Deep wastewater drive under way in Kansas Dec 2011
Paula Wallis, TunnelTalk
S J Louise Construction of Texas has mobilized to Johnson County, Kansas to start work on the Mill Creek wastewater tunnel. The 9,800ft (3km) tunnel will drain as much as 180 million gallons of treated wastewater/day from the Mill Creek wastewater treatment plant to the Kansas River. The tunnel will run eastward along the river to just east of Interstate 435 and will serve the cities of Shawnee and Lenexa (Fig 1).

Fig 1. Red line alignment of the drive from treatment plant to Kansas River

Work began early this month with the excavation of the 100ft (33.5m) deep working shaft. The TBM tunnel will run at depths of 110ft (33.5m) to 180ft (55m) through methane-containing shale. An 8ft (2.4m) diameter fiberglass-reinforced concrete carrier pipe will be installed and grouted into place.
"The tunnel reduces our carbon footprint and operating costs, since we won't need electricity to pump the effluent as we do now," said John O'Neil, General Manager at Johnson County Wastewater.
He added that relying on gravity to move the treated water will save Johnson County Wastewater about $200,000/year and will eliminate the risk of pump failure and of untreated sewage flows into nearby Mill Creek and the Kansas River during heavy rains.
Currently, treated water is pressure-pumped through a smaller 3.5ft (1m) diameter pipe to the same discharge point, but the pumping station doesn't have the capacity to handle flows in heavy rains.
Johnson County awarded the $32 million construction contract in July to S J Louise Construction. The Texas firm submitted the lowest of six bids ranging from $32 to $39.9 million. Designed by Black & Veatch, the Engineer's estimate was $41.6 million.
Construction is expected to take at least two years and involves boring beneath Mill Creek, active railroad tracks twice, and the six lanes of interstate highway 435. The existing pump station and force main will be taken out of service once the new wastewater line is completed in 2013.

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