NC0024201_staff comments_19941203

DIVISION OF ENVIRONMENTAL MANAGEMENT
MEMORANDUM
TO: Bobby Blowe
Rob Brown
December 3, 1994
FROM: Juan C. Mangles r
THROUGH: Steve Bevington �� V
Ruth Sw.(
Don S
Steve Tedder
SUBJECT: Roanoke Rapids WWTP
NPDES Permit No. NC0024201
Halifax County
In 1993, DEM issued a renewal of the subject NPDES permit with a condition
that, upon permit expiration in 1997, the facility be required to relocate the outfall from
Chockoyottee Creek to the Roanoke River mainstem. This requirement was based on the
facility being originally permitted to discharge into the Roanoke River proper. However,
the discharge has always been located in Chockoyottee Creek, approximately 200 ft. from
its confluence with the Roanoke River. NPDES permit limitations for the Roanoke
Rapids WWTP have always been developed on the basis that the facility discharges
directly into the Roanoke River. Thus, minimum release flows from Roanoke Rapids Dam
of 1,000 cfs and 2,000 cfs for toxicants and oxygen -consuming wastes, respectively, have
been used when allocating effluent limitations. The 7Q10 for Chockoyottee Creek at the
discharge site is 0.6 cfs.
Consultations among DEM's Water Quality Instream Assessment Unit, Permits
and Engineering Unit and the Raleigh Regional Office concluded that the NPDES permit
requirement to relocate the discharge to the Roanoke River may not be warranted for the
existing discharge at current permitted wasteflow. This decision was based upon the
recognition of significant dilution from the Roanoke River at the present discharge site and
preliminary findings from water quality data collected from June 30, 1994 to July 15,
1994 by the City of Roanoke Rapids, indicating that the 5 mg/1 DO standard in
Chockoyottee Creek is maintained. However, if the discharge is to remain at its current
location, the instream waste concentration (IWC) must be determined so that appropriate
toxicity limits can be set to protect water quality in Chockoyottee Creek.

Site visits by DEM personnel have indicated that water from the Roanoke River
enters Chockoyottee Creek creating an embayment at the mouth of the creek. This means
that dilution at the discharge point is determined both by the 0.6 cfs flow from
Chockoyottee Creek and some portion of the total flow of the Roanoke River. The water
quality data currently available are not sufficient to accurately estimate the IWC at the
discharge point.
�" � �Because DE11K does'riot°have enough`n�ormatiori�to deve op -comp ete�PD- -�"- �"�--�-` ° -
permit limitations at the current discharge site, Water Quality staff will develop a study
plan to collect the necessary water quality data to determine the actual dilution ratio
observed at and near the discharge site. This study will be conducted by DEM personnel,
in cooperation with the Roanoke Rapids Sanitary District. Potential results of the study
may include more stringent toxic limitations (including ammonia and whole effluent
toxicity test requirements) and a dissolved oxygen (DO) limit of 5 mg/l. The results of the
study will be used in the development of limits at the time of permit renewal in 1997.
If, during the study the DO concentrations are documented below the water
quality standard, relocation or upgrade of the wastewater treatment plant may be required.
The toxicant limits and toxicity test requirements will be established using the correct
instream waste concentration based on the study. Should relocation or additional
treatment be required, the Water Quality staff will work with the Roanoke Rapids Sanitary
District on a realistic schedule of compliance.
In addition to toxicity issues, the lack of effluent disinfection has been a major
point of concern expressed by the regional office. This concern is based upon the fact that
this segment of the river is heavily used for recreational activities. Water Quality strongly
supports ongoing efforts to install disinfection and dechlorination facilities at the Roanoke
Rapids WWTP.
In light of the above, it is recommended that Construction Grants ensures that the
current upgrade is designed such that future upgrades that would address potential more
stringent limitations could be easily incorporated in a cost effective manner.
If you need further clarification on this matter, please contact me at ext. 515.
cc: Raleigh Regional Office
Larry Ausley
Roanoke Rapids Sanitary District
Permits and Engineering Unit