NC0085359_Correspondence_20070518

Ms. Christie Putnam
Union County Public Works
400 North Church St.
Monroe, North Carolina 28112
Dear Ms. Putnam:
Michael F. Easley, Govemor
State of North Carolina
William G. Ross, Jr., Secretary
Department of Environment and Natural Resources
Alan W. Klimek, P.E., Director
Division of Water Quality
May 18, 2007
Subject: NPDES Permit'Medifteet ierr 6 V► i as N t e
Union County — Twelve Mile Creek
NPDES Permit No. NC0085359
Union County
This letter is offered in response to Hazen and Sawyer's request, on the County's behalf, for
speculative effluent limits for the potential expansion of the Union County Twelve Mile Creek
Wastewater Treatment Plant (WWTP). The plant is currently permitted for a wastewater discharge
of up to 6 MGD into Twelve Mile Creek located in the Catawba River Basin.
Division staff (Point Source Branch representatives and Mooresville Regional Office
representatives) appreciated the opportunity to discuss the very complex issues regarding Union
County's expansion request with you, Mr. Tye, and your consultants this past Friday, May 11.
As we discussed during the meeting, the Division has had concerns about the dissolved oxygen
level in the receiving stream since the last permit expansion to 6 MGD (this was stated in the
letter to Union County dated June 14, 2002). Even at that time, the Division did not believe there
was enough information to properly evaluate actual instream conditions and discern whether the
discharge would cause water quality problems; the Division therefore agreed to permit the
expansion with best available technology type discharge limits. DWQ now has strong water
quality data from both upstream and downstream of the Twelve Mile Creek WWTP discharge. The
data allows DWQ to draw more definitive conclusions regarding the current receiving stream
conditions, as well as the potential future impact of the discharge.
Analyses of the dissolved oxygen levels in Twelve Mile Creek, both upstream and downstream of
the existing WWTP discharge, revealed levels below North Carolina's water quality standard of 5
mg/L. Additionally, a percentage of the downstream dissolved oxygen values were lower than the
upstream values, indicating that the existing WWTP discharge is having an adverse impact on
dissolved oxygen levels in Twelve Mile Creek. Even with these obvious concerns, the Division
chose to run its EPA -approved water quality model to determine if the model would reflect existing
conditions (and therefore determine if it would be an appropriate tool to use to model the impacts
of any increase of the wastewater discharge). Because this one-dimensional model was unable to
reflect the existing conditions, we informed you that we could not model any expansion in
wasteflow.
Based on the current substandard instream conditions, we stated in the meeting that we could not
give speculative limits for any increase of wastewater discharge to Twelve Mile Creek above the
currently permitted flow of 6 MGD. Although gathering more instream data at the current
upstream and downstream sampling points, as well as further downstream, may be beneficial —
DWQ does not believe that this would alter the ultimate conclusion. Union County can make the
decision to gather actual stream cross sections, re -confirm the predicted 7Q l Os low flow stream
value, and pursue a more complex water quality model that may be able to predict actual and
future conditions. However, as we stated in our meeting last Friday, we believe this may not be
the best use of the County's monetary resources. DWQ believes that it is in the County's best
interest to review all other options prior to this one. Another concern with any discharge permit in
this portion of the Catawba River Basin is South Carolina's future adoption of a total phosphorus
Total Maximum Daily Load (TMDL), as well as any other standards promulgated by that state.
The Division understands that Union County has had discussions with South Carolina water
quality staff and is aware of the potential impact this may have on dischargers in this portion of
our state.
North Carolina Division of Water Quality
1617 Mail Service Center
Ralainh_ North Carolina 77699-1617
[phone]
FAX [phone]
On the Internet at htto://h2o.enr.state.nc.us/

Ms. Putnam
Page 2
Some alternatives to an increased discharge the County may wish to pursue, and that we
discussed, include all possible reuse/nondischarge options such as irrigation of any available golf
courses; diversion of flow to industrial users that may need a water source; and spray or drip
irrigation of undeveloped land within or outside the County. The County should also pursue
diverting flow to Charlotte Mecklenburg Utilities, to Lancaster County, South Carolina or to other
nearby municipalities if all parties are in agreement. As we also discussed during our meeting
Friday, the County does have speculative discharge limits for a potential discharge in the northern
part of Union County to the Rocky River in the Yadkin River Basin. However, as you are aware,
this would present a concern regarding interbasin transfer of wastewater. These are not likely to
be the only options available to the County, but are provided as possible solutions.
We hope this response provides some guidance for Union County's continued pursuit of
wastewater options as a result of its extensive growth. If you have any additional questions about
this response or our meeting May 11, feel free to contact me at [phone], extension 510.
Sincerely,
Sisan A. Wilson, P.E.
Supervisor, Western NPDES Program
cc: Mooresville Regional Office/Surface Water Section
Central Files
NPDES Program
PERCS
Jim Struve, P.E. Hazen and Sawyer, P.C.
4944 Parkway Plaza Blvd., Suite 375
Charlotte, NC 28217