San Bruno's exploded gas line runs through Mountain View
Pipeline runs through right of way for massive Hetch Hetchy aqueduct
The 54-year-old gas transmission line that blew up in San Bruno, killing seven people, also runs through residential areas of northern Mountain View, along with two other major gas pipelines slated for retrofitting.
Known as Line 132, the pipeline runs down the Peninsula from San Francisco along the Interstate 280-Junipero Serra Boulevard corridor but snakes into populated areas in Palo Alto and Mountain View on its way southward to Milpitas along State Route 237.
The cause of the explosion in San Bruno, which burned four blocks of homes and damaged many others, is still under investigation. But it has increased scrutiny of Pacific Gas &Electric's gas pipeline system and city officials are seeking information about Mountain View's large gas pipelines. Line 132 has not been replaced since its installation in 1956, PG&E spokeswoman Katie Romans said Friday.
In Mountain View, line 132 runs east from the Palo Alto border along Middlefield Road before cutting through the middle of the Whisman neighborhood along the Hetch Hetchy aqueduct right of way.
Public Works Director Mike Fuller said that an explosion of the gas line next to the Hetch Hetchy aqueduct would be a unique disaster as the massive water pipeline supplies water to San Francisco and much of the Peninsula, including parts of Mountain View.
Fuller said on Monday that the city had been trying for a week to schedule a meeting with PG&E to learn the condition of the gas lines in Mountain View, but apparently faces competition from other cities seeking the same thing.
"Our staff is working on this and ensuring that we are safe," said Mayor Ronit Bryant. "I know that they are monitoring the situation and will take whatever steps necessary to make sure (the pipelines) are safe."
"Terrible things like what happened in San Bruno are extremely rare," Bryant added. "Disaster can always strike but these are very rare events."
Older test methods
Line 132 and two other major gas lines in Mountain View are on a list of 10 aging pipelines scheduled for a multi-million dollar retrofit that will allow them to be assessed by the most current safety testing equipment. None of the aging lines currently can be inspected using the latest technology, called "smart pigging." Pigging is an industry term referring to the process by which a data-gathering instrument travels through the pipe to assess steel-pipe wall thickness and look for weakened metal, such as cracked welds and corrosion, according to a PG&E report.
PG&E spokeswoman Nicole Liebelt said the lines in the Mountain View area are typically tested through "external corrosion direct assessment," or ECDA, one of three federally approved methods for testing gas pipelines. The other two methods being smart pigging and pressure testing (pumping water into the pipe at high pressure to see if it holds.) The direct assessment involves "above ground electrical surveys," Liebelt said, which apply an electrical current to the pipe to determine its integrity by measuring the resulting electromagnetic field or electrical resistance. Suspect sections are excavated for more direct inspection. ECDA is the one method that does not involve turning off the gas flow in the pipe.
Of Line 132's 51.5 miles, a 31.9-mile segment has been identified for retrofitting as part of PG&E's In-Line Inspection major capital-improvements projects for 2012, according to a 2009 PG&E report. It was not immediately clear if any Mountain View gas line segments need retrofitting.
Two other major gas transmission lines that run through Mountain View — lines 101 and 109 — are also slated for that retrofit project, but PG&E spokespeople could not comment as to whether Mountain View's sections were part of the project.
Line 109 roughly follows alongside line 132 until Highway 85 when it turns north through populated areas before continuing east along Highway 101. Line 101 runs south west along the Highway 101 before turning east near Amphitheatre Parkway to run through office buildings, Shoreline Park and Moffett field.
The lines change diameter along the route, up to a maximum of 30 inches, Romans said.
The last corrosion check on Line 132 was done in November 2009 and the last routine gas-leak surveys, which are above ground, were done on March of this year, Romans said.
Liebelt added that the entire length of Line 132 was resurveyed after the San Bruno explosion.
On Monday, PG&E released a list of its top 100 riskiest gas lines, which are project priorities. None of the projects are located in Mountain View, with the nearest being located in the Stanford area. Liebelt stressed that the projects were not immediate problems, which PG&E would otherwise fix immediately.
Palo Alto Weekly staff contributed to this report.