Unveiling the Impacts: The UCLA Porter Ranch Study on the Aliso Canyon Gas Blowout

The Aliso Canyon gas blowout, a significant environmental crisis, began on October 23, 2015, and persisted until February 11, 2016. This disaster, the nation’s largest natural gas blowout, prompted a comprehensive, five-year study by UCLA scientists to understand the health consequences for the communities living and working in proximity to the blowout. The UCLA Aliso Canyon Disaster Health Research Study aims to assess both the short- and long-term effects of the disaster and routine emissions on the health of these communities.

Background of the Aliso Canyon Disaster

The Aliso Canyon disaster released more than 100,000 metric tons of methane and ethane gas into the atmosphere from the Aliso Canyon gas well. Owned by Southern California Gas Company, the well is located in the Santa Susana Mountains near the Porter Ranch community in the San Fernando Valley. At the time of the blowout, roughly 232,200 residents lived within a 5-mile radius of the facility, with over 130,400 people living within five miles of the disaster. Nearly 12,300 (23%) were under age 19 and 18% were 65 or older. The incident led to the evacuation of thousands of people, the shutdown of businesses, and the relocation of school children.

Reconstructing the Methane Plumes

A UCLA-led research team reconstructed the evolution of methane plumes from the 2015-16 Aliso Canyon gas blowout. By using a mix of airborne and satellite images, as well as data from ground sensors, they determined how the shape and reach of the methane plumes evolved during the 112-day disaster.

The study found that methane plumes from the Aliso Canyon gas storage facility likely reached at least 6.2 miles downwind from the blowout site into the nearby Porter Ranch neighborhood in northwestern Los Angeles County. This reach extended from the beginning of the disaster in October until its end in February. The study also confirmed earlier estimates of total emissions of nearly 100,000 metric tons of methane during the blowout, which is equivalent to 20% of all of California’s annual methane emissions and double the typical methane emission rate for the Los Angeles Basin.

To determine the reach and intensity of the methane plumes, the research team reviewed cloud-free images of the site captured by the Landsat-8 and Sentinel-2 satellites to see where methane was present in the atmosphere early in the blowout event and how far it moved from the source into the nearby areas. They then used additional images collected later during the blowout - some from the Hyperion satellite and others from an Airborne Visible/Infrared Imaging Spectrometer (AVIRIS), which was flown on an airplane. The final data sets came from the California Air Resources Board’s ground monitors in the Aliso community. The two monitors collected hourly methane concentrations from December 2015 through March 2016. Researchers collected the hourly methane concentrations for the dates and times that aligned with clear-sky remote sensing images to connect and quantify correlation between satellite and ground-based observations.

Health Impacts and Community Concerns

Residents reported various health issues, including headaches, bloody noses, vomiting, and rashes. The UCLA health study team initially shared its findings in early 2024, but the results were considered preliminary at the time.

Low Birth Weight Study

Combing through more than a million county birth records from October 2010 to October 2019, researchers focused on 666 births among women living within 6.2 miles of an “impact zone” downwind of the Aliso Canyon facility who were exposed to the gas blowout for at least a month during their final trimester. The first study, published in Science Advances, found that pregnant women living near the blowout had a nearly 50% higher-than-expected chance of having a low-birth-weight baby.

Before the 2015 blowout, 6.6% of women living within the impact zone gave birth to low-weight babies. In comparison, 6.8% of women in the rest of L.A. Before the blowout, 2.6% of babies within the impact zone had term low birth weight versus 2.7% throughout the rest of L.A. County. Research has linked low birth weight to developmental disorders, such as autism and attention deficit hyperactivity disorder, as well as chronic diseases in adulthood, including diabetes, high blood pressure and some heart diseases, Jerrett said. The researchers emphasized the low birth weight is not a guarantee of these long-term effects, but that it is “an important overall indicator in public health,” said Kimberly Paul, lead author of the study and assistant professor-in-residence in the department of neurology in the David Geffen School of Medicine at UCLA.

