Newly Advanced Methane Mitigation Design & Construction

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Methane vapor mitigation systems are among the youngest trades associated with construction projects in the modern-day. Initiated by the Ross Explosion in 1985, the city of Los Angeles’ Department of Building and Safety led the way in the vapor mitigation industry. The LADBS Methane Mitigation Code requires the process of conducting a Methane Test, a Methane Mitigation Design and Methane Mitigation Construction.

LADBS’ redundant Methane Mitigation System Code requirements provide protection that is needed to safeguard against harmful subsurface activities and historical abuse of environmental concerns. The LADBS Methane Code consists of collaborative systems from underground ventilation systems and sealants installed below foundations to active system components, including fans and sensors.  The extent of the Methane Mitigation Construction components is defined by the results of the Methane Test.  LADBS required the Methane Soil Gas Test to be conducted by a licensed Methane Testing Field Agency.

The Los Angeles Department of building and safety has led the way with the development of the Methane Mitigation Design Standard Plans. Other building jurisdictions, along with the EPA’s Department of Toxic Substances Control (DTSC), have shortly followed leading and updating code requirements reflecting vapor mitigation systems for harsh subsurface soil contamination caused by historical abuse of production and commercial activity.

Historical and modern-day activities such as dry cleaners, machine shops, and manufacturing facilities have introduced harsh contaminants in the subsurface that impose environmental concerns below ground and above ground. These environmental contaminants require remediation or mitigation to ensure they do not harm building occupants. LADBS and the DTSC are imposing building restrictions that require implementing Methane Vapor Mitigation Design and Construction.

Phase 1 and Phase 2 Environmental Reports

Vapor Mitigation system requirements will be driven by the phase 1 environmental history report investigation and a phase 2 environmental site assessment report.

The purpose of Phase 1 Reports is to research the history of a property to see what type of activity occurred over the years. If an action imposes a risk of possible contamination, a Phase 2 Environmental Site Assessment is initiated.

Various boreholes are advanced during a Phase 2 environmental site investigation based on the Direct Push Drilling ASTM Standards. A mobile Phase 2 laboratory will extract and analyze concentrations of various contaminants within the subsurface soil samples, including hydrocarbons, PCE, Radon, Benzene, TCE, and others.

Based on the results of the Phase 2, the consultant hired to conduct the Phase 2 will be required to make recommendations regarding how to remediate or mitigate the present contamination.

Historically, remediation methodologies have been extremely costly, and the options have been minimal. Based on the lessons learned and design development that has been occurring in the Methane Mitigation industry within LADBS jurisdiction, Vapor Mitigation Systems are becoming a more common solution according to DTSC and EPA’s latest reports on the Vapor Mitigation Advisory.

History of Sub Slab Depressurization System and New Improvements

An industry that is only 30 years old has made minimal progression in methodologies up until recently. Historically, Sub Slab Vent Systems and Methane vapor barriers have often been highly costly due to the required Methane Mitigation construction approaches.

The Methane Vapor Sub-Slab vent system exists as an underground ventilation system for your structure.  The methane sub-slab vent system gets installed beneath the methane impervious membrane.  The methane mitigation contractor is required to install the methane mitigation construction per the details as outlined in the methane mitigation design. A series of perforated pipes encased in a gravel blanket will route through the under slab and ultimately lead to methane vent risers which route through to the roof and exhaust out of vents.

This design approach guarantees minimal pressure accumulation under the slab of a structure. Although difficult to imagine, some of these underground contaminants can be heightened with increases in pressure at over 2 inches of water. Relative to the pressure present inside a structure (typically at atmospheric pressure), the pressure differential will force contaminants into a building. The sub-slab vent system acts as a depressurization system. It ensures that the pressure beneath the structure is always the same as the pressure outside of the structure’s atmospheric conditions. Limiting pressure differentials will reduce the diffusion coefficient and mitigate the ability of any gas to intrude into a structure.

The delivery and installation of three-quarter-inch gravel will need to be initiated into the trenches to act as perforations to allow gasses to pass through easily. Trenching requires heavy machinery, which is expensive to mobilize and operate. Additionally, other contaminants are caused by using this machinery during the construction process, increasing the carbon footprint of an already high CO2-producing process.

The installation of the sub-slab depressurization systems is cumbersome and inefficient, and until now, there have been no other viable options for the Sub-slab vent system construction process.

