Environmental Engineering and Contracting

Arroyo Geoscience Inc., Geotechnical Engineering, Glendale, CA
Arroyo Geoscience Inc., Geotechnical Engineering, Glendale, CA

Office: 818-967-5977

A-HAZ Engineering Contractor Lic. No. 1062092

Methane Zones in Los Angeles

A methane zone in Los Angeles refers to a specific area within the city that the local government has identified as having a significant amount of underground methane gas.
Gas methane bubbles frozen in blue ice.

A methane zone in Los Angeles refers to a specific area within the city that the local government has identified as having a significant amount of underground methane gas. Another type of zone, known as the methane buffer zone, surrounds these methane zones and indicates areas with lower methane gas concentrations.

To ensure the safety and success of construction projects within methane zones and methane buffer zones in Los Angeles, it is crucial to understand what they are, how to conduct appropriate tests and implement methane mitigation systems, if necessary.

What is a Methane Zone?

In Los Angeles, a methane zone refers to an area designated by the Los Angeles Department of Building and Safety (LADBS) where elevated concentrations of methane gas exist underground.

These concentrations correspond to the city’s current and historical oil wells and oil or natural gas production fields. City authorities may also designate methane zones around landfills or areas featuring naturally occurring methane sources, such as crude oil or tar.

A methane zone surrounds the Los Angeles City Oil Field. The LADBS has also designated methane zones in numerous other Los Angeles County areas and neighborhoods. Examples include Cheviot Hills, Inglewood, Venice Beach, Las Cienegas, Playa Del Rey, Union Station, and Boyle Heights.

What is a Methane Buffer Zone?

A methane buffer zone is a designated area surrounding a known buffer zone, acting as a border separating it from non-methane zones. Methane buffer zones contain lower concentrations of underground methane gas.

Methane buffer zones also help ensure the safety and protection of neighboring non-methane areas. They act as a protective barrier to prevent methane gas migration from the methane zones into surrounding regions.

Most methane zones are surrounded by methane buffer zones, except in select areas where construction is impossible, such as oceanfront locations.

Methane Properties and Safety Risks

Methane (CH4) is a colorless, odorless, highly flammable greenhouse gas. It is the main component of natural gas. Methane typically forms from decomposing organic material in natural environments, like swamps, marshes, and artificial areas, like landfills and sewage treatment facilities.

According to the United States Geological Survey (USGS), methane can migrate into water wells and accumulate in confined spaces. While methane gas is not toxic or irritant, its presence in the air displaces oxygen, presenting a risk of asphyxiation by oxygen deficiency.

Other methane risks are related to the gas’s flammability. When exposed to an ignition source, such as a spark or an open flame, even a small concentration (5% or more) creates a severe risk of fire or explosions.

Methane Hazards in Construction

Besides the health hazards and the risk of fire and explosion, construction projects in methane zones present additional risks if not mitigated. Common construction tasks, such as trenching or drilling, can release methane gas from underground pockets and accumulate in enclosed areas.

Proper monitoring and ventilation systems are essential to prevent methane buildup and ensure a safe working environment for construction workers. Additionally, specialized equipment, such as methane gas detectors, designed to handle methane-sensitive environments may be necessary to minimize the risks associated with construction activities in these zones.

How to Mitigate Risk in Methane Zone Construction Projects

Methane mitigation is crucial for the safety of construction workers and future residents of the construction project; it is also required by law in the Los Angeles Municipal Code (LAMC).

According to Ordinance 175,790, the LADBS can withhold construction permits for projects in methane and buffer zones. They may issue construction permits in two cases only:

  • Methane mitigation systems suitable for the highest risk level have been installed
  • LADBS-approved methane testing protocols have revealed the construction site has a lower risk level than the maximum
  • The construction project is for an excepted building under LAMC Sections 91.7104.3.2 and 3.3

Methane Zone Risk Levels Defined

The LAMC defines methane risk levels and appropriate mitigation methods with the Site Design Level designation in Table 71 (Section 91.7109.2). Site Design Levels range from Level I to Level V, with Level V representing the highest methane concentration levels.

  • Level I: 0 to 100 parts per million by volume (ppmv) of methane
  • Level II: 101 to 1,000 ppmv
  • Level III: 1,001 to 5,000 ppmv
  • Level IV: 5,001 to 12,500 ppmv
  • Level V: Over 12,500 ppmv

For construction projects located in a methane buffer zone, LAMC Section 91.7104.3.6 states that methane mitigation systems are not required if the area is:

  • Site Design Level I or II
  • Site Design Level III, if fitted with trench dams and seal fittings for cables or conduits.

Site Testing

The higher the Site Design Level, the more stringent the minimum methane mitigation requirements. By default, the LAMC requires construction project developers to submit a methane mitigation plan suitable for a Level V site.

The best and most accurate way of determining proper methane mitigation is to contact a geo-engineering contractor to perform an LADBS-approved methane test. If the methane test results demonstrate a lower risk level than Site Design Level V, the LAMC allows developers to apply the methane mitigation systems appropriate to that level.

Types of Methane Mitigation Systems

Various methane mitigation systems are defined as legal in the Los Angeles Municipal Code (Section 91.7102). Approved methods and construction techniques are divided into passive and active categories.

Passive methane mitigation includes barriers, membranes, and passive methane gas removal systems. They include:

  • Sub-slab ventilation systems
  • Vapor barriers
  • Gas-impervious membranes
  • Gravel blankets
  • Passive ventilation systems

Active methane mitigation includes all passive systems plus elements designed to detect and extract methane gas from the substrate. These approaches include:

  • Methane sensors
  • Alarm systems
  • Gas extraction systems
  • Active ventilation systems

What to Do if Your Construction Project is in a Methane Zone

If your project is in a methane zone, the best solution to maintain safety without going over budget is to contact a professional geo-engineer for a methane test.

While the law allows you to forgo methane testing if you implement methane mitigation suitable for a Level V site, doing so can be unnecessarily costly. A methane test lets you determine the exact methane concentration levels under your construction site.

If the test results demonstrate your Site Design Level is less than V, you can safely and legally implement the mitigation methods appropriate to the detected level. This maintains maximum safety while ensuring compliance with the law.