Presentation to AAAEA Technical conference


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Case Studies of Wet Weather Flow Issues

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Presentation to AAAEA Technical conference

  1. 1. CASE STUDIES OF WET WEATHER FLOW ISSUES Presentation To AAAEA Technical Conference Hala Baroudi, P.E. Anderson, Eckstein and Westrick MAY 13, 2006
  2. 2. Presentation Overview <ul><li>What are CSOs and SSOs? </li></ul><ul><li>Detroit Waste Water Treatment Plant Service Area </li></ul><ul><li>Example of a Combined Sewer System </li></ul><ul><ul><li>Southeast Oakland County Sewage Disposal System </li></ul></ul><ul><li>Example of a Separate Sewer System </li></ul><ul><ul><li>City of Center Line Sanitary District </li></ul></ul>
  3. 3. What are CSOs and SSOs? <ul><li>Need to understand first the basic of Sewer system design: </li></ul><ul><ul><li>Separate sanitary sewers </li></ul></ul><ul><ul><li>Combined Sewer System </li></ul></ul><ul><li>Separate sanitary sewers: </li></ul><ul><ul><li>Carry only sanitary sewage to WWTP </li></ul></ul><ul><ul><li>Storm water is directed to a nearby river, lake or stream via storm sewers. </li></ul></ul><ul><li>SSOs, are discharges of raw or inadequately treated sewage from separate sanitary sewer systems. </li></ul><ul><li>When an SSO occurs, sewage is released into areas such as streets and streams rather than being transported to a treatment facility </li></ul>
  4. 4. What are CSOs and SSOs? Separate Sewer System *Obtained From MDEQ
  5. 5. <ul><li>Problems that may cause chronic SSOs: </li></ul><ul><li>Infiltration through cracks into the sanitary system from groundwater </li></ul><ul><li>Rain water into the sanitary system through roof drains connected to sewers; </li></ul><ul><li>Footing drains and sump pump connected to the sanitary system </li></ul><ul><li>Undersized sanitary systems </li></ul><ul><li>System failures due to tree roots growing into the sewer, </li></ul><ul><li>Material building-up causing blockages </li></ul><ul><li>Failed prior CSO separation facilities (Bulkheads, etc) </li></ul><ul><li>Illegal storm to sanitary taps of catch basins, etc </li></ul><ul><li>Equipment and pump failures; and power failures. </li></ul>What are CSOs and SSOs?
  6. 6. What are CSOs and SSOs? <ul><li>Combined Sewer System: </li></ul><ul><ul><li>Generally older sewer systems </li></ul></ul><ul><ul><li>Designed to convey both sewage and storm water </li></ul></ul><ul><ul><li>Due to heavy rainfall excess diluted wastewater could overflow directly to nearby streams as CSOs </li></ul></ul><ul><ul><li>CSOs were among the major sources for beach closings and other water quality impairments. </li></ul></ul><ul><ul><li>Many combined sewer systems have recently installed retention/treatment basins (RTB) </li></ul></ul><ul><ul><li>RTB designed to capture a specific storm event and provide initial treatment and disinfection prior to any discharge is released into waters </li></ul></ul>
  7. 7. What are CSOs and SSOs? *Obtained From MDEQ Combined Sewer System—Dry Weather Conditions
  8. 8. What are CSOs and SSOs? *Obtained From MDEQ Combined Sewer System—Wet Weather Conditions
  9. 9. <ul><li>How are SSOs Addressed? </li></ul><ul><li>Michigan Department of Environmental Quality (MDEQ) requires the responsible entity to implement corrective actions within a defined schedule. </li></ul><ul><li>Frequently, DEQ works to achieve a voluntary settlement (“administrative settlements”). </li></ul><ul><li>These settlements are often embodied in legal documents called District Compliance Agreements, permits, or Administrative Consent Orders. </li></ul>What are CSOs and SSOs?
