Photo by trekandshoot/Shutterstock. Aerial view of the Southern California Gas Company Aliso Canyon storage facility near Porter Ranch, California, taken in January 2016. The facility was the site of the largest methane leak in US history.

Two years ago, on February 11, 2016, the methane leak from California’s largest underground gas storage (UGS) facility at Aliso Canyon was finally stopped after drilling a relief well, but not before the leaking SS-25 well had gushed approximately 100,000 tons of methane over nearly four months. At the time, Berkeley Lab scientists used computer simulations of flow in the complex well geometry to evaluate how to best plug the leaking well by injecting it with heavy fluids. This Aliso Canyon incident, and the impacts it had on the Porter Ranch community in Los Angeles, raised the visibility of UGS in California and across the nation.

Today, the California Council on Science and Technology (CCST), a nonprofit organization that provides expert advice from California’s scientists and research institutions on public policy issues involving science and technology, released a report on the safety and reliability of all of California’s underground natural gas storage fields. The report, “Long-Term Viability of Underground Natural Gas Storage in California: An Independent Review of Scientific and Technical Information,” was compiled in response to a request made by Gov. Brown in the wake of the 2015 Aliso Canyon incident, the largest methane leak in U.S. history. Modeled after the National Research Council, which responds to the United States government, CCST responds to requests from California’s State Legislature, the Governor, and State entities, and provides expert advice from California’s scientists and research institutions on public policy issues involving science and technology.

The report provides insight into the question on the minds of many Californians following the extreme event: What are the risks of storing natural gas underground and should we – or could we – reduce our dependence on natural gas storage?

Berkeley Lab senior scientist Jens Birkholzer co-chaired a 12-member CCST Report Steering Committee which supervised the report’s 21 authors whose expertise spans hydrogeology and engineering, risk assessment, public and occupational health, greenhouse gas emissions, and energy analysis and economics. Berkeley Lab’s Curt Oldenburg and Jeff Greenblatt served as lead authors on report chapter 1 on the risks posed by UGS to health, safety, environment, and infrastructure, and chapter 3 on the role of UGS in California’s energy future, respectively. The 1,000-page report was subject to a comprehensive independent peer-review process.

Birkholzer believes that without such exhaustive analysis, it would have been difficult for the report’s authors to generate conclusions and recommendations that sufficiently take into account both the widespread extent to which California depends on natural gas and the potential for mitigating the risks that come with storing it underground. He shared his thoughts on the key takeaways from the report prior to taking part in a briefing at California’s state capitol building in Sacramento today.

Q: The Aliso Canyon event generated unprecedented concern over the impact on the safety of surrounding communities from storing natural gas underground. Are there any findings within the report that could alleviate some of this concern?

A: We believe that what happened at Aliso Canyon could have been avoided with sensible regulation and oversight. Since the well blowout, the State of California has taken several steps in the right direction, such as developing a set of new regulations for underground gas storage that should significantly reduce the risk of future incidents. There is nothing systemic in the practice of storing gas underground that would place it at higher risk compared to other subsurface operations, provided that the new regulatory requirements are rigorously implemented and larger risks are appropriately assessed, managed, and mitigated.

Q: What does the report tell us about the future of natural gas in California? How long can we expect the state’s energy system to require underground natural gas storage?

A: California’s energy system currently requires natural gas and UGS facilities to run reliably, primarily because many residential and commercial buildings in California rely on natural gas for heating during the winter, and because natural gas provides electricity when solar and wind power are not available. In the near term, there are no obvious and feasible alternatives to natural gas storage. Closing any or all storage facilities would involve costly new pipeline infrastructure, which would bring its own risks and would further obligate the State to the use of natural gas for decades to come.

Q: The report assessed various risk-related characteristics across UGS facilities throughout California, and found a small number were potentially higher in risk than others. Report authors state that with any industrial operation some degree of risk to health, safety, and environment is unavoidable. Is there a way to put the degree of risk that accompanies UGS in perspective, when compared to the risks inherent to other industrial operations or types of energy systems?

A: Good question. Currently this type of comparison can only be done in a qualitative manner because the risk associated with operating underground gas storage has not been determined in formal quantitative risk assessments. We have recommended to the State that quantitative risk assessment should be part of the new regulations, so we expect to have this type of information available down the road. At this point it is a bit of speculation, but we would expect the risk of underground gas storage to be similar to the risk of other subsurface operations, such as geothermal energy or oil and gas production.

Q: Does the report reveal any opportunities that may exist for the future of underground gas storage? How might the role of natural gas evolve as California’s energy needs, or its climate policies, shift?

 A: The role of underground gas storage will surely change in the next decades as the State is implementing its ambitions climate goals for 2030 and 2050. We just don’t know how yet because there are no in-depth feasibility studies demonstrating which energy scenarios can meet GHG emission constraints and achieve energy reliability. Of the many scenarios that have been discussed, some would still require the use of natural gas and gas storage; others would not. The State needs to develop a more complete and integrated plan to develop technically, economically, and socially feasible energy scenarios that work. Such a plan will provide the basis for assessing how the role of natural gas might evolve.