NC0020354_Headworks Analysis_20010323

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Michael F. Easley
Governor
William G. Ross, Jr., Secretary
North Carolina Department of Environment and Natural Resources
March 23, 2001
MR. WALLY JENKINS
DIRECTOR OF WATER RESOURCES
TOWN OF NORTH WILKESBORO
PO BOX 759
PITTSBORO NC 27312
Subject: Pretreatment Unit Review of the Headworks Analysis (HWA)
Town of Pittsboro (NPDES # NC0020354)
Chatham County
Dear Mr. Jenkins:
Kerr T. Stevens, Director
Division of Water Quality
D
MAR 2 7 20U1
CENTS FILES
The Pretreatment Unit of the Division of Water Quality has reviewed the Headworks Analysis
(HWA) for the Town of Pittsboro. This HWA was received by the Division on February 16,
2001.
The review indicates that more information is needed to determine if the HWA meets the
minimum requirements of 15A NCAC 2H.0900 and 40 CFR 403.
In order for the Division to complete its review of the HWA, you are required to submit the
information outlined below by April 15, 2001. Examples and descriptions of some of the
following items are in the Comprehensive Guidance for North Carolina Pretreatment Programs
(Comprehensive Guide). It would be helpful to us if your resubmission included a disc or email
copy of any HWA and supporting spreadsheets.
1. BOD: The HWA provides documentation of Oxygen Demand capabilities using 240
mg/l BOD and 35 mg/l TKN. The Division would accept this documentation to
support an MAHL for BOD of 1501.2 lbs/day based on Design (0.7 MGD x 8.34 x
240 mg/1). Please advise the Division if this is what the POTW wants, or provide
alternative computations and/or documentation.
2. TSS: The HWA does not directly discuss a design influent criteria for TSS. The
Division will continue with the previously approved MAHL of 7112 lbs/day based on
Passthrough. Please advise the Division if this is what the POTW wants, or provide
alternative computations and/or documentation.
3. Ammonia: The HWA does not address Ammonia but does address TKN. The
POTW's current approved MAHL for Ammonia is 56.45 lbs/day based on
Passthrough and the IUP limit for Townsends results in over allocation based on this
MARL. The POTW must either provide a new MAHL for Ammonia that supports
the Townsends limit, or alternatively, reduce the IUP limit. Perhaps the POTW could
NC—DENR. DWQ, PRETREATMENT UNIT Telephone: [phone] Fax: [phone] V*A
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provide some documentation or calculations on translating the proposed TKN MARL
into an Ammonia MARL. We have made some preliminary computations (copy
attached) based on any Ammonia/TKN ratio developed using typical domestic levels
Ammonia and Organic Nitrogen values from Metcalf & Eddy. However, the SIU
data shows a remarkably different Ammonia/TKN ratio.
4. Phosphorus: The POTW's current approved MAHL for Phosphorus is 15.98 lbs/day
based on Passthrough. The SIU's current discharge has an average of 13.1 mg/l. At
0.2 MGD, this represents 21.8 lbs/day, more than the POTW's entire MARL. It is
understood from the IUP that the SIU will provide additional phosphorus removal
above the current treatment. However, in order for the SIU's discharge to represent
less than 5% of the current MAHL of 0.8 lbs/day at 0.2 MGD, the SIU can discharge
no more than 0.48 mg/l. The POTW must either submit an updated HWA for
Phosphorus or submit other documentation .
5. Short Term Monitoring Plan (STMP): The Division's June 30, 2000, HWA Review
letter required the POTW to respond by December 1, 2000, with an updated STMP.
A review of the Pretreatment Program files for the Town of Pittsboro by indicates a
response has not been received. Please review your files and submit the required
information.
Response to this letter is required by April 15, 2001. Please note our new mailing address and
fax number at the bottom of this page. Thank you for your continued cooperation with the
pretreatment program. If you have any questions or comments, please contact me at (919) 733-
5083 (ext. 523) [email: [e-mail]], or Tom S. Poe (ext. 522), Supervisor of the
Pretreatment Unit.
drf/pi ttsborohw a.003
enclosure: DWQ June 30, 2000, letter
cc: Central Files
DRF, Pretreatment Unit, with enclosure
Ken Schuster/Pretreatment files, Raleigh Regional Office
Sincerely,
Dana Rees Folley
Pretreatment Staff
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