Property Environmental Due Diligence

There has been considerable confusion and a high degree of inconsistency in the conduct of property environmental due diligence to evaluate the potential for VI resulting from soil and ground- water contamination on the target property or neighboring properties [3]. Moreover, there is even a question of whether or not this is an appropriate assessment to be included in Phase I conducted according to ASTM E 1527-05. Notwithstanding, an AAI-compliant Phase I may make it difficult for an environmental professional to ignore VI concerns.

VI can be particularly difficult to assess because vapors tend to migrate along the path of least resistance, without regard to w'hat is up-gradient or dow'n-gradient hydraulically. Considerable concern has already been raised about the significant percentage of false positives in using the screening criteria established by the EPA and state regulators. There are questions about the proper application of soil gas surveying and even more questions about the use of indoor air sampling.

The EPA has indicated that the potential costs and liabilities associated with VI impacts may be orders of magnitude greater than those associated with traditional groundwater contamination issues. With the growing trend of federal and state policy and regulations directed at this potential problem, it behooves the industry to provide consistent and reasonable guidance on how VI should be addressed in real estate transaction due diligence.

Control Options

For groundwater contamination in general, public health protective and cost-effective exposure controls (e.g., providing permanent alternate water supplies) have been used to successfully avoid a great deal of toxic exposure plus an unknown number of cases of disease over the years [2]. It is possible that similar measures for Vl-related exposures would have a similar positive outcome.

Providing alternate water supplies is a recognized technology “standard” for preventing inappropriate tap water exposures from contaminated groundwater. Traditional technology-based equipment, which have typically been used for the control of point source emissions to air, are recognized as providing some of the most effective and cost-effective improvements in environmental quality in this country. The pollution prevention approach could be another way to help manage the very large uncertainties that exist in the understanding of the VI exposure pathway. Such preventive approaches could help provide environmental managers, property developers, and decision makers with a more defensible and likely more cost-effective answer to VI problems.

EPA, State, and ASTM VI Activity

To respond to the growing problem of VI, in December 2001, the EPA issued its draft Guidance for Evaluating the Vapor Intrusion into Outdoor Air Pathway. This document was updated in November 2002.

States have also been a leading force in VI regulation and policy. New York’s comprehensive draft Guidance for Evaluating Soil Vapor Intrusion in the State of New York was first released for public comment in February 2005. New Jersey’s comprehensive draft Vapor Intrusion Guidance was published in June 2005. Alaska’s Evaluation of Vapor Intrusion Pathway at Contaminated Sites was published in September 2005. Today 16 states, including Alaska, California, Colorado, Connecticut, Indiana, Maine, Massachusetts, Michigan, Minnesota, Nebraska, New Hampshire, New Jersey, New York, Pennsylvania, Washington, and Wisconsin, have policy and regulations to address the VI problem.

In October 2005, the real estate, banking, legal, and insurance industries, together with the Phase I industry, seeking to resolve the uncertainty surrounding VI and clarify how it fits in the property environmental due diligence process, approached ASTM with a request for ASTM to develop a national standard for the assessment of VI. On October 28, 2005, ASTM approved the formation of a Vapor Intrusion Task Group (E50.02.06) with responsibility to develop a standard.

ASTM Task Group

ASTM was selected as the best venue to develop the standard because of ASTM’s internationally recognized consensus-based process that has been used so successfully over the years [4]. ASTM is able to bring together stakeholders representing all sides of an issue and work with them to achieve consensus.

More than 200 professionals volunteered to participate on the ASTM Vapor Intrusion Task Group, including representatives from the environmental consultant industry, lenders, lawyers, corporations, real estate investors and developers, and federal and state regulatory agencies. Both the EPA and the Interstate Technology and Regulatory Council (ITRC) are represented on the Task Group. The ITRC is a state-led, national coalition with representatives from environmental regulatory agencies in 40 states, the District of Columbia, and three federal agencies. In addition, representatives from the Aerospace Industries Association, Mortgage Bankers Association, American Petroleum Institute, Halogenated Solvents Industry Alliance and the Environmental Bankers Association participate on the Task Group.

The Task Group’s objective was to define good commercial and customary practice for conducting a VI assessment on a property parcel involved in a real estate transaction. The specific intent was to establish a methodology to determine whether there is a reasonable probability that VI could present an environmental risk and liability. For commercial real estate transactions, the VI investigation as defined by the standard could be used independently of or as a supplement to a Phase I environmental site assessment (ESA).