Community Perspectives

Invisible risks: Most participants shared that their earliest memory of the blowout was the smell of gas, which gave them a sensory indication that something was “off,” but delayed and conflicting communication by local authorities led them to feel that they were left to assess and manage their own risk. Invisible harms: Unknowns about the exposure levels, length of exposure and potential health effects created a heightened state of health anxiety that continues today. Participants shared constant worry about whether they or loved ones might experience new physical symptoms or diagnoses, and whether these symptoms could be attributed to the disaster. Invisible community: Participants described persistent anger at a lack of corporate accountability and government response. Invisible changes: Participants experienced a loss of comfort and safety and altered life plans, exacerbated by uncertain future health status. Most participants in the mid-aged and young adult groups who remained in Porter Ranch shared their desire to relocate permanently, primarily due to fears about persistent exposure. Across all age groups, participants expressed uncertainty about the future and felt a lack of closure related to the blowout. The findings underscore the need for public and mental health systems to better address the long-term psychological and social consequences of environmental disasters - especially those that are not immediately visible.

Ongoing and Future Research

Michael Jerrett, an environmental health sciences professor at the UCLA Fielding School of Public Health, is a principal investigator on the Aliso Canyon Disaster Health Research Study. Soon, Jerrett said, his team will survey about 2,400 people, a quarter of whom will be selected to take part in physical examinations. In early 2026, Jerrett anticipates getting data from the California Biobank, which keeps a record of blood samples for every baby born in the state. Researchers requested 2,600 blood samples of babies born two years before the gas blowout, during the disaster, and two years after.

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The research team also will study residents’ mental health, quality of life, stress levels and even economic consequences from the blowout. The broad economic consequences from the disaster that residents may have experienced include an inability to work because of illness, or costs of medical treatment, Dr. Pourat said.

Other research includes: Monitoring the air for fine particulate matter in 40 homes within and outside the Aliso Canyon impact zone and tracking methane levels in the air. Although methane - the main component of natural gas - isn’t toxic, when high levels of methane are detected, there tends to also be higher traces of toxic elements in the area, Jerrett said.

Funding and Oversight

The UCLA study is funded through the SoCalGas settlement with the state and city and county of Los Angeles. As part of that deal, the UCLA researchers must regularly report to a scientific oversight committee established by the L.A. County Department of Public Health.

Lessons Learned and Future Preparedness

“A big lesson learned from Porter Ranch was that there wasn’t a coordinated, rapid response in place,” noted organizer Batteate. “So, what are the institutional steps necessary to make sure that health departments can respond as quickly as they need to protect people?

“The event taught at least two lessons,” said Jerrett “First, we need ongoing monitoring around natural gas storage facilities for methane and air toxics. Second, the facilities are regular emitters of air toxics such as benzene and formaldehyde. So, beyond the uncontrolled leaks, these routine emissions could also be affecting the health of nearby residents. Of note, UCLA COEH and the California Air Resources (CARB) are now collaborating on exposure monitoring and data collection at four new sites in the region.

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Significance of the Study

The study’s findings form an essential foundation for the Aliso Canyon Disaster Health Research Study team’s work to investigate the health effects of the blowout. Without knowing how far into the surrounding neighborhoods the methane plumes reached, it would be more difficult to understand who might have been affected by the blowout. The results also demonstrated the usefulness of using remote sensing data to characterize potential exposures from similar disasters.

“Leveraging multiple satellite and airborne remote sensing platforms and connecting it with data we had on the ground provided valuable footing for us to better understand the size, shape, and intensity of the methane gas released from the event,” said Daniel Cusworth, director of science at Carbon Mapper and a UCLA Aliso Canyon Disaster Health Research Study team partner.

“What we learn from this study will provide practical information about what the degree of exposure actually is, the impact on people’s health and emotional state, and even the economic consequences,” Dr. Liu said.

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