  10. 10. <ul><li>How are SSOs Addressed? </li></ul><ul><li>Federal Regulations for SSOs require either the elimination of all SSOs or treatment of SSOs to the secondary wastewater treatment standard. </li></ul><ul><li>MDEQ acknowledges that total elimination or secondary treatment of all SSOs is not practical or economically </li></ul><ul><li>MDEQ requires a corrective action program which is equivalent to the remedial design standard of the 25-year/24-hour storm, </li></ul><ul><li>communities implementing corrective action programs to this remedial design standard will have on average less than one overflow per ten years. </li></ul>What are CSOs and SSOs?
  11. 11. <ul><li>How are CSOs Addressed? </li></ul><ul><li>Michigan initiated a CSO control program in 1988 </li></ul><ul><li>1994 the federal government developed a nationwide CSO Control Policy. </li></ul><ul><li>Requires CSO communities to implement interim measures “nine minimum controls” by January 1, 1997, and to develop CSO Long-Term Control Plans (LTCPs). </li></ul><ul><li>In Michigan, all municipalities with CSOs have completed the nine minimum controls and have developed LTCPs. </li></ul><ul><li>The LTCP must assess a range of control options including: </li></ul><ul><ul><li>Sewer Separation </li></ul></ul><ul><ul><li>Source reduction control (catch basin restriction, etc) </li></ul></ul><ul><ul><li>Additional treatment or storage basins to contain and control CSOs. </li></ul></ul>What are CSOs and SSOs?
  12. 12. Detroit Waste Water Treatment Plant Service Area Detroit WWTP <ul><li>Construction of the Detroit wastewater plant was completed in 1940. </li></ul><ul><li>The plant experienced several upgraded and expanded several times since the original construction </li></ul><ul><li>Primary treatment capacity is1,700 MGD </li></ul><ul><li>Secondary treatment capacity is 930 MGD </li></ul><ul><li>As of 2006, the Plant is the largest in the world as measured by primary treatment capacity. </li></ul>Southeastern Oakland County Sewage District System (SOCSDS) Center Line
  13. 13. Southeast Oakland County Sewage Disposal System <ul><li>SOCSDD serves all or parts of 14 communities </li></ul><ul><li>Drainage area 24,500 acre </li></ul><ul><li>One sewer that serve both sanitary and storm </li></ul><ul><li>Original sewer deemed inadequate and additional relief sewer known as “Twelve Towns Relief Drains” Constructed in 1960. </li></ul>* Obtained from CS-1314
  14. 14. Southeast Oakland County Sewage Disposal System (Contd.) <ul><li>1965 a 293-ft weir was constructed to provide 32 MG in-system storage </li></ul><ul><li>Reduction of CSOs from 50/year to 25/year </li></ul><ul><li>1972 a 62 MG RTF was constructed to further control CSO </li></ul><ul><li>Purchased additional peak interceptor capacity from the Detroit Sewer System (from 118 to 260 cfs) </li></ul><ul><li>RTF is also known as 12 Towns RTF </li></ul><ul><li>Reduction of CSOs from 25 (untreated)/year to 12 (treated)/year </li></ul>* Obtained from Project Plan
  15. 15. Southeast Oakland County Sewage Disposal System (Contd.) <ul><li>1974 MDEQ issued first 12 Towns NPDES Permit </li></ul><ul><li>1994 Recent closing of public beaches along Lake St. Clair. </li></ul><ul><li>Various reasons for the poor water quality, the media's focal point became the Twelve Towns RTF overflow </li></ul><ul><li>1996, (MDEQ) re-issued the NPDES permit for the Twelve Towns RTF with new, more stringent requirements. </li></ul><ul><li>Settlement permit, issued in October 1998, required implementation of RTF improvements. </li></ul>
  16. 16. Improvement to the SOCSDS <ul><li>Extend inlet weir / remove Broome Gates </li></ul><ul><li>30.1 MG additional storage structure </li></ul><ul><li>New 2000 l.f. intermediate weir </li></ul><ul><li>New dewatering Pumping Station </li></ul><ul><li>Screening </li></ul><ul><li>Disinfection </li></ul><ul><li>Disconnect Madison Heights storm drain inlets </li></ul><ul><li>Re-route of Madison Heights Combined Sewers </li></ul><ul><li>Remove Hazel Park Sanitary Sewer from RTF </li></ul><ul><li>Flow Meters & Miscellaneous Improvements </li></ul>
