Johnson, in a Monday County Council Committee hearing on the March 18 water main break in Chevy Chase, said an inspector who arrived at the scene determined the water bubbling on the surface near 8101 Connecticut Avenue was coming from a 24-inch valve vault connected to the 60-inch main.
A crew arrived and pumped out the vault. After no more water flooded the vault, the crew left for another pipe issue with the expectation to repair the valve the next day.
The leak turned out to be from the 60-inch main, which about five hours later burst into a geyser of water that left a 90-foot by 45-foot crater and 60 million gallons of water flowing into the stream below the roadway.
“I can’t escape the notion that, did they just want to get home for the day?” Councilmember Hans Riemer (D-At large) asked Johnson during Monday’s hearing.
“No, I don’t believe so. I think that the crews that work here are true professionals. These guys are out here 24 hours a day, seven days a week and they do this with a great deal of frequency and regularity. This was one where a mistake was made,” Johnson said. “They were anxious to get to another break. I think that was the issue, they had to get to another issue. It wasn’t shift change time.”
WSSC officials said the Chevy Chase break was one-of-a-kind – the acoustic fiber optic (AFO) monitoring system inside the pipe did not warn of the break because it only detects pings or snapping sounds of steel wires that support the system’s major PCCP mains.
Because the steel wires at the Connecticut Avenue break did not snap before the break, the AFO was essentially useless in predicting the break.
The hearing on Monday was the first time Johnson and other WSSC officials went before the Council since the full forensic report was finished.
The report found three separate conditions combined to cause the massive pipe failure:
- Inadequate Wire Pre-stress Found Between the Steel Saddle Plate Used to Attach the Factory Installed Outlet and the Steel Bell End Ring Compromised the Composite Structure of the Pipe Section
- A Slow Leak From the Gasket at the Bell End
- Chemically and Physically Weakened Pipe Joint Mortar Caused by the Leaking Potable Water (More Corrosive To Steel) Allowed Water to Enter the End of the Compromised Composite Structure and to Corrode the Wires and Steel Cylinder
The report found that without one of those three conditions, the pipe likely would not have burst in March. It was the first pipe failure of its kind in the 70 years WSSC has been using PCCP transmission mains.
There are 234 similar pipe sections in WSSC’s two-county coverage area. About 70 percent of those sections are in Montgomery County, so WSSC officials promised they would start inspecting water mains for similar conditions in the course of their scheduled FY14 pipe inspections.
Inspectors will start with the 48-inch PCCP water main that runs 6.18 miles from Rockville Pike, east through Rock Creek Park to Georgia Avenue.
WSSC Technical Services Group leader Dave Burke said officials should have data on the pipes in question by May or June of next year.
The WSSC report to the Council is available here.