WSSC crews work to repair a broken water main at Connecticut Avenue and Chevy Chase Lake Drive. The pipe ruptured Monday night.  (Katherine Shaver/The Washington Post)

Sensors installed in a large water main that exploded Monday night in Chevy Chase detected a problem with the pipe but not until it had ruptured and unleashed a towering geyser along Connecticut Avenue, utility officials said Wednesday.

The fiber-optic cables, similar to others being installed in large, concrete pipes in the Maryland suburbs, are designed to provide advance warning of water main breaks by detecting the “pings” of the pipes’ reinforcing steel wire as it begins to snap.

Utility officials are trying to figure out whether the acoustic sensors were slow to detect the pings or whether the rupture resulted from some other issue that the monitoring equipment was not designed to pick up.

Jim Neustadt, a spokesman for the Washington Suburban Sanitary Commission, said the system sent a flurry of alerts signaling that a “large event” was occurring as the 60-inch pipe burst about 8 p.m. Monday.

Neustadt said the WSSC did not receive any alerts prior to the break. Alerts that a pipe’s reinforcing wire is beginning to snap usually are received days — or at least hours — before a pipe breaks, giving a utility time to shut off the pipe before it explodes, he said.

What happens when water mains burst

The WSSC shut off a 96-inch pipe near Tuckerman Lane in Bethesda in 2010 after a series of pings signaled an impending break.

“I can’t say [the equipment] should have predicted this, because we don’t know what the cause is,” Neustadt said. “It might end up being a cause that the system isn’t designed to detect.”

Both possibilities left Della Stolsworth more worried than ever about the 66-inch water main buried beneath Tilden Lane in her Luxmanor neighborhood in North Bethesda. The street is lined with homes and Luxmanor Elementary School.

“Whenever we voice a concern, WSSC tells us: ‘Don’t worry. Your pipe has the acoustic equipment,’ ” said Stolsworth, president of the Luxmanor Citizens Association, which has almost 900 homes in the neighborhoods straddling Tilden. “Obviously, we’re very concerned and eager to find out what happened in Chevy Chase.”

Stolsworth said she did not recall WSSC officials saying that there were types of breaks the acoustic equipment cannot detect in advance. “I definitely never received that message,” Stolsworth said.

Neustadt said WSSC officials generally have explained that the acoustic equipment, like any technology, isn’t fail-safe.

He said he couldn’t comment on what WSSC experts and consultants found when they inspected the broken Chevy Chase pipe, which was buried along the eastern edge of Connecticut Avenue at Chevy Chase Lake Drive in 1980. He said the WSSC will announce the cause of the break only after a consultant completes a full “forensic” investigation, which usually takes several months.

Jerry Irvine, a spokesman for the Washington Suburban Sanitary Commission, explains how a 54-inch, highly pressurized water main burst along Connecticut Avenue in Chevy Chase Lake, just inside the Capital Beltway, late Monday night. (Katherine Shaver/The Washington Post)

Meanwhile, traffic in the area remained snarled for a second afternoon rush hour Wednesday as one lane of northbound Connecticut Avenue remained closed near Chevy Chase Lake Drive to make room for utility repair crews. A contractor worked to replace the broken 20-foot section of pipe Wednesday, Neustadt said.

Mandatory water restrictions remained in place Wednesday for 1.8 million people in Montgomery and Prince George’s counties. Residents were directed to take shorter showers, limit toilet flushing, and delay dishwasher and laundry loads until the system can replenish the more than 60 million gallons lost in the break.

Violations carry fines of up to $500, but Neustadt acknowledged that authorities were limited in their ability to enforce the restrictions. He said cutbacks in usage are needed so fire hydrants and hospitals can have adequate water pressure.

Officials across the country have struggled with aging infrastructure for years. Water pipes are considered particularly challenging because they’re buried out of sight and a water distribution system like the WSSC’s — which has more than 5,500 miles of water main — is too expensive to replace.

Timothy Firestine, Montgomery’s chief administrative officer, said the acoustic equipment has been a good investment because it “dramatically increases the probability” that the WSSC will get advance warning of a break. Even so, he said, county officials have never considered it to be “foolproof.”

Asked whether county officials knew that there were types of large breaks the acoustic system can’t detect, Firestine said: “The focus has always been on how the equipment works. Did anyone ever ask if there were types [of breaks] that could occur that the acoustics wouldn’t cover? I don’t know if that conversation happened.”