NC0026000_Correspondence_20170130

Al J. Leonard J.
Town of Tabor City
PO Box 655
Tabor City, NC 28463
Tel: [phone]
Ref:
ROY COOPER
Gov?r:wr
MICHAEL S. REGAN
.S'ecretary
January 30, 2017
December 2016 Facility Assessment/ Corrective Action Plan/Recommendations
Town of Tabor City WWTP; Permit No. NC0026000
Columbus County, North Carolina
Dear Mr. Leonard,
On December 07, 2016 the Water Quality Regional Operations Section (WQROS) received the
Draft Facility Assessment/Corrective Action Plan prepared by WK Dickson for the Town of Tabor
City. The conditions of the triplex influent pump station, flow equalization basin, headworks,
aeration basins and clarifiers, aerobic digester and disinfection were assessed and a corrective
action plan prepared. We are sharing our observations, providing suggestions, and requesting
pending items according to the facility assessment, our site inspections, and special conditions of
permit No. NC0026000. The Town shall address the following comments within 60 days of receipt
of this letter.
FACILITY ASSESSMENT AND CORRECTIVE ACTION PLAN
Influent Pumping, Flow Equalization Basin, and Headworks
1. Install VFD's on the influent pumps and same size motors to allow a constant flow of
wastewater into the plant. Schedule: Within six months of CAP and necessary permit
approvals.
`---Nothing Cornpares
State of North Carolina I Environmental Quality
127 Cardinal Drive Extension I Wilmington, North Carolina 28405
910-796-7215

2. Rotate use evenly between all three influent pumps to cut down on one pump becoming
more fatigued and having a potentially shorter useful life. Schedule: Upon approval of
CAP.
3. Install automated valves on the piping between the Influent Pump Station and EQ basin to
divert flow to the basin as needed so that influent flow to the plant will stay at a constant
level. Schedule: Within nine months of CAP and necessary permit approvals.
4. Add a staff gauge to the EQ basin to regulate levels within the basin. Schedule: Within one
month of approval of CAP.
5. Replace bar screen in influent wet well with an automated bar screen capable of capturing
both large rags and debris and smaller screenings (Auger Monster type system or repair
and move current mechanical bar screen to plant influent). Schedule: Within nine months
of CAP and necessary permit approvals.
The WiRO office believes that actions 1. through 5. will result in an increased reliability
at the head of the plant, offering solutions to problems the facility has experienced with
surcharges at the headworks not capturing large solids such as rags and debris
(implementation of item 5. requires an A-to-C). We further agree with automated diversion
of excessive flows to the equalization basin, as it was intended in the design. It is worth
noting that addressing I/I problems within the collection system could mitigate high
influent flows that aggravate the problem at the headworks.
To illustrate, following the last upgrade completed in 2009, it was reported to and/or
observed by Wilmington Regional Office (WIRO) staff that the headworks containing the
bar screen would overflow if all three pumps in the expanded and upgraded influent pump
station operated, and in some cases, surcharging the entire headwork would occur if two
pumps operated over a long period It appears that the third pump was designed to operate
if one of the other pumps failed or be used to divert flow to the side -stream surge basin
constructed during the same upgrade. However, diverting flow to the surge basin requires
a valve to be manually operated to initiate the process and again to cease the diversion.
Since the operation has been manual, it could lead to excessive flow surging into the
treatment system if the ORC is not present to operate the valve. These surges can cause the
excessive loss of activated sludge to the chlorine contact chamber and beyond (solid losses
have been documented in the past).
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Aeration Basins and Clarifiers
6. Move RAS piping from location at end of Clarifier #1 directly adjacent to effluent weir to
an area that is more conducive to proper mixing/aeration and longer detention times for
RAS flow. Suggested location is North side of Upper Aeration Basin #1 near the start of
the tank, directly across from the influent flow weir. Re-laying this pipe will remove the
possibility of short circuiting of the RAS flow. It is believed that this short circuiting may
have caused solids over -loading in Upper Clarifier #1. Schedule: Within six months of
CAP and necessary permit approvals.
