NC0051322_Speculative Limits_20201120

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Governor .
MICHAEL S.REGAN
Secretary *ft +oo.
S.DANIEL SMITH NORTH CAROLINA I
Director Environmental Quality
November 20,2020
Dana Hill
Director of Operations
Carolina Water Service
4944 Parkway Plaza Boulevard, Suite 375
Charlotte,North Carolina 28217
Subject: Speculative Effluent Limits
Ashley Hills WWTP
Permit No.NC0051322
Wake County
Neuse River Basin
I Dear Ms. Hill:
This letter provides speculative effluent limits for expansion to 0.750 MGD at the Ashley
Hills WWTP. Please recognize that speculative limits may change based on future water quality
initiatives, and it is highly recommended that the applicant verify the speculative limits with the
Division's NPDES Unit prior to any engineering design work.
Receiving Stream. Poplar Creek has a stream classification of C;NSW and waters with this
classification have a best usage for aquatic life propagation and maintenance of biological
integrity, wildlife, secondary recreation, and agriculture. Poplar Creek has a summer 7Q10 flow
of 0.28 cfs, a winter 7Q10 flow of 0.96 cfs, a 30Q2 flow of 1.1 cfs,and an annual average flow
of 3.4 cfs.Poplar Creek at this location is not listed on the 303(d)list of impaired waters.However,
the NSW denotes the nutrient sensitive waters supplementary classification for all Neuse River
Basin surface waters because of basin-wide chlorophyll a impairments. Nutrient limits are
governed by the Neuse River Basin point source strategy for NPDES discharges in 15A NCAC
2B .0700.
Based upon a review of information available from the North Carolina Natural Heritage Program
Online Map Viewer, there are not any Federally Listed threatened or endangered aquatic species
identified within a 5 stream miles 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.
Speculative Effluent Limits. Based on Division review of receiving stream conditions and water
quality modeling results, speculative limits for the proposed expansion to 0.750 MGD
are presented in Table 1. A complete evaluation of these limits and monitoring requirements for
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metals and other toxicants, as well as potential instream monitoring requirements, will be
addressed upon receipt of a formal NPDES permit application. Some features of the speculative
limit development include the following:
• BOD/NH3 Limits. Biochemical oxygen demand (BOD) and ammonia-nitrogen limits were
determined by water quality modeling and are protective of instream dissolved oxygen(DO)and
ammonia toxicity.
• Nutrients: Total Nitrogen(TN)and Total Phosphorus(TP) limits were assigned according to the
Neuse River Basin nutrient management strategy in 15A NCAC 2B .0700. The facility must
demonstrate that it will be able to meet these limits from either securing additional nutrient
allocation, or through demonstrated treatment technology that can achieve these limits prior to
the Division approving modification of the permit.
TABLE 1. Speculative Limits for Ashley Hills WWTP(0.750 MGD)
Effluent Characteristic Effluent Limitations
Monthly Weekly Daily Maximum
Average Average
Flow 0.750 MGD
BOD5 (Apr-Oct) 5.0 mg/L 7.5 mg/L
BOD5 (Nov-Mar) 10.0 mg/L 15.0 mg/L
NH3 as N(Apr-Oct) 1.1 mg/L 3.3 mg/L
NH3 as N(Nov-Mar) 1.3 mg/L _ 3.9 mg/L
TSS 30.0 mg/L 45.0 mg/L
Dissolved Oxygen Dail Average> 5.0 mg/L
TRC(if used for 23 µg'L
disinfection)
TNI 5,055 lbs/year
TP 1.0 mg/L
Fecal coliform(geometric 200/100 mL 400/100 mL
mean)
Chronic Toxicity,Pass/Fail 75.4%
(Quarterly test)
Notes:
1. Equivalent to a concentration of 2.2 mg/L.
Engineering Alternatives Analysis(EAA). 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 new/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 or expanding flow, a detailed engineering alternatives analysis (EAA) must be
prepared. The EAA must justify requested flows and provide an analysis of potential wastewater
treatment alternatives. A copy of the Division guidance for preparing the EAA can be found
at: https://deq.nc.gov/about/divisions/water-resources/water-quality-permitting/npdes-
wastewater/npdes-permitting-process
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Should you have any questions about these speculative limits or NPDES permitting requirements,
please feel free to contact David Hill at [e-mail] [phone].
Respectfully,
DocuSignsd by:
H.,
2E35935DF84D4AE...
David Hill
Environmental Specialist II
NPDES Industrial Permitting Unit
Hardcopy:
NPDES Permit File
Electronic Copy:
NC Wildlife Resources Commission,Inland Fisheries,
[e-mail]
US Fish and Wildlife Service, [e-mail]
DWR/Water Quality Regional Operations/Raleigh
DWRBasinwide Planning, Ian McMillan
DWR/NPDES Server>Specs
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