Digging To Begin On Maryland Tunnel Project

July 28, 2009
Tunnel, 5.3 miles long, is last link in Maryland suburbs’ water plan

Work will begin soon on the final major link in the Maryland suburbs’ water system, a 5.3-mile tunnel in Montgomery County, Md., The Washington Post reported.

The 10-ft Bi-County Water Tunnel will run 90 to 200 ft below ground, and will contain an 84-in. steel pipe to supplement a smaller water main that transports water between the Potomac treatment plant and the growing number of toilets, fire hydrants and swimming pools primarily in Prince George's County.

According to officials, more than 100 million gal of water will flow through the pipe each day.

Funding for the $168-million project will come from fees developers pay for new infrastructure, the newspaper reported.

In early August, bulldozers will begin clearing trees to build the tunnel's main construction shaft. In late September, workers will begin blasting the first large shaft, 35 ft in diameter.

Early next year, crews will blast a second shaft through the tunnel's eastern end. In spring, workers will begin building a third shaft at the tunnel's west end.

"This is going to be a critical component for the backbone of our water system," John Mitchell, the WSSC's manager for the project's five-year design, told the newspaper.

The steel pipe will be significantly more reliable than the large concrete mains that have burst in the past year, Mitchell said. Eighteen inches of cement grout will encase the steel pipe, limiting rust, Mitchell said, and it will also have a corrosion monitoring system that will warn of any signs of weakening.

"This will be a steel pipe inside a tunnel inside solid rock," Mitchell said. "There won't be any type of catastrophic incident."

Source: The Washington Post

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