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350 METROJOUARE BLDG. <br />7TH & ROBERT JTREEFJ <br />JAIAT PAUL mn 55101 <br />612 222.8423 <br />July 9, 1984 <br />p2[117 <br />jut_ 11 1984 <br />CITY OF <br />LITTLE CANADA <br />Mr. Thomas M. Sweeney <br />Sweeney, O'Connor & LeMay <br />Attorneys for City of Little Canada <br />Suite 1200 <br />Northern Federal Building <br />St. Paul, Minnesota 55102 <br />Subject: Little Canada Interceptor High Flow Period <br />Your Letter Dated June 14, 1984 <br />Dear Mr. Sweeney: <br />We have received your letter dealing with the wet weather related, high <br />wastewater flow period in June, when high flows resulted in bypassing of <br />untreated wastewater from the Little Canada Interceptor system. This <br />letter addresses: <br />(1) summary of events during June with regard to flows, system opera- <br />tion, and bypasses; <br />(2) NPDES permit and related issues; and <br />(3) status of capital improvement projects that will provide additional <br />conveyance capacity for Little Canada and upstream communities. <br />Summary of Events During June <br />The Little Canada interceptor system is shown schematically in Figure 1. <br />As you know, there was much higher than normal precipitation during the <br />first half of June, and there was a very large, intense rainstorm on <br />June 7, with 5 inches of rainfall in some areas. As a result, there <br />was a large amount of infiltration /inflow (I /I) into the sewer systems <br />upstream of the Little Canada Lift Station (L -10). Flows at Meter 035, <br />just downstream of L -10, were about 50% above normal during the week <br />following the June 7 rainstorm. Normal flow, in early June before the <br />heavy rainfall and in late June after the heavy rainfall, was about <br />4 mgd. Flow on June 8 was 6.7 mgd. This is the maximum capacity of <br />L -10 with both pumps operating continuously for 24 hours. <br />Despite operating L -10 at maximum capacity, the flows exceeded pumping <br />capacity at times during the June 7 -13 period. Another lift station, <br />L -37, was operated during this period to divert flow from L -10. Lift <br />stations in Forest Lake (L -2) and Hugo (L -3) were operated inter- <br />mittently to equalize flow in the upstream interceptor. The lift station <br />at I -694 and STH 61 (L -8) was shut off intermittently during this period <br />also. Commission crews worked 24 hours per day to minimize basement <br />flooding' and wastewater bypassing during this period. Crews also <br />physically inspected the interceptor system, looking for large I/I <br />sources, but none was found. <br />8 <br />