each 65,000 gallon, 30-ft diameter clarifiers
• one RAS tank [10,000-gal w/ centrifuge return]
• one 200,000-gallon aerated sludge holding tank
• one 154,000-gallon aerated sludge holding tank
• one 52,000-gallon sludge digester
• effluent treatment pump station with chlor/dechlor, dosing and chemical contact
o two (2) each 2.5-gpm pumps [chemical -feed, diaphragm]
o one 12,000-gal wastewater holding tank [disinfection
[NaC1O] chlorine -contact]
o two (2) each 11,500-gal post -aeration basins
o one 10,000-gal dechlor tank for dechlor mixing [CaO3S2]
• outfall pump station with two (2) each 20-hp effluent pumps [vertical turbine]
• effluent flow meter
• 34-ft receiving -stream effluent diffuser
• standby generator
Flow Summary — Jan2013-Ju12017
Year
Average
n
Minimum
Maximum
2017
0.261
365
0.142
671
2018
0.298
365
0.095
0.902
2019
0.226
365
0.049
0.838
2020
0.190
365
0.063
0.679
2021
0.187
365
0.055
0.742
2022
0.179
120
0.095
0.417
RPA — A Reasonable Potential Analysis
(RPA) was not applied for this renewal,
deemed unwarranted considering the
parameters of concern for this permit.
Page 2 of 7

PROPOSED SCHEDULE OF ISSUANCE
Draft Permit to Public Notice:
Permit Scheduled to Issue:
Effective Date
NPDES DIVISION CONTACT
12Ju12022 (est.)
19Aug2022 (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: 05JuL2022
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/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
Page 3 of 7

Table 2 Notes:
1. FW= Freshwater, SW= Saltwater
2. Calculatiol = 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 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, µg/1
Cadmium, Acute
WER*{1.136672-[ln hardness](0.041838)} •
3.1485}
e^{0.9151 [ln hardness]-
Cadmium, Acute Trout
waters
WER*{1.136672-[/n hardness](0.041838)} •
3.6236}
e^{0.9151[ln hardness] -
Cadmium, Chronic
WER* {1.101672-[in hardness](0.041838)} •
4.4451 }
e^{0.7998[In hardness] -
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[In hardness]-1.702}
Lead, Acute
WER*{1.46203-[ln hardness](0.145712)} •
1.460}
e^{1.273[ln hardness]-
Lead, Chronic
WER*{1.46203-[ln hardness](0.145712)} •
4.705}
e^{1.273[ln hardness] -
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[In 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.
Page 4 of 7

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
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, 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.
Page 5 of 7

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 + { [KA [sso+a)] [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.
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 = (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
Page 6 of 7

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)
[Total as, CaCO3 or (Ca+Mg)]
N/A
No metals monitored
Average Upstream Hardness (mg/L)
[Total as, CaCO3 or (Ca+Mg)]
N/A
7Q10 summer (cfs)
0.0
Tidal
1Q10 (cfs)
0.0
Tidal
Permitted Flow (MGD)
N/A
0.600
Page 7 of 7