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Proposed Combined Sewer Overflow Changes

Proposed Combined Sewer Overflow Changes. Environment Committee March 11, 2008. Keith Buttleman and Rebecca Flood. Roof Drain Connection. Street Drain Connection. Connected Foundation Drain. Combined Sewer. House Lateral Sanitary Sewer. Combined Sewer System. History .

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Proposed Combined Sewer Overflow Changes

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  1. Proposed Combined Sewer Overflow Changes Environment CommitteeMarch 11, 2008 Keith Buttleman and Rebecca Flood

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

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

  5. Continued 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 • 1986-97 construction program expended over $330 million; MCES $85 million began in 1986

  6. Continued 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

  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 1999: Minneapolis and MCES jointly initiated a study to evaluate the remaining CSO problem. Field work performed in 2000. 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

  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?

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