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Vapor Intrusion / Vapor Encroachment Assessments

An assessment of the risk for Vapor Intrusion and Vapor Encroachment can be an important part of the environmental due diligence process. Partner can perform a risk assessment for vapor concerns within the context of a Phase I Environmental Site Assessment, or as a separate assessment done to the ASTM standard E2600-15 Standard Guide for Vapor Encroachment Screening on Property Involved in Real Estate Transactions.

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Frequently Asked Questions

A Vapor Intrusion Condition or “VIC” is the presence or likely presence of chemicals of concern in the interior space of a building or at a planned building location. As such, the VIC term is applied not only to scenarios where contaminants have been documented in indoor air, but also to scenarios where there is the potential for these vapors to be intruding into the building.

“Vapor Intrusion Condition” is essentially a subset of the term “Recognized Environmental Condition,” which is used in the Phase I Environmental Site Assessment (ESA). The Phase I ESA identifies any Recognized Environmental Condition, which should also include the identification of Vapor Intrusion Conditions. A Recognized Environmental Condition (REC) is defined by ASTM as “the presence or likely presence of any hazardous substances or petroleum products on a property under conditions that indicate an existing release, a past release, or a material threat of a release of any hazardous substances or petroleum products into structures on the property or into the ground, ground water, or surface water of the property. The term includes hazardous substances or petroleum products even under conditions in compliance with laws.”.

Vapor Intrusion has been a concern in the environmental consulting community for the past several years.

More recently, the term “Vapor Encroachment” was coined which describes the migration of these vapors anywhere onto a property or near a property (not necessarily underneath or into a structure on the property). The ASTM definition of a Vapor Encroachment Concern or “VEC” is “the presence or likely presence of chemical of concern vapors in the subsurface of the target property caused by the release of vapors from contaminated soil and/or groundwater either on or near the target property.”

Vapor Encroachment is a broader concern than Vapor Intrusion, which really focuses just on the potential for vapors to exist inside a building.

Vapor Encroachment is the term used in the ASTM E2600-10 Standard for Vapor Encroachment Screening. A previous version of the ASTM Standard, ASTM E2600-08 used the term Vapor Intrusion, and many in the environmental consulting field still use this term, for reasons discussed below.

There is debate within the environmental consulting community regarding the use of the term Vapor Encroachment Concern versus Vapor Intrusion Concern, whether either of these items represents a Recognized Environmental Concern, and how to address these issues within the Phase I Environmental Site Assessment Report. This can all be quite confusing to users of the Phase I ESA.

It is important to distinguish between what is a human health concern and what is not.

ASTM already makes this distinction in its definition of what constitutes a REC versus what constitutes a less significant issue (a “de minimis” concern). From the ASTM E1527-13 standard for Phase I ESAs: “The term (REC) is not intended to include de minimis conditions that generally do not present a threat to human health or the environment and that generally would not be the subject of an enforcement action if brought to the attention of appropriate governmental agencies.”

Most environmental professionals would agree that a Vapor Intrusion Concern (VIC, where contamination is directly underneath a building and represents a human health risk) has always been a REC, because a VIC is a health concern (and therefore is not de minimus).

There is less clarity regarding the use of Vapor Encroachment Concern, (where contamination isn’t necessarily underneath the building but anywhere on the property). Many argue that so long as there is no risk of the vapor migrating into the building (thus posing no health risk), and the contamination originates from an off-site source for which the target property owner would not be liable, the VEC would not be considered a REC.

Common mitigation measures for vapor intrusion include:
Installing vapor barriers or vapor intrusion barriers beneath buildings to prevent vapors from entering indoor spaces.
Implementing sub-slab depressurization systems to reduce pressure differentials and vent vapors away from buildings.
Improving building ventilation systems to increase air exchange rates and dilute indoor air concentrations of volatile chemicals.
Monitoring indoor air quality and implementing indoor air monitoring programs to detect and respond to potential vapor intrusion events.


Digging Deeper

What is Vapor Intrusion?

Vapor Intrusion occurs when volatile chemicals migrate from contamination in the soil or groundwater up into a building’s interior space. Vapor Intrusion can pose a potential health threat to the occupants of the building, especially to sensitive populations such as children.

Vapor Intrusion has been a particular concern with regards to contamination caused by dry cleaning solvents (perchloroethylene or “PCE” being one of the most common), because these chemicals are highly volatile and toxic. But, Vapor Intrusion can also occur with other contaminants such as petroleum products, which can also pose a health risk.

Vapor Intrusion can be caused by contamination on-site or off-site from a property. Sometimes a plume of contamination from an off-site source (for example, a neighboring dry cleaner) can migrate onto the subject property and underneath (or in close vicinity of) the building, and thus pose a risk of entering the building.

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