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MMSD has captured and cleaned 98.4% of all the water and wastewater that's entered the regional sewer system since we started operating the Deep Tunnel in 1994.  The goal nationally is an 85% capture and clean rate for the more than 700 cities with sewer systems like ours.  

Lake Michigan
The Deep Tunnel has kept 100 billion gallons of pollution out of Lake Michigan.
Why do we need Deep Tunnels?

Water reclamation facilities can efficiently clean only a certain amount of water a day (about 600 million gallons for Jones Island and South Shore combined). When more water gets into the sewers than the water reclamation facilities can handle, you need somewhere to store it so the excess doesn't cause basement backups or sewer overflows.

 Sewer System

Most of the Deep Tunnel is carved out in bedrock 300 feet underground by what is called a boring machine. MMSD built its massive storage system in three phases starting in the 1980's.

Phase One 

Phase Two 

Phase Three 

Length: 19.4 miles

Diameter: 17ft. to 32 ft.

Depth Underground: 300 ft.

Storage: 405 million gallons    

Length: 7.1 miles

Diameter: 20 feet

Depth Underground: 135 - 175 ft.   

Storage: 89 million gallons

Length: 2 miles

Diameter: 21 ft.

Depth Underground: 300 ft.

Storage: 27 million gallons

Deep Tunnel Construction 1983

Deep Tunnel MapMMSD Service Area and Deep Tunnels