Los Angeles sits on top of one of the largest urban oil fields in the United States. For more than a century, drilling operations ran beneath what are now homes, schools, and shopping districts – and they left behind thousands of abandoned and idle wells. Many of those wells still leak methane today, and that invisible legacy is the reason much of the city is mapped into official methane zones that require methane testing before construction.
A City Built on Oil
From the Salt Lake Oil Field beneath the Fairfax District to the Inglewood Oil Field and the derricks that once crowded downtown, oil production shaped Los Angeles. As the city grew, wells were capped and built over – often decades before modern abandonment standards existed. Aging casings and improperly sealed boreholes create pathways for gas to migrate toward the surface.
The Explosion That Changed the Rules
In 1985, methane that had accumulated beneath a Ross Dress for Less store in the Fairfax District ignited, injuring more than 20 people. The blast led directly to the City of Los Angeles methane ordinance and the Methane Zone and Methane Buffer Zone maps that LADBS enforces today. If your property falls inside one of these zones, a methane soil gas survey is typically the first step of any permit.
Why Abandoned Wells Still Matter
Orphaned wells – those with no responsible operator left – can vent methane for decades. The gas moves through soil, collects beneath slabs and in enclosed spaces, and can reach combustible concentrations without any warning signs at the surface. State and local agencies continue to identify and re-seal legacy wells across the LA basin, but testing remains the only way to know what is happening under a specific site.
What Property Owners and Developers Should Do
If you are buying, developing, or re-permitting property in a methane zone – or near known historic drilling – plan for three steps: a records review of nearby wells, a soil gas investigation with shallow probes to measure methane concentrations and pressure, and, where levels warrant it, an engineered solution such as a sub-slab vent system and membrane through methane mitigation construction.
Sway Features designs and installs LADBS-compliant methane testing and mitigation systems across Los Angeles. If your project sits over the city’s oil-field past, contact us and we will help you find out what is under your site before it becomes a problem.