NC0085359_Regional Office Historical File Pre 2018 (4)

HAZENANDSAI
Environmental Engineers & Scientists
August 16, 2010
Mr, Rob Krebs
Supervisor, Surface Water Protection
Mooresville Regional Office
N.C. Department of Environment and Natural Resources
610 East Center Avenue, Suite 301
Mooresville, NC 28115
Dear Mr. Krebs:
Flaw and Sawyer„
494, Parkway Gaza Blvd.
Suite 375
Charlotte, N( 25717
f 7(141 357-315D
17041 357 if l52 :;Fax
Re: Expansion Alternatives Development Study
Twelve Mile Creek WWTP
Union County, North Carolina
NPDES Permit No, NC0085359
Please find attached two (2) copies of the Expansion Alternatives Development Study for Union
County's Twelve Mile Creek Wastewater Treatment Plant (1NWWTP). This study was referenced
in recent meetings and conversations with Mr. Tom Belnick and Mr. Jeff Poupart, and is being
sent to you on behalf of the County. If you could distribute a copy to Ms, Donna Hood, we
would appreciate it. Copies have also been sent to Mr. Belnick, Mr. Poupart, and Mr. Chuck
Wakild.
If you have any questions or would like additional information, please do not hesitate to contact
me at 704-357-3150 or at strove hazenandsaw er.corm
Very truly yours,
HAZEN AND SAWYER, P.C.
"r?
James N. Struve, P.E.
Vice President
cc: Mr. Ed Goscicki, Union County Public Works
Mr, Scott Huneycutt, Union County Public Works
Mr. Scott Alpert, Hazen and Sawyer
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North Carolina Department of Environment and Natural Resources
Division of Water Quality
Beverly Eaves Perdue / Coleen H. Sullins
Govemor Director
Mr. Edward Goscicki, P.E.
Director, Union County Public Works
500 North Main St. Suite 500
Monroe, North Carolina 28112
September 1, 2010
Dee Freeman
Secretary
Subject Speculative Effluent Limits-! 9/12/15 MGD
Union County - Twelve Mile Creek WWTP
Permit No. NC0085359
Union County
Dear Mr. Goscicki:
This letter provides speculative effluent limits. for 9, 12, and 15 MGD at the Twelve .Mile Creek WWTP
(currently pernutted at 6 MGD). The Division received the speculative limits request in a letter dated June 16,
2010 from James Struve, P.E., of Hazen and Sawyer. The Division also received suppl4mental information to
assist in the speculative limits evaluation, including: a) Scoping Level Assessment of Assimilative Capacity in
Twelve Mile Creek below the Union County WWTP (Tetra Tech, Apri12010); b) QUAT. stream water quality
model code (received July 7, 2010); c) Expansion Alternatives Development Study (Hazen and Sawyer),
received on August 17, 2010; and d) Union County Summer 2009 Stream Reconnaissance of dissolved oxygen
Receiving Stream. I •
Twelve Mile Creek is formed downstream of the convergence of West Fork Twelve Mile Creek and East Fork
Twelve Mile Creek and has a stream classification of C. Waters with this dassificatioii have a best usage for
aquatic life propagation and maintenance of biological integrity, wildlife, secondary recreation and agriculture.
Stream flow information was updated in 2002 by the United States Geological Survey (USGS) for a nearby
gaging station at Highway 16 just 2500 ft upstream of the Twelve Mile Creek WWII' discharge point. This
discharge point has a drainage area of 76.8 square miles and stream flow estimates of 72.7 cfs (annual average
flow), 0.1 cfs (summer 7Q10 flow), and 1.5 cfs (winter 7Q10 flow). Previously, Twelve Mile Creek was
considered a zero flow stream with 7Q10 flow =0 and 30Q2>0.
The current discharge location on Twelve Mile Creek is approximately 2 miles upstream of the NC/SC state
line. Twelve Mile Creek from its source to the NC/SC state line is listed on both the Final 2008 and Draft 2010
NC 303(d) Impaired Waterbody listing for both copper and turbidity.. The stream is nOt listed as impaired for
low dissolved oxygen (DO); however, historical data has shown low DO valus both upstream and
downstream of the discharge point during low summer flow conditions. In Summer 2009, Union County
conducted a DO reconnaissance survey which indicated that low DO values were common above the Twelve
1617 Mail Service Center, Raleigh, North Carolina 27699-1617
Location: 512 N. Sallsbuiy St Raleigh, North Carolina 27604
Phone: [phone] FAX: [phone] Customer Service.1-877-623.6748
Internet wewa.ncxaterqualitv.orq •
One
11orthCarolina
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Mile Creek discharge in the mainstetn and tributaries, indicating a background component to the low DO
values observed downstream of the discharge.
SS. eculative Limits.
Based on Division review of receiving stream conditions and water quality modeling results, speculative limits
are presented in Table 1 below. These speculative limits maintain the TP load limit originally allocated to
Union Cou.nty/Twelve Mile to comply with the South Carolina TP lake standard of 0.06 mg/L Likewise,
copper and zinc limits originally added to comply with South Carolina standards are maintained, and are
based on WER calculations. For listed parameters without limits, effluent monitoring will be required.
Monitoring within Twelve Mile Creek will also be required to ensure that the water quality model predictions
were accurate, and to ensure the discharge does not create more adverse conditions in the future.
