Excavation of a 110ft (33.5m) deep entrance shaft signals the beginning of site work in the construction of the Mill Creek tunnel and pipeline. Designed by Black & Veatch the new pipeline will carry up to 180 million gallons per day of treated wastewater by gravity nearly 2-miles (3.2km) from Johnson County Wastewater’s Mill Creek Wastewater Treatment Plant in Shawnee, Kansas, 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 a new means of conveying the effluent was necessary because the existing pumping station and force main do not have the capacity to pump extreme wet-weather flows. The tunnel will eliminate the risk of untreated wastewater flows into nearby Mill Creek and the Kansas River that periodically results with heavy rains.
When completed in late 2013, the 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 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.
S.J. Louis Construction of Texas leads construction of the 110ft (33.5m) to 180ft (55m) deep tunnel, in which a 96-inch (2.4m) 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.
Photo: Mill Creek Wastewater Treatment Plant (courtesy of Johnson County Wastewater)