NC0025453_Fact Sheet_20200720

Fact Sheet
NPDES Permit No. NC0025453
Permit Writer/Email Contact: Mike Templeton,[e-mail],919-707-3603
Date: July 17,2020
Division/Branch: NC DWR/Water Quality Permitting Section/NPDES Permitting
Fact Sheet Template: Version 09Jan2017
Permitting Action:
❑ Renewal
❑ Renewal with Expansion
O New Discharge
® Modification
1. Basic Facility Information
Facility Information
Applicant/Facility Name: Town of Clayton/Little Creek WRF
Applicant Address: PO Box 879,Clayton,North Carolina
Facility Address: 1000 Durham Street Extension,Clayton,NC
Permitted Flow: 2.5 MGD
Facility Type/Waste: MAJOR Municipal; 95%domestic, 5%industrial
Facility Class: Class 4
Treatment Units: Mechanical bar screens&grit removal, influent pump station,
anaerobic basin,anoxic tanks,oxidation basins,clarifiers,tertiary
filters,UV disinfection with backup chlorination/dechlorination,aerated
sludge digester, sludge holding tank, sludge thickener,non-potable
reclaimed water system
Pretreatment Program(Y/N) Yes
County: Johnston
Region Raleigh
Proposed Permit Action
By its letter of June 16,2020, signed by James Warren,WWTP Operations Superintendent,the Town of
Clayton requested modification of its NPDES permit to reflect its purchase of nitrogen offset credits.The
Division has reviewed the request and supporting materials and has made a tentative determination to
modify the permit as requested.
The purpose of this modification is to document the purchase of credits in the Town's permit.No limits or
other permit conditions are modified as a result. When the offset credits are used to increase the Town's
TN limit,that change will again be subject to public review in accordance with NPDES regulations.
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Facility Background
The Little Creek facility serves a population of 19,102 residents and operates a pretreatment program with
two pharmaceutical Categorical Industrial Users,Novo Nordisk and Grifols.Currently,Grifols discharges
to Johnston County's WWTP.Novo Nordisk's flow to Little Creek WWTP was 0.076 MGD. Clayton has
agreements with Johnston County and Raleigh's Neuse River WWTP to divert up to 1.3 MGD and 1.0
MGD to those plants respectively.Clayton also operates a reclaimed water system and land applies up to
237,840 GPD under permit WQ0022224. I&I was reported at 438,000 GPD.
The Town's permit was last reissued December 6,2019,and became effective January 1,2020.
2. Receiving Waterbody Information:
Receiving Waterbody Information
Outfalls/Receiving Stream(s): Outfall 001-Neuse River
Stream Segment: 27-41.3
Stream Classification: WS-IV;NSW,CA
Drainage Area(mi2): 1,150
Summer 7Q10(cfs) 186(regulated)
Winter 7Q10 (cfs): 186(regulated)
30Q2(cfs): 186(regulated)
Average Flow(cfs): 186(regulated)
IWC(%effluent): 1.6
303(d)listed/parameter: No
Subject to TMDL/parameter: Yes-Subject to Neuse nutrient rule 15A NCAC 02B .0234,
Statewide Mercury TMDL
Subbasin/HUC: 030402/03020201
USGS Topo Quad: E25NW/NW Clayton
3. Effluent Data Summary
Effluent nutrient data for the period May 2014 through December 2018 is as follows:
Table 1.Effluent Data Summary
Parameter Units Average Max Min Permit Limit
Flow MGD 1.55 5.82 0.46 2.5
TN mg/L 4.14 13.08 1.24
Kjeldahl Nitrogen mg/L 1.24 6.04 0.2
Nitrate+Nitrite mg/L 2.89 11.24 0.48
TN Monthly lb/mo 1,627 3,308 630
TN Yearly lb/yr 19,903 20,901 18,472 22,832
TP mg/L 1.08 6.53 <0.04
TP Quarterly Average mg/L 1.08 1.65 0.40 2.0
MA-Monthly Average,WA-Weekly Average,DM-Daily Maximum
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4. Instream Data Summary
The Permittee is a member of the Lower Neuse Basin Association(LNBA),which performs ambient
monitoring on behalf of its members per its Memorandum of Agreement with the Division of Water
Resources.
