55A - SAN LORENZO SEWER LIFT STATION

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Mr. Robert Silverstein, Esq. 0 0 Review Of The Recirculated DEIR And FEIR For The San Lorenzo Sewer Lift Station Project January 12, 2012 Page 15 of 18 This arrangement provides ample access space for maintenance and thus meets (and exceeds compared with the proposed project) the second project objective listed on Page 2 -8 of the RDEIR. An additional advantage of a submersible pump station is that the pumps can be fitted with grit -flush valves. The grit -flush valve is mounted on the side of the pump and allows much of the flow from the pump to squirt into the bottom of the wet well for a few seconds each time the pump starts. This stirs up the grit in the bottom of the wet well, which allows the grit to be pumped away. The maintenance records that were provided show that from time to time the City hires a contractor to pump grit and debris out of the bottom of the wet well. The grit -flush valves would reduce or perhaps even totally avoid this recurring cost, thus benefiting the City and its residents as compared with the design of the proposed project. Another advantage of submersible pumps is that because they are submerged, they cannot be heard, There is no noise impact, thus benefiting the City and its residents as compared with the design of the proposed project. The electrical control panel for the submersible pump station would be above ground at the back of the sidewalk, exactly where it currently is for the existing pump station. The existing pump station has two pumps, each rated at 2,600 GPM at 29 -feet total dynamic head (TDH). A submersible pump station alternative would include three submersible pumps, each rated at 1,300 GPM at 29 -feet total dynamic head (TDH). Two of the pumps would handle the peak flow. The third pump provides redundancy. A performance curve for a Flygt NP3153.181, MT, Curve No. 63- 435 -00 -4530, 217 mm impeller pump is included as Exhibit H. This pump has a capacity of 1,310 GPM at 29.30 -feet TDH, i.e. each pump has half the capacity of one of the existing pumps but the new pumps can still produce the same discharge pressure. If it is decided that the proposed hydraulic capacity of 2,600 GPM is in fact inadequate, similar submersible pumps are available to provide a higher capacity. At the bottom of the Lift Station Dimensions page (Exhibit E), it can be seen that the centerline to centerline spacing between the selected Flygt pumps is 24- inches (twice the PL dimension of 12- inches), thus three of these pumps can fit in the existing 8 -foot diameter wet well. 55A -164