VAPOR INTRUSION, A NEW CONCERN IN PHASE 1
ESA'S AND CASE CLOSURES

Vapor intrusion (VI) is a process by which gas phase chemicals in soil or groundwater migrate to indoor air above a contaminated site. Chemical vapors can move through floors of buildings and contaminate the air space occupied by residents or workers. Vapor intrusion into structures on a property can create human health hazards and therefore VI is a potentially significant liability issue, and also can negatively impact property values.
 
The increased recognition of VI has resulted in a growing concern form property owners, prospective purchasers of property, lenders, and the environmental professionals concerned about due diligence and conducting Phase 1 Environmental Site Assessments (ESAs).
 
Because of this emerging area of environmental concern the U S Environmental Protection Agency issued draft guidance in 2002 (http://www.epa.gov/correctiveaction/eis/vapor.htm) and in March of 2008, ASTM International issued the "Standard Practice for the Assessment of Vapor Intrusion into Structures on Property Involved in Real Estate Transactions," (ASTM E 2600-08 see http://en.wikipedia.org/wiki/ASTM ).
 
The ASTM E2600 standard is a vapor intrusion screening standard, and presents a defined screening methodology (in Tiers 1 and 2) to evaluate the potential for VI. Some States and regulatory agencies have standards for investigation and remediation. The ASTM E2600 standard does not specify what actions to take or how to determine if indeed vapor intrusion actually exists at a site; it is a screening tool to evaluate the potential VI to exist. Purposefully the ASTM E2600 standard does not conflict with existing federal or state guidance, policy or regulation for investigating or correcting VI impacts.
 
The ASTM E2600 standard is a screening tool that has two levels or “Tiers”. The method takes into consideration many site, structural, hydrogeologic, and contaminant factors. The screening considers among other things, the source of the potential contaminant, hydraulic and physical barriers between the site and the source, groundwater gradients, plume definition, known contaminant concentrations, etc. An excellent summary of the process is described by Tony Buonicore of Environmental Data Resources, Inc. at this link.