Vapor Intrusion Sub-slab Soil Gas Sampling

Summa® canister used for collecting soil gas samples.

Environmental consultants have been patiently awaiting the release of revised subsurface vapor intrusion guidance from the EPA and state regulatory agencies for several years now. The EPA’s and Pennsylvania’s Department of Environmental Protection’s (PaDEP) current guidance is over 10 years old. The current guidance for Pennsylvania specifically applies to the Land Recycling program’s (Act 2) Statewide Health Standard. To understand how to apply it to the Site Specific Standard you must navigate several pages of questions and answers. Many variables come into play when assessing and evaluating risks associated with vapor intrusion from soil and groundwater contamination that make it one of the most challenging exposure pathways to characterize.

On this Field day Friday, Element is collecting a sub-slab soil gas sampling using a Summa® canister. This structure being tested is located within a 100 feet radius of the contaminant source. The structures distance along with Vapor Intrusion modeling helped us determine that a vapor intrusion investigation was necessary to fully characterize the site.

There’s little question within the scientific community that vapor intrusion is a serious issue with the potential to impact the health of a building’s occupants. The rate and reach of vapor intrusion, along with sampling techniques continue to evolve as the science continues to improve. Soil gas sampling near the source or sub-slab soil sampling are screening tools to confirm if vapor intrusion is an issue, with sub-slab sampling being the preferred method. Due to the variables involved in soil gas sampling, some prefer to activity mitigate vapor intrusion by installing sub-slab depressurization systems or a vapor barrier, without going through the expense of confirming if vapor intrusion is really an issue. The PaDEP Cleanup Standards Scientific Advisory Board (CSSAB) has created a sampling method workgroup to develop guidance on standard operating procedures for vapor intrusion testing based on proven sampling techniques. We are hopeful that this will provide a consistent methodology for consultants and regulators to evaluate potential vapor intrusion impacts.

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