The Washington PostDemocracy Dies in Darkness

WSSC opens 5-mile tunnel in Montgomery to keep water flowing to Prince George’s

A view of the mouth of the pipe, photographed from the basket that transports visitors to the site. (Bill O’Leary/The Washington Post)

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 continue to 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’ Washington D.C. Temple.  The tunnel, which at 10 feet in diameter could contain some buses, holds a steel water pipe seven feet in diameter that connects two eight-foot water transmission mains.

Connecting those mains will help the Washington Suburban Sanitary Commission (WSSC) retain water pressure systemwide as Prince George’s County continues to grow, particularly during peak-demand periods such as summer, WSSC officials said. 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 service to our customers. That’s what we want.”