Workers examining a section of a PG&E gas main discovered a small leak near Palo Alto, a PG&E spokesman said Friday (Nov. 4). PG&E crews determined Tuesday (Nov. 8) that the leaking pipe was located under Page Mill Road's eastbound lane, between Hanover Street and Peter Coutts Road.
One lane was blocked Tuesday as crews dug the pipe out. Testing and repairs were scheduled to proceed through Wednesday, according to spokesman Brian Swanson.
On Nov. 3 PG&E employees noticed a slow drop in pressure during a hydrostatic pressure test on Line 132 near Palo Alto. The line is the same one implicated in the September 2010 explosion and fire in San Bruno that killed eight people.
PG&E has been testing the line using a sophisticated water-pressure procedure to ascertain the condition of its mains as a result of federal and state findings related to the aging pipe infrastructure.
The Palo Alto/Stanford section of Line 132 runs parallel to the Junipero Serra/Interstate 280 corridor and down Page Mill Road between El Camino Real and near Interstate 280. Nearly 21,000 feet of the this section of 24-inch seamless pipe was installed in 1947 and about 2,700 feet has a seam weld and was installed in 1957, PG&E spokesman Brian Swanson said.
The drop in pressure has the characteristics of a small pinhole leak of approximately one millimeter in diameter. The leak poses no public danger and won't impact service, Swanson said.
The initial one-hour phase of the hydrostatic pressure test was being done to identify small leaks using water. Small leaks such as this do not pose safety risks and are easily repaired, according to PG&E.
The leak was detected during the initial phase of the hydrostatic pressure test when the pipe is tested at 75 percent of the test pressure for one hour.
Mains are pressurized beyond their maximum allowable pressure to expose leaks. The pressure at the time of the water leak was 525 pound-force per square inch gauge (psig) -- roughly one third higher than the normal operating pressure of 375 psig, PG&E said.
The main is currently operating at a reduced pressure of 300 psig, per a California Public Utilities Commission mandate until safety of the lines can be verified.
The company is working to precisely locate the leak. Nearly four miles of pipe being tested will have the water removed today, Swanson said.
PG&E on Sunday (Nov. 6) began putting a helium/air mixture through the pipeline to locate the leak workers will walk the line and search for indications of the helium, Swanson said on Monday. The company will excavate the area, make repairs and re-conduct the hydrostatic pressure test. The work is expected to take several days to complete, he said.
Using salvaged, reconditioned pipe was common in the industry in the 1940s and 1950s, but PG&E no longer engages in the practice, he said.