Aliso Canyon Natural Gas Leak

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State Regulators Confirm Aliso Canyon Natural Gas Well is Permanently Sealed


On Mar. 28, state agencies announced the implementation of several actions to strengthen operational safety at Aliso Canyon and all gas storage facilities in the state, while protecting energy reliability within the Los Angeles Basin. Sealing this leaking well is only the first step among several necessary actions moving forward to protect safety, public health and air quality at and around Aliso Canyon and all other gas storage facilities in California.

On Mar. 25, the Department of Conservation launched a site that tracks the progress of Southern California Gas Company's (SoCalGas) testing of the Aliso Canyon storage field and posts all testing results. Test results are submitted by SoCalGas, reviewed by Division staff, and then posted on the page.
Additional Aliso Canyon information – including a description of the tests required and biweekly reports SoCalGas must file on its progress toward completing the safety review – can be found here.


On Feb. 18, state regulators confirmed that the leaking natural gas well at Aliso Canyon has been permanently sealed. The testing process to confirm that the well is sealed was developed in consultation with independent technical experts from the Lawrence Berkeley, Livermore and Sandia National Laboratories. This process and the testing results can be found at​​​

Recovery Phase – Local Assistance Center

Los Angeles Mayor Eric Garcetti announced that the Los Angeles Emergency Management Department (EMD) will lead recovery efforts for the Porter Ranch community now that the state has confirmed the leaking well at Aliso Canyon has been sealed. A Local Assistance Center in the community will provide a centralized location where residents and businesses can access programs and services from a variety of agencies to help facilitate their return home and to their normal routines.


On-going Air Monitoring & Public Health

Air measurements that have been collected using air flights, on-site observations, and monitors in the nearby communities all confirm that the leaking gas has diminished consistent with successfully controlling the leak. The South Coast Air Quality Management District (SCAQMD) and California Air Resources Board (CARB) staff have jointly developed a set of criteria to determine when air quality in the surrounding communities of the Aliso Canyon facility has returned to typical conditions – a checklist to determine when the air quality is no longer being impacted by the leak. The air quality criteria are based mainly on measurements of the chemicals in natural gas of concern: methane, hydrogen sulfide, mercaptans, and benzene.

Both agencies will continue to conduct to air quality monitoring in and around Porter Ranch for the foreseeable future with results available in the links posted below.


Independent Expert Scientific Advisory Panel

The O​ffice of Environmental Health Hazard Assessment (OEHHA) has convened an independent panel of scientific and medical experts to review public health concerns stemming from the gas leak and evaluate whether additional measures are needed to protect public health beyond those already put in place. OEHHA requested experts in toxicology, epidemiology, exposure science and medicine, to review the available data on exposures, symptoms and toxicity of constituents in the natural gas, and to provide their opinions on whether additional measures are needed to protect public health.

  • Expert Panel Information (OEHHA)

Investigations & Inquiries

​Investigators from Department of California Division of Oil, Gas and Geothermal Resources (DOGGR) and the California Public Utilities Commission (CPUC), as well as independent investigators, will continue to work at the Standard Sesnon 25 well site to determine the cause of the leak and whether violations of state regulations occurred.

Frequently Asked Questions

Some of these are questions asked before the leak was sealed, however, there are many helpful and informative answers to many important questions.


This page updated on February 18​​​​, 2016​


​​​Photo of Aliso Canyon​​

​​​​On Oct. 23, a natural gas leak was discovered at a well within the Aliso Canyon Underground Storage Field in Los Angeles County. The Southern California Gas Company (SoCalGas​), which owns and maintains the natural gas storage facility and is responsible for its wells, has been unable to stop the leak, which appears to be caused by damage to the well casing at approximately 500 feet underground. The damaged portion of the well is very difficult to access and cannot yet be seen with a camera. SoCalGas has placed certain fluids and materials down the well several times in order to stop the leak, which is a common industry practice. However, these attempts have not stopped the leak.

On Dec. 4, SoCalGas began drilling a relief well to intersect with the damaged well. This new relief well will connect to the leaking well through which SoCalGas will pump in cement to permanently seal off ​the original well.

On Jan. 6, Governor Edmund G. Brown Jr. issued a proclamation for a State of Emergency in Los Angeles County due to the ongoing natural gas leak. The proclamation allows all state agencies to use state personnel, equipment and facilities to ensure a continuous and thorough state response to the incident. Read more on the proclamation.

