Tomahawk Creek Wastewater Treatment Facility Improvements

Aerial view of Tomahawk Creek Wastewater Treatment Facility

Tomahawk Creek Wastewater Treatment Facility Improvements

Providing Sustainable Resources to Future Generations

Constructed in 1955, Tomahawk treats wastewater from parts of Leawood, Overland Park, Olathe and Prairie Village, Kansas. Originally a 10-million-gallons-per-day trickling filter plant, the facility could only treat 4 to 6 MGD to comply with its ammonia discharge limit. The remaining 15 MGD bypassed through a 72-inch interceptor to Kansas City, Missouri. 

In 2006, in response to a regulatory directive, JCW retained us to perform a feasibility study for converting from antiquated trickling filters to state-of-the-art nutrient removal. The study recommended upgrading to a 10 MGD biological nutrient removal facility. 

In 2011, as a result of the increasing cost of treatment by Kansas City, JCW returned to HDR for a study update. The outcome was a well-defined path forward. Full treatment of all flow — dry and wet — that would enable JCW to begin implementation of a $340M improvement project.

In 2014, the B&V/HDR team was selected for final design, permitting and bid phase services. Improvements to the 19 MGD Tomahawk facility included BNR, peak wet weather auxiliary treatment (up to 172 MGD) and biosolids processing. The discharge permit, developed with the Kansas Department of Health and Environment and the U.S. Environmental Protection Agency, incorporated auxiliary treatment, in lieu of wet weather storage, saving JCW over $200 million.

The expansion and upgrade of the Tomahawk Creek Wastewater Treatment Facility is the largest project ever undertaken by Johnson County. Completed on schedule and on budget, the updated facility will improve water quality while providing cost-effective long-term treatment solutions for Johnson County’s communities. Improvements included influent pumping, headworks, primary clarifiers, 5-stage BNR basins, secondary clarifiers, dual-purpose disk filters (tertiary treatment and auxiliary wet weather treatment), chlorine contact basin, chemical feed facilities, odor control, biosolids thickening, digestion, and dewatering, administration building, sidestream nitrogen removal and a flood mitigation swale. 

Construction, with McCarthy as the Construction-Manager-At-Risk, began in April 2018. As of April 2022, the facility is fully operational and in the final “punch list” phase leading to final completion in June 2022. 

Aerial view of Tomahawk Creek Wastewater Treatment Facility
Johnson County Wastewater

Lenexa, KS
United States

19 MGD average


Best Project Award (2023)
Water/Environment Category
Engineering News-Record Midwest
Grand Prize (2023)
American Academy of Environmental Engineers & Scientists