MMSD Deep Tunnel System Tunnel laborers install rails used for transporting material during mining operations. Convergence of the Crosstown and North Shore tunnels.
Miners begin their work shift after entering the tunnel through an access shaft.
About 17 miles of tunnels were bored through limestone, mostly beneath the Milwaukee, Menomonee and Kinnickinnic rivers. Utility lines, temporary lighting and rail systems were all required for construction of the Deep Tunnels. By storing wastewater until MMSD's treatment plants can treat it, average annual overflows into local waterways decreased from about 50 down to two as a result of the Water Pollution Abatement Program, which included the Deep Tunnel System. At peak periods, about 600 design personnel worked on designing projects for the program and approximately 1,000 construction personnel were on the job.