Vapor Encroachment Screening:A Necessary Task in Environmental Due Diligence


Real Estate, Banking, and Environmental professionals are very familiar with ASTM E 1527-05, Standard Practice for Phase I Environmental Site Assessments, used as a routine due diligence element for real property transactions.  Less widely known and less frequently incorporated as a formal element in the environmental due diligence process is ASTM Standard Guide for Vapor Encroachment Screening on Property Involved in Real Estate Transactions (E 2600-10).  Failure to consider vapor encroachment, also known as intrusion, could be a costly oversight, as response actions cost time and money and regulatory requirements continue evolves.  Occupants’ concerns remain heightened.  Lender guidelines/requirements should be expanded in response to real and perceived threats and liability associated with vapor encroachment onto commercial, residential, and industrial properties. 

 Vapor encroachment, also known as soil vapor intrusion, issues arises when hazardous vapors migrate from a contaminant source, collect beneath a building slab, and potentially enter overlying buildings. Typical contaminants for which vapor encroachment concerns arise include a wide array of volatile organic compounds such as gasoline and petroleum related products, cleaners, solvents, and other volatiles.  The source of contamination may be contaminated soil, a groundwater contaminant plume, or other spill or release.  The source does not need to be located within an affected property to cause a vapor encroachment / vapor intrusion concern to that property.  ASTM E 2600-10 establishes a formal process for conducting a defensible vapor encroachment screen (VES) to identify a vapor encroachment condition (VEC) on a target property. 

 Vapor Encroachment Screening incorporates Tier 1 and Tier 2 screening set forth in the new standards to assess property for a VEC.  Tier 1 utilizes information comparable to that generated during typical Phase I ESA, and Tier 2 utilizes existing or newly generated sample analytical data to evaluate onsite and offsite sources of concern.  Marginal costs for Tier 1 screening may be increased if conducted in concert with other typical Phase I ESA tasks.  Marginal costs for Tier 2 screening that includes sampling can range up to several thousand dollars.  The process is to be implemented by an environmental professional who exercises professional judgment and experience in conducting the screening to reach one of the following four conclusions: 

  1.  VEC exists;
  2.  VEC is likely to exist;
  3.  VEC cannot be ruled out; or,
  4.  VEC can be ruled out. 

ASTM E 2600-10 may be used in conjunction with, or independent of, the ASTM E 1527 Phase I ESA.  Note that the search distances differ between the two practices, and a VEC is not necessarily equivalent to a recognized environmental condition (REC) as defined under the E 1527 ASTM standard.  If further investigation is required beyond the initial two screening levels, the party conducting the assessment should consult with his/her environmental professional to determine appropriate next steps, so that property and transactional liabilities are managed efficiently and impacts to the property are fully understood and addressed.

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