NC0047384_Headworks Considerations_20171030

Water Resources
ENVIRONMENTAL QUALITY
Steven Drew
Water Resources Division
City of Greensboro
2602 South Elm -Eugene Street
Greensboro, NC 27406
October 30, 2017
Subject: Greensboro TZ Osborne NCO047384 Headworks Considerations
Dear Mr. Drew,
ROY COOPER
Governor
MICHAEL S. REGAN
Secretary
S. JAY ZIMMERMAN
Director
The Division of Water Resources (DWR) received a request from the City of Greensboro on October 27, 2017 for
determination of initial loading calculations of a yet to be submitted headworks analysis (HWA). Many POTWs are
unable to calculate site specific removal rates for calculating allowable pollutant loads. When insufficient data above the
practical quantitation limit (PQL) is available the default is to use decades old EPA reference removal rates. These
default values can in some cases be overly conservative.
A review of the TZ Osborne plant data was conducted with additional consideration of the sustained excellent
performance of the POTW, and plant treatment upgrades in progress. This review indicated that it may be more
appropriate to use the default removal rates associated with the 81 decile of the EPA study. The Division will therefore
allow the following initial removal rates to be used in HWA calculations.
-Cadmium 91 % -Lead 77%
The city also requested that if an analysis of the site-specific speciation of chromium was submitted the Division would
allow the study results to be used to calculate a proportional limit for trivalent chromium to be expressed as total
chromium in the NPDES permit. The Division will allow the results of a pilot chromium speciation study to be used for
NPDES limit calculation. It should be noted that mayor modification to the permit and appropriate fee would be required
for this study to be considered in permit limit calculation depending on the timing as related to permit reissuance.
The Division has previously stated in presentations and hereby confirms that if influent concentration of silver remained
below an appropriate PQL of 1 ug/L then no NPDES/WQS Pass -Through Allowable Headworks Loading calculation will
be required. If silver is consistently quantified in the effluent traditional calculation of loading, a minimization plan or
similar strategy may be required.
If you have any questions please feel free to contact meat 919-807-6309 orjeff poupartAnedenr.gov .
cc: Central Files
W SRO
Sincerely,
Je�Ppoupart
Water Quality Permitting Section Chief
Nothing Compares_
State of North Carolina I Environmental Quality I Water Resources
512 N Salisbury Street 1 1611 Mail Service Center I Raleigh, NC 27699-1611
9197079000