On Jan. 4, Gov. Brown, along with SoCalGas executives and state agency leaders, visited the gas storage facility to discuss the latest in the progress of capping the leaking well at Aliso Canyon gas storage facility. Gov. Brown also visited with residential neighborhood leaders of the Porter Ranch community to discuss the impacts of the gas leak on the area.​

​​Responding To The Leak

​The California Governor’s Office of Emergency Services (Cal OES) has established an incident command structure to coordinate local, state and federal actions to bolster SoCalGas’ efforts to stop the leak and ensure public safety. This effort includes operating a physical incident command post on-site at Aliso Canyon that is staffed by SoCalGas 24 hours a day, 7 days a week. Cal OES is also coordinating information sharing among governmental agencies to ensure governmental actions are efficient and publicly transparent.

Since discovery of the leak on Oct. 23, a team of experienced technical experts from the state’s Division of Oil, Gas and Geothermal Resources (the Division) has directed oversight of SoCalGas’ efforts to stop the leak at Aliso Canyon. These experts have been on-site during all operations and are evaluating every step of SoCalGas’ efforts to determine the most effective way to seal the well. These technical experts oversee all plans and actions at the site, including monitoring the wellhead and inspecting the well. The Division has also convened a panel of technical experts from the Lawrence Berkeley National Laboratory, Lawrence Livermore National Laboratory and the Sandia National Laboratory to provide independent expertise to assist in monitoring and evaluating SoCalGas’ actions.

On Nov. 18​, the Division Supervisor issued an emergency order to ensure no delay exists to execute all possible efforts to stop the gas leak, including the drilling of relief wells below the leak to stop the flow of natural gas. The Emergency Order was issued to ensure that SoCalGas is planning and implementing all feasible pathways to stop the leak. SoCalGas is currently complying with the Emergency Order. On Dec. 10​ a second emergency order to SoCalGas requests additional data, testing, daily briefings, and a schedule for identified pathways to seal the well.​​

On Dec.​ 18, Governor Brown issued a letter to the CEO of SoCalGas. The letter notes that the Governor has directed numerous state agencies to take action in investigating the well and the public health concerns surrounding the leak. Download the letter​​.

On Jan. 6, Gov. Brown issued a State of Emergency declaring, at the direction of the Governor's Office of Emergency Services, all state agencies will utilize state personnel, equipment, and facilities to ensure a continuous and thorough state response to this incident. The Governor's Office of Emergency Services will also provide frequent and timely updates to residents affected by the natural gas leak and the appropriate local officials, including convening community meetings in the coming weeks.

Infographics of relief well phases from SoCalGas
Graphic: SoCalGas

​​Public Health


​​On Nov. 19, the Los Angeles County Department of Public Health​ issued a Public Health Directive​ to SoCalGas. This directive ordered the gas company to continue the abatement process, eliminate odorous emissions and provide free, temporary relocation to residents that choose to relocate. View the department’s correspondence with SoCalGas. Los Angeles County Public Health Department also issued a Supplemental Directive to SoCalGas on Dec. 16​ requesting to work directly with Los Angeles Unified School District on logistical support in placing students and staff in alternate locations outside of the impacted area.​

On Dec. 15, South Coast Air Quality Management District filed an Order for Abatement that would require SoCalGas to comply with statues or rules being violated. A Hearing Board will hear the Order on Jan. 9 for further action.

On Jan. 15, Office of Environmental Health Hazard Assessment announced the appointment of eight physicians and scientists to the independent panel. Each of the members are recognized experts in areas related to the issues raised by the gas leak. They represent six campuses within the University of California (UC) system and include experts in medicine, toxicology, epidemiology, and exposure sciences. Read the full list of experts.

​​State Evaluation Of Public Health Concerns

​​California’s lead state agency for the assessment of health risks posed by environmental contaminants is the Office of Environmental Health Hazard Assessment (OEHHA​​). Experts at OEHHA have engaged in a review of public health concerns i​​n order to provide an independent assessment of the situation. These experts have also reviewed directives from local agencies and other measures that are in place to protect public health in order to determine if they are adequate. OEHHA experts have consulted with the South Coast Air Quality Management District (SCAQMD​​) and the Los Angeles County Department of Public Health to access air monitoring data that identifies any public health risks that may posed by Volatile Organic Compounds (VOCs​​) found in Porter Ranch neighborhood air samples.​ The SCAQMD has developed a website for issues concerning the gas leak and compliance.

​​​​​What Has Been Evaluated?

​The air quality samples being assessed by OEHHA measure the presence of VOC in the Porter Ranch community and are part of ongoing data from SoCal Gas air sampling collection sites. Learn more about OEHHA's evaluations and monitoring.

