Methane Mitigation System for Buildings 14

Methane Mitigation Systems for Buildings

A methane mitigation plan eliminates the hazards of methane soil gas intrusion. Without proper methane mitigation, vapors can migrate through foundations and into buildings. This causes an accumulation of methane gas and leads to explosive and asphyxiation hazards.

In Los Angeles, these plans are created for projects within Methane Zones or Methane Buffer Zones. Additionally, plans require review and approval of the building department. Furthermore, design parameters of a  methane mitigation system are based on the results of a methane soil gas test.

The geologists and engineers at Geo Forward, Inc. are experienced with the latest design standards and building codes. Geo Forward, Inc. specializes in designing these systems for commercial and multi-tenant residential projects.  Moreover, Geo Forward, Inc. specializes in subterranean parking garages, underground vaults, basements and more. Comprehensive mitigation plans summary reports are provided. Lastly, Geo Forward, Inc. provided construction support and oversight. Call us at (888) 930-6604 to speak with a licensed geologist or engineer.

Methane Mitigation Barrier System. Methane Barrier Deputy Inspection Photo.

Methane Mitigation Barrier System. This photo taken during methane deputy inspection.

City of Los Angeles Methane Mitigation Requirements

The City of Los Angeles established high-risk “Methane Zones” and “Methane Buffer Zones.” These zones may require mitigation. For properties in a Methane Zone or Buffer Zone, the needs to abide by the Los Angeles Department of Building and Safety (LADBS). Per Ordinance No. 175790 of the Los Angeles Municipal Code, buildings shall provide a methane mitigation system based on the appropriate Site Design Level.  A Site Design level is based on the data reported during the methane soil gas test.

There are five LADBS Site Design Levels. Each requires different parameters. The methane mitigation requirements increase with each Site Design Level. Mitigation Plans can include specialized ventilation systems that are either “Passive” or “Active.”

Methane Mitigation Methane Barrier Installation

© MTA Capital Construction

Passive Vapor Mitigation Systems

Passive Methane Mitigation Systems (also referred to as Passive Ventilation Systems) are designed to remove methane gas from the subsurface, without mechanical influence.  A Passive Methane System relies on the natural rising characteristics of methane to capture the accumulations of gas underground. The gas naturally flows upwards into the atmosphere by earth pressure.

Passive Methane Mitigation Subsurface Piping

Passive Methane Mitigation System

Active Vapor Mitigation Systems

Active Methane Mitigation Systems (also referred to as Active Ventilation Systems) are comprised of subsurface gas extraction systems. These systems are blower or pump activated. Moreover, HVAC systems accelerate indoor ventilation. Additionally, an Active Methane Mitigation System includes methane gas sensors and an alarm system. This warns occupants of peaking methane concentrations.

Active Methane Mitigation Systems Include a Methane Gas Alarm

Active Methane Mitigation System – A Methane Gas Alarm

De-watering & Waterproofing in Methane Mitigation

De-watering systems lower the groundwater table to a level below the bottom of a soil-gas ventilation system. Waterproofing barriers prevent groundwater from passing through a methane barrier. Geo Forward, Inc. specializes in designing de-watering systems and waterproofing barriers. This process involves communication with the architects and local building departments.

For more information about methane mitigation plans, call (888) 930-6604 to speak with an expert. 

Geo Forward, Inc.

Forward-Thinking Geologists, Engineers & Contractors!

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14 thoughts on “Methane Mitigation System for Buildings

  • Azad A. Kaligi, PG Post author

    Hi Harvey. The quick answer to you question is: Yes.

    As mentioned above, there are different methods (and design-parameters) for methane mitigation systems. Low level methane sites will normally require just a passive methane mitigation system. On the other hand, high level methane sites will generally require both: a passive system and an active methane mitigation system. Typically, sites with higher methane soil gas concentrations will require a greater amount of design-effort, and therefore will cost more than lower the level sites. Sometimes a de-watering system may be required, and is typically designed hand-in-hand with the methane mitigation system. De-watering can also factor into a higher cost for design and construction.

    Lastly, pricing can also vary depending on the complexity of the proposed development. Structures with larger building footprints, multiple subterranean levels and intricate architectural features can increase the time and effort required to properly design a methane mitigation plan.

    I hope this helped. If you have any other questions, feel free to call me anytime at (888) 930-6604 extension 700.


    Azad Kaligi, PG

  • Andrew Ramos

    We need to build an underground vault to house solar electrical components. The vault will be outside and away from the building. After the methane probe survey we learned that the property needs a passive methane mitigation system and active methane mitigation system. Methane gas in soil was high. Is it possible to install both an active mitigation system and a passive mitigation system in a underground vault? Will the methane mitigation plan change our electrical plan?

    • Azad A. Kaligi, PG Post author

      Hi Andrew, Yes: It is possible (and practical) to design and install a methane mitigation system for an underground vault that consists of both: a passive mitigation system; and an active mitigation system. Your electrical plan is not likely to change. However, the methane mitigation plan will most-likely call for certain electrical components to be used (inert and fireproof materials) and will also require the use of sealed conduits and fittings. Id be happy to look through your plans and provide more information about methane mitigation. Please feel free to call me at (888) 930-6604 extension 700 for details.


      Azad Kaligi, PG

    • Azad A. Kaligi, PG Post author

      Hi Travis.

      (When dealing with the Los Angeles Department of Building and Safety for methane mitigation)

      Although similar, sites which require methane mitigation in “methane buffer zones” have slightly different design parameters than sites in “methane zones.” These parameters ultimately depend on the level of methane soil gas concentrations detected during your methane probe test. In some cases, methane mitigation may not even be required for sites in a “methane buffer zone” with low enough concentrations. On the other-hand, all sites within a “methane zone” will require some level of methane mitigation, even if the methane probe test results are low. Hope this answers your question.


      Azad Kaligi, PG

    • Azad A. Kaligi, PG Post author

      Hi Gregg. Yes it is. A de-watering plan can also be prepared separately from a methane mitigation plan if preferred by the design team and plan checker. Per the standards of the City of Los Angeles Department of Building and Safety and most other agencies such as the Hunting Beach Building Department and Los Angeles County Public Works, the de-watering plan is best integrated into the passive methane mitigation system design.

    • Azad A. Kaligi, PG

      Hello Janet.

      In most areas around Southern California: Yes. There are different methods of methane mitigation for single-family residential structures than there are for commercial and industrial structures. For the most part, multi-family residential methane mitigation plans parallel the commercial and industrial standards. In the grand scheme of things, the intention is to design a system which is economically feasible to developers, practical for the building and functional to the occupants, meanwhile meeting all the minimum requirements of the local methane mitigation building departments.

    • Azad A. Kaligi, PG Post author

      Hi Kristen, Generally – Yes. However conditions vary. For an example: a larger slab-on-grade project (25,000 square feet warehouse) can be costlier than a smaller sub-grade project (1,500 square feet parking garage).

    • Azad A. Kaligi, PG Post author

      A passive mitigation system is a sub-slab ventilation system designed to remove methane gas from the area directly under a building. This does not include mechanical devices, and solely relies on the natural rising effect of CH4 gas. Pipes redirect the soil gas into the atmosphere above the building. It is purposed to prevent soil vapor intrusion into buildings.