WQ0035706_NOV-2020-LV-0458 Response_20200624

ENVIROLINK
Robert Tankard
Assistant Regional Supervisor
Washington Regional Office
943 Washington Square Mall
Raleigh, NC 27889
RE: Moyock Regional WWTP NOV-2020-LV-0458
Mr. Tankard,
IIFCEI11
EQ1NC)I_NR/pw
A
Ilk 9 2020
wZIa watt, g4wlnY
n
June 241' Athce lOn
Please accept this response to the NOV listed above on behalf of Currituck County.
The BOD violation is related to effluent results of effluent samples pulled on 3/12/20 and
3/17/20. The on -going struggle of the media in the aeration chambers is a result of an unidentified fibrous
material entering the plant through the 5mm bar screen. The bar screen is being raked and screenings are
being removed 3 times daily but even with this effort enough material is making it to the aeration
chambers blinding the media, clogging the screens between tanks causing media to make it all the way
through to the clarifiers. Without the proper amount of media in each aeration chamber the detention time
is not adequate to remove the BOD.
A 2mm Rotary Drum Press has been installed before the 5mm bar screen removing enough
fibrous material to allow us to proceed with a complete rehab of each aeration chamber returning each
chamber to engineered design specifications. Each chamber will be drained, cleaned, diffusors rehabbed,
media reinstalled, and biological seed brought in from another WWTP. With the high strength of the
influent to the plant it is imperative the proper amount of media be in each aeration chamber to insure
BOD compliance.
The fecal coliform violation is related to effluent results of effluent samples pulled on 3/12/20
and 3/17/20. The UV disinfection system was cleaned between samples but still did not provide an
adequate kill. We are now adding C12 in the form of slow dissolve tablets post UV prior to discharge to
the basin. This practice will continue until both trains have been rehabbed back to engineered
specifications.
The NO3 as N and TN as N violations are related to effluent results of effluent samples pulled on
3/12/20 and 3/17/20. TN is a summation of TKN and NO3/NO2.On 3/12 the NO3/NO2 was 50.5 but the
NH3 was 2.81.On 3/17/20 NO3/NO2 was 48.6 but the NH3 was 1.12. The NH3 is being converted to NO2
and then to NO3 but due to a lack of nitrifying bacteria we are unable to finish the conversion and removal
of NO3/NO2.
As noted in the Metcalf and Eddy Wastewater engineering, nitrifying bacteria are extremely
sensitive organisms and susceptible to a wide variety of inhibitors, including high ammonia, nitrous acid
concentrations, temperature and PH. The Moyock Regional plant is susceptible to high ammonia, low PH,
temperature and high strength wastewater entering the plant, thus making it difficult for the system to
grow and maintain Nitrosomonas and Nitrobacter. Once again, the modification to the head works and the
aeration rehab should add a solution to these issues.

The NH3 violation is related to effluent results of effluent samples pulled on 3/17/20. The permit
states the sample is to be pulled "south of the check dam". The day the sample was pulled the ditch south
of the dam was dry, so the sample was incorrectly pulled from the moat in front of the dam. I have since
been instructed to not pull a sample if the ditch is dry but rather notate on the NDMR as sample dry. It
does make sense to me as there could be more filtration from the dam affecting the sample and reducing
the result.
I appreciate your time and respectfully request the Division consider the efforts and resources
Currituck County has devoted to improving the treatment and operation of the facility and not penalize
any further.
Regards,
Dave Robertson
Assistant Area Manager
cc: Ben Stikeleather, Currituck County Manager
Eric Weatherly, Currituck County Engineer