Tunnel Dewatering Pump Station

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MWH is providing preliminary and final design service for the Tunnel Dewatering Pump Station (TDPS) project, one of the largest combined sewer pump station projects in the U.S. This critical component is the second scheduled as part of the $3 billion CSO Plan Improvements Program for the Northeast Ohio Regional Sewer District (NEORSD). This project will enable NEORSD to meet critical requirements associated with a possible Consent Decree, resulting in fiscally sound solutions for the community and meeting Board expectations.

    Location: Cleveland, Ohio, United States
    Region: Americas
    Market Sector: Water & Wastewater
    Status: In Progress
    Previous studies conducted by NEORSD developed a Base Project Alternative for the project, estimated at roughly $150M.  Upon completing a thorough evaluation of the project, MWH identified a cavern alternative design that will provide the client more than $50 million in savings. The cavern design minimizes the amount of excavation and concrete needed since the project will encounter about 100 feet of overburdened soils, which are of glacial origin and are comprised of stiff clays, with minor layers of silt and sand overlaying bedrock that include Devonian Chagrin Shale. The pump station will be 230 feet underground and will be approximately 185 feet long by 45 feet wide by 60 feet high. The 45-ft-diameter main shaft will contain an elevator, main stairwell, and equipment removal shaft. A 40-ft-diameter auxiliary shaft will house the auxiliary stairwell pump discharge piping and HVAC ductwork. The majority of the pumping equipment will be located in the cavern.

    The current Easterly collection system contains both combined and sanitary sewers. The combined sewer system has regulators that divert excess flows to local waterways and Lake Erie.  Intercepted flows are routed to the Easterly Wastewater Treatment plant (Easterly WWTP) through three individual interceptors. The TDPS will provide the means to entirely dewater the storage tunnel system at the end of each wet weather event and pump combined sewage to the Easterly Interceptor for transport to the Easterly WWTP. Equipped with seven dewatering pumps, it will enable these tunnels to capture flows in a controlled fashion that would have otherwise been discharged into surface waters. Two additional submersible pumps are provided for emergency in the event of cavern flooding.   The pumps include:

    • Main dewatering pumps
      – four 40-mgd vertical non-clog
      – one 20-mgd vertical non-clog
    • Final dewatering pumps
      –  two 10-mgd horizontal non-clog
    • Sump/emergency drainage pumps
      –  two 1-mgd dry pit submersibles
    The current plan proposes to dewater the tunnel in a 24-hour period in anticipation of back-to-back storm events. The TDPS will be activated about 80 times per year; it will completely fill about four times per year; and the pumps will operate about 340 hours per year.
    • Preliminary and detailed design
    • Geotechnical investigation
    • Risk management
    • Hydraulic analysis
    • Instrument and controls
    • Construction phasing and administration
    • Innovative Cavern alternative design provided over $50 million in savings.
    • 160-mgd capacity pump station 230 feet deep, one of the largest in the U.S. to address combined sewer overflows.
    • Sustainable features include low impact development, carbon footprint analysis and energy efficiency management.

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