Methane Testing and Soil Gas Survey 4

Methane Testing Reports and Soil Gas Survey

Methane testing is the environmental engineering process that examines the in-situ soil gas under a property for explosion hazards. This process consists of drilling, vapor probe installation, sampling, laboratory work and a final report stamped by a professional geologist. In fact, the data from a methane test aids building departments in health and safety determinations and mitigation requirements. Methane testing and methane mitigation systems are essential for properties inside “special hazard zones.” For example, the City of Los Angeles has “Methane Buffer Zones” and “Methane Zones.” Whereas the City of Huntington Beach has “Methane Districts.” And these special zones are a result of petroleum fields and landfills. Updated March 29, 2020.

About Methane Soil Gas

Methane soil gas is flammable, colorless and odorless. Methane has a chemical formula of “CH4,” and is highly explosive. Furthermore, the gas is not detectable by a photo-ionization detector (PID), but rather a flame ionization detector (FID). Primarily, it acts as a simple asphyxiant without other significant physiologic effects when apparent in high concentrations in air.

Methane Testing Drilling

Geo Forward Methane Testing – Drilling

The Science of Combustion

The term “Lower Explosive Limit” (or LEL) means the minimum concentration of gas in the air allowable for the gas to burn (upon exposure to ignition ). This value traditionally reports in percent by volume. If the methane to air ratio is below the LEL, the mixture is “too lean” to burn or explode. On the other hand, the “Upper Explosive Limit” or “UEL” means the maximum concentration for the gas to burn. If the methane gas to air ratio is above the UEL, the mixture is “too rich” to ignite.

Methane gas has a lower explosive limit (LEL) of 5 percent, and an upper explosive limit (UEL) of 15 percent. Thus, the range of concentrations between the LEL and UEL is the hazardous explosive range. Within this range, the methane-gas-to-other-air mixtures will allow for combustion to occur.

Natural Gas Hazards

Methane is the predominant chemical compound (by volume) of natural gas. Soil gas and can migrate through geological formations into confined structures above ground. As a result, the gas accumulates inside buildings and can concentrate to combustible levels overtime. Typically, this hazard is a consequence of historical oil drilling, natural crude oil surfacing, and landfill activities. With this in mind, a methane test determines the concentrations of in situ CH4 at a property. And consequently, a methane mitigation system helps eliminate the risk of combustion.

The first oil district in Los Angeles

The first oil district in Los Angeles – Methane Testing

Hydrogen Sulfide

Hydrogen Sulfide is a product of the decomposition of sulfur-containing organic matter. This gas is easily identifiable by its initial “rotten egg” odor. Hydrogen Sulfide has the chemical formula “H2S” and it is found in many of the same areas as methane. For example, landfills, swamplands, sewer systems, petroleum fields, and waste-water treatment facilities. One dangerous characteristic of H2S is that it can impact a person’s ability to detect it’s distinct odor, overtime. For instance, at high enough concentrations, persons within a room comprising hydrogen sulfide may no longer be able to smell it after a short period of time.

H2S Exposure

Overexposure to hydrogen sulfide can lead to respiratory failure and death by asphyxiation. Upon exposure, general symptoms include dizziness, nausea, and headaches. Per the Occupational Safety and Health Administration (OSHA) the permissible exposure limit (PEL) for H2S is 10 ppm. And this value bases itself on an 8-hour time-weight average.

1985 Methane Gas Store Explosion in Los Angeles

1985 Methane Gas Store Explosion in Los Angeles – Photo by Michael Haering, courtesy of the Herald-Examiner & KCET

Purpose of a Methane Test

Methane testing is usually the prerequisite to the methane mitigation system design. Awareness on the hazards of combustible soil gas rises from a series of explosions in Los Angeles during the 1980s. Consequently, the Los Angeles Department of Building and Safety (LADBS) implements methane testing and mitigation requirements in these special zones. Similarly, other agencies, such as the County of Los Angeles, County of Orange, City of Huntington Beach, and more enforce LADBS codes. Please Click Here to view the County of Los Angeles Building Code.

