Vapor Encroachment Explained

In a Phase I Environmental Site Assessment (ESA) report, these days you are likely to see an evaluation of vapor encroachment conditions at the site. If you haven’t, you will. The upcoming update to ASTM’s Phase I Standard proposes to treat vapor encroachment like any other source of contamination, and thus a routine component of environmental due diligence.  So, what is it?

Think of vapor encroachment as a cousin of vapor intrusion.

According to the EPA, vapor intrusion occurs when there is a migration of volatile chemicals from contaminated groundwater or soil into an overlying building. Evaluation of vapor intrusion identifies contamination sources on- site. Vapor encroachment, on the other hand, also considers off-site sources. Think of vapor encroachment as a screening tool.

Vapor encroachment screening identifies releases in the vicinity of the subject property and, based on the contaminant plume, evaluates the likelihood of vapors migrating to the subsurface of the subject property. Vapors, in this case, consist of any chemical of concern (COC); and their presence or likely presence constitutes a vapor encroachment condition (VEC). The ASTM standard for this screening (E2600-10) uses a two-tiered approach (not to be confused with the EPA’s three-tiered vapor intrusion guidance!)

Tier 1 of vapor encroachment screening uses state and federal database records to identify those sites with the potential to affect subsurface vapor conditions. Much like the radius search for a Phase I report, Tier 1 employs a 1/3 mile radius for releases of non-petroleum products, and a 1/10 mile radius for releases of petroleum products. If a VEC cannot be ruled out, i.e. there are open sites within the search distance, then on to Tier 2.

Tier 2 starts out as a non-invasive records review. If you’re lucky, the state will have regulatory files for sites identified in Tier 1, and those files will contain the location of the source and contaminant plume. Based on the relation of the plume to the subject property, it is possible to rule out a VEC. If you don’t have access to plume info, or, if a VEC cannot be ruled out non-invasively, the next option is sampling – of soil, soil gas, and/or groundwater.

Ultimately, there are four possible outcomes of a vapor encroachment screen: 1) VEC exists; 2) VEC likely exists; 3) VEC cannot be ruled out; or 4) VEC can be ruled out. In the context of a Phase I ESA, the environmental professional determines if a VEC represents a recognized environmental condition (REC) for a specific site.

As vapor intrusion receives more attention from regulators, vapor encroachment screening can be a useful tool to delineate vapor concerns originating on-site and off. The intent is to provide an evaluation of vapor in the soil, thus refining the determination of vapor that may end up indoors. Some agree, some disagree, either way it is here to stay. Have you found vapor encroachment screening to provide insight or headaches? Leave a comment below, and please feel free to contact me at with your vapor encroachment questions.

Reviewing the ASTM Phase I ESA Standard

ASTM LogoThe American Society for Testing and Materials (ASTM) is a standards organization headquartered right outside of Philadelphia in Conshohocken, PA. ASTM publishes technical standards for a range of products, materials, and services. REPSG conducts our famous Phase I Environmental Site Assessments (ESAs) in accordance with the ASTM Phase I Standard entitled “Standard Practice for Environmental Site Assessments: Phase I Environmental Site Assessment Process.” This standard is commonly referenced as E 1527.

ASTM E 1527 was last revised in 2005, when the United State Environmental Protection Agency (USEPA) released the ‘All Appropriate Inquiries Rule’. According to the ASTM by laws, standards must be updated at least every eight years, and beginning last fall, an ASTM Task Group has been meeting to once again review the text of E 1527. Revisions to the standard have been proposed that would strengthen and clarify the requirements of E 1527.

Some of the key proposed updates to E 1527 were highlighted by Environmental Data Resources (EDR). Three of the proposed revisions include:

  • Introduction of the term “Controlled Recognized Environmental Condition.” Past soil and/or groundwater contamination which had been remediated would be classified as a CREC. This designation will be addition to recognized environmental conditions (RECs) and historical recognized environmental conditions (hRECs).
  • Expanded discussion on how vapor encroachment should be addressed in a Phase I ESA. In the new E 1527 draft, a vapor plume is proposed to be treated as any other source of contamination. (ASTM published a vapor encroachment standard in 2010 entitled “Standard Guide for Vapor Encroachment on Property Involved in Real Estate Transactions” E 2600-10. Stay tuned for upcoming blog posts about vapor!)
  • Clarification about when regulatory file reviews need to be completed during the course of a Phase I ESA.

The ASTM Task Group is anticipated to publish the updated E 1527 in 2013, but the standard will have to be approved by the USEPA.

As E 1527 evolves, REPSG will continue to provide the most current, highest quality reporting to its clients. If you have any questions about what these updates will mean for you and your property, drop us a line! Each of us on the Phase I team have copies of E 1527 and E 2600 within arms’ reach (and no, I’m not kidding!)