The risks and condition of Pacific Gas & Electric's (PG&E) aging natural-gas pipeline infrastructure on the Peninsula remain subject to speculation, despite numerous requests by news organizations for details about the age, size and maintenance and replacement schedules.

What is known about Palo Alto's gas system is that three PG&E transmission lines run through or near the city, including down portions of Middlefield Road, Oregon Expressway/Page Mill Road and Junipero Serra Boulevard, according to maps by the U.S. Pipeline and Hazardous Materials Safety Administration and the California Department of Conservation. PG&E owns and maintains those lines.

City of Palo Alto Utilities maintains the remainder of the gas system. That includes nearly 70 miles of steel gas mains that are 12 inches in diameter or smaller and approximately 1,152 miles of steel gas-service lines, Utilities Director Valerie Fong said.

During 2009, the department checked all 19,311 gas-service lines for leaks and did a mobile survey of 207 miles of city gas-main pipes, according to Greg Scoby, Palo Alto's engineering manager for water and gas.

The surveys found 75 main and 142 service leaks, which were repaired.

City of Palo Alto Utilities replaces every gas line in the city in 34.5 years (6 miles per year of distribution and 600 service lines); the average expectancy of such pipes is about 40 years, according to the city.

City officials this week sent out a detailed press release in order to quell fears that Palo Alto's gas lines could be unsafe. But the city has refused to provide information and maps regarding PG&E's network, citing terrorism risks and the courtesy between the two utilities agencies not to provide information about each other's property -- including maps within the city's possession.

Trying to get that information out of PG&E has also been met with refusal or silence, again citing fear of terrorists over the public's right to know.

PG&E would not provide information about the diameter or age of its transmission lines and did not return e-mails and phone calls requesting information about maintenance and service to its lines through Palo Alto.

While the City of Palo Alto Utilities buys gas from PG&E, it refers service calls about PG&E pipelines within Palo Alto to the company. This week the city confirmed that it referred calls about a small leak near Oregon Expressway and Alma Street, reported Sept. 12, to PG&E. The city said PG&E fixed a leak but the company has not confirmed the repair.

In light of the San Bruno accident, however, the California Public Utilities Commission has ordered PG&E to inspect all of its gas lines from Eureka to Bakersfield by Oct. 12.

The aging pipeline that exploded in San Bruno could also be running through or near Palo Alto.

Line 132, the more than 50-year-old, 30-inch transmission pipeline that exploded on Sept. 9, runs up the Peninsula from San Jose toward San Francisco, according to a 20-year-old gas system map reviewed by Michael Florio, senior attorney for The Utility Reform Network (TURN).

Florio said the pipe likely runs through Palo Alto in or near the Interstate 280 corridor. An unnamed PG&E transmission line is noted on the national pipeline safety administration map running near Junipero Serra.

A 31.9-mile segment of line 132 is listed for retrofitting or replacement as part of PG&E's In-Line Inspection major capital improvements projects for 2012, according to a 2011-2014 report.

Aged pipes or lines that are convoluted cannot have in-line inspections, also known as "smart pigging." Pigging is an industry term referring to the process by which a data-gathering instrument travels within a pipeline to accurately assess steel-pipe wall thickness and look for weakened metal due to corrosion and damage, according to a PG&E report.

PG&E and City of Palo Alto Utilities won't confirm if the Junipero Serra pipeline is number 132 or when the pipe might have been put in.

Scoby said on Wednesday, however, that online maps by the U.S. Pipeline and Hazardous Materials Safety Administration are inaccurate. The maps were removed from the Internet after the Sept. 11 terrorist attack. When the maps were posted again, less-accurate versions were used.

But moving -- and the expense of redirecting -- the entire length of 24- or 30-inch transmission lines seems unlikely, although PG&E does note in documents that it moves some sections of pipeline upon request from entities, such as utilities companies.

Gas explosions are not unprecedented in Palo Alto.

In September 2009, a home on Maureen Avenue exploded due to a gas leak. After smelling an odor, the homeowners had consulted with a furnace installer, whom they said dismissed their concerns.

In 1966, El Carmelo Elementary School was damaged when a "shattering explosion and fire that 'burned like a blow-torch'" destroyed most of a wing, according to the Palo Alto Times.

The city had completed its annual survey of gas lines just two weeks prior to the explosion and no leaks were found in the lines, according to a Nov. 3, 1966 article.

From roughly 1958 to 1966, six explosions took place in Palo Alto as a result of leaking gas pipes. Two explosions occurred when workmen lit cigarettes while working in sewer ditches in which gas was escaping and the other four were due to leaking gas ignited by starting electrical equipment, according to the article.

Most unintentional natural gas releases are relatively small and do not cause personal injuries or death, according to a PG&E Sacramento Natural Gas Storage Project report on system safety.

Florio of TURN agreed.

"While the San Bruno incident was a real tragedy ... it is important that people understand that these types of incidents are less common than airplane crashes, and the majority of incidents are caused by construction equipment contacting the lines, not spontaneous explosions. So folks shouldn't panic, even if they have a line in their area," he wrote in an e-mail.

Between 2000 and 2009, there were no incidents of injury or death in Palo Alto from PG&E lines, according to the U.S. Pipeline and Hazardous Materials Safety Administration.

"Significant incidents" -- causing more than $50,000 damage, death or injury requiring hospitalization -- occurred in Los Altos in July 2005 (injuring one person, causing $463,784 in damage and caused by pipe corrosion) and in March 2008 in Mountain View (causing $104,973 in damage due to miscellaneous causes), according to the report. Five other incidents occurred in San Jose, with only one related to weld or material failure and most others related to excavation accidents. A 2003 incident in Cupertino was also caused by excavation.

Palo Alto residents this week said information regarding pipe age and replacement schedules should be more forthcoming.

"We were told several years ago that some of the gas lines in Barron Park would be replaced, like those under Laguna, but that was delayed because they want to mesh utility line replacement with repaving, and the repaving of Laguna was pushed back," Barron Park resident Bob Moss said.

"Many of the streets in south Barron Park, from Los Robles almost to Maybell, will be dug up this year to replace sewers. I am hoping that when they do that they will also inspect the gas and water lines and make sure they know where they all are, and that they are in good shape.

"Utilities says they are replacing gas lines when they are 33 or 34 years old, which is fine since they should last at least 40 years. Question is how many miles of gas line are 40 years old or more and haven't yet been replaced, since the program takes years to cover the whole system and replacement after less than 35 years is a relatively new policy," he said.

Fong said the city has 2,900 isolation valves to control or stop the flow of gas to city blocks. But Moss voiced concerns that the valves must be closed manually.

"I asked what would happen if many of them have to be closed at the same time due to lots of line failures after El Grande (The Big One). No answer. Another question is, 'Do the crews know where all the valves are?' Probably, but I haven't had any proof of that," he said.