Improvements to the Myron K. Nelson Wastewater Treatment Facility in Johnson County, Kansas, have reached 60 percent completion, and the project is on track for final completion in November 2029.
The roughly $610 million project includes construction of a new, modern wastewater treatment facility on the site of the county’s existing 1940s-era facility, which serves roughly 130,000 residents in the northeast portion of Johnson County.
Owned by Johnson County and designed by the engineering team of Black & Veatch, HDR, and GBA, the project is being developed and constructed by managing contractor McCarthy Building Companies Inc. under a construction manager at risk (CMAR) delivery approach.
“We engaged with Johnson County very early on this project and served as a consultant during the design phase through CMAR,” said Cale George, a Senior Project Manager at McCarthy.
McCarthy had previously constructed Johnson County’s Tomahawk Creek Wastewater Facility, completed in spring 2022. That earlier work resulted in a ready-built relationship with the county that served as a foundation for the Nelson Wastewater Treatment project, George said.
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The county’s existing Nelson Wastewater Treatment Facility is at the end of its usable life, both from a structural standpoint and from an environmental stewardship perspective. The original facility’s treatment processes were not designed to meet more robust clean water standards — including restrictions on acceptable ammonia and phosphorus limits — established in recent years by the Environmental Protection Agency and the Kansas Department of Health and Environment.
To meet the new environmental standards and accommodate wet weather flows in the northeast portion of Johnson County, plans for the new facility called for the installation of all new, modern systems. Specifically, the new treatment operations will include pump stations, preliminary treatment, two primary clarifiers, biological nutrient removal (BNR) basins, three final clarifiers, three solids digester tanks, a digester control building, an effluent filtration facility, ultraviolet (UV) light disinfection facilities, and high-tech odor control systems, among other upgrades.
McCarthy teams broke ground on the new construction in February 2023, using a staged approach that has allowed the existing facility to remain active on the 40-acre site while new construction occurs nearby.
“The unique thing about this project has been the logistical sequencing required to build it,” George said. “When we worked with the county on a previous wastewater treatment project [Johnson County’s Tomahawk facility], we were able to divert wastewater to a different facility while we built the new plant. With this project, the existing plant has remained active and continues to treat wastewater while we build the new facility, so we’ve had to adopt a much more phased approach to our construction.”
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“There’s been a lot of collaboration and coordination with leadership at Johnson County on a weekly and even daily basis to ensure they have all the operational access they need to be successful in maintaining and operating the existing wastewater plant, all while we’re building the new facility alongside it,” George added.
The new Nelson Wastewater Treatment Facility will combine and streamline treatment operations. The new plant is slated to operate as a 15 million gallons per day (MGD) biological nutrient removal facility, with 105 MGD wet-weather treatment capacity.
To aid in sequencing the project, facilities have been constructed and placed into service in open areas of the site, to allow for additional facilities to be removed from service and construction to continue.
As of summer 2026, crews have completed a portion of the new facility’s liquids treatment (disk filters and UV disinfection), and they are actively constructing its headworks facility, BNR basins, digester control building, primary clarifiers, and final clarifiers.
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“Most of the construction for the new plant will be complete in late 2027. Following that, there will be some periods of startup and commissioning to bring the new operations facilities online. Once complete, it’s all going to lead to cleaner waterways for the community,” George said.
Most of the new structures have been constructed using structural concrete, and many exist primarily underground, within the site’s subsurface. McCarthy self-performed all of the structural concrete on the build, as well as all of the civil and yard pipe installations, the process mechanical installations, and the miscellaneous metal installations.
This summer, McCarthy crews will begin to demolish the existing facility’s final clarifiers and chlorine contact basins. By early 2027, teams should be finished with all structural concrete, opening the door for process mechanical, HVAC, and electrical teams to finalize their installations sometime next year.
By late 2027, McCarthy expects to move into the final phase of operations, focused on removing all remaining, older plant structures. Once those are demolished, crews will complete work on the new facility’s modern administration building and the new roads and final landscaping designed for the site.
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“We’ve planned landscaping berms as well as tree screenings to reduce the view of the facility from any of the neighboring communities,” George said. “Plus, the planned state-of-the-art odor control systems should help reduce, or even eliminate, any nuisance odors to the surrounding community.”
In addition to building alongside a still-operating wastewater treatment facility, McCarthy crews faced another challenge: the ground structure itself. Under the build site, deep layers of limestone required extensive grinding and excavation before new pipelines and facility structures could be constructed.
The design initially called for the removal of the rock and import of fill material — a process that would have entailed more than 70,000 miles of truck traffic on local roads. Instead, McCarthy “engaged in conversations early on about alternatives to hauling all this rock off,” George said.
Ultimately, plans evolved to allow McCarthy teams to subcontract with a local firm to process and crush the excavated limestone rock on site. Crews then loaded the crushed rock and reused it as backfill. By project completion, McCarthy expects to have recycled roughly 50,000 cubic yards of rock.
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“We were able to get our design team on board to develop a creative approach that resulted in about $2 million in savings to Johnson County,” George said. “It ended up being a great, creative solution to less-than-ideal subgrade conditions.”
“There’s been a lot of problem-solving opportunities on almost a day-to-day basis with this project,” George added. “I’ve been really proud of how our project team has communicated and collaborated with the county and with our contracting partners to work toward common goals and solutions. It’s been awesome to see everyone on the same page, working toward a common goal.”
- Owner: Johnson County, Kansas
- General Contractor: McCarthy Building Companies Inc., St. Louis, Missouri
- Engineer/Designer: Black & Veatch, Overland Park, Kansas; HDR, Omaha, Nebraska; GBA, Lenexa, Kansas
- Other Contractors: McCarthy/Castle Joint Venture (concrete/civil), McCarthy/MCI (process and MOPO), RS Electric (electrical), American Fire Sprinkler (fire sprinkler), Coreslab Structures (precast), DN Tanks (precast holding tanks), Hayes Drilling (drilled piers), Heitkamp Masonry (CMU and brick), HME (structural steel), KCSS (structural steel), JR & Co. (roofing), Larry Bair Excavating (rock crushing), Midwest Glass and Glazing (windows and glazing), Musselman & Hall Contractors (asphalt and site concrete), Superior Bowen (asphalt and site concrete), MVP Painting (painting), Nucor Rebar Fabrication (reinforcing steel supply), P1 Construction (odor control ductwork), Penn Services (reinforcing steel installation), R.E. Pedrotti (I&C), Rand Construction (plumbing and HVAC), Remco Demolition (demolition), S&W Waterproofing (waterproofing), Desco Flooring (resinous flooring), DH Pace (door, frames, and hardware)
- Equipment Manufacturers: Aerzen USA (high speed turbo blowers), Andritz Separation Technologies (centrifuges), Aqua Aerobics Systems (disk filters), Clearstream Environmental (clarifiers), Cogent (pumps, tanks, covers, strainers), Enviromix (compressed air mixing), Environmental Dynamics International, Hydro International (grit system), Graybar (electrical switchgear), Henry Pratt (wier gate and stop logs), Hobas Pipe (FRP pipe), Environmental Solutions (odor control), Letts, Van Kirk (pumps), Netzsch (progressing cavity pumps), JCI Industries (pumps), Ovivo (mixers and digester covers), Trojan Technologies (UV equipment)
