Due to the recent change in regulatory screening levels and oversight, vapor intrusion mitigation (VIM) is a leading service within the environmental consulting industry. These changes coincide with booming development in the San Francisco Bay Area, the state of California and beyond. The regulatory changes affect developers, property owners, realtors, and others.
Key regulatory changes are:
- In October 2011, CalEPA issued its Vapor Intrusion Mitigation Advisory (VIMS) for ensuring public safety until soil vapor concentrations considered safe for human exposure indoors.
- In 2014, new legislation (SB445) provided funding for agencies to identify properties with potential VOC contamination and issue directive letters requiring action.
- In January 2019, environmental screening levels were lowered significantly (by a factor of approximately 15, or one order-of-magnitude). For example, the commercial screening level for PCE reduced from 2,100 ug/m3 to only 67 ug/m3).
These changes first forced many projects and properties to perform additional testing to demonstrate if subsurface chemicals posed a significant risk, such as a cancer risk greater than 1-in-a-million. The estimated risk level dictated the amount of remediation required to render a project safe for site use without any vapor intrusion controls. For many projects, extensive remediation is cost prohibitive, infeasible, or too time consuming to avoid the requirement for vapor intrusion mitigation controls.
A visual model for how engineering controls can mitigate vapor intrusion.
We use Calculated Risk Maps to select appropriate engineering controls for vapor mitigation.
A vapor barrier installed in an Oakland, California warehouse.
From our recent experience, nearly all projects with petroleum hydrocarbon or chlorinated solvent contamination require some form of VIM evaluation or engineering controls. After obtaining initial chemical data at a property, risk screening is performed to determine what level or engineering controls are required to safeguard human health from VOC vapors. Occasionally significant assessment is necessary to evaluate site conditions, and site remediation employed to remove the primary source of vapors at the site.
Beyond the associated assessment, remediation, and construction-related services, our VIM services include:
- Risk screening evaluation and Risk Map preparation.
- Agency interaction for VIMS decision making and requirement determination.
- Preparation and evaluation of VIMS alternatives.
- Selection of appropriate VIMS controls to meet client needs.
- Preparation of VIMS plans for agency review and approval.
- Design of VIMS construction drawings.
- Contractor bidding and selection assistance.
- Installation oversight, construction quality control
- Certification of VIMS installation and Construction Documentation.
- VIMS Performance Testing (Indoor Air and Radon Surrogate Testing) to confirm and quantify VIMS effectiveness.
- Help secure Certificate of Occupancy concurrence from oversight agency.
- VIMS Operation, Maintenance & Monitoring Plan Preparation.
- Long-term O&M testing (annual and 5-Year testing) as required.
COMMON VAPOR INTRUSION MITIGATION STRATEGIES — FOR NEW BUILDINGS
For new buildings, there are a variety of strategies and systems to consider depending on risk, subsurface conditions and building features. Passive ventilation systems are less costly to install and maintain than active systems.
Subslab ventilation piping and gravel layer is a primary required control for new buildings to capture and route vapors away from building.
A chemical vapor barrier is a primary required control for new buildings to effectively block vapors from entering the building.
Smoke testing is used to identify leaks requiring repair and verify final quality construction of the vapor barrier.
COMMON VAPOR INTRUSION MITIGATION SERVICES — FOR EXISTING BUILDINGS
For existing buildings, there are a variety of strategies and systems to consider depending on risk, subsurface conditions and building features. Passive ventilation systems are less costly to install and maintain than active systems.
Specific polyurethane sealants and epoxies are used to seal penetrations for vapor intrusion.
Passive ventilation and active depressurization systems are used to capture vapors and safeguard human health.
Specialized epoxy coatings are used to seal concrete floors for added protection, especially when existing subgrade soil is not very permeable.