MMSD's Deep Tunnel system has prevented more than 92 billion gallons of wastewater from polluting Lake Michigan.

Why do we need Deep Tunnels?

Water reclamation facilities can efficiently clean only a certain amount of wastewater each 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.

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, the last of which is currently under construction.

Phase One:

• Length: 19.4 miles
• Diameter: 17ft. to 32 ft.
• Depth Underground: 300 ft.
• Storage: 405 million gallons

Phase Two:

• Length: 7.1 miles
• Diameter: 20 feet
• Depth Underground: 135 ft. to 175 ft.
• Storage: 89 million gallons

Phase Three: 

27th St. Deep Tunnel

• Length: 2 miles
• Diameter: 21 ft.
• Depth Underground: 300 ft.
• Storage: 27 million gallons