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West CSO Tunnel

West Tunnel Frequently Asked Questions

The new West Area Combined Sewer Overflow Tunnel (West Area CSO Storage Tunnel) will be constructed below the ground’s surface in bedrock. The West Area CSO Storage Tunnel will capture, store and convey CSO from the Clear Creek, Tanyard and North Avenue CSO Basins. The West Area CSO Storage Tunnel will be approximately 8.5 miles long with a 24-foot finished diameter and will store up to 177 million gallons (MG) of overflow from a rainstorm. When the rainfall is over, the CSO will be conveyed to a dedicated CSO treatment plant for pollutant removal and ultraviolet (UV) disinfection before discharge to receiving waters.

A new 85-million gallons per day (MGD) submersible pump station will be constructed at the end of the tunnel (at the R.M. Clayton Water Reclamation Center [WRC]) to lift the stored flow from the tunnel for treatment at the new dedicated CSO treatment plant. The pump station will be sized to allow a full tunnel to be emptied within a 2-day period.

The new dedicated CSO treatment plant will be constructed on the site of the decommissioned steam plant next to the existing R.M. Clayton WRC. The plant will have a treatment capacity of 85 MGD. The combined sewage stored in the tunnel system will undergo both physical and chemical treatment prior to discharge into receiving waters. The treatment processes will include clarification and filtration to remove suspended solids and disinfection by UV light to destroy viruses and bacteria to protect public health. The UV disinfection is comparable in effectiveness to traditional chlorine disinfection but is more protective of aquatic life. The overflow then is discharged into the Chattahoochee River.

Approximately 100 CSOs occur annually at each overflow site. Under the approved plan, all overflow volumes will be captured and treated, except for approximately 4 large rain events per year, when the volume of overflow exceeds the storage capacity. In these cases, the excess volume will be disinfected and dechlorinated before discharge to a receiving stream. This means that the discharge will meet water quality standards.

1.
Notice to Proceed
April 2003
 
2.
Mobilization and site preparation:
July 2003
(includes site-specific work such as:  
  • Moving in and setting up staff ande crew facilities (trailers)
  • Moving in heavy equipment (front end loaders, backhoes, etc.)
  • Erecting silt fences, other erosion and sediment control measures
  • Clearing and grubbing)
  • Pre-blast survey and monitoring
     
    Easements and land acquisitions as required (design of alignment confines easements and acquisitions to commercial or vacant properties where possible)
     
    3.
    Shaft Construction - (8-10 months)
    May 2004
     
    4.
    Install Tunnel Boring Machine and begin boring (18-20 months)
    January 2005
     
     

    Milestone Completion Date for West Tunnel

    October 2007

     

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