Johnson County Wastewater's Mill Creek Wastewater Treatment Plant

Nov. 30, 2011 -- An underground tunnel and pipeline designed by Black & Veatch will convey as much as 180 million gallons of treated wastewater per day nearly two miles from Johnson County Wastewater's Mill Creek Wastewater Treatment Plant in Shawnee, Kan., to a discharge point downstream of a water intake on the Kansas River.

An average of 10 million gallons per day of plant effluent currently is pumped to the same discharge location. But because the existing pumping station and force main do not have the capacity to pump extreme wet-weather flows, a new means of conveying the effluent was necessary. The tunnel will eliminate the risk of untreated wastewater flows into nearby Mill Creek and the Kansas River that periodically results with heavy rains.

Excavation has begun on the tunnel's 110-foot deep entrance shaft. When completed in late 2013, the gravity-fed tunnel will reduce the county's carbon footprint and operating costs by eliminating the current need for electricity to pump the effluent. It is estimated to save more than $200,000 annually in moving ultimate future flows, which will partially offset the cost of the essential upgrade.

The pumping station and force main will be taken out of service after completion of the project, which includes construction of new plant piping to convey treated wastewater from the plant's final treatment processes to the tunnel as well as piping within the tunnel. Black & Veatch designed and is providing construction services for the project.

S.J. Louis Construction of Texas leads construction of the 110- to 180-foot-deep tunnel, in which a 96-inch-diameter fiberglass-reinforced pipe will be grouted into place. Design and construction challenges include tunneling adjacent to the Kansas River through methane-containing shale and the potential for high groundwater inflows in the shaft excavations.

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