NC0036277_Speculative Limits_19940729

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State of North Carolina
Department of Environment,
Health and Natural Resources
Division of Environmental Management
James B. Hunt, Jr., Governor
Jonathan B. Howes, Secretary
A. Preston Howard, Jr., P.E., Director
July 29, 1994
Barry M. Gullet
Deputy Director
Charlotte -Mecklenburg Utility Department
5100 Brookshire Blvd.
Charlotte, NC 28216
3�v
Ift
D E H N R
Subject: Spgculative Permit Limits for CMUD McDowell Creek WWTP
NPDES Permit No. NCO036277
Mecklenburg County
Dear Mr. Gullet:
Your request for speculative effluent limits for the proposed expansion of the
CMUD McDowell Creek WWTP to 3.5 and 6.0 MGD has been completed by the
Technical Support Branch. In order to receive final permit limits, a formal application
will have to be submitted to the Division's Permits and Engineering Unit.
It should also be noted that an expansion of more than 0.5 MGD for an existing
facility will require that an environmental document be prepared by the applicant. The
N.C. Environmental Policy Act and its associated rules require that an environmental
assessment (EA) and Fonsi (Finding of No Significant Impact) be prepared before an
application for a permit expansion is submitted. If deemed appropriate, an environmental
impact statement (EIS) might be necessary. Monica Swihart of the Water Quality
Planning Branch can provide further information regarding the EA requirement.
Based on available information, the following permit limitations may be expected
upon expansion.
Summer
Winter
Summer
Winter
Waste Flow (MGD)
3.5
3.5
6.0
6.0
BOD5 (mg/1)
5.0
11
5.0
10
N113-N (mg/1)
2.0
2.0
2.0
2.5
DO (mg/1)
5.0
5.0
5.0
5.0
TSS (mg/1)
30
30
30
30
Fee. Col. (#/100 ml)
200
200
200
200
P.O. Box 29535, Raleigh, North Carolina 27626-0535 Telephone [phone] FAX [phone]
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In addition, under current DEM procedure, dechlorination and chlorine limits are
now recommended for all new or expanding dischargers proposing the use of chlorine for
disinfection. To prevent acute toxicity, an acceptable level of chlorine in your effluent is
23 µg/1 at 3.5 MGD and 20 µg/1 at 6.0 MGD. The process of chlorination/dechlorination
or an alternate form of disinfection, such as ultraviolet radiation, should allow the facility
to comply with the total residual chlorine limit.
The instream waste concentration is 75% at 3.5 MGD and 84% at 6.0 MGD. A
chronic toxicity testing requirement with quarterly monitoring will remain a condition of
the NPDES permit. A complete evaluation of limits and monitoring requirements for
details and other toxicants will have to be addressed at the time of formal NPDES
application. Information concerning these constituents is not readily available but CMUD
can assume that effluent limits and/or monitoring for cadmium, chromium, nickel, lead,
cyanide, phenols, copper, zinc, selenium and silver should be included.
As you may be aware, DEM and Mecklenburg County are presently in the middle
of a two year study of nutrient loading in the Mr1?6well Creek watershed and the
eutrophic response in Mountain Island Lake. Preliminary data suggests that the CMUD
McDowell Creek WWTP discharge is the largest source of nutrients to the McDowell
Creek arm of Mountain Island Lake. In addition, the data suggest that the lake arm is
impaired by current nutrient loading. A final report detailing this study is due in the fall of
1994. It is likely that the McDowell Creek management plan will call for nutrient removal
from the McDowell Creek WWTP. Given the high IWC at the discharge point it is
probable that best available nutrient technologies will need to be employed to address
eutrophication in Mountain Island Lake. Until the final report is complete, speculative
nutrient limits for the McDowell Creek WWTP at 6.0 MGD are 1.0 mg/1 total phosphorus
and 4 mg/l total nitrogen (8 mg/l winter). However, these limits are based on preliminary
data and analyses, and are provided for planning purposes only. When designs for the
proposed 6.0 MGD facility upgrade are evaluated, CMUD should consider flexible designs
that can be adapted to meet advanced nutrient removal levels if more stringent limits are
needed to protect water quality in McDowell Creek.
5083.
If you have any questions, please call Steve Bevington of my staff at (919) 733-
inc' ely,
onald L. S 't, 1
Assistant Chief for Tech ' ort
Water Quality Section
SRB/DLS
cc David Parker, Black & Veatch

BLACK & VEATCH
8604 Cliff Cameron Drive, Suite 164, Charlotte, North Carolina 28269, [phone], Fax: [phone]
Charlotte -Mecklenburg Utility Department
McDowell Creek WWTP
Mr. Stephen R. Bevington
Water Quality Section
Division of Environmental Management
N.C. Department of Environment, Health,
and Natural Resources
P.O. Box 29535
Raleigh, North Carolina 27626-0535
Dear Mr. Bevington:
B&V Project 15847.024
B&V File A
T June 27, 1994
P
ii
Subject: NPDES Permitif
Speculative Limits
U
3 Igo!
Thank you for meeting with us this week to discuss the proposed expansion
of the McDowell Creek Wastewater Treatment Plant. As we discussed, Black &
Veatch is working with the Charlotte -Mecklenburg Utility Department (CMUD)
on the design of the plant expansion. The expansion of the 3 MGD plant is
planned to be completed in two phases. The first phase will consist of
replacing the existing sock diffuser aeration system with a new flexible
membrane diffused aeration system. Based on the increased aeration
capacity provided, a 0.5 MGD increase in rated capacity will be requested.
The second phase of the improvements are planned to include headworks and
influent pump station improvements, a new primary clarifier, new effluent
filtration, and ultraviolet disinfection. With these improvements, a
capacity increase to 6 MGD total will be requested.
On behalf of CMUD, we are requesting speculative discharge limits for the
McDowell Creek WWTP for each phase of the proposed expansions, first to 3.5
MGD, then to 6.0 MGD total capacity.
We look forward to hearing from you soon regarding this project. If you
have any questions, please call.
Very Truly Yours,
BLACK & VEATCH
David M. Parker
cc: Barry Gullet, CMUD