NC0023884_Staff Comments_19940706

DIVISION OF ENVIRONMENTAL MANAGEMENT
Water Quality Section
TO:
Cecil Madden
Construction Grants Section
FROM: Betsy Johnso
Water Quality1S ction
THROUGH:
Steve Bevington �D
Ruth Swanek J , for
July 6, 1994
Subject: Salisbury Relocation
NPDES Nos. NC0023884 (Grants Creek) and NC0023892 (Town Creek)
Rowan County
In response to your inquiries regarding the proposed relocation of the City of Salisbury's WWTPs, I provide the
following comments. The Division has initiated 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 promulgated by 1998 and a draft version will be available for public comment sometime in
1997. In the meantime, discharge limits will be based on existing procedures. In addition, the Instream Assessment
Unit is currently developing a nutrient response model of High Rock Lake. The outcome of this model will affect
future permits for discharges to High Rock Lake.
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, both streams have been impacted
by receiving municipal wastewater discharges. A 1989-90 field survey conducted by DEM ranked Town Creek as
the most nutrient enriched tributary of High Rock Lake . Total nitrogen and total phosphorus exceeded target levels
set by DEM for the control of algal growth. Chlorophyll -a levels 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. Grants Creek is similarly impacted, ranked second by DEM in nutrient impairment. In addition, Salisbury's
self -monitoring data indicate violations of the state's DO standard at the mouth of Grants Creek. Based on the
documented water quality problems, the Water Quality Section supports the relocation.
NO RELOCATION
The permits for Grants and Town Creek were renewed this year at existing limits. However, the City was notified
that nutrient removal was likely pending completion of the High Rock Lake report. This report has been drafted
and may be finalized by Fall 1994.
In addition to more stringent nutrient requirements, upon renewal in 1998 (basin plan), more stringent limits for
conventional limits may be required due to existing water quality problems in both Grants and Town Creek.
Advanced treatment to meet summer limits of BODS = 5 mg/1, NH3-N = 1 mg/1, and DO = 6 mg/1 may be required.
The fecal coliform limits will be 200 colonies/100 ml. In addition, dechlorination or alternate disinfection may be
required in conjunction with a plant upgrade. Chemical specific limits at or near the water quality standards and
toxicity testing at 90% will be required.

RELOCATION
• No expansion
If Salisbury chooses to relocate its discharges to the Yadkin River with no increase in permitted flow,
existing limits for conventional limits, i.e., BOD5 and NH3-N, will be required. Nutrient removal may be
recommended pending the completion of the High Rock Lake report. 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 will be required.
• Expansion
Speculative limits have been developed for relocation to the Yadkin River with expansion to 20 MGD. On
the basis of the information available, tentative limits for conventional constituents for a new 20 MGD
facility are as follows:
summer winter
BOD5 5 mg/1 10 mg/1
NHS-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
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 will be required.
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 relocation or expansion. If you have any questions
concerning the above issues, please call me at [phone].
cc: Mooresville Regional Office
Central Files (2 copies)
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