5. Compliance Summary
Compliance with Nutrient Limitations:
Clayton is a co-permittee member of the Neuse River Compliance Association and is subject to the
combined Total Nitrogen(TN)limit in the Association's group permit.The Association has consistently
complied with its TN limit since the group permit became effective in calendar year 2003.The Town is
not subject to the TN limit in its individual permit as long as the Association complies with the group
limit;nevertheless,it has consistently complied with its own individual allocation.
6. Water Quality-Based Effluent Limitations (WQBELs)
Neuse River Nitrogen TMDL and Nutrient Management Strateav
The Neuse River estuary has an extensive history of nutrient-related water quality impacts and was
classified as Nutrient Sensitive Waters in 1988.Nutrient Management Strategy rules were first adopted in
December 1997 and modified in 2000 and 2020.The wastewater discharge rule, 15A NCAC 2B .0713
(formerly.0234),established requirements for control of Total Nitrogen(TN)from point source
discharges. It requires TN limits for all dischargers with a permitted capacity of 0.5 MGD or greater and
allows the transfer of allocation among the Neuse dischargers so long as the total of estuary allocations
and loads do not exceed those allowed in the 1999 TN TMDL.
The Town of Clayton was assigned a Total Nitrogen(TN)allocation of 21,400 lb/yr at end-of-pipe
(10,700 lb/yr at the estuary),which was the basis for its first TN discharge limit,in accordance with the
rule.Based on its location relative to the estuary,the facility was assigned a transport factor of 50%,as its
allocation numbers indicate.
The wastewater rule also provides a group compliance option through which dischargers can work to
comply with their collective TN limit. Clayton is a co-permittee member of the Neuse River Compliance
Association,whose group NPDES permit,NCC000001,was last re-issued December 12,2008.Co-
permittee members are deemed to be in compliance with the TN limits in their individual permits and
nitrogen is limited by the combined limit established in the group permit.
The Town's TN active allocation is 22,832 lb/year at the discharge,which,after transport losses in the
river,is equivalent to a 11,416 lb/yr loading at the estuary. The allocation includes the Town's original
allocation and supplemental allocations obtained through purchases from other permittees in the basin.
The Town has experienced significant growth since the Neuse strategy was established and,as a result,
expanded to 2.5 MGD pursuant to its 2006 permit. Anticipating continued growth,it acquired additional
allocation from SGWASA(NC0026824)and UNIFI-Kinston(formerly,and once again,DuPont-Kinston;
NC0003760).The combined allocations exceed the limit allowed for the expanded facility, and the excess
is held in reserve until it can be used for future expansions.Details are provided in Table 2.
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Table 2. Town of Clayton—Current TN Allocations
ALLOCATION AMOUNT1
SOURCE STATUS
Estuary Discharge
(Ib/yr) (Ib/yr)
Assigned by Rule 10,700 21,400 Active
(T15A NCAC 02B .0234)
Purchased from 3,668 7,336 Reserve
South Granville WSA (NC0026824)
1,645 3,290 Mixed
Purchased from 716 1,432 Active
UNIFI-Kinston (NC0003760)
929 1,858 Reserve
TOTAL 16,013 32,026 Mixed
11,416 22,832 Active
4,597 9,194 Reserve
Purchase of Nutrient Offset Credits
The Town of Clayton plans to request approval of an expansion to 5.0 MGD in the near future,in order to
meet its growing wastewater treatment needs. Its TN allocations in Table 2, including those held in
reserve,would be equivalent to 2.1 mg/L TN at the increased flow.The commonly accepted limit of
economically achievable treatment technology is 3 mg/L;thus,the Town's current allocations are not
sufficient for the planned expansion.
To meet the additional needs,the Town entered into a contract to purchase nutrient offset credits in
accordance with the Neuse River nutrient strategy. The Nutrient Offset Credit Sales Agreement for the
sale of 715,858.18 lbs TN(or 23,862.94 lb/yr for 30 years)was signed by representatives of Restoration
Systems,LLC, and the Town of Clayton on March 8,2020.
Restoration Systems is the Bank Sponsor for the RS Flat Swamp Nutrient Offset Mitigation Bank,a
mitigation project undertaken to generate nutrient offset credits.Restoration Systems issued a Statement
of Nutrient Offset Credit Availability on March 17,2020,confirming that it has generated and is
authorized to sell credits under the approved Mitigation Banking Instrument,which became effective
December 20,2019. (Normally,the Statement of Availability precedes the Sales Agreement.)The
Statement of Availability certifies that credits in the amount of 715,858.18 lbs(or 23,862.94 lb/yr for 30
years)have been generated and released and are currently on hold specifically for sale to the Town of
Clayton for the planned expansion.The Statement was approved by the Division, also on March 17,2020.