TAB
S eculative L isnits for Twe
Flow
D5 A ril - October
BC D5 overnber - l aacli
f us N A - Cctobe�r
NH3 as N (November - Larch°
Fecal corrrt ; earnetric me
Dissolved �► en
TRC
To co er
Total zinc
Turbidi
To losphorus-11onthly Avg
Tc Lil Phos • h arus- s ,nuai Av
To Nitro en
Chronic, Toxicity Pass/Fail
90 Quarter1 test
ire Creek
on Av
9/l2 '1.S MGD
.0m�/L
1.0 m,
2.0/1.9/1.9
2 100
30 rn • /
12.9 u
41.7lbs/day
2i1.851bs da
ded.
.0an;/L
6.0/.7/ 5.7
Note: At 9 MGD, TP mass 1%mits equate to 0, 5 mg/l (Monthly avg) and 0.28 mg/ I (Annual avg,;
Note: At 12 MGD, TP mtass lixrtits equate to 0, 42 mg/I (Monthly avg) and 0.21 mg/l (Annual avg.)
Note:_ At 15 MGD, TP mass limits equate to 0. 33 mg/I (Monthly avg) and 0.17 mg/ 1(Annualavg,)
Issuance of these speculative limits allows Union County to proceed to SEPA submission for the proposed
expansion. If a FONSI is ultimately obtained for the SEPA submission, then Union County will need to apply
to the NPDES Unit for a permit modification for expanded flow. However, please note that these speculative
limits do not guarantee that an NPDES permit will be issued for the proposed expansion. Likewise,
speculative limits are provisional and may change with future changes in water quality standards, TMDLs,
policy, etc. Please note the following concerns and/or review requirements that Union County will need to
address:
GD..
QUAL2E I °fadei. Review. Division staff from the Modeling Unit reviewed the draft scoping level
assessment of Twelve Mile Creek and the modeling files in. July 2010 (comments attached). The
QUAL2E scoping level model was developed to evaluate assimilative capacity downstream of the
WWTP. Staff review determined that the model as a scoping level assessment tool was created
based on limited data. The model must be validated with additional data collection and results

evaluated by DWQ to provide confidence accepting the model results. Data should be collected
during summer conditions (low flow, high temperature) at three DO sag points1 predicted by the .
model: at downstream sites about 2 miles, 10 miles, and 12.5 miles below the discharge. There is
particular concern about the second dissolved oxygen sag point that occurs 7-10 miles below the
discharge in South Carolina, when DO decreases substantially below the standard of 5 mg/L ;Y titi
Model results indicate that the sag is not caused by the Twelve Mile Creek WWTP discharge;
however, the lack of data makes it difficult to confirm conditions in this segment of the stream.
• State Environmental Policy Act (SEPA) Requirements. A SEPA EA/EIS document must be
prepared for all projects that: 1) need a permit; 2) use public money or affect public lands; and 3)
might have a potential to significantly impact the environment. For elristing discharges,
significant impact is defined as an expansion of > 500,000 gpd additional flow. Since Union ,
County is proposing a discharge of >500,000 gpd flow, a SEPA document that evaluates the
•
potential for impacting the quality of the environment is required. A SEPA document should
contain a dear justification for the proposed project. If the SEPA Environmental Assessment (EA)
demonstrates that the project may result in a significant adverse effect on the quality of the
environment, then a SEPA EIS (Environmental Impact Statement) must be prepared. Since this
expanded discharge is subject to SEPA, you must also fold into the SEPA document all the
requirements specified in the NPDES Engineering Alternatives Analysis (EAA) Guidance
(attached). The EAA must justify requested flows, and provide a detailed analysis of potential
wastewater treatment alternatives. The SEPA process will be delayed if all EAA requirements are
not adequately addressed. Please note that the Expansion AIternatives .Development Study
previously submitted to DWQ will need to be. expanded to include flo4 justification and
alternatives analyses/cost comparisons for a full 15 MGD expansion. If you have any questions
regarding SEPA requirements, please contact Hannah Stallings with the DWQ kanning Branch at
[phone]. '
• NPDES Permit Modification Requirements. The NPDES Unit will not accept an NPDES permit
modification request for expanded flow until the Division has approved the SEPA document and sent
a Finding of No Significant Impact (FONSI) to the State Clearinghouse for review and comment. In 2
accordance with the North Carolina General Statutes, the practicable wastewater treatment and
disposal alternative with the least adverse impact on the environment is required to be implemented.
Any NPDES permit modification for expanded flow will be subject to 30-day ublic comment. Since
this is a Major permit, US EPA must approve any proposed permit changes and South Carolina
DHEC will have an opportunity to comment. Documentation will need tol address any projected
impacts to NC/SC water quality.
Should you have any questions about these speculative limits or NPDES permitting requirements, please
feel free to contact Jackie Nowell at [phone] or Tom Belnick at [phone].
esnectful
m Belnick
Supervisor, Complex Permitting Unit
cc: Michael J. Montebello SCDHEC, 2600 Bull Street Columbia SC 29201
US Fish and Wildlife Service, Ecological Services, PO Box 33726, Raleigh, NC 27636 Attn: Sara Myers
NC WRC, Inland Fisheries, 1721 Mail Service Center, Raleigh, NC, 27699-1721 Attn: Fred Harris
Mooresville Regional Office/Surface Water Protection Section
Construction Grants and Loans
Kathy Stecker, Pam Behm/Modeling TMDL Unit
Hannah Stallings/Planning Section
Central Files
NPDES Permit File/NC0085359