HomeMy WebLinkAboutAUTH-10-2022-183144.TIF PIEDMONT DESIGN ASSOCIATES, P.A.
125 East Plaza Drive, Suite 101 Engineering
Mooresville, NC 28115 Surveying
Telephone(704)664-7888 Fax(704)664-1778 Planning
Email: dmundayt pdapa.com
December 4, 2023
Mr. Robbie Phelps, REHS
Catawba County Health Department
Environmental Health Division
PO Box 389
Newton, NC 28658
Re: Pump Sizing Calculations for Offsite Effluent Force Main Serving
1400 Astoria Parkway(Lot 43), Sherrills Ford,Catawba County, NC
Dear Mr. Phelps:
The purpose of this letter is to recommend an effluent pump to convey effluent from Lot 43 Astoria Subdivision to its
offsite disposal lot (COS-24) located on the east side of Regal Blvd. It is our understanding that there is an existing 3-
inch PVC force main already installed with turn up(s) located at each of the two lots. The following analysis and
recommendations are based on survey information provided to our firm for Lot 43 & COS-24, Catawba County GIS
data,and elevation data from original subdivision construction drawings.
The design flow of the system was based on 5 subsurface laterals dosed by a Pressure Manifold with(5) 1/2-inch SCH
80 PVC taps.These taps,when dosed at 2 feet of operating head deliver 5.48 G/M each or 27.40 G/M. The number of
required taps were provided by Steven Price, REHS with Catawba County Environmental Health. It is recommended
that the tap sizes be increased to'/.-inch SCH 80 taps to achieve a scour velocity of 2 ft per second.
The Total Dynamic Head of the pump is calculated by adding Static Head, Friction Head &Operating Head. The static
head was based on a hydraulic profile of the existing ground surface created from original subdivision construction
drawings. The low point elevation was determined to be 782 feet(plus an additional 7 feet for pump tank depth). It is
the Engineer's understanding that the pump tank is to be in the front yard due to setbacks and a grinder pump required
for the basement plumbing. The hydraulic profile showed that the highest elevation along the pump line is at the offsite
lot. The elevation at the high point of the offsite septic lot was determined to be 855 feet, therefore, a static head of 80
feet will be used.
The pump line from the proposed pump tank location to the drainfield measured horizontally to be 2,685 LF. Using
Hazen-Williams formula for friction loss calculation, based on a flow of 47.34 G/M in a 3-inch SCH 40 PVC pipe, the
friction head is 19.47 feet(includes an additional 20%to cover minor losses). The operating head to be used is set at a
minimum of 1.75 feet, however 2 ft is recommended if the pump will deliver. By combining these numbers, we have
determined that the system requires a pump capable of providing a flow of 47.34 G/M at a Total Dynamic Head of
101.22 feet. We recommend a Liberty FL200-Series High Head Submersible Effluent Pump or Engineer approved
equal for this proposed operating condition.
These comments and recommendations are based on information provided to the Engineer by the client and previously
stated sources and are limited to that discussed in this letter. Any conditions that may come forth that are different from
those discussed herein should be reported to the Engineer immediately for further evaluation. Any questions regarding
the recommendations should be addressed to the Engineer for elaboration. Thank you for allowing us to provide this
service to you.
Sincerely,
Pied ont Design Associates, PA ``01t l 1111//77,
i/ d4*4411 re.
•- SEAL
Donald L. Munday, P.E. = 17327 —
NC Registration No. 17327 — Q '; ;
President
Cc.: Tim Zimmerman,Owner L. M ```��
Richard Abernathy, Installer 7'1204//04/ 023
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