Air Sampling Collection SItes Google Map

What Were The Results?​​​​

Natural gas by itself is odorless. Tertbutyl mercaptan and tetradydrothiophene are added to the gas so it can be detected by smell. These odors have a similar sulfur-like smell of rotten eggs. These chemicals were not detected in the Porter Ranch neighborhood air samples. Also, these odorants are not toxic to the human body nor do these odorants present a sustained risk to a person’s health at the levels found in the community​. However, the strong odors these materials create can provoke temporary symptoms such as headaches and nausea in some individuals.

The most notable, and expected, Volatile Organic Compound that emerged in the sample results was Benzene – a chemical that is a colorless or light yellow liquid at room temperature. It has a sweet odor and is highly flammable. Benzene is found in the air from emissions from burning coal and oil, gasoline service stations, motor vehicle exhaust, cigarette smoking. At certain levels, it is considered very harmful to health. Learn more about Benzene​.

​​​​The highest benzene level in the Porter Ranch community (observed on 11/10/2015) was approximately half of the level that is considered a potential short-term health risk.​​​

​What Do State Experts Conclude?

Based on the air sample data from the Porter Ranch neighborhood and measured levels of Volatile Organic Compounds found, there does not appear to be an acute toxicity health hazard from Volatile Organic Compounds in the Porter Ranch neighborhood as a result of the Aliso Canyon natural gas leak.

However, this does not mean that the adverse physical symptoms reported by many Porter Ranch neighborhood residents are not real. The natural gas odorants have strong odors that can be perceived at concentrations below the levels that can be detected in air samples. These odors can evoke physiological responses (such as nausea and headaches) without inducing toxicity and lasting health impacts (such as eye or respiratory system damage).

Learn more a​bout how experts evaluate the health risks and Acute REL’s​.​

Report public health issues or  file a complaint online​ to the Los Angeles County Department of Public Health​.

​​Measuring Methane Emissions

The California Air Resources Board (CARB​​) is monitoring total methane emissions — a powerful greenhouse gas — over the duration of the leak using measurements from the ground, airplanes and satellites. The air board has also directed SoCalGas to provide its data on the volumes of gas within the storage field in order to refine its estimates on total emissions. Natural Gas is composed primarily of methane (approximately 80%), which is a potent greenhouse gas. Methane is in a category of greenhouse gases known as short-lived climate pollutants. These types of gases remain in the atmosphere for a much shorter period of time than longer-lived climate pollutants, such as carbon dioxide (CO2); but when measured in terms of how they heat the atmosphere, their impacts can be tens, hundreds, or even thousands of times greater than that of carbon dioxide. In order to quantify the methane release rate from the Aliso Canyon gas leak, state agencies in collaboration with the research community, are collecting measurements at the well site near the ground, from towers, airplanes and satellites.​

​Aliso Canyon Air Sample Results​​

A complete calculation of the total methane emitted from the gas leak based on a full set of data and an assessment of any changes in methane release rate over the duration of the leak will take several months to complete. View a preliminary estimate of the ​methane release rate​.​  View the page on Community Methane Monitoring in Aliso Canyon​​​​.​

The California Air Resources Board conducted another fly over survey of the leaking well site on Jan. 21. Information from this flight indicates a reduction of 70 percent in the amount of leaking methane since the peak in late November. View more flight information.

Investigations Into The Leak

​The Division​ has launched an investigation to determine the cause of the gas leak and whether any regulatory or statutory violations occurred. This investigation will include analyzing the inner workings of the leaking well.​

The California Public Utilities Commission (CPUC​), which regulates natural gas utilities, has also launched a staff investigation​ of SoCalGas’ actions before and after the incident, including whether proper public notification was provided and maintenance of the gas storage field in general. CPUC staff also requested information from the company on the costs of containing the leak. The Division and CPUC have also directed SoCalGasCo to retain an independent, third party to perform a technical analysis of the well failure and its cause. SoCalGas will cover the expenses of this independent analysis at no cost to ratepayers. Analysis results will be shared with regulators and the public. View more specific analysis. The Division and CPUC, on Dec. 11, also ordered the company to explain how quickly the storage field can be drained to reduce pressure on the leak while preserving reliability of gas for ratepayers.

CPUC and the California Energy Commission (CEC​)​ is also working to ensure there are adequate energy supplies for homes and businesses through the winter.

​On Jan. 15, the Department of Conservation issued notice of its intent to propose the adoption of emergency regulations necessary to protect public health, safety, and the environment by ensuring the immediate implementation of protective standards for all underground gas storage projects in the state. The emergency regulations will be established under the emergency rulemaking process to ensure that regulations are in place while the permanent regulations are being finalized. View the public notice.

