NC0021474_WASTELOAD ALLOCATION_19900918

NPDES ®®CUWENT SCANNING COVER SHEET
NPDES Permit: NCO021474
Mebane WWTP
Document Type: Permit Issuance
i
asteload Allocatio
Authorization to Construct (AtC)
Permit Modification
Engineering Alternatives Analysis
201 Facilities Plan
Instream Assessment (6713)
Correspondence re: draft permit
Permit History Date Range:
Document Date: e tember 18 199
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MEMORANDUM:
TO: WLA File
FROM: Betsy Johnson�?J
SUBJECT: Mebane WWTP Modification
In May, 1990, the City of Mebane applied for a modification to their
NPDES permit. The request was for an additional 1 .3 MGD, increasing
the plant' s design flow to 2 .5 MGD. The discharge is to Moadams
Creek, a low flow stream with zero summer 7Q10 and positive 30Q2 .
Approximately 1 mile below the discharge is a small shallow pond
which is heavily impacted by the discharge. An algal mat covers the
pond (Latham Lake) and drives the surface DO to 3. 4 mg/l .
The facility currently has BOD5/NH3-N limits of 11/4 (15/9) with
Total P limit of 2 mg/l . At 2 .5 MGD, 5/1 (10/1 . 8) limits will
apply. The facility has a history of toxicity problems due mainly
to lack of pretreatment compliance. The City has recently hired a
pretreatment specialist to oversee the program. Additionally,
stringent metals limits were assigned based on pretreatment
information and a priority pollutant analysis.
An analysis of the eutrophication issue found that a Total P limit
of 0 .5 mg/l (BAT) may not be sufficient to eliminate eutrophication
in Latham Lake. Technical Support recommended that the discharge
relocate below the lake and possibly to Back Creek. However, after
meeting with the City, a compromise was reached allowing the
facility to retain its 2 mg/l Phosphorus limit in exchange for
removing the lake (which is City-owned) .
The City was told that no further expansion above 2 .5 MGD would be
permitted at this site. The City acknowledged that they would not
request any additional flow.

DIVISION OF ENVIRONMENTAL MANAGEMENT
August 24, 1990
MEMORANDUM
TO: Greg Price
SEP -0 4 1990: -
THROUGH: Trish MacPherson Tw- TECHt I1rp., SUp?op gRAP1CH
FROM: Karen Lynch Y./-
RE: Latham Lake, Alamance County
Algal bloom samples were collected from Latham Lake on July
10, during ambient lakes monitoring. Thick algal mats were
prevalent on the lake's surface. During sampling at 1:25 in the
afternoon, low dissolved oxygen concentrations ranging from 3.4
mg/I on the surface to 2.2 mg/1 at 1.5 meters depth were found. An
elevated conductivity of 820 uhmos was also present. The town of
Mebane's wastewater treatment plant is located approximately one
mile upstream. Elevated conductivities are often associated with
wastewater treatment plant operations.
Quantitative phytoplankton counts revealed moderately low
algal biovolume (1,134 mm3/m3) and density (2,811 units/ml).
Corresponding chlorophyll-a was moderate at 21 ug/l.
Phytoplankton growth was perhaps being limited by shading or some
other factor.
Nutrient levels in Latham Lake were excessive with total
nitrogen, total phosphorus and ammonia/ammonium reaching 5.9,
1.1, and 0.32 mg/l, respectively.
Because of hypereutrophic conditions in Latham Lake, Mebane
will not be able to expand its treatment plant facilities. In order to
expand in the next few years, the town plans to drain Latham Lake.
cc: Trevor Clements
Steve Mauney, WSRO

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