- Associated Press - Saturday, March 7, 2015

ROCKVILLE, Md. (AP) - A massive tunnel dug near the Capital Beltway in Montgomery County over the past five years is now carrying 100?million gallons of water daily, completing a major piece in suburban Maryland’s water distribution system that will keep toilets flushing and fire hydrants working as the suburbs grow, the area’s water utility said.

The 5.3-mile tunnel through solid bedrock is 90 to 200 feet underground, depending on the topography. It runs between Tuckerman Lane and Interstate 270 in Rockville to Kensington, near the Church of Jesus Christ of Latter-day Saints’ Temple in Washington. The tunnel, which at 10 feet in diameter is large enough to contain some buses, holds a steel water pipe seven feet in diameter that connects two other eight-foot water transmission mains.

Connecting those mains will help the Washington Suburban Sanitary Commission retain water pressure systemwide as Prince George’s County continues to grow, particularly during peak-demand periods such as summer, WSSC officials said Thursday. Areas in Wheaton and Silver Spring were most susceptible to losing water pressure because of growing demand from Prince George’s, utility officials said.

The new pipe, which was first planned in the 1970s, will help WSSC accommodate future development through at least 2040, utility officials said.

Construction on the tunnel started in 2009. Water began flowing Feb. 16.

“We’re pretty excited about a project that’s underground and no one will see,” said John Mitchell, WSSC’s project manager. “It will provide reliable services to our customers - that’s what we want.”

Mitchell said engineering and construction challenges included using a tunnel boring machine to chew through more than five miles of granite and then building a small railroad inside the tunnel to transport 50-foot pieces of steel pipe several miles before they were welded into place - all within tight confines underground.

At $146 million, it is the most expensive infrastructure project WSSC has undertaken, said spokesman Jim Neustadt. Funding came from fees charged to developers, he said.

Like other water and sewer utilities nationwide, WSSC has struggled with the costs of maintaining its aging infrastructure - including water mains that have burst after years of neglect - while expanding its system to keep up with new development. In addition to keeping up with future growth, the new pipe will help WSSC divert water around other large concrete mains that need to be inspected and repaired, Mitchell said.

While WSSC’s concrete mains have drawn national attention for bursting without warning and causing significant flooding, the new pipe is made of steel, Mitchell said. Any weaknesses in it would be detected through the pipe’s corrosion monitoring system, and the pipe would leak water to the surface before it burst suddenly, as the concrete mains do, he said. A concrete coating between the pipe and bedrock tunnel will help protect it from corrosion, he said.

Tunneling continues in the Washington region as DC Water digs tunnels that will capture and hold stormwater runoff to prevent sewage overflows into the Anacostia River during heavy rains.


Information from: The Washington Post, https://www.washingtonpost.com

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