A 60-inch water main that burst in March in Chevy Chase failed because of a manufacturing flaw and a slow leak in the steel-reinforced concrete pipe, according to an analysis of the break by an engineering consultant.

The pipe exploded March 18, spewing a 40-foot geyser, and blew a crater 20 feet deep and 90 feet long at Connecticut Avenue and Chevy Chase Lake Drive. The failure was the first to occur without warning in a Washington Suburban Sanitary Commission main equipped with technology to detect an impending break.

The WSSC provides water and sewer services in Montgomery and Prince George’s counties.

The reinforcing steel wire in the 20-foot section had not been pre-stressed, or strengthened, enough in a critical area near a joint, according to a “forensic analysis” done for the WSSC by Dacco Sci, a Columbia-based engineering firm.

Then, a slow leak allowed the chlorinated water to corrode the steel cylinder and the reinforcing steel wire within the concrete pipe, the report said. The break-detection system is not designed to discover leaks.

The pipe was manufactured in 1978 by a defunct New Jersey company, Interpace, which the WSSC and other utilities successfully sued years ago for manufacturing flaws in its concrete mains.

The break led to mandatory water restrictions and spilled about 60-million gallons of drinkable water before the WSSC could shut off the geyser, the report said.