Vapor Intrusion Studies

Andersen Environmental (AE) certified environmental consultants conduct Vapor Intrusion Studies, as specified by the ASTM E2600 -08 “Standard Practice for the Assessment of Vapor Intrusion into Structures on Property Involved in Real Estate Transactions”. AE will assist clients in determining and conducting the relevant “tier” level of study, as specified below.

Description of Vapor Intrusion

Vapor intrusion occurs when contamination in soil or groundwater volatizes and enters overlying buildings as a gas, creating indoor air quality problems and potential health risks to occupants or employees. The seepage of harmful vapors often occurs through cracks or openings in foundations, such as utility conduits, and is exacerbated by pressure differentials created by heating and air conditioning systems that literally suck contaminated vapors into subsurface structures. Vapor intrusion can be a problem at any contaminated property, though it is encountered primarily at sites contaminated with volatile and semi‐volatile organic compounds (e.g., chlorinated solvents, metal treatments and coatings, and plasticizers), petroleum fuels and a small range of volatizing inorganic compounds such as mercury.

In the past, vapor intrusion has remained out of the spotlight of state and federal regulators, chiefly due to the difficulty of reaching definitive answers to the question of how to assess the risks of vapor intrusion, the apparent mischaracterization of vapor migration pathways, and the impact of vapor intrusion on human health and the environment. The finalization of the ASTM standard and the release by the EPA of assessment guidelines should be taken as a signal to property owners, developers and investors that vapor intrusion is an issue that can no longer be ignored. Users should be ready to incorporate assessment and mitigation into their due diligence activities for all properties where contamination exists or is suspected. Doing so will greatly reduce the risk of liability posed by vapor intrusion.

Below are the various “tier” levels specified by the ASTM E2600-08 standard:

• Tier One

  Tier One provides an initial screening of the possibility that potential vapor intrusion conditions (“pVICs”) exist at a property and is structured to serve as a relatively inexpensive add-on investigation to coincide with a Phase I. The information required to conduct the Tier One assessment includes current and historical site use, governmental records and physical setting information. These are many of the same information sources that a Phase I would require. Using this noninvasive information, the Tier One assessment determines if sources of contamination are located close enough to on-site buildings to create a pVIC. If a pVIC is found to exist, or can not be ruled out, further assessment will be warranted.

• Tier Two

  The Tier Two process is a more refined pVIC screening assessment. The Tier Two assessment attempts to identify pVICs by determining if existing or newly collected soil or groundwater contamination data exceeds risk-based concentrations (“RBCs”). The RBCs may be either generic (e.g., culled from state guidelines) or site‐specific RBCs developed by an environmental professional. If the Tier Two screening indicates that a pVIC exists, the user may wish either to confirm using the more exacting Tier Three analysis or to proceed to mitigation per Tier Four.

• Tier Three

  Tier Three calls for a sophisticated investigation to determine definitively if a VIC exists at a property. The investigation uses data collected during interior or exterior testing and compares the data to either site specific modeling or site‐specific indoor air quality standards. As this type of vapor intrusion investigation is parallel to guidance issued by the EPA and several states, the standard directs users to scope the investigation to adhere to any applicable guidelines.

• Tier Four

  Tier Four is the mitigation segment of the standard, detailing types of mitigation techniques proven to be effective in treating vapor intrusion issues. The categories of mitigation techniques discussed in Tier Four are institutional controls, engineering controls and intrinsically safe building design. Institutional controls are legally enforceable restrictions or conditions placed on property, such as restrictions on the use of groundwater, zoning or use restrictions and conditions on the depth or location of excavations. In contrast to the legal nature of institutional controls, engineering