Recently, new advancements in Sub Sab Vent System technology have been released. This updated Subs Slab vent system design is a roll-in-place ventilation system designed using a plastic dimple drain mat along with the geotextile fabric. The dimpled drain mat is designed in a fashion to withstand the compression of the poured slab directly over it. The result is a passageway for air or other gases to migrate through the dimpled mat and lead to a vent riser adapter. The Contaminated Gas will then vent through these Vent Risers to the roof.  The extent of the contaminated gas will need to be analyzed by means of a methane test for the LADBS Methane Mitigation Code, or a Phase 1 & Phase 2 for the DTSC Vapor Mitigation Systems.

Similar to the manufacturing of methane and vapor barriers, the source of this technology was initially developed for below-grade waterproofing systems. The dimpled drain mat is a system that is frequently used for drainage systems on French Drains on retaining walls or shoring lagging walls. Methane Barrier manufacturers observed the design methodologies of these Dimpled Drain mat French Drain Systems.

They observed that the system could be similarly implemented within Vapor Mitigation Depressurization Systems. The French Drain System is designed to prevent high-pressure water build-up behind Structural walls. Although this system has been used for several decades in waterproofing applications, some building jurisdictions still do not permit these systems for Methane Barrier applications in replacement of Sub Slab Vent depressurization systems. It’s essential to bring up this option to your Methane Mitigation Designer to see if it’s possible to be implemented in your Building jurisdiction.

The Evolution of DTSC Vapor Barriers and Methane Impervious Membranes

There have been significant advancements in methane vapor barriers. Historically, the sources of methane mitigation barriers had come from below-grade waterproofing systems. Historical methane barriers were developed urgently to establish a system that would protect structures with readily available infield testing data. Unfortunately, the evolution of Methane Barriers has not evolved at a sufficient rate. For decades, all barriers required the installation of an asphalt emulsion spray applied membrane that was extremely difficult to install and needed heavy equipment and knowledge to operate efficiently.

New technologies have emerged for Methane Barriers that implement “roll out” methods, similar to how you roll out the carpet in a home. This new Methane Vapor Barrier technology requires either seam welders or chemically reactive adhesive to ensure no voids in the continuous membrane. Previous asphalt emulsion spray-applied Methane Barriers acted as a seamless continuous monolithic barrier throughout a slab. Engineers at the time felt this was the only way to successfully create a sealed continuous surface that would meet the size requirements of a methane vapor barrier. As a result of high raw material costs, Asphalt Emulsion Methane Vapor Barriers have been significantly higher in price. An Asphalt emulsion Methane Barrie or Vapor Barrier costs between $7 to $8 per square foot to have installed. New LADBS and DTSC Approved Methane and Vapor Barrier will cost $5 – $6 per square foot.

Reducing costs is extremely important in the methane vapor barrier industry; Vapor Barriers will likely be required in all future construction projects. The competitive nature in the industry is excellent evolution to see newer and more optimal technologies at lower costs.  Methane Mitigation Designers hold the responsibility to analyze the Methane Test Data and corresponding mitigation requirements.  After reviewing the methane mitigation construction scope of work as required by the LADBS Code, the Methane Mitigation Designer will need to specify which methane barrier will be an optimal choice to specify for a specific project.

New Design Applications for Active Vapor Mitigation Systems

In areas that contain high concentration levels of methane gas as outlined in the LADBS Methane Test, or other carcinogenic or toxic vapors as deemed by the DTSC, the requirement of having an Active Vapor Mitigation System is possible. Active Methane Mitigation systems have historically included the implementation of sensors beneath the foundation of structures to measure the concentrations of methane build-up and pressure sensors to monitor the extent of the pressure differential. Methane Detectors are also placed in the lowest level of the building to monitor the possible intrusion of Methane Vapor Gas contaminates. These Active Systems continuously monitor the concentrations and pressure of the Methane Vapor Mitigation System and communicate via control panels to Fans.  If concentrations or pressure exceed a defined threshold, the system will activate to ventilate the toxic vapors.

LADBS led the way with the Active System Vapor Intrusion Mitigation design approach for their methane gas mitigation program, which implemented explosion-proof systems for sensors, ventilation, and control systems. The corresponding cost of these systems is extremely high, and the related code requirements are maintained this way to this day.

Neighboring Building jurisdictions like the Los Angeles County of Public Work’s Environmental Programs Division, the Orange County Fire Authority, or the Environmental Protection Agency’s Department of Toxic substance control have established different approaches for the Active Vapor Intrusion or Mitigation System Design. The new Advanced Vapor Mitigation Systems process has taken on a much more cost-effective method. Mechanical Engineers design continuous Sub Slab extraction systems to provide higher pressure differentials throughout the SubSlab The system constantly allows for more minimal control systems to reduce costs.

