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Gearing Up: First Big Tunnel Of St. Louis Sewer System Upgrade

Updated 2/7/14 to correct the timeline of the lawsuit against MSD.

The Metropolitan St. Louis Sewer District is preparing for its first big dig.

Starting in a few days, MSD will begin construction of a 3,028 foot-long tunnel under the River Des Peres, just south of Carondelet.

Credit StandPoint Public Affairs
The Tunnel Boring Machine, fully-assembled in the SAK warehouse in November, 2013.

The tunnel will hold a pressurized pipe that will carry sewage to the Lemay Wastewater Treatment Plant.

MSD spokesperson Lance LeComb said the new pipe will increase the plant’s capacity to take in sewage, and also serve as a back-up in case the existing "force main" ― which dates back to the 1960s ― has a problem.

The project is the first of about a dozen tunnels, totaling nearly 33 miles in length, that the MSD will be digging under St. Louis in the next couple decades. Most of the tunnels will hold a mix of stormwater and sewage. “The longest one will be nine miles long, running underneath the River Des Peres, almost 200 feet below ground,” LeComb said. “And 30 feet in diameter.”

The current tunnel project will be a lot smaller, but building it will require the use of similar technology; specialized workers equipped to spend many hours deep underground; and massive Tunnel Boring Machines.

The machine digging the first tunnel in St. Louis County weighs 300,000 pounds and has a cutting head almost 12 feet in diameter. “When it is fully assembled in the tunnel, it will be 250 feet long, chewing and eating away at that rock and earth underground," LeComb said. "And almost like a train, that material, that debris, that earth, will go back on the conveyor belt, where our contractors will take it up to the surface and dispose of it.”

Working at a peak rate of 50 feet a day, the machine is expected to complete the 3,000-foot-long tunnel by mid-April.

Credit RiverCity Images
Workers prepare to lower the cutterhead of the Tunnel Boring Machine into the starter tunnel shaft.

All this sub-surface construction is the result of a 2007 lawsuit filed against MSD by the U.S. Environmental Protection Agency and the Missouri Department of Natural Resources. The Missouri Coalition for the Environment, a local environmental advocacy group, joined the suit about four months later. A settlement agreement finalized in 2012 requires MSD to make $4.7 billion in improvements to the St. Louis City and County sewer systems over 23 years.

LeComb said more than $2 billion of that will go towards building tunnels.

And he said MSD's customers will end up shouldering all the costs.

"Right now, the average single family homeowner, they pay a bill in the low-to-mid $30 per month," LeComb said. "That's going to go up into the $40 range here, in a couple years.” LeComb estimated that by early next decade, a family's average monthly sewer bill will be more than $80.

The sewer system upgrades are needed to keep sewage out of St. Louis-area rivers and streams and to prevent basement back-ups, he said.

Existing infrastructure routinely gets overwhelmed during storms, dumping hundreds of millions of gallons of untreated sewage into area waterways every year ― in violation of the federal Clean Water Act.

Follow Veronique LaCapra on Twitter: @KWMUScience