If you’re involved in a construction project or building rehab, chances are you’ve heard an important phrase floating around: methane barrier installation. These three words hint at a specific problem that the Los Angeles Department of Building and Safety takes incredibly seriously. Methane soil gas intrusion poses an extremely dangerous risk to occupants of a building, particularly buildings that are constructed atop certain terrain like oil fields. That’s where methane barriers come into play: they’re a critical tool for making sure buildings are up to code and every visitor is safe and sound.
Installation of Methane Mitigation Systems
Methane (CH4) is a naturally occurring gas that is also the primary gas piped to your home by the utility company for cooking and heating use. In the southern California area, methane gas is found naturally in the shallow subsurface, and can be an extremely dangerous hazard that can be trapped in subterranean garages and cause explosions and fires due to its high flammability. The city of Los Angeles adopted its Methane Code in 2004, requiring methane mitigation of sites in former oil fields, in or near landfills, or swamps and marsh areas. Other agencies have followed, and now, close to 25% of all new construction in southern California needs to install some form of soil gas mitigation system to prevent vapor intrusion into crawl space or subterranean levels of buildings.
Phase I – Methane Site Testing
The first step is always to test a site for presence of methane gas. At AES, we test for concentration of methane as well as gas pressure. Sites with no methane concentration, but with high gas pressure, are often treated by agencies the same as sites with high concentrations of methane… since high pressure in the shallow subsurface can often create (or lead to) pockets of high methane concentration. Similarly, sites with evidence of former oil field-related facilities, tar seeps, and tar-stained soils are treated similarly, i.e. are designed for highest methane concentration.
Phase II – Design of Methane Mitigation System
Once the site is tested, a Site Design Level is determined, and a methane mitigation design is prepared by a professional. Suresh Basnet is an expert design engineer and Associate Partner on our Arroyo Geo team who leads design efforts at AES. In order to design a methane mitigation system, we need the Site Design Level determined during site testing, foundation plan and footing detail, and architectural site plan and cross sections to prepare a methane mitigation plan. This plan is submitted along with other construction documents for city approval.
Phase III – Installation of Approved Design
Once the plan is approved, the methane mitigation system is ready to be installed. For most projects, installation of methane mitigation system occurs early in the construction schedule, typically after grading and before concrete work. In order to work within the construction schedule, we ask our clients to provide a minimum two-week lead time prior to the installation window, to order materials and arrange labor and supervision. The installation work needs to be observed and inspected by both the city inspector as well as the deputy methane inspector at typically three stages of the installation. Most installation projects involve three primary phases of the installation, starting with subslab ventilation/piping, methane barrier installation, followed by connection of subslab ventilation to risers.
Why Are Methane Emissions Bad?
Methane is a useful resource for humans, and an abundant gas on this planet. That said, having large quantities of it leak into buildings — and into our atmosphere — is not desirable at all. Yes, methane is a greenhouse gas, making it a primary culprit in terms of negatively impacting climate change. It’s also quite noxious for humans to inhale, making it equally dangerous for both us and the planet we live on.
To this end, the city of Los Angeles has implemented some pretty strict requirements when it comes to making sure that buildings (particularly their subterranean portions) do not needlessly leak methane into the surroundings.
If you’re looking for a geotechnical engineering firm that knows how to mitigate methane leakage in a safe and cost-effective way, look no further than Applied Earth Sciences. We’ve been installing methane barriers and consulting on methane mitigation issues for years — and we have a solid established track record of proven, professional quality work.
When you’re engaged in a construction or retrofitting project, you can’t afford not to pay attention to the earth underneath your building. If you have questions about the best way to mitigate methane leakage at your site, contact the professionals at AES today!