Well Blowout and Public Health Disaster

On October 23, 2015, the largest gas blowout in the history of the United States began at the Southern California Gas Company’s Aliso Canyon gas storage facility. An estimated total of 109,000 metric tons of methane flowed uncontrolled from Aliso Canyon Well SS-25 until it was successfully sealed 111 days later, on February 11, 2016.

As a result of the blowout, people in neighboring communities experienced “rotten egg” odors, oily mists, and acute health symptoms, including eye, nose, and throat irritation, headaches, and respiratory symptoms. Public Health responded to thousands of health problems experienced by residents and directed relocation of over 8,000 households. Many residents reported ongoing health problems after returning home from relocation and expressed concerns about potential long- term health effects.

Detailed information on the Well SS-25 failure is now available.

Public Health’s Role in the Blowout and Disaster

From the beginning of the blowout, SCAQMD collected and analyzed air samples to monitor the levels of chemicals being released at the facility and reaching the community. In January 2016, Public Health reviewed air data on a daily basis and made recommendations to expand sampling to include more community air sampling locations, expand testing for additional chemicals, and increase sample collection times.

Public Health issued a directive to the Southern California Gas Company to expedite efforts to stop the blowout and, in the interim, offer free, temporary relocation to affected residents. Public Health also directed the Southern California Gas Company to work directly with the Los Angeles Unified School District to assist in relocating affected students to alternate locations outside of the impacted area.

Following the sealing of the well, outdoor air monitoring was continued by the California Air Resources Board and the South Coast Air Quality Management District, with Public Health addressing community health concerns and consulting with local and state regulatory agencies. Public Health also continued to actively monitor and assess environmental and health issues related to the disaster, recording ongoing symptoms reported by residents. Public Health tested indoor air and dust in some area homes and, based on the results, directed Southern California Gas Company to pay for professional comprehensive cleaning of the homes of area residents. Public Health designed a cleaning protocol and secured a ruling from the Los Angeles Superior Court requiring the Southern California Gas Company to offer interior cleaning to residents relocated at the time of the ruling.

The County joined with local and state public agencies in the lawsuit against Southern California Gas Company, successfully advocating for the inclusion of a health study in the Settlement.

Detailed information on Public Health’s response is now available.


On August 8, 2018, California Attorney General Xavier Becerra, along with the California Air Resources Board, Los Angeles City Attorney Mike Feuer, and the County of Los Angeles secured a $119.5 million settlement with Southern California Gas Company over the Disaster. As part of this settlement, $25 Million was secured for a long-term health study.

A Breakdown of the settlement is now available.

Detailed information on the settlement is now available.