The WSSC engineer, appearing before a Montgomery County Council committee, said the utility has not determined how to detect when such pieces of highly pressurized pipe are about to fail or how close these types of segments are to homes and other buildings.
“We assume there’s something we need to be doing, but we’re not sure exactly what,” Gumm said.
He said the March 18 incident was the first rupture that the WSSC has had in a pipe with this design. The break occurred along northbound Connecticut Avenue at Chevy Chase Lake Drive and created a geyser 40 feet high. An outside investigation will attempt to determine whether the particular piece of pipe had a flaw or whether the rupture signals a wider problem.
That investigation is expected to be completed by early June, Gumm said.
The WSSC has known of problems with its largest mains for years but has focused primarily on inspections and trying to detect when the pipes’ reinforcing steel wire begins to snap. That allows the utility to shut down a weakening pipe before it breaks. The WSSC, aided by a 50 percent increase in customers’ bills during the past six years, has spent $21.2 million since 2007 to install and monitor acoustic equipment inside the largest pipes.
However, the Connecticut Avenue pipe, which exploded without warning, broke between the steel ring joint and a “saddle,” which is a wider piece of steel about a half-inch thick that wrapped around the pipe adjacent to the steel joint. There are no reinforcing wires between the joint and the saddle, Gumm said.
“We didn’t know this type of pipe might fail without wires breaking first,” Gumm told the council.
The 60-inch pipe along Connecticut Avenue broke where it connected to a 54-inch pipe. The 60-inch pipe was installed in 1980.
The question of when and how the WSSC detects imminent breaks in its largest transmission mains has come under scrutiny amid a series of massive breaks in the Maryland suburbs over the past decade. Because the mains are highly pressurized and relatively large — some are big enough to contain a minivan — they explode with a force of up to 200 pounds of dynamite.
The March 18 break blew a 50-by-70-foot crater into Chevy Chase Lake Drive and a nearby stream bank, WSSC officials said.
No one has been seriously injured in a water main break, WSSC officials say, but local officials say residents are increasingly worried about massive pipes exploding without warning. WSSC officials have said 1,768 homes and other buildings in both counties are too close to their largest mains. It would be too costly and take decades to move the aging mains, utility officials say.
“What does this mean for the pipes underneath our other communities?” asked council member Roger Berliner (D-Potomac-Bethesda), who chairs the infrastructure committee and whose district has had several major breaks. “They are nervous.”
Gumm said no problems were found with the Chevy Chase pipe when it was last inspected, in 2009. Inspection crews left behind the fiber-optic cables that monitored for breaking wires.
The Chevy Chase break also has renewed attention to a WSSC proposal to limit new building within 80 feet of its largest mains to better protect the public from the force of potential breaks. Some local officials had questioned the need for expanding the building setback — the current setback is 25 to 33 feet — because the pipes already had acoustic monitoring to warn of a problem.
A WSSC panel established almost a year ago to study the issue is scheduled to meet April 23.