NC0020354_correspondence_19910802

State of North Carolina
Department of Environment, Health, and Natural Resources
Division of Environmental Management
512 North Salisbury Street • Raleigh, North Carolina 27611
James G. Martin, Governor
William W. Cobey, Jr., Secretary
August 2, 1991
George T. Everett, Ph.D.
Director
Mr. Ken Comatzer
Town of Pittsboro
P.O. Box 753
Pittsboro, North Carolina 27312
Subject: Chlorine Toxicity
NPDES Permit No. NC0020354 - Town of Pittsboro WWTP
Chatham County
Dear Mr. Cornatzer:
Chlorine, a widely used wastewater disinfectant for the treatment of coliform organisms, often
remains instream in residual amounts that may prove to be toxic under critical low stream flow
conditions. In the last decade, EPA assessed the potential adverse effects of chlorine to the aquatic
environment and has taken steps to reduce the impacts through the development of federal criteria.
In 1986, EPA recommended that all states have a chlorine standard by their next triennial review of
water quality standards.
In revising its water quality standards in 1989, North Carolina developed an action level for
chlorine of 17 µg/1(freshwater classes only). In addition, the fecal coliform limit was reduced from
1000 colonies/100 nil to 200 colonies/100 ml. Under a new DEM procedure, dechlorination and
chlorine limits are now recommended for all new or expanding dischargers proposing the use of
chlorine for effluent disinfection. The Division is reviewing chlorine levels from all existing
dischargers as part of its NPDES permit renewal process.
Our records indicate that chlorine from your facility's effluent discharge may be toxic to aquatic
life in the receiving stream under low flow conditions, i.e., the amount of chlorine discharged causes
an exceedance of the instream criteria for chlorine (17 µg/1 for chronic effects and 28 µg/1 for acute
effects) under 7Q10 conditions (the lowest average daily flow for seven (7) consecutive days during
a ten (10) year period). Action should be taken to reduce the effluent concentration of chlorine to an
acceptable level. An acceptable level of chlorine in your effluent is 17
s
level is not feasible, you should consider dechlorination or alternate methodss of or dis di17 sinfection foryourfacility to ensure that both chlorine and bacterial limits are met. In addition, if your facility plans to
undertake any phase of construction, dechlorination or alternate disinfection should be included.
Pollution Prevention Pays
P.O. Box 29535, Raleigh, North Carolina 27626-0535 Telephone [phone]
An Equal Opportunity Affirmative Action Employer

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However, please note that an authorization to construct must be obtained from this Division prior to
any alteration to your treatment plant.
The Division is currently reviewing its water quality regulations pertaining to chlorine. In the
future, effluent limits and/or dechlorination may be required of existing facilities with chlorine
problems. If the chlorine levels in your facility's effluent remain unchanged, a chlorine limit or
whole effluent toxicity requirement may be added to your permit limitations.
Please feel free to call Mr. Tim Donnelly of the Raleigh Regional Office at [phone], if
you have any questions or comments regarding this issue.
Sincerely,
Steve W. Tedder
Water Quality Section Chief
SWT/DAG
cc: Raleigh Regional Office
Central Files