NC0023884_Speculative Limits_19940511

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
David W. Treme
City Manager
P.O. Box 479
Salisbury, NC 28145
May 11, 1994
Subject: Speculative NPDES Limits for relocation to the Yadkin River
City of Salisbury
NPDES No. NC0023884
Rowan County
Dear Mr. Treme:
My staff has completed an evaluation for speculative effluent limits for the City of Salisbury. On
the basis of projected growth, the City has requested discharge limits at 20 MGD for a new discharge site
to the Yadkin River at the headwaters of High Rock Lake. The Division is initiating a basinwide water
quality management strategy for the state's surface waters. All NPDES permits within a given basin will
be renewed in the same year, allowing the Division to examine interaction among all point and non -point
sources of pollutants for that basin. The basin plan for the Yadkin Basin will be finalized in 1998 and a
draft version will be available for public comment sometime in 1997. In addressing interaction of sources,
wasteload allocations may be affected. Those facilities that already have high levels of treatment
technology are least likely to be affected. The City of Salisbury may want to consider implementation of
this basinwide strategy in planning its expansion.
The assimilative capacity at the current discharge sites of the City of Salisbury, Grants Creek and
Town Creek, is limited. Each stream provides less than 2:1 dilution for wastewater. As a result, water
quality in both streams has been impacted by receiving municipal wastewater discharges. There are
violations of the state standards for dissolved oxygen and chlorophyll -a in each stream. In addition, there
have been effluent violations of mercury at the Grants Creek location as well as toxicity test failures. If
the City chooses to expand its discharges at either of the existing locations, technology based limits will be
required for most effluent parameters. A regional WWTP with a discharge to the Yadkin River is
recommended over continued discharge to either of the lake tributaries.
On the basis of the information available, tentative limits for conventional constituents for a
Yadkin River discharge are as follows:
Summer winter
BOD5 5 mg/1 10 mg/1
NHz-N 2 mg/1 4 mg/1
DO 6 mg/1 6 mg/1
TSS 30 mg/1 30 mg/1
Fecal Coliform 200/100 ml 200/100 ml
pH 6-9 su 6-9 su
Chlorine 28 ug/1 28 ug/1
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2
Due to the magnitude of this discharge, the water supply classification, and the recreational usage
of the Yadkin River at this point, state-of-the-art treatment is recommended. The available instream data
indicate that the dissolved oxygen level at the lake headwater is at the state standard of 5 mg/1 at this time.
These limits will ensure that the total load of oxygen consuming wastes to High Rock Lake will be
maintained and allow for future expansion.
Chlorophyll -a levels throughout High Rock Lake regularly violate the state standard for lakes.
Algal blooms have caused high dissolved oxygen (DO) levels at the water surface while leaving the
bottom waters anoxic. Nutrient limits may be required upon completion of the High Rock Lake
management plan. Biological nutrient removal of both nitrogen and phosphorus should be considered in
designing the new plant.
Dechlorination and chlorine limits are now recommended for all new or expanding discharges
proposing the use of chlorine for disinfection. An acceptable level of chlorine in Salisbury's effluent is 28
ug/1 for protection against acute toxicity. However, alternative methods of disinfection such as ultraviolet
should be considered. Other chemical specific limits will be determined based on near field dilution
induced by a diffuser and a review of pretreatment information. A quarterly chronic toxicity test at 10%
will be required.
My staff has completed its review of Pierson & Whitman's outfall design for a 20 MGD discharge
through a 3 port diffuser which provides 10:1 dilution. Tentative limits for chemical specific parameters
are:
Cadmium (ug/l) 20
Chromium (ug/1) monitor
Cyanide (ug/1) 50
Nickel (ug/l) monitor
Lead (ug/1) monitor
Mercury (ug/l) 0.12
Copper (ug/1) monitor
Zinc (ug/l) monitor
Aluminum (ug/1) monitor
Silver (ug/1) monitor
The above limits are speculative and are for use in an engineering review of discharge
alternatives. Final limits will be provided upon receipt of an application for permit expansion. If you
have any questions concerning the above issues, please contact Betsy Johnson of my staff at (919) 733-
5083.
Donald L.
Assistant Chic
Water Qyplity Section
DLS/eaj
cc: Mooresville Regional Office
Mike Aquesta, Pierson & Whitman
Central Files