While the WSSC planned to have the pipe shut off Tuesday night, Hudson said, the taps would not go dry immediately. The system has about 12 to 14 hours’ worth of water, he said. People are being asked to restrict their water use during that time to stretch out the supply.
WSSC crews stood ready at valves throughout the day in case they needed to shut off the pipe in an emergency, Hudson said.
The pipe is in a wooded area just inside the beltway, between Forestville Road and Suitland Parkway. It is “not that far” from the Beltway, Hudson said, but it is downhill from the road, so any water from a break would flow away from it. No buildings are in the immediate area, he said.
Because such pipes are so large and carry so much water under pressure, they literally can explode. WSSC engineers, who have sought building restrictions within 80 feet of such pipes, have compared the force of such a blast to a bomb that can hurl rocks and other debris “like shrapnel.”
The main, which was installed in 1965, is unusual in the WSSC system because there is no way to route supplies around it, he said.
The utility was first alerted to a problem with the pipe on Thursday, when acoustic cable that had been installed just a few weeks earlier “started to pick up a bit” with alerts, Hudson said. The equipment is designed to detect the sounds of the concrete pipe’s reinforcing steel wire as it begins to snap from corrosion, signaling that the pipe is weakening in that spot.
As of Monday night, the pipe had registered 30 alerts “in fairly quick order,” Hudson said.
“It tells us this pipe is headed out,” he said. “We can’t just sit back and wait.”
WSSC spokesman Jim Neustadt said the prestressed concrete cylinder pipe involved was essentially the only water source for the area served, making it necessary for people “to fill up on water” ahead of the shutdown.
Before the flow of water through the pipe is cut, WSSC would try to fill up its storage facilities so that some water could be delivered through smaller pipes, said Jerry Irvine, another utility spokesman.
This is at least the third time in the past several years that acoustic equipment installed in a pipe has alerted the WSSC to a potential break, allowing for a preemptive shutdown.
One such shutdown occurred in the Rockville area this spring, utility officials have said. In 2010, water restrictions were imposed over the Fourth of July weekend after an eight-foot-wide pipe was shut down in Potomac.
The utility is still reviewing the March break of a five-foot-wide pipe in Chevy Chase, where the force of the blast blew a crater 20 feet deep in a side street off Connecticut Avenue and created a 40-foot geyser. In that case, utility officials said, no warning was received because the break occurred near a joint where there was no wire being monitored.
The main that triggered the latest alarms is inside the Beltway between Suitland Parkway and Forestville Road. The WSSC said it is in a relatively inaccessible spot, and officials said a road was constructed by Tuesday morning to bring in repair equipment.
The WSSC’s 350 miles of prestressed concrete cylinder pipe form the backbone of its distribution system for 1.8 million people in Montgomery and Prince George’s counties.
Lori Aratani, William Branigin, J.D. Harrison, Michael Laris, Trishula Patel, Miranda S. Spivack, Martin Weil and Ovetta Wiggins contributed to this report.