NC0025071_Correspondence_19900601

0
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. Mardn, Governor George T. Everett, RLD.
vy111arn W. Cobey, Jr., Secretary June 1, 1990 Director
Steven L. Routh
City of Eden/Mebane Bridge WWTP
350 W. Stadium Drive
Eden, NC 27288
Subject: Chlorine Toxicity
NPDES Permit No. NCO025071
Rockingham County
Dear Mr. Routh:
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 ug/l (freshwater classes
only). In addition, the fecal coliform limit was reduced from 1000
colonies/100 ml 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 their NPDES permit renewal process.
Our records indicate that chlorine from your facility's effluent
discharge is considered toxic to the receiving stream under low flow
conditions, i.e., the amount of chlorine discharged causes a
violation of the instream action level for chlorine (17 ug/1) under
700 conditions (the average 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. Based on
your facility's instream waste concentration of 4.3% (during the
SOC), an acceptable level of chlorine in your effluent is 398 ug/l.
(At 13.5 MGD, your chlorine concentration should be 271 ug/1). If
this level is not feasible, you should consider dechlorination or
alternate methods of disinfection for your facility 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. However, please note
that an authorization to construct must be obtained from this
Division prior to any alteration to your treatment plant.
PoBudon PreveMlon Pays
P.O. Box 27687, Raleigh, North Carolina 27611-7687 Telephone [phone]
-- C.- —I (1..A.-— LmnlM nr

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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 facility's with
chlorine problems. If the chlorine levels in your facility's
effluent remain unchanged, a chlorine limit or a whole effluent
toxicity testing requirement may be added to your permit limitations.
Please feel free to call Steve Mauney of the Division's Regional
Office at [phone], if you have any questions or comments
regarding this issue.
Sincerely,
Steve Tedder
Water Quality Section Chief
cc: Winston-Salem Regional Office
Central Files
WLA File

City of Eden
Steve Tedder
Water Quality Section Chief
NC Department of Environment, Health,
Natural Resources
Division of Environmental Management
512 North Salisbury Street ' ""� y eu(y'.•
Raleigh, NC 27611 .Iuw 181990
QUALITY
Dear Mr. Tedder: SECTION
Subject: Chlorine Toxicity
NPDES Permit No. NC0025071
Rockingham County
The city's consulting Engineers Finkbeiner, Pettis, and Strout
are designing an expansion of the Mebane Bridge Wastewater
Treatment Plant. Their plans include dechlorination facilities.
Until the planned expansion is complete the city will make every
effort 'to reduce effluent chlorine concentrations to the minimum
level which will allow us to meet our NPDES Bacteria limits of 200
colonies/ 100 ml. Operating experience indicates that the level
of disinfection required by our NPDES permit cannot be achieved
without chlorine concentrations above the levels mentioned in your
letter of June 1, 1990, to Mr. Steven L. Routh. Once construction
of the expanded facilities is complete the dechlorination process
should allow us to comply wittl both the disinfection and effluent
chlorine concentration rdquirements.
Sincerely,
Dennis Asbury
cc: Steven L. Routh, City Manager
Terry Shelton, Wastewater Superintendent
David Cain, Finkbeiner, Pettis and Strout
CA"'i,-A. ( -4,' (e s
enclosure
350 West Stadium Drive • Eden, North Carolina 27288-3299 • Fax [phone]