While relocation of the RAS piping to the opposite end of the aeration basin will likely
remove the possibility of RAS short-circuiting, it does not offer an explanation of the
reported low flow or clogging. A hydraulic profile and calculated flow velocities, and an
internal evaluation of pipes such as camera inspection would help to insure the proposed
solution will alleviate the issue.
7. Install valves on piping and flow meters to be able to control RAS/WAS flow to/from
Upper Clarifier #1 (also if there is not a flow meter on RAS/WAS valves for Lower
Clarifier #2, install flow meter on that piping as well). Schedule: Within six months of CAP
and necessary permit approvals.
Agree. The installation of valves and flow meters in the RAS/WAS lines are necessary to
control the plant and are a welcome addition. Implementation of item 7. requires an A-to-
C.
8. Dig and replace/reconfigure piping leading into Upper Clarifier #1. Use larger pipe sizes
and less severe bend angles to reduce possibility of pipes clogging. Schedule: Within six
months of CAP and necessary permit approvals.
What piping is the statement addressing? It seems that it refers to the 4" WAS line. Please
clarify. Changes in piping configuration are expected to be shown in updated drawings of
the subject treatment unit (i.e. Clarifier #1). Implementation of item 8. requires an A-to-C.
9. For Lower Aeration Basin #2: Tie DO level results from DO probe in Lower Aeration
Basin #2 to existing VFD's on the three floating aerators. This will allow for more efficient
power usage so that aerators are not operating continuously and will only turn on as needed
to keep oxygen at required levels. Schedule: Within two months of approval of CAP.
Agree.
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Aerobic Digester and Chlorine Contact Basin
10. Replace the mixer in the Aerobic digester with a larger size mixer/aerator. This will result
in better mixing and aeration for the aerobic digester. Schedule: Within nine months of
CAP and necessary permit approvals.
Agree.
11. Coat the walls of the chlorine contact basin with a coal tar epoxy to help protect the basin
walls from the corrosive nature of chlorination. Schedule: Within nine months of CAP and
necessary permit approvals.
To assist with cleaning of the chlorine contact chamber given that filters will not be
provided, WiRO recommends to provide dual disinfection system or to install a
gating/diversion system to allow half of the unit to be taken off-line at a time during ideal
flow conditions. It is also recommended to switch from gas to liquid disinfection.
Otherwise, consider flow paced dosing of chlorination/dechlorination chemicals.
PENDING ITEMS
1. Mercury Minimization Plan (MMP)
This is a reminder that a MMP is required by [Special Condition A. (4.)]. The condition
indicates that the MMP shall be developed within 180 days of the NPDES Permit Effective
Date. The MMP should place emphasis on identification of mercury contributors and
goals for reduction, and shall be available for inspection. Please provide a copy of the
MMP with the response to this letter.
2. Updated Drawings, Specifications, and Operation and Maintenance Plan.
During one of our inspections in 2015, it was observed that updated drawing(s) depicting
the current/operating units and its hydraulic profile was not available. Part of the CAP
submittal should include (1) drawings of the current and proposed layouts (plant view and
profiles) of the facility treatment units and their hydraulic profile; (2) Updated
Specifications and Operation and Maintenance Plan.
3. Time Lines and Funding Availability
Part of the CAP submittal should include realistic timelines for completion of proposed
work according to funding acquisition and agency's approvals (i.e. A-to-C, etc.).
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If you would like to discuss the CAP before submittal of the final document, please contact me at
morella.sanchez-kinga,ncdenr.gov and we can set up a meeting as needed.
Sincerel
Mor King, PhD, PE
Environmental Program Supervisor III
Water Quality Regional Operation Section
Wilmington Regional Office: 127 Cardinal Drive Extension;
Wilmington, NC 28405
cc. WK Dickson & Co., Inc. 616 Colonnade Drive II Charlotte, NC 28205 IlAtt: Jimmy Holland
Central Office File- Attention: John Hennessy
WiRO/WQROS file NC0026000
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