Alert June 19, 2008

New ASTM Standard Provides Limited Tool for Assessing Vapor Intrusion Risks

Environmental regulators across the country have been scrambling to establish guidance for investigating and addressing an exposure pathway they had not previously considered in setting cleanup standards – vapor intrusion.

Vapor intrusion occurs when volatile contaminants migrate from contaminated groundwater or soil to the indoor air of a building. The most common vapor intrusion cases involve either petroleum contaminants or chlorinated solvents such as tetrachloroethylene and trichloroethylene. These substances may have found their way into soil or groundwater from leaking underground storage tanks, spills, or buried waste. Vapor intrusion does not encompass other instances of indoor air contamination, such as exposure to asbestos, mold, or other potentially hazardous building conditions.

Although regulators agree that developing guidance to address vapor intrusion concerns is now a priority, they are taking disparate and frequently inconsistent approaches. Several key differences relate, for example, to the reliability of modeling and sampling techniques, derivation and utility of screening numbers for groundwater and soil vapor, determination of background concentrations of contaminants in indoor air, and quantification of risk resulting from potential inhalation exposures.

EPA has tried unsuccessfully for six years to finalize its Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils (67 Fed. Reg. 71169, 11/29/02). In the meantime, more than 26 states have developed guidance documents, some of which establish groundwater or soil vapor screening levels for assessing vapor intrusion. The Interstate Technology and Regulatory Council, a coalition of state regulators and other stakeholders, attempted to address the many variations in policy among regulatory agencies in Vapor Intrusion Pathway: A Practical Guideline, published in 2007 (“ITRC Guidance”), which provides a general framework for evaluating the vapor intrusion pathway, rather than prescriptive standards or methods, for use in conjunction with applicable federal or state requirements.

The new concerns about vapor intrusion, coupled with uncertainties about regulatory responses, have proven serious impediments to a variety of transactions. Companies that thought they had resolved their liabilities for waste sites, for example, are finding in some cases that regulators are now seeking to reopen remedies based on vapor intrusion, creating new concerns in acquisitions or financing transactions. Companies addressing contaminated sites in the first instance are now being required to address vapor intrusion concerns in remedy selection, causing similar issues in these companies’ transactions. And, of course, real estate transactions involving properties with actual or potential vapor intrusion concerns face new hurdles.

In an effort to respond to these transactional challenges, ASTM International (formerly the American Society for Testing and Materials) (“ASTM”) formed a task group to develop a consensus vapor intrusion screening standard to facilitate transactions in much the way that ASTM’s E 1527 standard facilitated transactions by establishing an industry standard for Phase I environmental site assessments (“Phase I’s”). ASTM has now issued its “Standard Practice for Assessment of Vapor Intrusion into Structures on Property Involved in Real Estate Transactions” (ASTM E 2600 – 08) (the “ASTM Standard”). Although the ASTM Standard, like the ITRC Guidance, outlines a phased approach to vapor intrusion assessment, its purpose is uniquely limited. The objective of the ASTM Standard is to establish a screening standard for evaluating the potential for vapor intrusion on a property as part of environmental diligence conducted by a prospective buyer, investor, or lender. The ASTM Standard states that it may be used as a voluntary supplement to a Phase I, but evaluation of vapor intrusion remains outside the scope of ASTM E 1527 and the requirements it establishes for satisfying the “all appropriate inquiry” standard under CERCLA.

This advisory summarizes the ASTM Standard, its intended uses, and its explicit limitations. It also highlights strategic issues that both prospective sellers and purchasers should consider in determining whether a vapor intrusion assessment should be performed and how its results should be interpreted.

Overview of the Standard

The ASTM Standard’s purpose is to “define good commercial and customary practice in the United States of America for conducting a vapor intrusion assessment (VIA) on a property parcel involved in a real estate transaction with respect to 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.” Like ASTM E 1527, the ASTM Standard focuses on identifying potential conditions resulting from historical releases of hazardous substances to the environment that may give rise to liability or affect the value of a property that is the subject of a proposed transaction.

