NC0024872_staff comments_20010828

To:
From:
Subject:
DIVISION OF WATER QUALITY
August 28, 2001
Milt Rhodes
Local Government Assistance Unit
Susan A. Wilson, Environmental Enginee
NPDES Unit
Davie County - Cooleemee WWTP
(Cooleemee WWTP 201 Plan)
Rehabilitation Issues
NPDES No. NC0024872
Davie County
I have reviewed the 201 Wastewater Facilities Plan submitted by Cavanaugh & Associates on
behalf of Davie County. The proposed project includes rehabilitation of the existing treatment
plant to meet future growth needs and provide better treatment and operation at the plant.
The plan also includes measures to reduce inflow & infiltration to the plant.
The document should be modified to state that the renewal permit has been publicly noticed
May 19, 2001 and should be issued soon (hopefully, Davie County will get a copy of the
reissued permit prior to revision of this 201 plan). Please refer to p. 6 of the document and
Exhibit C.
The NPDES Unit is very much in favor of refurbishment of the existing treatment plant. The
plant is currently underloaded even with the decreased permitted flow of 1.5 MGD and has
experienced some compliance problems.
Based on the flow projections presented on p. 8 of the document, the NPDES Unit would
recommend that Davie County further reduce the permitted flow (the permitted flow should be
based on the actual daily design flow of the refurbished plant). This should not adversely affect
the currently permitted limits, as this would be a decrease in flow. Should the permitted flow
be reduced below 1.5 MGD, the chronic toxicity testing percentage would subsequently be
reduced (the testing concentration would be less than 2.1%), which may be advantageous to
Davie County/ Cooleemee.
The NPDES Unit would also recommend that with this refurbishment the facility install
dechlorination. The Division of Water Quality's next review of state water quality standards
may include the adoption of total residual chlorine as a water quality standard, instead of an
"action level" water quality standard. This could mean that the NPDES Unit will implement
chlorine limits upon the next renewal of the Cooleemee WWTP permit. Traditionally, for new or
expanding facilities, in which a major modification/capital investment is projected, the NPDES
Unit has implemented chlorine limits into permits. Although, technically, Cooleemee is not
"new" or "expanding", this refurbishment is a major capital investment and the NPDES Unit
would highly recommend that Davie County/ Cooleemee be proactive and install
dechlorination.
If the existing sand drying beds are to be used for dewatering of sludge removed from the
aeration basins (p. 11), Davie County should ensure that all underdrains are routed back to
the head of the plant (the Division has found that older treatment plants were sometimes
designed with underdrains connected directly to the effluent outfall). Davie County or
Cavanaugh & Associates may wish to contact the Division's Nondischarge Permitting Unit
regarding proper disposal of residuals.
Cc: WSRO/WQ/Abner Braddy
NPDES Unit
Central Files
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