WQ0019755_NOV-2021-PC-0324 Response #2_20211007

DIEHL & PHILLIPS, P.A.
CONSULTING ENGINEERS
1500 Piney Plains Rd., Suite 200
Cary, North Carolina 27518
Telephone [phone] — Fax [phone]
October 7, 2021
Mr. Lon T. Snider, Regional Supervisor
Water Quality Regional Operations Section
Division of Water Resources, NCDEQ-WSRO
450 West Hanes Mill Road, Suite 300
Winston-Salem, NC 27105
Re: Notice of Violation (NOV-2021-PC-0324)
Oak Ridge Commons
Permit No. WQ0019755
Dear Mr. Snider:
WILLIAM C. DIEHL, P.E.
JOHN F. PHILLIPS, P.E.
ALAN R. KEITH, P.E.
As a follow-up to our previous correspondence regarding the subject Notice of
Violation, we offer the following information regarding the violations cited in the NOV
letter dated June 22, 2021.
Tertiary Filters:
The tertiary filter tank for this treatment plant was furnished with an inlet trough to
distribute the influent flow to the two filters. In addition to the outlet pipes to the two
filters, the trough had a third outlet pipe, located at a higher elevation. The third pipe
was designed by the manufacturer to only receive flow if the water level in the trough
became abnormally high due to an excessive headloss through one or both filter cells. As
originally furnished, any flow into the third pipe would be released into the clearwell.
After being in operation for a number of years, there were several instances of the filters
becoming partially blinded, causing some unfiltered water to be diverted to the clearwell
(it was subsequently discovered that one of the return sludge airlift pumps had been
improperly constructed, causing periodic clarifier upsets which would sometimes lead to
the filters receiving excessive solids; the airlift pump has since been repaired).
The occasional discharge of solids into the clearwell caused the backwash pumps to pump
solids into the filter nozzles in the filter floor, which reduced the hydraulic capacity of the
filters and led to additional solids being discharged into the clearwell.

Mr. Lon T. Snider
October 7, 2021
Page 2of3
These problems were addressed in 2017 by the following actions:
1. A pipe was installed over the clearwell, to convey any overflow from the influent trough
to the inlet trough for the tablet chlorinators, keeping solids from being deposited in the
clearwell.
2. The filter media was removed, and filter nozzles were replaced or cleaned as required.
3. The original filter media consisted of 12 inches of sand under 12 inches of anthracite.
The sand had an effective size in the range of 0.80 to 1.20 mm and a uniformity coefficient
of 1.4 to 1.7. The anthracite had an effective size of 1.08 mm and a uniformity coefficient of
1.42. It was observed that the original anthracite layer had been washed into the mudwell
over time, most likely due to backwashing with an excessive flowrate in an attempt to clean
the filters.
The original media (total depth of 24 inches) was replaced with 36 inches of a coarser sand
media. The replacement media was gravel pack no. 3 from Southern Products & Silica
Company, Inc. of Hoffman, NC. The replacement sand had an effective size of 1.91 mm and
a uniformity coefficient of 1.39. It was my belief that a monomedia filter would allow vigorous
air scouring and backwashing of the media while eliminating the concerns of anthracite
washout or poor re -stratification of the sand and anthracite after backwashing. The resulting
filter effluent quality was consistently improved with the replacement media.
Mudwell Pump Discharge Piping:
The original plant construction included a 2-inch force main for the mudwell pumps to
return the backwash wastewater to the flow equalization basin. The operators noted that
during peak wastewater flow periods the flow equalization basin would be at a relatively
high level, and a filter backwash would have to be delayed until the FE basin level
declined. To provide more operational flexibility, the operators added a 2-inch PVC
connection from the force main to one of the sludge holding tanks so that the mudwell
pumped flow could be discharged there, if the level in the sludge holding tank would
permit the additional flow. The clearer liquid would subsequently be decanted into the
aeration basin.
In addition to the pipe connection described above, a second 2-inch PVC pipe (and
valving) was added to allow the mudwell pumps to discharge into the 6,000 gallon non -
reclaimed quality wastewater treatment system included under WQ0019755. This allowed
the backwash volume to be removed from the 30,000-gallon reclaim wastewater
treatment system, but still be disposed of properly in the 6,000 gallon treatment system.
I have enclosed two plans sheets that show the pipe and valve additions, and the changed
filter media.

Mr. Lon T. Snider
October 7, 2021
Page 3of3
Summary:
The modifications detailed above were considered by JPC Utilities, LLC and me to be
to be maintenance repairs/improvements. They did not change the permitted
treatment process or expand the plant capacity, but they did improve the plant
operations and performance. Your letter implies the Permittee diverted or bypassed
"untreated or partially treated reclaimed water from the subject facilities". I would
disagree with that characterization. If one or both filter cells experienced a high water
level and caused some flow to bypass the filters and the clearwell, that flow was still
disinfected and its turbidity was still measured. If the turbidity exceeded 10 NTU, the
control system would automatically divert all of the plant effluent to the non -reclaim
storage pond, and subsequently to the non -reclaim irrigation zones. Once the turbidity
levels dropped below 10 NTU, the controls would then re -direct the flow to the reclaim
storage pond and irrigation fields. It should also be noted that while any effluent
diverted to the non -reclaim pond may have had a turbidity in excess of 10 NTU, that
water had received secondary treatment and disinfection before being diverted. The
diversion of effluent to the non -reclaim storage pond is not a bypass of any process;
it is the disposal of non -reclaim quality effluent as allowed under the permit.
We apologize if these maintenance modifications should have been preceded by an
application for an Authorization to Construct. If the enclosed updated drawings and
this letter are not sufficient to update your files, please advise how you wish for us to
proceed.
Yours very truly,
Diehl & Phillips, P.A.
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John F. Phillips, P.E.
Cc: Ms. Jennifer Graznak
Ms. Caitlin Caudle
Mr. Philip Cooke
Mr. Doug Smith

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