  17. 17. SOCSDS System Schematics * Obtained from GWK Basis of Design
  18. 18. Goal of SOCSDS System Improvement <ul><li>Reduce Number of Treated CSO Events </li></ul><ul><li>Reduce Volume of Treated CSO Events </li></ul><ul><li>Improve Quality of Treated CSO to Meet Public Health Goal </li></ul><ul><li>Improvement Program meets the MDEQ definition of “adequate treatment” </li></ul><ul><ul><li>Total capture of the 1-year, 1-hour storm event </li></ul></ul><ul><ul><li>30 minutes detention of the 10-year, 1-hour storm event </li></ul></ul>
  19. 19. Photo of the RTF Improvement Aerial View of Screens * Construction Cost $79,460,000
  20. 20. Photo of the RTF Improvement
  21. 21. Center Line Sanitary District <ul><li>Sewerage system constructed prior to World War II as a combined sewage system </li></ul><ul><li>A program for sewer separation was undertaken after World War II. Included downspout disconnection and construction of storm sewer system </li></ul><ul><li>Footing drains in Center Line remain connected to the sanitary sewer system </li></ul><ul><li>All sanitary collector sewers in Center Line discharge to the pumping station located at Stephens and Van Dyke </li></ul>
  22. 22. Center Line SSO Pathway <ul><li>overflow weir located downstream of the P.S. allows for overflow from the 24&quot; interceptor to a 36&quot; RCP storm sewer and then to the Lorraine Drain. </li></ul><ul><li>The weir was discovered in early 2000 during ongoing infrastructure rehabilitation work within the City. </li></ul><ul><li>The weir was constructed in the early 1960’s pursuant to a State construction permit </li></ul><ul><li>April 2000, DEQ informed the City that it considers overflows associated with the overflow weir to be SSO </li></ul>
  23. 23. Center Line SSO Pathway
  24. 24. Center Line SSO Volume and Frequency
  25. 25. Storage Requirement to Eliminate SSO Based on 2000/2001 records (April through October)
  26. 26. City Rehabilitation Efforts to Mitigate SSO <ul><li>Flow management and flow monitoring </li></ul><ul><ul><li>Constructed additional weir height and optimized the pump station controls to maximize system storage. </li></ul></ul><ul><ul><li>Increased transport capacity to DWSD and eliminated potential maintenance related SSOs by the elimination of the inverted siphon along the 24-inch interceptor. </li></ul></ul><ul><ul><li>On going efforts to negotiate additional sewage capacity, either with DWSD or the City of Warren. </li></ul></ul>
  27. 27. City Rehabilitation Efforts to Mitigate SSO (Contd.) <ul><li>I/I reduction </li></ul><ul><ul><li>Continued investigation through flow monitoring </li></ul></ul><ul><ul><li>Correction of potential causes of excessive infiltration and in-flow (I/I) to the sanitary sewer. </li></ul></ul><ul><ul><li>Footing drain removal: about 12 homes </li></ul></ul><ul><ul><li>Evaluated option for sump pump disconnection (about 220 homes) </li></ul></ul><ul><li>Ongoing rehabilitation efforts have included: </li></ul><ul><ul><li>Manhole repairs </li></ul></ul><ul><ul><li>Cured in-place pipe lining </li></ul></ul><ul><ul><li>Open cut excavation </li></ul></ul><ul><ul><li>Pipe & lateral grouting/repairs </li></ul></ul><ul><ul><li>Pump station rehabilitation </li></ul></ul>
  28. 28. SSO Vs. City Efforts to Mitigate SSO
  29. 29. Approach to Demonstrate City Efforts to Mitigate SSO Storage to eliminate SSO based on the 2000/2001 records: 2.72MG Storage to eliminate SSO based on the 2003/2004 model: 0.82MG
  30. 30. Assessment of Corrective Activities
  31. 31. Assessment of Corrective Activities Projected Flows for 8/3/04
  32. 32. Assessment of Corrective Activities
  33. 33. Assessment of Corrective Activities
  34. 35. Questions and Discussion