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Vapor Pin and Soil Gas Well Sampling

August 3, 2022

Due to the volatile nature of solvent and petroleum-related contaminants, the volatilization to indoor air pathway (VIAP) is often relevant during an environmental investigation at a manufacturing facility, dry cleaner, or gas station. The concern is that vapors, which off-gas from a contaminant body, will seep into a building and create unsafe conditions for the inhabitants. If groundwater or soil contaminant concentrations exceed criteria for the VIAP in close proximity to a building structure (existing or future), additional vapor characterization may be necessary.

To further assess the VIAP, a soil gas (vapor in the subsurface) sample can be collected from a shallow soil gas well (approximately five feet deep) immediately outside the footprint of a building or from a Vapor Pin®. A Vapor Pin® allows for the collection of a soil gas sample directly beneath a foundation floor (known as a sub-slab soil gas sample) by installing a brass pin into the floor and then drawing a sub-slab soil gas sample through the pin. Soil gas wells can also be utilized at a vacant property where a future structure is planned or along a utility corridor that may serve as a preferential pathway for vapors.

At two of Envirologic’s site investigations where gasoline was released into the subsurface, potential VIAP concerns warranted additional investigation. At one of the locations, sub-slab soil gas samples were collected after elevated contaminant concentrations were identified in groundwater and soil samples near the building. Results from the sub-slab samples, in conjunction with additional lines of evidence, suggest that the VIAP does not present an unacceptable exposure risk, and no further evaluation is needed with respect to this pathway. At the second site, soil gas wells were installed immediately outside of the on-site building. While initial soil gas results indicate a potential VIAP issue, Envirologic is currently working with the liable party to address the exposure risk through additional characterization.

Due to biodegradation, soil gas concentrations (particularly from petroleum-related contaminants) typically decrease as vapors migrate towards the surface. The benefit to relying on shallow soil gas data, as opposed to soil or groundwater data collected at depth, is that the near-surface soil gas samples are more representative of conditions immediately beneath the floor of a building. If soil gas results indicate the potential for an unacceptable exposure risk, the focus for the VIAP investigation shifts towards indoor air sampling (which has limitations), remediation (excavation, air sparging, etc.), or mitigation (installation of a vapor barrier, sub-slab depressurization system, etc.). You can learn about our vapor intrusion and mitigation services here.

There are often sampling needs as part of an environmental investigation; let Envirologic support your project using our experienced Environmental Investigation team. For a complete list of our services, please visit our website or contact a member of our team at (269) 342-1100 or by email.

Posted in Blog, Environmental Investigation & Remediation, Vapor Intrusion

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