Johnson County Tomahawk Creek Wastewater

Johnson County, Kansas

Best Water/Environment

Submitted By: McCarthy Building Cos.

Region: ENR midwest

Owner: Johnson County Wastewater

Lead Design Firm: Black & Veatch/HDR

General Contractor: McCarthy Building Cos.

Civil Engineer: Black & Veatch/HDR

Structural Engineer: Black & Veatch/HDR

MEP Engineer: Black & Veatch/HDR

Subcontractors: McCarthy/Castle JV; RS Guarantee; Ambassador Steel; Hamm


A growing population, aging infrastructure and more stringent effluent limits spurred the need for a large-scale expansion of the Tomahawk Creek Wastewater Treatment Facility, which first began operations in 1955 in Johnson County, Kan. The $268-million expansion encompassed the construction of 30 new structures, more than 130 installed pumps, 50,000 cu yd of concrete, nine miles of underground utilities and 792 deep-foundation drilled shafts. It’s the largest infrastructure project ever undertaken by the county, increasing the facility’s footprint by approximately 30%.

Also, the project nearly tripled the facility’s average treatment capacity to 19 MGD during dry weather, and up to 172 MGD during wet weather. Construction could not advance without diverting flow, which presented a challenge. The team devised a strategy to temporarily divert all flow to neighboring Kansas City, Mo., which eliminated extensive maintenance of plant operations and accelerated construction by an estimated 1.5 to 2 years.

“Ultimately, diverting the flow aided in simultaneous demolition of the old plant and construction of the new plant,” says BJ Peterson, vice president of operations for McCarthy Building Cos.’ national water team. “Despite other challenges like the pandemic, wettest year on record and peaking craft and trades onsite above 400, the team finished ahead of schedule and under budget, saving costs through early flow treatment into the new treatment facilities.”