The City of Minneapolis Public Works Department is constructing a new storm tunnel parallel to an existing tunnel located under Washington Ave. S. between Nicollet Mall and Chicago Ave, enlarging a portion of the existing storm tunnel, which is located under Chicago Ave. between Washington Ave. S. and the Mississippi River, and constructing a new tunnel access in Downtown Minneapolis.   

The existing downtown Central City storm tunnel system consists of 6.28 km (3.9 miles) of 21.34 m (70 feet) deep drainage tunnels of which the majority was built from 1939 to 1940 and was designed to handle the storm-water drainage requirements at that time.  Land development since has led to a significant increase in the amount of storm-water that is directed into the tunnel system, resulting in over pressurization of the system.  This over pressurization has led to degradation in the tunnel infrastructure - voids either above or below the tunnel structure, cracking and failure of the tunnel’s liner, erosion of the surrounding sandstone and infiltration of ground water and sand - and an increase in maintenance spending to inspect and maintain the system.    

The construction of a new parallel primary tunnel would reduce the pressurization in the tunnel system, resulting in a reduced risk of tunnel failures, extended tunnel system service life, reduction in tunnel repair costs, and a decrease in long term maintenance with the operation of the tunnel system such as surface flooding and blowing manhole covers.  

For further information on this project please click here and visit https://www.minneapolismn.gov/government/projects/central-city-tunnel/. 15/22.