The Westerly Storage Tunnel (WST) project is one part of Project Clean Lake, a program with the goal of capturing 98% of all combined sewer overflows for treatment. WST will help control overflows at two locations along the Cuyahoga River and will reduce overflow pollution into the river by 328 million gallons per year. Construction includes three shafts over 200 ft. deep and 2 miles of 25 ft. diameter tunnel. The tunnel will be excavated in shale and lined with precast concrete segments. Slurry walls were installed as support of excavation for the shafts.