01-13-2014 Council Packet - Laserfiche WebLink

Home Browse Search

rated capacity of 39 gallons per minute (gpm). Drawdown testing performed on the station on August 8, 2013 indicated the two pumps have capacities of 26 gpm and 46 gpm. The average sewage generation rate used by MCES is 274 gallons per day (gpd) for single family homes. Grinder Station 9 currently serves 9 homes and adding the 6 homes served by the proposed extension yields a total of 15 homes. Based on MCES criteria, the total daily volume of sewer flow would be 5206 gpd or 3.6 gpm. This would require the pumps to run an average about 2.4 hours per day. Sewer flow varies throughout the day and MCES criteria assumes the peak flow rate to be 4 times the average flow or 14.4 gpm. This is well below the pump capacities, however this does not include infiltration and inflow (I/I) into the system which also needs to be pumped. Review of the weekly pump run meter data for 2012 and 2013 indicated that the peak week pump run time, which occurred in June 2013, was 57.8 hours, or an average af 8.3 hours per day. The peak day during this week would have been higher than the daily average for the week. The added flow from the 6 homes on Green Trees Road would require an average pump run time of 0.8 hours per day and therefore the extension is not expected to significantly increase the peak flow to Grinder Station 9 and the station has adequate capacity for the additional units. B. ALTERNATE 2- GRAVITY SEWER Review of the estimated basement floor elevations of the Green Trees Road homes indicates that a gravity sewer could be extended at elevations low enough to provide gravity sewer service to each lot which is typical for most service connections. This would eliminate the need for a grinder pump station on each lot. The gravity main would be 8-inch diameter which is the minimum size for municipal gravity sewer. The proposed sewer is shown on Figure 2 in the Appendix. The existing onsite systems would be abandoned, the same as with Alternate 1. A portion of the gravity sewer will need to be constructed at the minimum slope which is about 5 inches drop in 100 feet. The sewer can be constructed by trenchless method but the methods differ from the directional drilling for the forcemain due to the flat slope. The method proposed is described as guided boring which uses a laser to precisely guide the boring. This does not allow for curves in the sewer route and therefore the route shown on Figure 2 is straight lines from manhole to manhole. The boring would be done from the center manhole which will require a 15 foot diameter access shaft. The sewer depth at this location is about 19 feet. An access shaft about 14 feet deep will also be required at the north end to receive the boring equipment and construct a manhole. The gravity sewer service stubs will be constructed by open cut Page 5