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VOLUME 1
Standard Practice for Assessment of Vapor Intrusion (ASTM Standard E 2600-8)
by Rick Henterly
The Standard Practice for Assessment of Vapor Intrusion into Structures on Property Involved in Real Estate Transactions (ASTM Standard E2600 -08) defines good commercial and customary practices for conducting a vapor intrusion assessment (VIA) for properties involved in real estate transactions with chemicals of concern (COC) that may migrate as vapors into existing or planned structures on a property due to contaminated soil and groundwater on the property or within close proximity to the property. This practice is designed to be used in conjunction with ASTM E1527 Standard Practice for Environmental Site Assessments: Phase I Environmental Site Assessment Process, or used independently assuming the environmental professional is familiar with the data collection requirements of ASTM E1527 (as referenced in Practice E2600).
ASTM Standard E 2600-08 is a screening evaluation to determine whether the vapor intrusion exposure pathway is complete (and a vapor intrusion condition (VIC) exists) and, if so, whether it poses or may pose an unacceptable risk to human health. The VIA process consists of four tiers, with Tier 1 as the initial step. However, depending on cost analysis, knowledge of the site, contaminated plume, and source areas, one may progress directly to Tier 2, 3 or 4. This summary describes the tiers in the VIA process:
Tier 1: Initial Screening
Tier 1 is an initial screening to determine if a possible VIC exists in connection with the target property. When conducted as a supplement to a Phase I ESA, Tier 1 is designed to make use of the maximum extent of possible information collected. Tier 1 uses non-numerical information designed to identify conditions and/or physical settings where a possible VIC (pVIC) is unlikely to occur. This information includes planned use of property, types of structures, surrounding area description, government records noting potential COC sources at or near the target property, historical records, physical setting, conduit knowledge, usersupplied specialized knowledge of the target property. The practice lists approximate minimum search distances both for surrounding the target property and up gradient of the target property.
The Tier 1 screening assessment will include (1) a search distance test to determine if there are any known or suspected contaminated sites in the primary area of concern; (2) a chemicals of concern test for those known or suspect contaminated sites within the area of concern whether or not COC are likely to be present; (3) a plume test to determine whether or not COC in the contaminated plume may be within the critical distance, and, if so, whether risk-based concentrations (RBCs) are exceeded. If it is concluded during the Tier I assessment that a pVIC is unlikely to exist, then the process is complete; if however a pVIC exists, the other Tiers must be considered.
Tier 2: Semi-Site Specific Numeric Screening
Tier 2 provides a more refined screening using existing or newly collected soil, soil gas, and/or groundwater testing results. Tier 2 involves two data collection components: non-invasive (review of Phase II reports on known or suspected contamination sources identified in Tier 1) and invasive (sampling near the target property).
The invasive component centers on the nature of the plume geometry and conditions
and its relationship to the target property. If the plume test in Tier 1 identified a plume in the area of concern, the data collected in Tier 2 related to the COC concentrations will be compared with the applicable RBCs, and any exceedences indicate a pVIC requiring additional investigation. If none of the COCs exceed the RBCs, then the process is complete and it is unlikely that a VIC exists. However, the user may choose to apply mitigation based on the possibility of plume migration.
Tier 3: VIC Assessment
If vapor intrusion cannot be ruled out in Tier 1 or 2, then Tier 3 provides for a more sophisticated testing tool to determine if a VIC exists. It includes data based on interior and/or exterior testing. The Tier 3 evaluation consists of determining
an endpoint (i.e., pVIC exists, does not exist, cannot be determined); identifying regulatory standards, models, and requirements; indentifying and collecting necessary data; and evaluating data to determine if a VIC exists.
Tier 4: Mitigation
The three main mitigation categories are summarized, along with their distinct advantages and disadvantages. These include institutional controls, engineering controls (source removal/treatment, barriers/venting, both passive and active, and pressurization), and intrinsically safe building design (such as well-ventilated underground parking).
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