Methane Mitigation Design

Methane Mitigation Systems are implemented within designated areas to ensure that methane soil gas vapor is incapable of intruding into buildings. Improper Methane Mitigation Designs can leave structures at risk of methane gas accumulation which may impose an explosive hazard.

The Methane Mitigation requirements are typically based on the proximity of current or historical oil and gas production, landfills, or other areas specified by your building department. The design process and requirements can vary depending on the code requirements for the city of which your property falls within. Several building departments within Southern California have establish Methane Mitigation Design code requirements including Los Angeles Department of Building and Safety, Orange County Fire Authority, County of Los Angeles Public Works Environmental Division, City of Brea, City of Montebello, and more.

Los Angeles Building and Safety Methane Mitigation Requirements

Methane Mitigation System requirements are established by the results of a Methane Test. Sway Features’ team of Engineers are experienced with the latest design standards and building codes. Our team of environmental professionals implement design optimization methods to cost effectively prevent the migration of methane gas into buildings.

Sway Features specializes in designing Methane Mitigation Systems for commercial buildings, multi-tenant residential projects, subterranean parking garages, underground vaults, basements and single-family dwellings.

The City of Los Angeles has established high-risk “Methane Zones” and “Methane Buffer Zones” based on the proximity of current or historical oil and gas production. The Department of Building and Safety developed Methane Mitigation standards which must be followed if construction falls within a Methane Zone or Buffer Zone.

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 Test.

Vapor mitigation system
Methane Mitigation System Design Features

Methane Mitigation System Design Features

There are five LADBS Site Design Levels, each requiring different Methane Mitigation System design features. The Methane Mitigation system features may include a trench dam, specialized methane extraction systems that are either “Passive” or “Active”, a ventilation system for the lowest space, and a Methane Alarm system.

Trench Dam

Trench Dams are designed to prevent Methane Gas migration through trench backfills for subsurface utilities. The design approach includes implementing a material with low permeability as a backfill substitute. Sway Features’ team implements proprietary backfill material composition that is low cost and high performance.

Passive Methane Extraction Systems

Passive Methane Extraction Systems are designed to remove subsurface methane gas without mechanical influence. A Passive 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’s pressure.

Active Methane Extraction Systems

Active Methane Extraction Systems are comprised of subsurface gas extraction fans. These mechanical Fans provide forced flow to migrate methane gas away from the sub surface of a structure. Forced Flow provides induced pressure gradients in a region to prevent the accumulation of methane below grade of a structure. sway Features implements the latest Fan Sizing data to reduce material costs and complexity of Active Methane Extraction Systems.

Methane Ventilation Systems

Methane Ventilation Systems are designed to prevent the accumulation of Methane Gas in the lowest space of a structure. Ventilation systems implement Exhaust Fans and blowers to ensure that the Indoor Air quality of a structure is continuously safe for the occupants. Sway Features’ Engineers are experienced HVAC consultants who optimize the ventilation approach to ensure that a particular design satisfies both the Methane Mitigation Code, and the ASHRAE Standard 62.2 for Indoor ventilation. Sway Features’ engineers will often collaborate with the hired HVAC consultant to ensure that ventilation designs are efficiently implemented.

Methane Alarms and Sensors

Methane Sensors are installed in the subsurface areas of a structure as well as the lowest space. These sensors are continuously monitoring concentrations of methane. If concentrations reach a threshold an active alarm system will be triggered to notify occupants of the possible Methane Hazard.

Dewatering & Waterproofing in Methane Mitigation

Dewatering 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. Sway Features specializes in designing dewatering systems and waterproofing barriers. This process involves communication with the architects and local building departments.

Methane Mitigation Construction

Sway Features offers methane mitigation construction services in all areas of California. Click Methane Mitigation Construction to learn more.

Methane Mitigation Systems

What is Methane Mitigation?

Methane Mitigation is a system installed to prevent and eliminate methane vapor intrusion into a building’s foundation and concrete walls. Methane Mitigation is necessary for buildings situated in the Methane Zone or Methane Buffer Zone. These are zones categorized by the Los Angeles Department of Building and Safety (LADBS) as those with significant methane concentration levels due to the abandoned oil wells and fields. ZIMAS can be used to verify if a project is in one of these zones and thus would need methane mitigation construction.

