WQ0042456_Application Attachment_20210428

TOWN OF ANGIER
Memo
To: Trent Allen, NC DEQ
From: William Dreitzler, P.E., Town Engineer
Date: April5, 2021
Re: Spring Village Subdivision FTSE — Planning Assessment Addendum
Mr. Allen,
As per our previous discussion, I am providing a supplemental memorandum for the Planning
Assessment Addendum for an FTSE you will be receiving for Spring Village in Angier, NC.
This development will pass through 2 Angier Pump Stations. PS6 which is at the lagoon but
pumps to our outfall that gravity flows to PS9. PS9 is at our old oxidation ditch treatment
facility that pumps to the North Harnett Regional WWT.
Our last submitted FTSE that ended up at PS6 was for Lynn Ridge Subdivision. In that FTSE
we had the Design ADF at 0.576 MGD and the ADF at 0.349 MGD. Both were thought to be
accurate at the time of submittal. However, a few months later staff noticed there was a
significant discrepancy between the flows received at PS9 and the flows received at PS6. We
have a small amount of flow that enters the collection system between PS6 and PS9; however,
generally the numbers should be close and they were not. The ADF's at PS9 were over 0.500
MGD. Public Works had the flow meter at PS6 evaluated and determined it needed to be
replaced. Our first monthly readings for the new meter at PS6 were in September 2020. The
3-month period (September to November) was we and the flow average was 0.609 MGD.
After the first month we new we had an issue and contracted with Timmons Group to provide
an evaluation of PS6. The evaluation included a drawdown to evaluate the actual Firm
Capacity, assessment of the upstream drainage basin for future growth and recommendations.
Resulting actions were to replace PS6 with a new submersible pump station with a pumping
capacity of 1700 GPM. Based on the drawdown test, PS6 currently as a pumping capacity of
about 850 GPM (single pump).
Therefore, for Spring Village we have updated and we believe more accurate numbers for
PS6. Firm Capacity of 0.482 MGD (Lynn Ridge was 0.576 MGD) and ADF of 0.508 MGD
(Lynn Ridge was 0.349 MGD). As noted, this means we are showing PS6 as over capacity
prior to accounting for the 0.171 MGD in not -yet -tributary. However, as you are aware, we
have PS7 adjacent to PS6 at the Lagoon. The Town uses PS7 for flow equalization when we
have heavy rainfalls. PS7 pumps into the lagoon and we land apply. Our Irrigation Treatment
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Facility has a permitted capacity of 199,000 MGD. We only use a fraction of that amount
yearly. A splitter box is engaged during these high rain events and sends flow to both PS6 and
PS7. Because of this design feature at the lagoon, and the significant amount of available
capacity in the land application facility, we do not believe we run a risk of having an incident
at PS6 due to an over capacity situation.
The Town has engaged Timmons Group for the PS6 replacement that will achieve the 1700
GPM flow rates. The Agreement and the project schedule will be provided as further
documentation with the FTSE submittal for Spring Village. The initial schedule had the PS6
replacement active in November 2021. However, the Town has funding arranged and is
scheduled to go before the LGC for approval in August 2021. The LGC wants bid numbers in
lieu of estimates and Timmons has adjusted the project schedule accordingly. With the
approval of the Spring Village Permit Application, we do not anticipate receiving any flows
prior to completion of the PS6 replacement. If you have any further questions or concerns,
please contact me at your convenience.
Sincerely,
William W. Dreitzler, P.E.
Angier Town Engineer
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