2004-10-26_PWETC_AgendaPacket - Laserfiche WebLink

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continue for extended periods of time as the water percolates through the overlying soil. These sources come from private property. Since the late 1960s the law has not allowed connections of sump pumps, foundation drains and rain leaders from houses to the local sanitary system. However, many homeowners are still connected via these sources to the sanitary sewer system. Communities have found that reducing 1/1 from private property sources is politically difficult even though it is not legal for these sources to exist. Impact of III on MCES Facilities The Metropolitan Council has projected significant growth in the metropolitan area by 2030. These population and employment projections were used to predict wastewater flows throughout the interceptor system and at each treatment plant. For the interceptor system, peak hour flows were projected; and for the treatment plants, annual average, peak month, and peak hour flows were projected. The infiltration/inflow component of peak hour flow rates was estimated based on a computer model simulation of how rainfall generates infiltration/inflow in areas tributary to the interceptor system, Results of simulating the projected conditions in 2030 using current levels ofI/I indicate the need for a significant investment in relief sewers and pump stations. As shown in Exhibits ES-2, and at the end of this document, segments ofthe interceptor system would require extensive parallel sewers and many pumping stations would require expansion. Peak hour flows to each plant in 2030 were projected with the interceptor model using 25- year and IOO-year storm events. The peak flow to the Metro plant could reach over 1.3 billion gallons per day if enough relief sewers were constructed. This is nearly twice the rate that the twin banel joint interceptor can carry into the plant today. The feasibility of doubling the hydraulic capacity of the Metro plant is not possible because of site constraints. MCES staff has concluded that simply adding more capacity to convey and treat 1/1 is not a feasible option. Impact of III on Local Sewer Systems III is currently causing backup problems in several communities, independent of the interceptor system capacity. In these communities the peak III is so significant, the local collection system is overloaded and raw sewage is backing up into low-lying basements. Where the local collection system is overloaded by III, the Minnesota Pollution Control Agency (MPCA) can prohibit additional connections to the local sewers. This overload condition essentially stops growth or redevelopment that increases wastewater flow. In a few communities served by an MCES pump station, the peak flows during a significant rain exceed the firm capacity of the MCES pump station, These problems are severe and frequent enough for the Council to advise these communities that either 1/1 must be reduced or local sewer connections must be halted. Excessive 1/1 rates can put the regional conveyance system at risk of being overloaded, consuming capacity that should be available for downstream communities. In some cases, the excessive 1/1 from one community can cause an overflow to occur in an adjacent community in either direction. To reduce the risk of this occurrence, MCES (as the regional wastewater 4