NC0025453_Speculative Limits_20200904

ROY COOPER f
Governor /
MICHAEL S.REGAN ` •��,
Secretary 4t,cuoc 0s
S.DANIEL SMITH NORTH CAROLINA
Director Environmental Quality
September 4,2020
James Warren
Wastewater Operations Superintendent
Town of Clayton
PO Box 879
Clayton,North Carolina
Subject: Speculative Effluent Limits
Little Creek WRF
Permit No.NC0025453
Johnston County
Neuse River Basin
Dear Mr. Warren:
This letter provides speculative effluent limits for expansion to 6.0 and 10.0 MGD at the Little Creek WRF.
The Division received the speculative limits request in a letter dated August 7,2020. Please recognize that
speculative limits may change based on future water quality initiatives,and it is highly recommended that,
if expansion does not proceed in the near future, the applicant verify the speculative limits with the
Division's NPDES Unit prior to any engineering design work.
Receiving Stream. The Neuse River has a stream classification of WS-IV;NSW at the proposed discharge
location. Waters with this classification have a best usage for all class C criteria: aquatic life propagation
and maintenance of biological integrity, wildlife, secondary recreation, and agriculture; as well as a water
supply source for drinking,culinary,and food-processing purposes. The Neuse River has a regulated flow
of 186 cfs for all permitted critical flows.The river at this location is not listed on the 303(d)list of impaired
waters; however, the entire river basin has been designated nutrient sensitive waters (NSW) because of
multiple algae impairments in the basin.
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-mile radius of the proposed discharge location. If any threatened/endangered species are identified, 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 the Division's review of receiving stream conditions and water
quality modeling results, speculative limits for the proposed'expansions to 6.0 MGD and 10.0 MGD are
presented in Tables 1 and 2. A complete evaluation of these limits,limits and monitoring requirements for
metals and other toxicants,as well as potential instream monitoring requirements,will be conducted upon
receipt of a formal NPDES permit application. Some features of the speculative limit development include
the following:
No of Quality I D 512 NorthrthCarolina SalisburyDepartment Street 1617 MailEnvironmental Service Center 1 Raleigh.Division NorthofWater Carolina
Resources 27699 1617
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Speculative Effluent Limits
Little Creek WRF
Permit No.NC0025453
September 4,2020
• BOD/NH1 Limits. Biochemical oxygen demand (BOD) and ammonia-nitrogen limits are based on
review of a 2020 QUAL2K model which demonstrated that the proposed limits are protective of the
dissolved oxygen water quality standard.If future modeling indicates that seasonal limits at the expanded
flows would be protective of water quality,and if such limits are justified per 15A NCAC 02B .0404(b),
the Division may develop seasonal limits for oxygen-consuming wastes.
• Nutrients:Total Nitrogen(TN)and Total Phosphorus(TP)limits are in accordance with the Neuse River
nutrient management strategy (see 15A NCAC 2B .0700). TN mass limits are the sum of the Town's
initial allocation and its additional allocation and offset credit purchases, the last of which is pending
approval through permit modification (public noticed July 23, 2020). The additional allocation and
credits will continue to be held in reserve until expansion to 6.0 MGD.At that time,they will be activated,
and the resulting limit(63,842 lb/yr)will be equivalent to 3.5 mg/L TN at the permitted flow.
If the offset credits(31,816 lb/yr)are not purchased as planned,the TN limit will be the sum of the initial
and added allocations only.The resulting limit(32,026 lb/year)would be equivalent to 1.75 mg/L at 6.0
MGD and 1.05 mg/L at 10 MGD. Even if the credits are purchased, the TN limit(63,842 lb/yr)would
only be equivalent to 2.10 mg/L at 10 MGD. In each of these cases, the required level of treatment is
beyond typical treatment capabilities, and the Town will have to demonstrate in its application for
expansion how it will achieve the required level of treatment.
The 2.0 mg/L TP limit applies as long as the permittee remains a member of a compliance association,
otherwise a limit of 1.0 mg/L Quarterly Average applies.
TABLE 1. Speculative Limits for Little Creek WRF(6.0 MGD)
Effluent Characteristic Effluent Limitations
Monthly Average Weekly Average Daily Maximum
Flow 6.0 MGD
BOD5 5.0 mg/L 7.5 mg/L
NH3 as N 1.0 mg/L 3.0 mg/L _
Dissolved Oxygen Daily Average>6.0 m L
TSS 30.0 mg/L 45.0 mg/L
TRC(if used for disinfection) 28 µg/L
TN Load 63,842 lbs/year
TP 2.0 mg/L Quarterly Average
Fecal coliform(geometric 200/100 mL 400/100 mL
mean)
Chronic Toxicity,Pass/Fail 4 8%
(Quarterly test)
Notes:
1. With the proposed credits,equivalent to a concentration of 3.5 mg/L.
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Speculative Effluent Limits
Little Creek WRF
Permit No.NC0025453
September 4,2020
TABLE 2. Speculative Limits for Little Creek WRF(10.0 MGD)
Effluent Characteristic Effluent Limitations
Monthly Average Weekly Average Daily Maximum
Flow 10.0 MGD
BOD5 5.0 mg/L 7.5 mg/L
NH3 as N 1.0 mg/L 3.0 mg/L
Dissolved Oxygen Daily Average>_6.0 m
TSS 30.0 mg/L 45.0 mg/L
TRC(if used for disinfection) 28 µg/L
TN Load 63,842 lbs/year
TP 2.0 mg/L Quarterly Average
Fecal coliform(geometric 200/100 mL 400/100 mL
mean)
Chronic Toxicity,Pass/Fail °
(Quarterly test) 7.7�°
Notes:
1. With the proposed credits,equivalent to a concentration of 2.1 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
Should you have any questions about these speculative limits or NPDES permitting requirements, please
feel free to contact David Hill at david.hill ncdenr.gov(919) 707-3612.
Sincerely,
� I
Michael E.Templeton,P.E.
Water Quality Permitting Section
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
DWR/Basinwide Planning,Ian McMillan
DWR/NPDES Server>Specs
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