Middletown, OH — Downtown Combined Sewer Overflow (CSO) Storage Basin

The Downtown Combined Sewer Overflow (CSO) Storage Basin provides critical wet-weather storage capacity for the City of Middletown’s combined sewer system. The project included construction of an underground storage basin capable of holding up to 5.1 million gallons of combined flows during wet weather events, with stored overflow pumped back into the existing collection system once capacity is available. 

The project required a complex 40-foot-deep excavation within a constrained urban environment, with the excavation extending approximately 15 feet into an aquifer connected to the Great Miami River. To safely execute the work, the team developed a sophisticated support of excavation and dewatering approach. Limited site space and deep excavation logistics also required the use of two tower cranes to efficiently move rebar, formwork, and other materials into the excavation.

Additional complexity included work within a large-diameter sewer that needed to remain operational throughout construction. Careful coordination, confined-space planning, and weather monitoring were essential to safely complete work while maintaining system functionality.

Shook served as the design builder, partnering with Gresham Smith as the design engineer. The team provided design, preconstruction, and construction services aligned with the city’s vision for the project. Shook also secured key self-perform scopes, including concrete and general trades, supporting quality, schedule control, and successful delivery of this major urban infrastructure project.

As part of a future phase, a public amenity will be constructed above the basin, integrating essential infrastructure with community-focused improvements in the heart of downtown Middletown.