1985 Department Store Explosion - Methane Test

Historical Department Store Explosion – Photo by Mike Sergieff, courtesy of the Los Angeles Public Library

1985 Department Store Explosion Due to Methane Soil Gas

On March 24, 1085, an explosion took place in a department store located in the Wilshire-Fairfax District of Los Angeles. Numerous people were injured and hospitalized, and the streets were littered with debris and structural remains. Furthermore, the disaster blew out the windows and compromised the structural integrity of the store. Based on a forensic investigation within the City of Los Angeles, scientists eventually determined the explosion was the result of high-pressure methane soil gas which accumulated inside the department store from underground.

Other Environmental Agencies

Moreover, various local, state and federal agencies, under the jurisdiction of the United States Environmental Protection Agency, have recently formed departments and units in charge of methane mitigation. In fact, the growing concern for hazardous methane gas and other subsurface contaminants is prompting these agencies to strengthen the environmental policies for developments moving forward. For example, the Texas Commission for Environmental Quality implements a Landfill Gas Management program comprised of soil gas monitoring, reporting and mitigation.

Methane Soil Gas on Fire off Sidewalk - Los Angeles 1985

Underground Methane Gas on Fire, Between Sidewalk Cracks – Los Angeles 1985

Methane Buffer Zone vs Methane Zone

The typical root causes of natural gas in the soil are historical oil fields, oil wells, gas extraction wells, crude oil pipelines, and storage ponds, as well as natural surfacing petroleum deposits. Consequently, properties with oil wells on-site usually yield higher methane gas concentrations than others. Additionally, landfills are also common sources of methane gas hazards in shallow soil. Although undocumented, there is speculation that Methane Buffer Zones and Methane Zones are a reflection of a property’s proximity to landfills and petroleum resources.

Methane Soil Gas on Fire in Storm Drain - Los Angeles 1985

Subsurface Methane on Fire, Inside Storm Drain – City of Los Angeles 1985

Reading the Hazard Zone Map

The City of Los Angeles established high-risk boundaries that define “Methane Buffer Zones” and “Methane Zones.” Consequently, these zones require a methane mitigation system when developing, unless testing results show otherwise. Similarly, other government agencies apply the same mitigation standards within their respective jurisdictions. The Los Angeles Mitigation requirements can be reviewed in Ordinance No. 175790 and Ordinance No. 180619. The diagram in the section below is a snapshot of the official LA City Methane Zone and Methane Buffer Zone Map. The purple areas represent “Methane Buffer Zones.” And the pink areas represent “Methane Zones.”

Methane Zone Map Los Angeles

Methane Buffer Zone Los Angeles vs. Methane Zone Los Angeles

Huntington Beach Methane District Testing

The City of Huntington Beach and the Orange County Fire Authority oversees engineering projects within the local “Methane District.”  The Huntington Beach Methane Overlay District is a portion of the city area which has a high methane soil gas hazards. This area is determined by historical methane testing data and information from the Huntington Beach Oil Well Finder Database. Some of the methane gas occurrences are reportedly natural and as a result of decaying shallow surfacing crude oil. However, the primary hazards are a reflection of the current and historical crude oil production wells. As a result, the City of Huntington Beach enforces methane soil testing and methane mitigation plan review for all proposed projects within the “Methane District.”

Other Hazard Zones

Additionally, some portions of Yorba Linda are similarly reported as hazard zones due to historical oil production. And the City of Santa Fe Springs (in Los Angeles County) also regulates high methane soil gas testing zones as a result of the petroleum and landfill activities.

Methane Soil Gas on Fire off Building - Los Angeles 1985

Methane Soil Gas on Fire Underneath a Building – Los Angeles 1985

Methane Testing Agency Roster

Most building departments and oversight agencies refer consumers to an official roster of certifiable testing consultants. Without valid certification, consultants are not authorized to perform methane testing and mitigation design services. Typically, agency rosters disclose each laboratory license number, a specialized area of practice and contact information. Furthermore, the rosters display each laboratory license expiration date for consumer review.

