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Spokane River Forum 23 May 2011

This document outlines the Spokane River Forum's assessment of Combined Sewer Overflows (CSOs) as of May 2011. It details the history and statistics of CSOs in Spokane, including the significant reduction in outfalls and untreated discharges due to regulations and infrastructure improvements. The report emphasizes the importance of stormwater management and wastewater treatment in preventing CSO events, along with the implementation of control measures and new facilities to enhance water quality.

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Spokane River Forum 23 May 2011

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  1. CSO Reduction 2011 Status Spokane River Forum 23 May 2011

  2. What is a CSO? wastewater stormwater CSO Regulator Treatment Plant

  3. Why do CSOs overflow? Flow Stormwater Runoff Overflow Threshold Wastewater Flows Time

  4. CSO Regulator is an Overflow Threshold Old style “Leaping Weir”

  5. CSO Reduction HistoryBaselineas of 1980 • 33 outfalls • 1000 average CSOs / year • 550 avg million gallons / yr

  6. CSO Reduction HistoryPhase 11980s storm separation • 24 outfalls • 450 average CSOs / year • 80 avg million gallons / yr

  7. CSO Regulations Chapter 173-245 WAC: Frequency: “… control of each CSO such that an average of one untreated discharge may occur per year.” – Applied to each outfall Water Quality: “CSOs shall not violate water quality standards in receiving waters (numeric standards or the beneficial uses).” Spokane CSO Compliance - 2017

  8. CSO 16 Construction

  9. CSO 16 Tank

  10. CSO 16 Sump Tank Fills During Storm... ... Tank Drains to Sewer After Storm

  11. CSO 16 Self-CleansAfter Tank Drains

  12. CSO 16 Self-Cleans After Tank Drains

  13. CSO 16 Self-Cleans After Tank Drains

  14. CSO 16 Site Restoration

  15. CSO 16 Monitoring & Cleaning Controls

  16. 5 CSO Facilities Constructed CSO 2 CSO 10 In Construction CSO 42 CSO 16 CSO 19 Tank not required

  17. 2 CSO Outfalls Eliminated CSO 3 CSO 18

  18. 4 Facilities In Final Design CSO 38/39/40 Eliminates 2 outfalls CSO 41 CSO 33-2 CSO 34-3

  19. 9 Interim Weir Modifications CSO 6 CSO 7 CSO 40 CSO 12 CSO 39 CSO 14 CSO 15 CSO 25 CSO 26

  20. Weir Modification “Before”

  21. Weir Mods provide: • Less dry weather plugging • More response time • Improved monitoring

  22. Weir Modification“After”

  23. Weir Modification“After”

  24. CSO Reduction HistoryPhase 2Storage Tanks by 2011 • 22 outfalls • 350 average CSOs / year • 70 avg million gallons / yr

  25. CSO Reduction HistoryPhase 22017 Projected Results • <20 outfalls • <20 average CSOs / year • <8 avg million gallons / yr

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