Agenda - 03-02-2006-10b - Laserfiche WebLink

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HLLtT WILLL HI'IJ I'dX •JJOLLOJUJ4 I'Idl 1 GUVO 14 •Jl !'. VJ '~ 03224 ANALXSIS OF FLOWS TO THE INDUSTRIAI. DRIVE PUMP STATION Febn~ary 21, 2006 This section swnmarizes the estimates of flows tributary to the City of Mebane Industrial Drive Pump Station as related to the proposed construction of the Buckhozzr Pump Station and Force Main Project, including the proposed STAG Project on the north and south side of interstate I-40/85. During the review of the subject pzoject by the Construction Grants and Loan Sections, questions have been raised regazding the available capacity in the Industrial Drive Pump Station. Following a review ofthe actual pump performance using calculated pump drawdowns, it was determined that the existing Industrial Drive Pump Station is actually operating at 501.2 GPM. While the station was oziginally rated at 350 GTPM, actual system head (TDI~ is less than estimated and the pump is operating at a point on the pump curve where it is pumping 501.2 GPM. This difference in head is attributed to fording trapped air in the force main due to a malfunctioning air release valve, Following manual release of the air, the pump opezated at its true system head (approximately 100 feet) and yielded the 501.2 GPM pumping zate. Due to the age of these aiz release valves, the City of 1vlebane has ozdered new valves for replacement to achieve consistent system operation. With the pumping capacity of the Indrrstrial Drive Pump Station being established at approximately 500 GPM, the receiving line was then evaluated for adequacy to accommodate these flows. Dozing the pump evaluation, the receiving manhole was observed during actual pump operation. While some pipe submergence occurred in the 8" receiving line, no manhole overflow occurred. Modeling for this 8" line does indicate pipe submergence of almost 3 feet at 500 GPM; therefore, it is zecommended that approximately 1200 feet of 8" gravity sewer being upsized to 12", A 12" Line can accommodate appzoximately 1300 GPM when flowing full at a slope of 0,65% (slope of the existing 8" line). The Industrial Drive Prunp Station currently has existing flows of approximately 45,000 CrPD from businesses flowing to this station, It also accepts flows fiom another pump station (L,. J. Rogers Pump Station) that currently has approximately 1,000 GPD of wastewater that flows into it. While the L. J. Rogers station currently pumps only 2-3 cycles per day, it has pumps that are rated at 200 GPM. These pumps are currently over designed for the existing flow and it is zecommended that this station be downszzed to a 100 GPM station. TfLis downsizing will provide additional capacity in the Industrial Drive Pump Station while providing capacity to accept additional users tnibutary to the L.J. Rogers Station. We have modeled these two stations as if connected to the existing 8" force main with the current pumps when operating sepazately and when operating simultaneously. This modeling indicates the following: Page 1