Metropolitan Council Environmental Services Proposed Combined Sewer Overflow

Metropolitan Council Environmental Services Proposed Combined Sewer Overflow Changes Environment Committee March 11, 2008 Keith Buttleman and Rebecca Flood A Clean Water Agency

Combined Sewer System Roof Drain Connection Street Drain Connection Connected Foundation Drain House Lateral Sanitary Sewer 2 Combined Sewer

History n Prior to 1938, Minneapolis and St. Paul sewers went directly to the Mississippi River n Interceptors constructed in Minneapolis/ St. Paul collected both sanitary flow and stormwater flow and conveyed it to the treatment plant n During storm events, when combined flow exceeded interceptor capacity, overflows were discharged to the river 3

Typical Control and Monitoring Regulator Overflow Weir To River To Interceptor 4

History Continued n CSO issues were studied late 70 s - early 80 s n Selected alternative was sewer separation n NPDES permits issued in 1984 authorized CSO discharges and committed Minneapolis/St. Paul and Metropolitan Council to a construction program with the intention of eliminating regulators and CSOs n 1986 -97 construction program expended over $330 million; MCES $85 million began in 1986 5

History n Overflow volume reduced: 1984: 1998: 1999: 2000: 2001: 2002: 6 77 events, over 1 billion gallons 5 events, 2 million gallons 5 events, 25 million gallons 7 events, 57 million gallons 3 events, 40 million gallons 3 events, 1 million gallons Continued

History n Overflow volume reduced: 2003: 2004: 2005: 2006: 2007: 7 5 events, 7. 96 million gallons 4 events, 2. 2 million gallons 7 events, 3. 1 million gallons 5 events, 431, 000 gallons 0 events

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Separation Evaluation Study 1999: Minneapolis and MCES jointly initiated a study to evaluate the remaining CSO problem. Field work performed in 2000. The key objectives were: n Determine the source of remaining CSO, i. e. city or suburbs n Evaluate alternatives to eliminate remaining CSO n Utilize report and recommendations for NPDES permit re-issuance 10

Current Status n Minneapolis is not fully separated n Permits recognized that additional work may be necessary before all regulators could be closed and all CSO eliminated n MCES is continuing with I/I removal in the interceptor system and continuing to optimize conveyance n The Systemwide I/I Reduction Program will continue reductions in clear water to our system 11

Current Status n Although no overflows in 2007, some CSOs expected to occur in Minneapolis during heavy rainfall events based on 1999 Study n CSO NPDES permits expired June 2001; n Benefit of permits – legal structure for dealing with overflows – CSOs authorized n St. Paul has requested permit termination 12

Implications/Unknowns n Meet March 12 with MPCA & St. Paul n Meet April 1 with MPCA & Minneapolis n MPCA has indicated permits may not be reissued n What happens the next time there is an CSO event? 13