View the proposed emergency regulations.


Worker Safety​

T​he Division of Occupational Safety and Health (Cal/OSHA​) has monitored the well breach site to ensure worker safety and compliance with workplace safety laws and regulations.​​​​​​​


Related Documents

Many state agencies have a role in the oversight to the response of the natural gas leak at Aliso Canyon. Read the fact sheet (pdf).

On Dec. 18, Governor Brown issued a letter to Chief Executive Officer of SoCalGas Company. The letter notes that the Governor has directed numerous state agencies to take action investigating the well and the public health concerns surrounding the leak. Read or download the letter.


State of California Natural Resources Agency Department of Conservation Division of Oil, Gas, and Geothermal Resources issued an Emergency Order to SoCalGas to provide data.​​


State Oil and Gas Supervisor Dr. Bohlen's statement from the Dec. 2 Porter Ranch Community Meeting.


CARB sent a letter to SoCalGas noting that CARB is coordinating activities to measure the leak rate and estimate total emissions over the duration. The letter includes questions for SoCalGas in regards to support of ongoing efforts to quantify emissions.

Information from the Department of Conservation about the Aliso Canyon Natural Gas Leak.


The Air Resources Board has released monitoring information regarding Aliso Canyon.

Additional​ Resources

​​​SoCalGas Aliso Can​y​on Icon Los Angeles Unified School District Logo ​City of Los Angeles Emergency Management Department​ LogoCity of Los Angeles 311 Logo
​​​​ LA Mayors Office Logo Notify LA Logo LA County Office of Emergency Management Logo LA County Logo
​​​​​LA County 211 LogoLA County Public Health Logo



Is it possible or practical to close down the Aliso Canyon storage facility? Is it possible or practical to close down the Aliso Canyon storage facility? <p>​The CPUC has been working diligently with the Division of Oil, Gas & Geothermal Resources (DOGGR) to support DOGGR’s efforts to shut down the leaking well. It is not clear at this time that shutting down the facility would abate the leak. It is also not clear what the ramifications for gas reliability and electricity prices would be from a sudden shut down of the facility.​</p>
The California Public Utilities Commission (CPUC) doesn’t have a lot of authority over natural gas storage wells, but could the CPUC could (or is it considering) expanding its oversight of storage facilities, in light of SB 1371 and the Porter Ranch leak?The California Public Utilities Commission (CPUC) doesn’t have a lot of authority over natural gas storage wells, but could the CPUC could (or is it considering) expanding its oversight of storage facilities, in light of SB 1371 and the Porter Ranch leak?<p>​The CPUC does not have operational and safety jurisdiction over the injection/withdrawal wells at natural gas storage facilities. However, the CPUC has regulatory, safety, and operational authority over SoCalGas and gas pipelines. The intention of SB 1371 and subsequent CPUC proceedings was to consider methane emissions from gas pipelines. The assigned Commissioner and Administrative Law Judge will consider any requests for expansion of scope through the standard proceeding procedure. In addition, the CPUC could exercise its regulatory authority over gas storage fields to reduce methane emissions pursuant to Public Utilities (PU) Code Section 451 and AB 32 – after the CPUC determines the breadth of this issue and identifies possible solutions. The CPUC has required SoCalGas to hire an interdependent third-party to conduct a root cause analysis to determine the reason for the leak. After this analysis is completed, the CPUC will use the information to inform future actions.​</p>
What authority does the CPUC currently have and could it take on more oversight of storage facilities?What authority does the CPUC currently have and could it take on more oversight of storage facilities?<p>​The CPUC grants operating permits – Certificates of Public Convenience and Necessity – to natural gas storage providers pursuant to PU Code Section 1001. One of the CPUC’s primary jurisdictional responsibilities with respect to gas storage fields is to ensure there is enough storage in California to meet demand. See PU Code Section 3368. SoCalGas and PG&E are rate regulated utilities, so the CPUC has authority over the recovery of costs of the utilities for operating the gas storage facilities that they own, like Aliso Canyon. The CPUC also has authority to ensure that SoCalGas’s actions in response to the leak are reasonable.<br></p>
What impact would a shutdown have on consumers?What impact would a shutdown have on consumers?<p>​The CPUC is analyzing this issue, in conjunction with other agencies including DOGGR, the California Energy Commission, and the California Air Resources Board. At this time, it is not clear what the magnitude of the impact would be. Due to the size of the storage facility, the CPUC is concerned about the cost and reliability impacts of a sudden shutdown.<br></p>


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