Certificate for Laboratory Testing Agency

The City of Los Angeles tends to compile all certifiable testing laboratories (of various trades) into one roster. Often times, consumers are misled into contacting welders or concrete tests when in need of methane testing. Thus, it is advised to use the “Find Tool” on your browser (Ctrl+f) to search the words “Methane Field Testing.” Additionally, consumers should also know the agency rosters lineup consultants in alphabetic order, and NOT the order of preference. Best practice suggests obtaining bids and price quotes from a variety of companies throughout the LADBS Methane Testing Consultant List.

Official Methane Soil Gas Testing Laboratory

Geo Forward is an official methane soil gas testing and mitigation design consultant for various oversight agencies and building departments across the nation. Methane test services include locating hazardous conditions, field drilling and constructing, periodic sampling, technical reporting and more. Furthermore, Geo Forward subsurface assessments are fast, reliable and include an open dialog with clients.


There are many facets to the fieldwork process of a methane test. At a minimum, the fieldwork comprises a geophysical survey and underground utility mark-out, in order to prevent damage of subsurface lines. Additionally, a state-licensed driller must advance numerous boreholes on-site, to depths ranging from 20 to 50 feet. Meanwhile, a geologist performs site mapping, soil sampling, and soil logging in detail. Soil gas probes with nested vapor implants are then constructed within each borehole, per ASTM, DTSC, EPA, and building department standards. Moreover, upon the successful calibration of laboratory analytical testing equipment, soil gas samples are collected and analyzed. And quality assurance procedures require multiple phases of sampling and analysis.

Soil Gas Survey Probe Set

Permanent Methane Testing Soil Gas Survey Probe Set


Upon the completion of fieldwork, the site-specific data is compiled into one report. The reports provide details about the standards, methods, equipment, and findings of the test. Furthermore, the reports include informative figures and tables to visually demonstrate the data. Lastly, conclusions and recommendations are provided, along with the official stamp and certification of a geologist. Methane test reports do not include mitigation plans. Instead, they determine the necessity for a methane mitigation system altogether and also provide parameters and specifications for the mitigation plan to be designed.

Soil Gas Test Containers

Soil Gas Test Containers

Landfill Gas Field Analyzer

Landfill Gas Field Analyzer


Methane Mitigation Design

A methane mitigation system prevents methane soil gas from entering a structure. The professional service is a division of the environmental engineering industry and involves intensive planning to protect the occupants of a building. Mitigation plans are custom designs and site-specific. And methane engineers utilize architectural and structural plans, as well as the methane test report, to design their system. Moreover, mitigation plans must achieve final approval by the building department, as well as the fire department. Plan checkers make sure the system parameters are in accordance with methane test data and respective building codes.

Methane Barriers & Impervious Membranes 

The overall purpose of the methane testing process is to determine the necessity for a methane barrier and mitigation system. The type of development on-site and final site design level dictates the overall requirement for a methane barrier. And depending on groundwater levels, the methane mitigation construction process may also require waterproofing and de-watering barriers.

Click here to learn more about Mitigation Design

Geo Forward is the chief provider of methane testing services and methane mitigation design services, throughout the nation. Geo Forward designs strive to meet all agency requirements, as well as developer budgets for construction. For more information or a private consultation, call (888) 930-6604. 

Forward-Thinking Geologists, Engineers & Contractors!

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4 thoughts on “Methane Testing and Soil Gas Survey

  • E. Waterra

    Hello, is it possible to predict which level classification my property will be using my neighbors methane soil test report?

    • Project Geologist II Post author

      Unfortunately not. Typical Los Angeles basin soils are known to be “non-homogeneous.” The means the soils underlying your neighbor’s lot are not likely to be exactly like yours. Especially in regards to depths, gas-mobility, moisture, gas-content, and more. As a result, methane test results at your neighbor’s lot are likely to differ from yours. We’ve been hearing complaints from callers, about one company out there saying they can “predict methane test results” with “30 years of experience.” This seems to just be a sales hook, and an unethical business tactic. The reality is that these results differ from site to site.

  • David Erickson

    Is repetitive soil gas testing a requirement for commercial buildings with permanent subslab methane testing sensors?

    • Project Geologist II Post author

      Typically yes. However, this ultimately depends on your site specifics. In general, the fire department and your methane mitigation engineer determine this necessity. It may be quarterly, semi-annual or annual.