Inspections will begin this fall on water pipes similar to one that exploded this spring in Chevy Chase and was later found to be defective, utility officials told the Montgomery County Council on Monday.
The Washington Suburban Sanitary Commission has identified 234 sites — 70 percent of which are in Montgomery — where a large pipe has the same design as the 60-inch main that burst along Connecticut Avenue at Chevy Chase Lake Drive.
The March 18 break, which snarled traffic and led to mandatory water restrictions in Montgomery and Prince George’s counties, has drawn particular scrutiny because it occurred without warning, despite having equipment designed to detect an impending break.
An investigation found that the pipe’s reinforcing steel wire had not been prestressed sufficiently, which left it unable to produce sounds loud enough for the monitoring equipment to detect as it began to break because of corrosion, officials said. Two separate leaks also caused chlorinated water to corrode the steel cylinder and the reinforcing steel wire within the concrete pipe, the report said.
The first inspections will be on a 48-inch transmission main that runs through central Montgomery and has 17 of the 234 sites, officials said. The sites at issue are on large pipes that connect to a smaller one or have some other “entry port,” such as for an air-release valve. The Chevy Chase break occurred where the 60-inch pipe connected to a 24-inch main.
By June, when the current fiscal year ends, “we’ll have a much better idea of the severity [of the problem] and whether or not this was an isolated incident or more systemic,” said David Burke, who leads the WSSC’s technical services group.
Burke said the 35-year-old pipe was made by Interpace, a defunct New Jersey company that the WSSC and other utilities successfully sued over product flaws. However, officials said, those flaws pertained to reinforcing steel wire that was particularly prone to corrosion. The problem in the Chevy Chase pipe was wire that was too weak.
Gary Gumm, the WSSC’s chief engineer, said he’s not concerned that any of the 234 sections of pipe are particularly vulnerable to breaking because the Chevy Chase pipe was further weakened by the leaks.He said it was the first failure in a pipe with that design in 70 years.
Utility officials say the break also prompted them to train crews to pay closer attention to leaks found near concrete mains. A Chevy Chase resident had reported water bubbling up adjacent to Connecticut Avenue seven hours before the break. Utility crews responded, officials said, but thought the water was coming from a leaky valve — a repair that they decided could wait.
The WSSC’s general manager, Jerry N. Johnson, called the workers “professional’’ and said they left only to answer another call. Even so, he told the council, “This was one where a mistake was made.”