NC0025381_correspondence (WWTP history)_20210512 (2)

VINGINEERING
163 Heritage Lane, Bostic, NC 28018 • 828.245.4080 office • 828.223.2265 mobile • 828.245.2189 fax
May 12, 2021
Mr. Landon Davidson, P.G.
Regional Supervisor — Asheville Regional Office
Water Quality Regional Operations Section
NCDEQ— Division of Water Resources
2090 U.S. HWY 70
Swannanoa, NC 28778
REFERENCE: The Lake Lure Wastewater Treatment Plant
NPDES Permit No. NC0025381
SUBJECT: History of Operation
Dear Mr. Davidson,
Per our conversation on Tuesday, May 11, 2021 I am providing you with the history of the
operation of the Lake Lure Wastewater Treatment Plant (WWTP) as you requested. The following
is based on both my understanding of the WWTP as well as that of Mr. Maurice Walsh, P.E.,
LaBella Associates who is the main Project Manager for the ER & EID for the proposed Clean Water
State Revolving Fund (CWSRF) project as well as Mr. Don Byers, past ORC of the WWTP.
The WWTP was originally constructed as a 0.350 MGD activated sludge plant in 1969. Prior to this,
the wastewater was discharged directly into the Broad River. From interviews with various
stakeholders and from reviewing previous upgrades, it is apparent that the initial 1969 WWTP
utilized an activated sludge process. The original WWTP utilized three necessary components of
an activated sludge process, which were aeration, mixing, and a return activated sludge (RAS)
system. Fixed surface mechanical aerators accomplished the aeration and mixing. The RAS/WAS
pump station pumped either to the digester or the head of the aeration basin. Figure 1.1 shows
the original flow scheme for the biological treatment process.
In 1991, the WWTP was renovated and converted into a physical -chemical process (P/C). Primary
treatment was added, which included a flash mix and flocculation basin. The mechanical aeration
equipment was removed, and the aeration basin converted into a sedimentation basin. The

Mr. Landon Davidson, P.G.
May 12, 2021
Page 2
RAS/WAS pump station was converted to a sludge pumping station and transfers settled sludge to
the digester.
The method of operation for this P/C WWTP is to add a coagulant (Alum) at the influent of the
WWTP in the flash mix. The resulting sludge is intended to settle in the sedimentation basin or
secondary clarifier. Additionally, a post coagulant (Poly Aluminum Chloride) is added to the
influent to the secondary clarifier to further facilitate settling. The settled solids are then pumped
to the digester for thickening and subsequent removal. The ability of thickening the sludge was
lost some time ago due to significant issues with the digester. Figure 1.2 shows the 1991 flow
scheme for the P/C process.
In 2008, the WWTP was renovated to improve the settled sludge transfer process. A new step
screen and dumpster was added to the headworks. A submerged collection system was installed
in the sedimentation basin. In addition, the sludge pump station was modified to utilize the new
submerged collection system.
In summary, the WWTP utilized a biological process from 1969 to 1991. The 1991 renovations
removed any capability for a biological process and converted the WWTP to a P/C process. There is
no aeration and there is no activated sludge in this system. Biological treatment does not take
place.
The reason the P/C conversion was performed was due to the dilution of the influent wastewater
by lake infiltration and the inability to sustain a biological process because of the weakened
strength of the influent wastewater. The lack of food in the influent wastewater could not sustain
biological activity. The intent of the current SRF project is to the start the replacement of the
submerged sanitary sewer system (SASS) in phases. This will eventually enable the return to a
biological treatment process when the lake water is removed. Due to the magnitude of the SASS
replacement, the biological conversion of the WWTP is estimated to be completed by 2034.
Intermediate improvements to the WWTP are proposed in the ER & EID which would improve and
optimize the P/C process; however, it is recommended that the biological conversion follow the
SASS replacement.
If you should have any questions regarding the above, please do not hesitate to contact me.
Very truly yours,
/vi)''
Kurt Wright, PE, BCEE, PWAM
Town Engineer — Town of Lake Lure (by contract)
CC: Mr. Shannon Baldwin; Mr. David Arrowood; Mr. Maurice Walsh, P.E.; Mr. Don Byers

Mr. Landon Davidson, P.G.
May 12, 2021
Page 3
Figure 1.1-1969 Flow Scheme — Biological
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$CAL: 1"= 40.
INFLUENT LINE
SPLITTER BOX
AERATION BASIN
CHEMICAL
BUILDING
ADMIN.
BUILDING
DIGESTER
RASIWAS
PUMP STATION
LEGEND
1969 STRUCTURE
PROCESS FLOW
EFFLUENT LINE TO
BROAD RIVER
CHLORINE CONTACT
2N0. CLARIFIER
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Mr. Landon Davidson, P.G.
May 12, 2021
Page 4
Figure 1.2 —1991 Flow Scheme — Physical/Chemical
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SCALE: I' = 40'
INFLUENT LINE
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FLOCCULATION
BASIN
SPLITTER BOX
SEDIMENTATJON
BASIN
CHEMICAL
BUILDING
ADMIN.
BUILDING
SINN
DIGESTER
SLUDGE PUMP
STATION
e
LtLitNL7
n 1991 MODIFICATION
1969 STRUCTURE
PROCESS FLOW
EFFLUENT LINE TO
BROAD RIVER
CHLORINE CONTACT
2ND. CLARIFIER
Lake Lure, North Carolina
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