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METROPOLITAN COUNCIL Suite 300 Metro Square Building, St. Paul, Minnesota 55101 612-291-6359 DATE: September 18, 1984 TO: Metropolitan Systems Committee FROM: Environmental Planning Department (Karl Burandt, Jack Frost)d �- SUBJECT: Metropolitan Waste Control Commission (MWCC) Project Plans an Specifications on Maple Plain Interceptor Metropolitan Council District No. 13 Metropolitan Council Referral File No. 11806-4 INTRODUCTION The MWCC has submitted plans and specifications on the Maple Plain Interceptor for Council comments. This project consists of a 27,350-foot force main and Pump station that phases out the Maple Plain Sewage Treatment Plant (STP) to the existing Long Lake pump station which is served by the Blue Lake STP. The MWCC has sized the force main as a 12-inch diameter pipe. The attached letter from the city of Orono, dated Aug. 31, 1984, indicates they understood a 10- inch diameter pipe would be used. The city wishes to respond to the present Proposal of sizing the pipe at 12-inch diameter. AUTHORITY FOR REVIEW The Metropolitan Reorganization Act provides for the Metropolitan Council to comment on MWCC plans and specifi these pi cations of Capital Projects, for consistency ans to the approved Development Program and Capital Budget. BACKGROUND CKGROUND The Maple Plain STP phase out is a part of the Water Resource Management Policy Plan of 1981. This project •'s included in the MWCC 1984-1988 Development Pro- gram approved by the Council in June 1984. The project is described as a pump station at the Maple Plain plant site with a sewage force main from Maple Plain to the Long Lake pump station. The Long Lake pump station is served by the Blue Lake STP. The design capacity approved in the Development Program is tt.e average day/peak month flow of .4108 million gallons per day (mgd). The city of Orono is concerned that the recommended force main size is larger than necessary, and will cause premature development pressure in the Orono rural service area. ISSUES AND CONCERNS The detailed engineering report for this project recommends a design flow of 403 mgd (average daily) and a peak flow of 2.43 mgd (1,700 gallons per minute (9Pm)). This is based on a current average daily flow of .35 mgd and a peak flow of 2.2 mgd. Standard engineering practice recommends that the total dynamic head of a force main not exceed 200 feet. If pressures exceed this amount structural failures can become more prevalent. Therefore, for the design of this facility the design engineer chooses a pipe size so the total dynamic head will not exceed 200 feet at peak pumping conditions. That pipe size is a 12-inch diameter pipe Pumping at 1,700 gpm.