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What the WPCP Expansion Project Is

What the WPCP Expansion Project Is. Increase treatment capacity to 12 million gallons per day (mgd) ADWF Replace and increase capacity of WPCP Outfall Diffuser in Sacramento River. Existing Outfall. Installed in 1970s, repaired/modified in 1992

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What the WPCP Expansion Project Is

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  1. What the WPCP Expansion Project Is • Increase treatment capacity to 12 million gallons per day (mgd) ADWF • Replace and increase capacity of WPCP Outfall Diffuser in Sacramento River

  2. Existing Outfall • Installed in 1970s, repaired/modified in 1992 • Existing outfall capacity is limited to 11 mgd ADWF or 27.5 mgd PWWF • Existing outfall diffuser design will not provide optimized dilution in the future

  3. New Outfall Design Criteria • Able to convey 15 mgd ADWF or 37.5 mgd PWWF by gravity • Sized for buildout flows to minimize number of times work must be done in river • Outfall design incorporates features to maximize dilution

  4. History of Gravel Bar Encroachment

  5. Alternatives Considered by City’s Geomorphologist • Continued dredging • Spur dikes • Relocate gravel bar • Pilot channel to Big Chico Creek • Moveable diffuser • Relocate outfall downstream

  6. Continued Dredging • Not a permanent solution • Dynamics of river unpredictable • High cost • Extensive permitting requirements

  7. Spur Dikes • Could limit growth of gravel bar • City would still need to replace outfall diffuser in current location to achieve 12 mgd capacity • City would still need to increase capacity of existing outfall pipeline to achieve 15 mgd capacity

  8. Relocate Gravel Bar • Existing bar excavated and moved to opposite bank • Remaining east bank reshaped • West bank riprapped • Two to three spur dikes to maintain flow alignment

  9. Channel excavated through park to Big Chico Creek Provides constant flow through creek to prevent sediment from filling in east bank Channel to Big Chico Creek

  10. Moveable Diffuser • Drive piles in toe of levee • Extend pipeline downstream as needed • Work in the river multiple times

  11. Relocate Outfall Downstream • Move outfall diffuser 1200’ downstream • Route new outfall pipe to new location • Expected life of 15-20 years • May have to move outfall again in future

  12. Alternative Evaluation Evaluation Criteria Alternatives Lifetime Regulatory Issues Cost Dredging - - - Spur Dikes + - o(1) Relocate Bar ? - - Pilot Channel ? - - Moveable Diffuser o - o Relocate Diffuser o + + (1) Based on CALTRANS Butte City Project and MWH report prepared for steering committee.

  13. Recommended Alternative • Needed for City to move forward with EIR process for project • EIR mentions M&T project and potential for joint project • Not all M&T project alternatives present a joint benefit • City’s EIR proceeding with relocation of outfall diffuser 1200’ downstream

  14. Expected Outfall Project Timetable • EIR public review period ends 3/21/05 • Design complete late spring 2006 • Construction start late summer 2006 • Outfall work most likely summer 2007

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