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What's the Default Solution (Tunnel & EHRT)?
The U.S. EPA is requiring MSD to design a deep storage tunnel and enhanced high rate treatment (EHRT) facility to eliminate 2 billion gallons1 of annual overflows within the Lower Mill Creek watershed. This solution will cost more than $244 million (in 2006 dollars) to construct and additional funds to operate and maintain.
MSD is simultaneously evaluating lower-cost alternative solutions - which include "source control" projects that prevent or delay stormwater and natural drainage from reaching combined sewers.
Facts about the Proposed Lower Mill Creek Tunnel and EHRT Facility
Size
- 30 feet in diameter
- 1.5 miles long
Estimated Capital Cost (in 2006 dollars)
- $244,000,0002
This cost includes:
Three tunnel shafts and four CSO drop shafts
6,500 feet of consolidation sewers and associated tunnel shafts
Connections to existing CSO structures
Submersible 40 million gallon per day (MGD) pump station
84 MGD Enhanced High-Rate Treatment Facility (EHRT)
Operations & Maintenance Costs
- $1,100 per MG of treatment
Estimated power demand of pumping 6.4 billion gallons each year
- 208,000,000 kilowatts
Estimated CO2 emissions from pumping each year
- 143,000 metric tons
1 A reduction of 400 million gallons has already been accounted for through real-time controls at CSO outfalls. Real-time controls include gates, pumps and inflatable dams, etc., that are constructed inside sewer lines to divert excess flows to a different part of the sewer system.
2 Costs will continue to be refined based on additional design and assessment.