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

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

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

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

5 History CSO issues were studied late 70s - early 80s Selected alternative was sewer separation 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 construction program expended over $330 million; MCES $85 million began in 1986 Continued

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

7 History Overflow volume reduced: 2003:5 events, 7.96 million gallons 2004:4 events, 2.2 million gallons 2005:7 events, 3.1 million gallons 2006: 5 events, 431,000 gallons 2007: 0 events

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

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

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

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