The standard in development prescribes a tiered process designed to quickly screen out properties with a low risk of VI. The standard introduces a number of new terms:

1. Vapor Intrusion Condition (VIC) is defined as the presence or likely presence of any chemicals of concern in the indoor air environment of existing or planned structures on a property caused by the release of vapor from contaminated soil or groundwater on the property or within close proximity to the property, at a concentration that presents or may present an unacceptable health risk to occupants.

The standard only deals with indoor air emissions emanating from contaminated soil or groundwater.

  • 2. Potential vapor intrusion condition (pVIC) is defined by the standard when screening indicates the possibility of a VIC, but where there is insufficient data to ascertain the presence or likely presence of chemicals of concern (COC) in the indoor air environment.
  • 3. COC is defined as a chemical in the subsurface environment that is known or reasonably expected to be present, that can potentially migrate as a vapor into an existing or planned structure on a property, and that is generally recognized as having the potential for an adverse impact on human health. COC meet specific criteria for volatility and toxicity and include VOCs, semi-VOCs, and collative inorganic analytes such as mercury. An appendix in the standard lists common COC meeting the criteria.

The process defined in this practice begins with a reasonably conservative screening effort requiring information that would be collected as part of an ASTM E 1527 Phase I ESA. If a pVIC is identified in this initial screening, the process gradually progresses toward a more complex assessment involving increasingly greater use of site-specific data. For those sites unable to be screened out, the process provides alternative methods to determine whether a VIC exists. If a VIC is found to exist, the process describes general mitigation alternatives.

Specifically, the evaluation process consists of four tiers. The first two tiers are screening tiers designed to assess the “potential” for a VI condition (i.e., pVIC) to exist so that properties with a low risk of VI can be screened out quickly and inexpensively as the data justify. If the potential for VI cannot reasonably be eliminated at the Tier 1 and/or Tier 2 levels, the process identifies three options: (a) proceed with a more site-specific and comprehensive investigation (Tier 3), in the hope that this investigation will eliminate VI concerns; (b) proceed directly to mitigation (Tier 4), on the assumption that mitigation conducted preemptively may be more cost effective to address a pVIC; or (c) gain more certainty on the presence of a pVIC through additional investigation. Tier 3 presents a “toolbox” of activities that can accomplish this. Tier 4 addresses mitigation alternatives.

Timeliness may be more important than investigation or mitigation costs during real estate transactions. As such, a user can proceed to any of the tiers in the process. It is not necessary to progress sequentially through each tier. In most cases, however, it is the real estate transaction responsibility to conduct a Tier 1 screening evaluation and possibly a Tier 2 screening evaluation before proceeding to a more costly and time consuming Tier 3 investigation or to Tier 4 mitigation.

The VI assessment process described in the standard is designed to complement existing federal or state VI policies or guidance. The flowchart in Figure 13.1 indicates the four tiers of the VI assessment process when conducted in conjunction with Phase I. Additional details are available in the literature [5].

Future Trends

In many ways, VI presents a major environmental challenge, but it also provides a tremendous opportunity for regulators and responsible parties to work together toward a better future by helping implement the cost-effective protection of public health by preventing further unnecessary VI exposures today.

Vapor intrusion (Vl)-tiered assessment approach

FIGURE 13.1 Vapor intrusion (Vl)-tiered assessment approach.

Numerous VI information internet links are available to assist the technical community. The two most useful (EPA) are provided below.


OSWER Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils (Subsurface Vapor Intrusion Guidance)


RCRA Draft Supplemental Guidance for Evaluating the VI to Indoor Air Pathway Additional sites are provided in the literature [6].


  • 1. Schuver, H„ Vapor Intrusion: Risk and Challenges, EM, A&WMA, Pittsburgh, February 2007.
  • 2. A.J. Buonicore, Upcoming ASTM standards for assessment of vapor intrusion, A&WMA Specialty Conference on Vapor Intrusion, September 2007.
  • 3. A.J. Buonicore, Private communication, 2006.
  • 4. A.J. Buonicore, Private communications, 2007.
  • 5. A.J. Buonicore, Upcoming ASTM Standards for Assessment of Vapor Intrusion, A&WMA Specialty Conference on Vapor Intrusion, September 2007.
  • 6. M. Traister, Understand the Emerging Issue of Vapor Intrusion, CEP, New York, 2007.
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