WQ0029945_Pilot Study Request_20191101

October 31, 2019
Ms. Tessa Monday, Environmental Engineer
NCDEQ Division of Water Resources, Non -Discharge Branch
1617 Mail Service Center
Raleigh, NC, 27699-1617
4
ONWASA
on wasa corn
228 Georgetown Rd
Jacksonville, NC 28540
RE: Request for Approval - Pilot Testing of Infiltration Basin #2
Permit No. WQ0029945 Summerhouse Water Reclamation Facility
Onslow County
Dear Ms. Monday:
This letter is sent to request review and approval of a proposal to conduct pilot
testing of an existing infiltration basin serving the Summerhouse Water Reclamation
Facility (SWRF). Primary goals of the testing are: to determine if the basin can support a
higher flow rate than the approximately 100,000 GPD it is now receiving; provide
documentation for a future permit modification request; and, to assist ONWASA in long-
term planning efforts now underway for this facility.
ONWASA will be utilizing The Wooten Company and Edwin Andrews &
Associates, PLLC to perform the pilot test field work, prepare a report of the findings,
certify the basin capacity, and prepare a permit modification request (if necessary). As
we anticipate treated effluent flow from the SWRF will not be great enough to achieve the
desired loading rate, groundwater from an existing groundwater pumping well adjacent to
Basin #2 will also be discharged to the basin during the pilot test. This groundwater well
was previously used for loading the basin during the original basin capacity testing. It is
proposed that the pilot testing be performed over an approximate four to five -week period,
with a target starting date in mid -November 2019.
The proposed testing process is described below:
1. An initial loading test will be made by filling and testing the capacity of the full basin
for two (2) weeks. The purpose of this initial testing is to establish an apparent
maximum capacity. Treated WWTP effluent and groundwater will be used to
initially fill the basin as quickly as possible (estimated at 200,000 gallons per day)
to the current maximum water level design elevation of 9 feet above mean sea
level (maintaining two feet of freeboard). As the water level approaches 8.5 feet
above mean sea level, the loading rate will be adjusted (reduced or increased), if
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necessary, to maintain operational levels below 9 feet above mean sea level. This
initial loading rate will be recorded.
2. After the initial stable loading period as described above is completed, an
additional two (2) week test will commence at the stabilized design loading rate.
The purpose of this additional two weeks of testing is to confirm that the maximum
rate is sustainable. Three to four piezometers will be installed in a line between
the pond and one of the existing drains. Water levels in these piezometers and
the basin will be monitored with data loggers. The basin loading rate (gallons per
day) and the ground water lowering flow (gallons per day) will be monitored during
the second testing phase. Flow meters are already present to measure the WWTP
effluent flow, the groundwater flow, and the groundwater lowering flows. The water
level changes in the basin will be monitored to determine if the basin loading rate
can be increased or if it needs to be decreased.
3. Pilot test results will then be analyzed and a short report prepared detailing test
conditions and results, with a proposed sustainable capacity of the basin. Part of
the analysis will include comparison of pilot results to the original MODFLOW
modeling results for the basin. The report will include a hydrogeologic certification
for the proposed loading rate.
4. If determined justified by the results of the pilot testing, the test report and a Permit
Modification Application will be submitted to your office for consideration.
If you should have any questions, please do not hesitate to contact Carl Scharfe
at the Wooten Company (919-828-0531) or myself at the contact information provided
below. Thank you for your consideration of this request, and we look forward to starting
the test as soon as the plan is approved.
Sincerely,
David M. Mohr, PE
Engineering Director
Onslow Water and Sewer Authority
Ph. (910)-937-7521
[e-mail]
Cc: Carl Scharfe, PE, The Wooten Company
Eddie Caron, ONWASA
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