09-24-1984 Council Packet - Laserfiche WebLink

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The pea, flow for Maple Plain is more than six times the average daily flow. Orono contends that the peat design flow should only be 3.5 times the average daily flow, which is normal engineering practice. The city of Maple Plain has infiltration/inflow (I/1) problems in their local collection system. Several years ago Maple Plain conducted an I/I analysis that concluded excessive 1/I existed and it would be cost-effective to elimi- nate a portion of this 1/I. However, the city has not proceeded with the more detailed sewer system evaluation survey which pinpoints the problem areas and assesses the likelihood of removing the I/1. Based on the fact that excessive flow up to a peak of 2.2 mgd currintiy exists the, MWCC designed this facility to accommodate the existing peak flows. If Maple Plain can reduce this peak flow from six to 3.5 times the average daily flow the MiCC would still recommend utilizing a 12-inch diameter pipe. A 10- inch diameter pipe would have a total dynamic head of slightly over 200 feet. While this size may be marginally acceptable, better engineering practice would dictate going to the next size pipe for 3n additional safety factor. Further- more, it is uncertain that Maple Plan can reduce their peak flows to allow for the smaller pipe. Orono"s chief concern with the construction of a 12-inch force main is the development pressures the city will receive for development in their rural service area which the force main will go through. Since a 12-inch force main is needed for Maple Plain alone, whether they remove I/1 or not, no additional capacity is designed into this force main for rural Orono. This being the case Orono should be able to control development in accordance with their approved Comprehensive Plan. The Long Lake pump station which the Maple Plain force main discharges into may require an additional pump to accommodate the peak flows from Maple Plain. How- ever, provisions were made in the Long Lake pump station to add an additional pump. The Long Lake 16-inch force main is adequate to supply the needs to the areas presently sewered and presently committed to be sewered. However, as long as the high peak flows from Maple Plain remain, little additional capacity is available in the Long Lake force main to serve additional rural areas of Orono west of Long Lake. At present, the NPOES permit for the Maple Plain plant and the construction per- mit for the force main limit service connections to local service areas only. No rural area is to be provided sewer service. The current Council policy also prohibits rural area development from receiving metropolitan sewer service. These conditions are adequate for the current sewer service areas. FINDINGS OF FACTS AND CONCLUSIONS The MNCC has submitted plan,. and specifications for Council comments on the Maple Plain pump station and force main to phase out the Maple Plain STP. The plans provide for a 12-in:h force main capable of pumping 1, 700 gyallons of wastewater per minutc. This capacity is needed, according to MNCC records because of the excessive I/I from the Maple Plain sewerage systems. RECOMMENDATION That the Metropolitan Council find the Maple Plain pump station and 12-inch force main consistent with the Council Policy Plan and the MWCC 1984-1988 Development Program. JL1669-PHENV2 09.18 84