The start-up cost of the Responsive Active Mitigation System includes the fans’ fees and the sensors and Controls Systems charges, which are all notoriously high in price. Operating power costs for the Continuous Vapor Mitigation Fans may be increased due to this, but in comparison to the upfront construction costs, the power consumption costs are minimal. In addition to the methodology of active monitoring systems implemented by the methane mitigation system in LADBS jurisdiction, other local building jurisdictions have taken a different approach and proposed the use of passive monitoring probes installed beneath the foundation of the structure. These probes are then set up on a monitoring program where manual measurements are taken by the consultant periodically, which is set up on the maintenance and control system instruction manual prepared by the Methane Mitigation Consultant.

The Active Methane Mitigation System must be installed by a licensed Methane Mitigation Contractor with experience in Methane Active System Control Systems and Methane Impervious Membranes.  The Methane Mitigation Design must be referenced during the Methane Mitigation Construction, and the corresponding Active System Single Lines, and Voltage drops need to be prepared by a licensed engineer.

Optimized Methane Vapor Mitigation System Contingency Plans

The newly optimized Vapor Mitigation design requirements established by building jurisdictions require the preparation of a Contingency Plan. Depending on the results of a Methane Test, Methane Vapor Soil Gas Test or a Phase 2 Environmental Investigation, a risk analysis is completed to determine the extent of possible vapor intrusion into a structure. Based on this Vapor Intrusion Risk Analysis, corresponding Vapor Intrusion Mitigation Advisory requirements are established. They must be implemented in the Vapor Intrusion Mitigation System (Also known as the VIMS System). This Vapor Mitigation System Design can include retrofitting various Active System Components as a Contingency Plan. These Contingency Active Mitigation System Components can be implemented in a scenario in which there is a failure in the original installed Methane Vapor Mitigation System. The VIMS contingency plan may consist of a series of active Fans, Methane detectors for periodic or continuous Active Monitoring, an Extensive Vapor Mitigation Control System and even a Soil Vapor Extraction System for Remediation purposes.

Upgraded Active Vapor Mitigation System Fans

The design of Methane Vapor Mitigation Active System Fans has evolved significantly over the past decades. Different Vapor Mitigation Systems will have specific design requirements for the type of material or fan design that can be implemented. Design requirements can vary from the ability for explosion-proof motors to be implemented to ensure that methane gas does not have an ignition source. In addition to the explosion-proof motors, 100% polymer-based fans are designed with no metallic features that could potentially create an ignition source.

The Chemical Compatibility of the materials used in the manufacturing process of the fan must be analyzed against the imposed contamination present in the subsurface. The most frequent issue associated with Methane Vapor Mitigation fans is the “Fan Sizing” process that must be implemented to specify a Fan Design correctly. This process must be prepared and stamped by a licensed Mechanical Engineer. Mechanical Engineers will Calculation a System Curve of the Methane Vapor Sub Slab Vent System and Compare this to the Fan Performance curves to verify the compatibility of Fan Designs with Methane Vapor Ventilation Systems. Lastly, the form size is critical for the new Active System Design Process.

The size of Fans has reduced substantially to fit within walls or in the attic of a building. Typically, you want to discreetly position these fans to avoid imposing architectural issues on a project.  Methane Mitigation Designs will outline the requirements of the mitigation system which is driven by the results of the Methane Test per the LADBS Methane testing Standards.

A licensed C10 contractor must construct the Active Methane Mitigation System to comply with the specifications of the Los Angeles Department of building code and California building code. There have been milestone advancements in the single-family dwelling Methane Vapor Mitigation code for Active Systems. Building Codes have established exceptions that may be applied to Single Family Dwelling or their accessories that permit the substitution of Control Panel Monitoring Systems with standalone detectors.

Methane Gas standalone detectors plug into the wall and measure methane concentrations; if a concentration threshold is detected, the onboard speaker will sound notifying building occupants. This new Methane Mitigation Construction methodology has brought considerable advancements to the industry to allow cost-effective, safe practices to be implemented within residential properties. These exceptions, coupled with the New California Building code for Accessory Dwelling Units, help motivate developers and homeowners to hire methane mitigation contractors at a more cost-effective approach.  The responsible methane mitigation contractor will review and verify that the methane mitigation design and methane test all comply with the LADBS methane Testing code.  The Methane Mitigation Designer shall verify that all specifications are outlined per the New Advanced Methane Vapor Mitigation Design and Construction.


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