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Methane Soil Gas Survey

Methane Soil Gas Survey

The purpose of a methane soil gas survey is to test a property for subsurface methane and hydrogen sulfide hazards. This is in order to determine the proper methane mitigation design parameters for future development. Methane is an odorless gas that can migrate underground (through soil and structure foundations), and accumulate inside buildings. In fact, it stems from natural gas, which originates from the geological decomposition of subsurface organic matter. In most cases, the hazardous accumulations of the gas are in association with oil and gas fields, natural gas extraction wells, and landfills. Awareness of the hazards of subsurface natural gas rises from methane gas explosions in Los Angeles during 1985. Since then, various building departments and public works agencies require a methane soil gas survey or a comprehensive mitigation plan within specific methane hazard zones.

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Where are Methane Soil Gas Surveys Needed?

During the late 1800s and early 1900s, oil and gas production was predominant in central and southern California. In fact, southern California is rich in crude oil and has an extensive history of oil and natural gas drilling and extraction.

Methane Zones Map

In recent years, the City of Los Angeles established high-risk “Methane Zones” which require methane soil gas surveys or mitigation before undergoing construction or demolition. Per the city’s map, there are methane buffer zones and methane zones. And each zone applies a specific set of mitigation standards, on the basis of methane test results. Similarly, various public works agencies across the nation are beginning to implement the mitigation standards. Citywide methane mitigation requirements (for Los Angeles) are available in Ordinance No. 175790 and Ordinance No. 180619.

Other Hazard Zones

Unincorporated cities within Los Angeles County boundaries fall under the jurisdiction of the County’s Methane Mitigation Unit. For instance, the City of Long Beach is outside of the LADBS (LA City) jurisdiction but is within the LA County’s boundaries. Thus, cities within the LA County jurisdiction generally require methane soil gas surveys at sites within 1,000 feet of a landfill or 300 feet of an oil & gas well. Accordingly, the County Los Angeles Building Code and it’s methane soil gas policies are available in Ordinance No. 2002-0076. Similarly, the City of Huntington Beach (as well as other cities in Orange County) also require a methane soil gas survey and mitigation standards in hot spots.

Typical Soil Gas Probe Set schematic for a Methane Soil Gas Survey

City of Los Angeles Methane Soil Gas Probe Survey Diagram

Building Department Methane Soil Gas Surveys

Geo Forward offers methane and hydrogen sulfide testing services to meet the requirements of all building jurisdictions in California. Our sampling and testing plans include determining site design levels, locating nearby zone boundaries or hazards, installing soil gas probes, and conducting air quality analysis when necessary. A standard methane soil gas survey tests the shallow soil gas underlying a property, for fast results from the field.

Limited Methane Soil Gas Surveys for Real Estate Due Diligence

When a comprehensive methane soil gas survey is not a requirement by local building departments, property owners can request a limited methane survey for due diligence and risk assessment purposes. However, if concerning levels of the natural gas substance is observable, the findings of a limited test may warrant a follow-up methane survey, in order to achieve a comprehensive understanding of subsurface conditions. This process can also be an addition to the Phase 2 Subsurface Investigation process, when necessary.

Methane Soil Gas Survey Probe Set

Permanent Methane Soil Gas Prove Set at a Landfill Site

Methane Mitigation Plans

After a methane gas survey, engineers prepare a methane mitigation plan to eliminate the hazards of the natural gas intrusion. Local building departments may also require methane mitigation plans to reduce health-related dangers such as asphyxiation or explosion. Additional to natural gas investigations, Geo Forward also provides methane mitigation design services and methane mitigation plans for all types of construction projects. Moreover, Geo Forward also offers deputy inspection services during construction.

For more information about methane soil gas surveys and mitigation, please call (888) 930-6604 to speak with a professional geologist.

Sources of Information:

U.S. EPA Guidance for Methane Landfill Gas Sampling & Testing
City of Los Angeles, Department of Building & Safety
The Methane Zone – The Land Developer’s Guide

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