Design-build solution tames combined sewer overflow discharges

The $78 million Southwestern Parkway Combined Sewer Overflow (CSO) Basin project, a component of Louisville and Jefferson County (Ky.) Metropolitan Sewer District’s federal Consent Decree to mitigate CSO discharges to local waterways, received the Design-Build Institute of America’s 2019 Best in Engineering Design Award and National Award of Excellence (Water/Wastewater) recognition.

PHOTOS: Brown and Caldwell, Lakewood, Colo.


An underground basin of the Shawnee Park magnitude created daunting issues: Pouring large amounts of concrete efficiently during six- to eight-hour schedules; measures to eliminate honeycombing or cracking; and, ensuring proper concrete flow around reinforcing steel and wall ties. Allied Ready Mix used GCP Concera admixtures to yield control flow, segregation-resistant mixes. With a target 22-in. spread, the mixes came to a rest more quickly than self-consolidating varieties.

Located in Louisville’s Shawnee Park, part of the National Register of Historic Places-listed Olmsted Park System, the project consists of a large “capture and release” system to temporarily store CSOs during wet weather events and gradually return them to the collection system for treatment as capacity becomes available. Environmental engineer Brown and Caldwell drew up a plan encompassing a 20 million-gal. storage basin; associated washdown systems; 30 million-gal./day effluent pump station; CSO diversion structures; and, associated conveyance piping.

Preservation of Olmstedian design features in Shawnee Park, particularly the Great Lawn’s pastoral, undulating surface, made it vital that the project team deliver a facility virtually invisible to the public. Hence, the basin was constructed below the surface of the Great Lawn, with park topography concealing a walk-out operational access point.

The $60 million Shawnee Park Basin Project is part of a federal mandate to prevent wastewater from pouring into the Ohio River. The reinforced concrete roof of the watertight basin is 36 inches thick and supports 12 feet of soil harboring Great Lawn.

One of Indiana’s largest concrete contractors, Wilhelm Construction, was tasked with overseeing the concrete quality control for the project, including managing the mix design, temperature and testing. The enormity of the basin’s design required over 30,000 yd. of concrete from Allied Ready Mix Co., Louisville.