NC0024210_Speculative Limits_20230328

DocuSign Envelope ID: 4A7FO632-9C77-4207-BCE5-4F42ED4C57B5
ROY COOPER
Governor
ELIZABETH S. BISER
Secretary
RICHARD E. ROGERS, JR.
Director
Mr. Robby Stone, Public Works Director
City of High Point
211 South Hamilton St.
High Point, NC 27760
Dear Mr. Stone:
NORTH CAROLINA
Environmental Quality
3/28/2023
Subject: Speculative Effluent Limits
City of High Point Eastside WWTP
NPDES Permit No. NCO0242 10
Guilford County
Cape Fear River Basin
The Division of Water Resources (DWR) Modeling and Assessment Branch (MAB) has completed review of
the Highpoint Eastside WWTP expansion revised modeling files submitted to DWR by Tetra Tech for review
on December 22, 2022. Tetra Tech has addressed the previously identified concerns by both MAB and
NPDES and submitted full documentation, including modeling files. The Municipal Unit (NPDES) has
completed our assessment of this material and the following speculative effluent limits have been developed.
Receivin2 Stream. The Deep River is located within the Cape Fear River Basin. The Deep River has a stream
classification of WS-IV; CA:*, and waters with this classification are used as sources of water supply for
drinking, culinary, or food processing purposes as well as for aquatic life propagation and maintenance of
biological integrity, wildlife, secondary recreation and agriculture. It is also designated as a critical area (CA)
which means the area adjacent to a water supply intake or reservoir where risk associated with pollution is
greater than from the remaining portions of the watershed. North Carolina regulation 15A NCAC 2B .0202
(20) provides a more thorough definition of critical area. In addition, it is recommended that 15A NCAC 2B
.0216 also be reviewed in its entirety for the water quality standards that are applicable to WS-IV CA streams.
The USGS responded to a low flow request with the following revised flows: the Deep River has a drainage
area of 96.1 sq mi, a surnmer (annual) 7QIO flow of 2.4 cfs, a winter 7QIO flow of 6.5 cfs, a 30Q2 flow of 9.1
cfs, and an annual average flow (AAF) of 93.2 cfs. Note: For the expansion, an elimination of the 2' outfall is
expected, and the speculative limits proposed reflect this future condition.
The Deep River at Outfall 001 [stream segment 17-(4), from dam at Oakdale Cotton Mills, Inc. to dam at
Randleman Lake] is not currently listed as an impaired waterbody on the 2022 North Carolina 303(d) Impaired
Waters List. There is a Total Maximum Daily Load (TMDL) on the Deep River for turbidity and fecal coliform.
Based upon a review of information available from the North Carolina Natural Heritage Program Online Map
Viewer, there are Federally Listed threatened or endangered aquatic species identified within a 5-mile radius of
the proposed discharge location. If there are any identified threatened/endangered species, it is recommended
that the applicant discuss the proposed project with the US Fish and Wildlife Service to determine whether the
proposed discharge location might impact such species.
North Carolina Department of Environmental Quality I Division of Water Resources
512 North Salisbury Street 1 1617 Mail Service Center I Raleigh, North Carolina 27699-1617
919.707.9000
4NORT�HCA�RCLINA�

DocuSign Envelope ID: 4A7FO632-9C77-4207-BCE5-4F42ED4C57B5
Speculative Effluent Limits. Based on the revised materials provided, NPDES concludes that an expansion to
32 MGD should include the following permit limits (in Table 1). A complete evaluation of these limits and
monitoring requirements for metals and other toxicants, as well as potential instrearn monitoring
requirements, will be addressed upon receipt of a complete NPDES permit application.
Every applicant shall also submit documentation of any additional pollutants for which there are certified
methods with the permit application if their discharge is anticipated. These pollutants may be found in 40
CFR Part 136, if there are additional pollutants with certified methods to be reported, please submit the
Chemical Addendum to NPDES Application and, if applicable, list the selected certified analytical method
used.
