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0 <br />NZ. <br />- - McCOMBS-KNUTSON ASSOCIATES, INC. <br />CONSULTING ENGINEERS ■ LAND SURVEYORS M SITE PLANNERS <br />September 15, 1977 <br />Dick Benson <br />City of Orono <br />P.O. Box 66 <br />Crystal Bay, Minnesota 55323 <br />Subject: Orono - Long,Lake Interceptor <br />Gentlemen: <br />LZ-) L ! � <br />.i <br />Scr i4u <br />��-AGF �0;= ►i :`-:'_� _� <br />The decision that an 18" force main is required for the Orono <br />line was based on hydraulic problems in operating two pumping <br />stations that discharge into the same line. There is no greater <br />capacity for Orono designed into the 18" nipe. <br />When detailed design of the pumping stations was done, it <br />became apparent that the Orono station operating with a 16" forcemain <br />could cause the Long Lake station to lose the capability of u_umping <br />its design flow. <br />The 18" forcemain allows a selection of pumps which are <br />essentially the same for both stations. This means operating conditions <br />will be such that the overall system will act like a single pumping <br />station with two pumps and 100% standby. <br />The hydraulics of a system which includes two pumping stations <br />with long force mains discharging to a single force main is very complex. <br />These operating problems were not analyzed in the preliminary design <br />phase of this project. <br />An added benefit of the 18" forcemair- is that, instead of <br />125 or 150 horsepower motors that would be required for each of the <br />Orono pumps with the 16 line, 100 horsepower motors can be used. This <br />results in a substantial energy saving. Even with the 18" forcemain <br />the Orono station will be unable to handle more then the flows projected <br />in the report and approved by Orono. <br />12805 OLSON MEMORIAL HIGHWAY, MINNEAPOLIS, MINNESOTA 55441 TELEPHONE 1612) 559-3700 <br />22 NORTH MAIN STREET. HUTCHINSON, MINNESOTA 55350 TELEPHONE (612) 879-8029 <br />SOUTHWEST ENGINEERING DIVISION, MARSHALL, MINNESOTA 56258 TELEPHONE (507) 532-5820 <br />printed on recycled paper <br />