There is a higher risk of methane vapor intrusion if the project has a subterranean feature such as an underground garage or a basement. Methane gas vapor can quickly become explosive and asphyxiation inducing if continuously built up inside a structure. Naturally, highly concentrated methane gas from the surrounding soils would migrate into less potent spaces, usually inside a basement.

A methane mitigation plan that abides by the LADBS Methane Mitigation Standard Plans must be created to address this phenomenon. The LADBS Methane Mitigation Standard Plans were established around the time of the Ross Store explosion. To prevent another unexpected and damaging explosion from happening, the components in these tested and verified methane mitigation plans must be implemented in the methane mitigation design of all succeeding properties with a high risk of methane vapor intrusion.

The Methane Mitigation Construction will be initiated by the methane testing within the soil using soil gas probes with vapor implants placed at 5, 10, and 20 feet depths. Methane test results will use Levels 1 through 5 to categorize your project depending on the detected methane concentration. The level will dictate the number of methane mitigation requirements to be followed. Suppose results show that your property has the methane concentration level for a Level 5 property. In that case, there will be many more requirements to be followed than a project categorized as Level 1.
The methane mitigation requirements must be outlined in the methane mitigation design and ultimately implemented in the methane mitigation construction.

As you can see, methane testing must be done by a licensed methane testing agency listed on the LADBS database. A licensed methane testing consultant should then prepare the methane soil gas report. If an unlicensed company completes methane Testing, LADBS may reject the test results leading to higher methane mitigation costs.

What are the components of a Methane Mitigation Design?

The methane mitigation design must be prepared by a licensed Engineer and will reflect the methane mitigation based upon what level the property is categorized as. A project classified as Level 5 usually requires all of the components in a methane mitigation construction—a complete methane barrier, “Passive” or “Active” methane extraction systems, a trench dam, a ventilation system for the lowest space, and a Methane Alarm system.

Passive Methane Extraction Systems work with the natural flow of highly concentrated gases such as methane into areas with less concentration. Without using any mechanical arrangements, subsurface methane gas will be captured and removed through these systems.

Active Methane Extraction Systems, on the other hand, use extraction fans that are installed below the ground surface to prevent methane gas vapor accumulation and force methane migration away from the subsurface of a building, ultimately decreasing the mass diffusion rate of methane.  

Ventilation systems such as the sub-slab vent system become necessary to decrease the mass diffusion rate of methane gas. It includes exhaust fans and blowers, a perforated pipe, and a gravel blanket. Implementing this system will also depressurize the subfloor from the methane gas buildup in the area.

For a project categorized as Level 5, methane concentrations must be monitored continuously. Methane Alarms and Methane Sensors are installed for this purpose so that if concentrations reach a threshold, the alarm will be triggered to warn occupants of the possible Methane Hazard.

These components must be effectively and efficiently installed to ensure safety for the occupants. That’s why a licensed Methane Mitigation Contractor must be consulted for the methane mitigation construction to ensure all the LADBS standards are satisfied.

The methane mitigation design will change if the methane test result shows that your property is at a Level 1 Methane Buffer Zone area. It might not even require a methane mitigation construction at all. All projects are different, and the corresponding methane mitigation requirements will change; it is best to consult with the LADBS plan checker to evaluate to establish the final Methane Testing, Mitigation Design, and Methane Mitigation Construction requirements.

The methane barrier is one of the key components of a methane mitigation system. It is an impermeable membrane installed underneath the foundation and serves a seal for the concrete slab. Methane Barriers and Vapor Mitigation System have come a long way since the 1980s when the industry was initiated due to the Ross store explosion.

Methane Mitigation engineers had to immediately come up with a solution after the destructive explosion. They thought of a methodology that included the construction and installation of a sealant beneath the foundation of a structure to prevent any penetration of harmful gases such as methane into the interior of a building.