TABLE 1. Speculative Limits for City of High Point Eastside WWTP (Proposed Expansion to 32
MGD)
EFFLUENT
CHARACTERISTICS
EFFLUENT LIMITS
Monthly
Average
Weekly
Average
Daily
Maximum
Flow
32 MGD
BOD5
5.0 mg/L
7.5 mg/L
Dissolved Oxygen (minimum)
Daily average > 6.0 mg/l
TSS
30 mg/L
45 mg/L
NH3
0.8 mg/L
2.4 mg/L
Total Nitrogen
4.68 mg/L
1,249 lbs/day
Total Phosphorus
0.40 mg/L
107 lbs/day
Total Residual Chlorine
18 ug/L
Fecal coliform (geometric mean)
200/100 rriL
400/100 mL
1,4-Dioxane
1.0 �tg/L
2.87 gg/L
Total Phosphorous (TP) concentration under the expansion scenario is shown as 0.40 mg/L to avoid an increase
in TP load. It should be noted that BOD5 is not proposed as "hold the load" concentrations but retain the same
concentration as in the current permit for 26.0 MGD. The report implies that BOD5 reduction is limited by the
proposed facility's planned treatment technologies, although not specifically discussed. This raises an
uncertainty with regards to impact on DO with the expansion. There are also uncertainties with regards to
chlorophyll -a concentrations in the reservoir. Additionally, there are uncertainties resulting from model and
data limitations (e.g., input parameters, model formulations). Due to these uncertainties, if a permit is eventually
issued for a 32 MGD discharge, reservoir monitoring requirements below the discharge for DO (surface) and
chlorophyll -a (May -Sep only, photic zone composite) cannot be waived by participating in the Upper Cape
Fear River Basin Association.
1,4-Dioxane. For the direct discharge to Class WS-IV; CA:* Deep River, I x 10` risk level ITV of 0.35 �Lg/L
for water supply waters at an AAF of 93.2 cfs and a permitted design flow of 32.0 MGD was considered. This
calculation yielded a chronic allowable discharge concentration of 1.0 gg/L. A daily maximum limitation has
been calculated for from the chronic monthly average limitation. Derivation of the maximum daily limit is
based on EPA's Technical Support Document (TSD, USEPA 19911).
USEPA (1991). Technical Support Document for Water Quality -Based Toxics Control. EPA50512-90-001. Office of Water
Enforcement and Permits.
North Carolina Department ofEnvironmental Quality I Division ofWater Resources
512 North Salisbury Street 1 1617 Mail Service Center I Raleigh, North Carolina 27699-1611
e,�­oREQ5
919.707.9000

DocuSign Envelope ID: 4A7FO632-9C77-4207-BCE5-4F42ED4C57B5
According to the TSD, developing final permit limits for pollutants affecting human health is somewhat
different from setting limits for other pollutants because the exposure period is generally longer than I month.
Therefore, the EPA -recommended approach for setting water quality -based limits for human health protection
with statistical procedures is as follows:
• Set the AML (Average Monthly Limit) equal to the WLA (to meet the instrearn target value of 0.35
gg/L)
• Calculate the MDL (Maximum Daily Limit) based on effluent variability and the number of samples
per month using the multipliers provided in TSD Table 5-3.
This approach ensures that the instrearn criteria will be met over the long-term and provides a defensible method
for calculating an MDL.
The daily maximum final limit was developed using the recommended approach in TSD Section 5.4.4, for
human health protection. Input variables for the multiplier table consulted (TSD Table 5-3) included:
• A coefficient of variation (CV) of 1.47 based on the most recent 58 data points (August 2020 — January
2023) and after removing outlier values,
• AML exceedance probability of 95' percentile,
MDL exceedance probability of 99th percentile,
A weekly sampling frequency (n = 4/month).
Outlier values were identified as reported data points with a calculated Z score > 3 or < -3. To determine these
outlier values, effluent data from November 2018 through January 2023 were assessed. The data ranged from
less than I gg/L to 237 gg/L, with an average of 25.3 gg/L during the period reviewed. As part of this
assessment, 2 data points were deemed outliers and removed. Based on this assessment and TSD Table 5-3, a
multiplier of 2.87 was calculated. This multiplier was applied to the average monthly limitation of 1.0 gg/L to
obtain the maximum daily limitation of 2.87 gg/L.
