The thousands of miles of pipelines and seven underground natural gas fields in the Sacramento region offer little surface-level evidence of the billions of cubic feet of natural gas under storage.
Some of the infrastructure sits close to schools and houses. A few of the underground storage fields are abandoned oil or gas repositories refitted to hold natural gas. The largest field, PG&E Corp.’s McDonald Island facility near Stockton, can hold 82 billion cubic feet of natural gas in a sandy formation reservoir more than 5,000 feet deep.
That sprawling and aging energy network is now receiving tighter scrutiny by environmental and watchdog groups as a major gas leak at the Aliso Canyon storage facility in Southern California spews tons of methane, a potent greenhouse gas, into the atmosphere. Experts say the state’s natural gas infrastructure is largely safe, but the Aliso Canyon accident demonstrates the ever-present risk.
“The public needs to know the possibility of engineering failures and how important maintenance is,” said Rosa Dominguez-Faus, a researcher with the UC Davis Institute of Transportation Studies. “So the culture needs to change, and if it doesn’t change from within, then external pressure is necessary in the form of regulation and enforcement.”
Studies have found that such pipelines, valves and other above-ground infrastructure regularly leak measurable, but safe, amounts of methane even when they are operating normally. Methane is a major component of natural gas and extremely flammable. It also affects breathing in high concentrations, according to the National Institutes of Health. For household use, methane is commonly mixed with the gas mercaptan, which gives methane a distinctive odor to help people sense leaks but can also sicken in high doses.
The advocacy group Environmental Defense Fund argues that utilities and regulators are not doing enough to prevent methane leaks.
Timothy O’Connor, an environmental policy expert with the group, said storage facilities are exempt from state greenhouse gas emission limits, which makes enforcement tougher. The fund has also demanded the state require utilities to install automatic valves that shut off the flow of natural gas at storage facilities in case of accidents.
“These facilities have no obligations to inspect and reduce emissions, and they do not do it because they are not obligated to do it,” O’Connor said.
The cause of the leak at Aliso Canyon has not been established, giving officials little indication whether similar storage facilities around the state could be at risk.
PG&E spokesman Nick Stimmel said the Northern California utility has been proactive in safeguarding the integrity of its wells.
“During the nearly 60 years that PG&E has been operating its three underground storage facilities, we have found and fixed nine leaks on our well equipment,” Stimmel said.
He added that the utility is piloting a leak-monitoring system in collaboration with the industry-led Pipeline Research Council International, using state-of-the-art technology to gauge higher levels of methane and other emissions from storage facilities.
Nonetheless, the California Air Resources Board found that the amount of methane in the air over the Central Valley in 2013 was 30 percent to 70 percent higher than expected ambient levels. In 2012, the Environmental Protection Agency estimated that natural gas systems contributed to about 23 percent of annual U.S. methane emissions.
The state Division of Oil, Gas and Geothermal Resources had anticipated problems in the industry when it announced a new plan two weeks before the Aliso Canyon leak for regulations on underground storage facilities. Rules on natural gas storage have since been turned into emergency regulations slated to go into effect this month, said division spokesman Don Drysdale.
Despite the attention drawn by the Aliso Canyon accident, a bulk of the state’s pipelines are found in Northern California, especially around the Central Valley, with 7,100 miles of pipes connecting hundreds of natural gas wells and pipelines entering from the Pacific Northwest.
An additional 20 active wells are part of the PG&E-run Los Medanos storage facility in the eastern Bay Area city of Concord, holding up to 17 billion cubic feet of gas in a location near four schools.
Amy Jaffe, director of energy and sustainability at the UC Davis Institute of Transportation Studies, said studies have found that methane leakage happens along the entire gas supply chain, such as at drilling sites and pipelines. The McDonald Island facility, with almost as much capacity as the Aliso Canyon field, was cited for minor violations in 2013 by the state Public Utilities Commission.
Still, Jaffe said, the Aliso Canyon leak is a rare event not likely to repeat in the Sacramento region.
“Honestly, I cannot recall a similar incident at a deep storage facility in recent years,” she said.
More than 84 million kilograms of methane have escaped from well SS-25 in Aliso Canyon, equivalent to the amount of greenhouse gas emitted by 440,000 cars in one year. The leak has prompted Gov. Jerry Brown to declare a state of emergency. The Southern California Gas Co. said it expects to bring the leak under control by late February.
Investigators are exploring whether the age of well SS-25, which dates back to the 1930s, may have been a factor in the leak. State inspectors have found methane leaks at another 15 wells at Aliso Canyon, according to the governor’s Office of Emergency Services.
In a meeting with The Sacramento Bee, Southern California Gas President Dennis Arriola said the company had stopped the leaks at the other 15 wells at Aliso Canyon, even as it worked to contain the main methane release.
“Leaks happen all the time through the system, and the problem is typically with the materials and the age of the materials, both in well casings and in smaller distribution pipelines,” Dominguez-Faus said.
At McDonald Island, some initial wells were drilled in 1936, when the field was owned by Standard Oil.
Already, the industry is taking action because of Aliso Canyon. On Jan. 26, the Public Utilities Commission, along with the Division of Oil, Gas and Geothermal Resources, directed owners and operators of underground gas storage facilities throughout the state to inspect their facilities.
Edward Ortiz: 916-321-1071, @edwardortiz