Utilizing products that are already tested, proven and had decades of proven field data seemed like the best option. At that time, waterproofing products had long been established as effective and efficient. If these products can prevent water from seeping into structures, there is also potential of prevention of methane vapor intrusion in these products.

A licensed LADBS testing agency tested some of these already existing membranes as methane barriers. Through the conducted methane tests, it was confirmed that spray-asphalt emulsion waterproofing products decreased the mass diffusion rate of methane. Upon verifying this, methane consultants and the LADBS developed specifications for methane barriers that are currently being used to determine the most appropriate membrane for specific projects.

Methane Mitigation Systems are still continuously evolving, expanding, and optimizing. When initially started, there were only one or two methane barriers that were utilized. This lasted several decades until recently when various Methane barriers have been introduced to the lineup of products used in mitigating methane intrusion into structures.

Historically, a spray-applied asphalt emulsion would be used. The manufacturer offering this expanded very quickly, ultimately having handfuls of approved spray-applied Methane barriers. Methane barriers are used simply to prevent the diffusion of methane through a surface, so several materials can meet this requirement. Modern companies introduced new methods for this. Some introduced spraying onto a geotextile surface to allow for a base material to be used.

Another significant change in the industry is one that doesn’t require a spray application. Some of these products are sheet or film membranes, built-up or laminate membranes. Other methane mitigation contractors use peel-and-stick products consisting of rubber, bitumen, bentonite clay, polyethylene, and plastic sheet compositions.

Although these products have their own advantages, they each have their own disadvantages. Peel-and-stick materials typically cost less, require less skilled labor and no curing time. Since they are prefabricated, they have controlled thickness in every single application. One significant disadvantage of peel-and-stick products is its moisture sensitivity. There is a high risk debonding or membrane peeling.

The more common spray-applied asphalt emulsion requires skilled labor, curing time, and equipment which all increase the cost. However, the result is a more reliable and stable system that will typically last longer.

Each of the applications available need detailing which results in additional labor and material parts. But the detailed work in methane mitigation constructions especially in the installation of the methane barrier is the defining factor of the quality of the construction as a whole.

Are Methane Mitigation Designs Required?

Methane Mitigation or a Vapor Mitigation Designs are becoming a key component of the design and construction phase for all projects. The necessity of Methane Mitigation or a Vapor Mitigation Systems stems from environmental contamination concerns. One requirement may be driven by local building jurisdictions intent to prevent explosive gases migrating into structures while others may be driven by Department of Toxic and Substances Control’s (DTSC) approach to minimize toxic vapor intrusion into the interior space of structures.

If Design requirements specify that a Methane or Vapor Mitigation System must be included in the construction, a Design that includes the specifications of the Vapor Mitigation system must be available for the contractor that will be completing the work.

The Vapor Mitigation Design will specify the sub slab depressurization system also known as sub slab vent systems. It will also include vapor probe monitoring programs along with vapor or Methane Barrier specifications.

Design specifications may vary depending on the responsible Methane Vapor Mitigation Consultant. Generally, based on the code requirements for both Methane Mitigation and the EPA’s DTSC Vapor Mitigation Advisory, design will include these details the sub slab vent system and methane or vapor barrier.

During the construction, Methane Vapor mitigation system will be inspected by a special inspector. This requirement is usually driven by local building jurisdictions, or the manufacturer themselves to provide the corresponding warranty for the work that’s been provided.

Often, for lower budget projects, the developer may want to save on cost by not having a Mitigation design prepared. Although this surely will save on cost during the design phase of the project, this is not a recommended process for mitigation system. Come time for construction, during the bidding phase of a project if there is no mitigation design available in the plan set, the methane mitigation scope will likely be overlooked.

Additionally, if the methane mitigation design is not included in the plan set, your General Contactor may not have any ability to comprehend what the requirements will be. The Methane Mitigation and Vapor mitigation requirements are a recent addition to projects, and it is common for General contractors to not be aware of the construction practices. The preparation of the Methane Mitigation Construction Bid and or vapor mitigation design is always recommended for mitigation systems.