Please note that the same approach described above has been used to develop a chronic monthly average
limitation of 1. 16 gg/L and a maximum daily limitation of 3.3 3 gg/L at the current 26. 0 MGD flow tier.
Enizineeriniz Alternatives Analysis (EA& Please note that the Division cannot guarantee that an NPDES permit
for a new or expanding discharge will be issued with these speculative limits. Final decisions can only be made
after the Division receives and evaluates a formal permit application for the expanded discharge.
In accordance with North Carolina Administrative Code 15A NCAC 2H.0105(c), the most environmentally
sound alternative should be selected from all reasonably cost-effective options. Therefore, as a component of
all NPDES permit applications for new and expanding flo includes a detailed engineering alternatives analysis
(EAA) that must be prepared. The EAA must justify the requested design flow and provide an analysis of
potential wastewater treatment alternatives. A copy of the Division guidance for preparing EAA documents is
attached and/or can be found online at:
https:llfiles.nc.jzovincdeqlSurface%20Water%2OProtectionINPDESIpermitsleaa-guidance-20140501 -
dwr-swp-nipdes 13.pdf.
State Environmental Policy Act (SEPA) EVEIS Requirements. A SEPA EVEIS document may be required
for projects that: 1) involve $ 10 Million or more of state funds; or 2) will significantly and permanently
impact 10 or more acres of public lands. Please check with the DWR SEPA coordinator (David Wainwright,
919-707-9045) as to whether your project requires SEPA review. For projects that are subject to SEPA, the
EAA requirements discussed above will need to be folded into the SEPA document. If required, a FONSI
must be issued prior to issuance of the NPDES permit for the expansion. Details related to FONSI can be
found on-line at: htlps://deq.nc.go�L/permits-regulations/sepa/review-process and at:
https://deq.nc.gov/about/divisions/water-infrastructure/documents/cdbgi-fonsiea
North Carolina Department ofEnvironmental Quality I Division ofWater Resources
512 North Salisbury Street 1 1617 Mail Service Center I Raleigh, North Carolina 27699-1611
e,�­oREQ5
919.707.9000

DocuSign Envelope ID: 4A7FO632-9C77-4207-BCE5-4F42ED4C57B5
We understand this expansion project is moving forward rapidly; however, we would expect that any request
for NPDES permitting action for the expansion be taken within a five-year period from the date of this letter,
or the noted speculative limits in Table I would be subject to reassessment and review.
Should you have any questions about these speculative limits or NPDES permitting requirements, please feel
free to contact Kristin Litzenberger at [phone] / kristin.litzenbergerkncdenr.gov or Michael Montebello
at Michael.Montebello(&ncdenr.gov.
Respectfully,
DocuSigned by,
E khKh'kVh
644'FE
Michael Montebello
NPDES Program Branch Chief
Attachment: Link to EAA Guidance Document, Chemical Addendum Form, and NPDES application information:
hLtps:Hdeg.nc.gov/about/divisions/water-resources/water-qualily-pennittin2/npdes-wastewatgL/npdes-permittin2-process/�pdes-
individual-permit-Uplications
ec: NPDES Files [Laserfiche]
City of High Point / Robby Stone, Public Works Director [[e-mail]]; Derrick Boone, Public Services
Assistant Director [[e-mail]]
Tetra Tech / Hillary Yonce [[e-mail]]; Trevor Clements [[e-mail]]
DWR / Richard Rogers [[e-mail]]; [Julie Grzyb [e-mail]]; Pam Behm
[[e-mail]]; Nick Coco [[e-mail]]; Bongghi Hong [[e-mail]]; Adugna Kebede
[[e-mail]]; Doug Dowden [[e-mail]]; Derek Denard [[e-mail]]
Winston-Salem Regional Office / Jenny Graznak [e-mail]]
NC VvIRC / Olivia Munzer [[e-mail]]
US FWS / Sara Ward [sara [e-mail]]
DWR / Basinwide Planning / Nora Deamer [[e-mail]]
U.S. EPA Region W / Daniel Holliman [[e-mail]]
North Carolina Department ofEnvironmental Quality I Division ofWater Resources
512 North Salisbury Street 1 1617 Mail Service Center I Raleigh, North Carolina 27699-1611
e,�­#REQ5
919.707.9000