As part of our series on Remedial Investigation - Find, Define, Refine, Project Geologist Derrick Lingle recently completed a white paper discussing various sampling methods. The first methodology we explore is Vapor Pin and Vapor Well Sampling.
Due to the volatile nature of solvent and petroleum-related contaminants, the vapor intrusion pathway 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 vapor intrusion screening levels in close proximity to a building structure (existing or future), additional vapor characterization may be necessary.
To further assess the vapor intrusion pathway, a soil gas (subsurface vapor) sample can be collected from a shallow vapor well (approximately three to five feet deep) immediately outside the footprint of the 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 vapor sample) by installing a brass pin into the floor and then drawing a sub-slab vapor sample through the pin. Vapor wells can also be utilized at a vacant property where a future structure is planned.
At two separate gasoline release investigations that Envirologic has been involved with, potential vapor intrusion concerns warranted additional investigation. At one of the locations, sub-slab vapor 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 vapor intrusion pathway is not of concern, and no additional evaluation is needed in respect to this pathway. At the second site, vapor wells were installed immediately outside of the on-site building. While initial soil gas results indicate a potential vapor intrusion issue, Envirologic is currently working with the liable party to address the exposure risk through additional characterization.
Due to biodegradation, vapor 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 vapor samples capture conditions immediately beneath the floor of a building. If soil gas results indicate the potential for a vapor intrusion issue, the focus of the vapor investigation shifts towards indoor air sampling (which can present a handful of limitations), remediation (excavation, air sparging, etc.), or a presumptive remedy (installation of a vapor barrier, mitigation system, etc.).
If you have questions about this sampling method, please contact Derrick Lingle at 800.272-7802 or by email. Our next post will discuss other specialized methodologies used to characterize contaminated sites.
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vapor pin • vapor well sampling • remedial investigation • derrick lingle • site characterization • contaminants • vapor intrusion • subsurface vapor