NC0020648_correspondence_20061107

City of Washington
P.O. Box 1988, Washington, NC 27889-1988
November 7, 2006
Mr. Al Hodge
Surface Water Protection Section
Division of Water Quality
943 Washington Square Mall
Washington, NC 27889
Dear Mr. Hodge,
NOV 1 3 2006
DENR - WATER QUALITY
POINT SOURCE BRANCH
As you are aware, in June 2005 the City of Washington began operating a second
oxidation ditch. Since that time we have struggled to achieve effective denitrification in
the older section of the plant. This is primarily due to the fact that 40% of the flow and
food source was redirected to the new oxidation ditch.
We have experimented with several operational schemes over the past 16 months to
improve the efficiency of the older section of the plant and have come to the conclusion
that, at our current flows, we simply do not have enough food source coming into the
older section of the plant to support the biomass we have there. Our last adjustment was
to isolate the pre -aeration basin in the older section of the plant and direct the entire 60%
of the plant flow directly to the older oxidation ditch. This eliminated approximately
17,000 lbs of MLSS from the system. The system has been operating under this scheme
for two weeks now and the nitrates have fallen from 2.0 -1.5 mg/1 to <0.1mg/1 in that
oxidation ditch effluent.
My request is to remove the aeration ditch from service and direct all of the flow for that
section of the plant directly to the oxidation ditch. We also propose to clean out the
aeration basin, and maintain it and its related equipment in operational condition to use in
the future as the influent flows increase. I feel this change will improve the quality of our
discharge and the receiving stream. Thank you in advance for your consideration in this
matter.
If you have any questions concerning this request, please feel free to contact me by
telephone at 252-975-9310.
102 E. Second St. • Telephone [phone] TDD 1-800-735-2962 • Fax [phone]

Respectfully Submitted
4a,
Adam Waters
Water Resources Superintendent
City of Washington
Cc File
Jeffery Manning, NCDENR DWQ WARO
Teresa Rodriguez, NCDENR NPDES Unit