Work crews dug up a block of 15th Avenue several times before a water main there ruptured and flooded 23 homes Feb. 27. City officials are now investigating whether the work — most recently three months before the accident — disturbed or damaged the water pipe before it burst.
The 16-inch cast-iron water main, which dates to 1952, “pulled apart at a joint” on the 15th Avenue hill that leads from Wawona Street to West Portal Avenue, according to the San Francisco Public Utilities Commission.
The break occurred in front of a home at 2733 15th Ave. Water then flowed down the hill toward the intersection of Wawona Street and 15th Avenue, damaging 23 homes, three of which have been deemed unsafe to occupy.
From Oct. 29 to Nov. 19, contractors with Precision Engineering worked to replace the sewer main that runs from West Portal Avenue to Wawona Street, records show. The two pipes meet at two places along that block of 15th Avenue, according to city engineering maps. Also, the sewer main is below the water main.
The SFPUC is investigating the “possibility that the sewer work had an impact on the integrity” of the water main, said spokesman Tyrone Jue. A faulty weld at the joint also might have led to the break, he said.
A full tally of the damage has yet to be made, according to Stacey Lawrence, whose home is on the 2600 block of 15th Avenue. Six homeowners have filed preliminary claims against The City, which could seek to shift blame — along with legal bills — if another party is found to be at fault.
Precision Engineering was one of seven companies to place bids on the sewer replacement project, records show. At a base bid of $2.6 million, Precision’s was the second-lowest.
It’s unknown if the section of water main that broke was exposed during the sewer work. It’s not typical procedure for pipes to be inspected for damage while exposed during unrelated projects, according to the SFPUC.
The street also had been dug up between 2007 and 2009 during construction of new homes in the 2700 block of 15th Avenue. Gas and electric lines, along with sewer hookups, were installed for the new homes, which are valued between $1.5 million and $1.8 million, according to records.
An investigation into the accident is ongoing. Preliminary findings are expected in mid-April at the earliest.
At 61 years old, the pipe “is not an old pipe by our standards,” said Jue, adding that most water mains are designed to last 100 years.
The street will eventually have to be dug up again so the offending water main can be replaced, Jue said. In the meantime, the pipe has been patched where it broke and an extra safety valve — which can be closed to shut off water in the case of a break — has been installed on nearby West Portal Avenue, Jue said.