Calculation of Applicable Offset Credits
Consideration of Transport Losses.The transfer of nutrient allocations among point source dischargers in
a river basin is routinely adjusted to account for differences in delivery rates("transport factors")in
different parts of the basin.In the case of nonpoint source controls,the Division's nutrient strategies have
required that offset credits generated in the basin be applied within the same hydrologic unit or subbasin
in which they were generated. Each approach ensures that differences in transport of nutrients at two
different locations does not result in an increased nutrient load to the waterbody of concern.Transport
factors have not been employed in nonpoint source transactions.
In June 2020,the NC General Assembly ratified,and the Governor signed, Senate Bill 315 (S.L. 2020-
18),known as the Farm Bill. Section 15.(a)of the bill required that transport factors be applied when
transferring offset credits to wastewater permits. Section 15.(b)limited its applicability to local
governments"with a customer base of fewer than 15,000 connections",in effect,Clayton.
Calculations.The Town purchased 23,862.94 lb/yr of TN credits for 30 years.The Neuse wastewater rule,
15A NCAC 02B .0713 (formerly 02B .0234) specifies an uncertainty ratio of 1.5:1,meaning that the
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Town must purchase 1.5 lb of credits for every pound required for its discharge. In other words, 1/1.5, or
two-thirds of the credits purchased can be applied to the Town's discharge.
2/3 of 23,862.94 lb/yr = 15,907.96 lb/yr credits applied to discharge
The remaining 7,953.98 lb/yr TN offset credits are required to satisfy the uncertainty provision of Rule
.0713 and cannot be applied to offset any activity, whether point source or nonpoint source in nature.
The transport factor for the area in which the Flat Swamp Bank is located is 100%; that for the Town of
Clayton discharge is 50%. Per the 2020 Farm Bill,the amount of offset credits available at the Town's
point of discharge is:
15,907.96 lb/yr(at estuary) x 100%/50% = 31,815.92 lb/yr(at point of discharge)
The Town's TN allocations and the new offset credits are listed in Table 3. The new credits also exceed
the allowable technology-based limit for the existing facility, per the Rule, and so will also be held in
reserve pending future expansion.
Table 3.Town of Clayton—TN Allocations and Offset Credits
ALLOCATION/ CREDITS
AMOUNT1
SOURCE STATUS
Estuary Discharge
(Ib/yr) (Ib/yr)
Assigned by Rule 2 10,700 21,400 Active
Purchased from South Granville 3,668 7,336 Reserve
WSA(NC0026824)
Purchased from UNIFI-Kinston 1,645 3,290 Mixed
(NC0003760) 716 1,432 Active
929 1,858 - Reserve
Purchased from 15,908 31,816 Reserve
Restoration Systems
TOTAL 31,921 63,842 Mixed
11,416 22,832 Active
20,505 41,010 Reserve
7. Technology-Based Effluent Limitations (TBELs)
Not applicable to this permit action.
8. Antidegradation Review (New/Expanding Discharge):
Not applicable to this permit action.
9. Antibacksliding Review:
Not applicable to this permit action.
10. Monitoring Requirements
Monitoring requirements are not affected by this permit action.
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11. Electronic Reporting Requirements
Electronic reporting requirements are not affected by this permit action.
12.Summary of Proposed Permitting Actions:
The proposed modification will record the Town's purchase of nutrient offset credits.The credits will be
held in reserve but may be applied to increase its TN limit upon with future expansions in accordance
with Rule 02B .0713.The modification makes no substantive changes to the effluent limitations,
monitoring requirements,or other conditions of the permit.
13. Public Notice Schedule:
Permit to Public Notice: July 24,2020.
Per 15A NCAC 02H .0109& .0111,The Division will receive comments for a period of 30 days
following the publication date of the public notice. Any request for a public hearing shall be submitted to
the Director within the 30-day comment period and shall indicate the interest of the party filing such
request and the reasons why a hearing is warranted.
14. Fact Sheet Addendum (if applicable):
Not applicable to the fact sheet for the draft permit modification.
15. Fact Sheet Attachments (if applicable):
Not applicable.
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