The primary objective of a VIA under the ASTM Standard is to determine whether a property may be impacted by vapor intrusion, that is, whether a “potential Vapor Intrusion Condition” (“pVIC”) exists. The ASTM Standard defines a “Vapor Intrusion Condition” (“VIC”) as “the presence or likely presence of any COC in the indoor air environment of existing or planned structures on a property caused by the release of vapor from contaminated soil or groundwater either on the property or within close proximity to the property, at a concentration that presents or may present an unacceptable health risk to occupants” (emphasis added). Accordingly, a VIC or pVIC does not include “de minimis conditions” that pose no “unacceptable health risk” and that would not be subject to enforcement action by regulators. A VIC or pVIC is intended to be analogous to a recognized environmental condition (“REC”) identified in a Phase I.

Another aim of the ASTM Standard is to clarify the scope of ASTM E 1527, which EPA regulations deem sufficient to meet the “all appropriate inquiry” requirement established by the 2002 Brownfield Amendments to CERCLA. Under ASTM E 1527, “indoor air quality” is expressly excluded as “non-scope.” The Phase I standard, however, also defines “REC” as including hazardous substances released “into structures on the property.” The ASTM Standard makes clear that vapor intrusion issues are not within the scope of a Phase I and should be addressed instead through a VIA conducted under the ASTM Standard. The ASTM Standard also says, however, that it is not intended to preclude an environmental consultant from opining in a Phase I regarding “the impact of potential vapor migration onto a target property if deemed necessary to satisfy ‘all appropriate inquiry’” (emphasis added).

Overall, the clear intent of the ASTM Standard is to provide a prospective purchaser, lender, or other user with a quick and inexpensive process for screening out properties with a low risk of vapor intrusion, together with a framework for investigating further should it elect to do so. The ASTM Standard establishes a four-tiered process. The process progresses from a reasonably conservative screening process for determining whether there is a potential vapor intrusion condition to more complex methods of assessment involving increasingly greater use of site-specific data. As they become more site specific, the assessment methods become less and less detailed and prescriptive. Only the first two tiers, which are limited to screening, are considered “in-scope.” The second two tiers, which include full-scale assessment and mitigation, are “non-scope considerations” that are described for informational purposes only.

Tier 1:  Initial Non-Invasive Screening

Similar to a Phase I, the first tier of the ASTM Standard requires screening the target property for vapor intrusion warning signs, through non-invasive means such as government records review. Specifically, Tier 1 screening requires the application of three “tests” to the collected site information. If detailed information is available for contaminated sites in the property’s vicinity, it is more likely a Tier 1 VIA will be conclusive regarding pVICs that may affect the property.

  • First, the “search distance” test identifies any sites known to be contaminated with petroleum or hazardous substances, within a “primary area” near the property and a “secondary area” hydrogeologically upgradient of the property. Search distances are shorter for identifying sites contaminated only with petroleum.
  • Second, the “chemical of concern” test determines whether substances that may result in vapor intrusion impacts are present at any contaminated sites located in the course of the “search distance” test. If a site or sites identified during the search distance and chemical of concern tests are hydrogeologically upgradient of the property and are contaminated with, or suspected to be contaminated with, any COCs, and there is no further information available regarding the extent of the contamination, a pVIC is presumed.
  • Third, the “plume” test evaluates the potential vapor intrusion threat of any known plume of petroleum or hazardous substances (in vapor phase in soil gas or, more likely, in groundwater) in the property’s vicinity, if information is available that delineates or characterizes the plume. The plume test determines whether the plume’s boundaries (or, if the contamination is downgradient from the property, any off-site source of contamination) are within a “critical distance” of structures on the property (or the lot boundary of the property, if there are no structures). “Critical distance” is defined as a lineal distance of less than 30 feet for petroleum hydrocarbons and less than 100 feet for other hazardous substances (including petroleum present as non-aqueous phase liquid or “NAPL”). The environmental consultant conducting the VIA may use a different “critical distance,” however, at his or her discretion based on site-specific conditions, or as required by state regulations or policy. If a plume extends into the critical distance, the test results in a presumption that a pVIC exists; if not, the test deems a pVIC unlikely. Where the available information shows a plume extending into the critical distance but also demonstrates that the plume’s contaminants do not exceed the locally applicable “risk-based concentrations” for assessing vapor intrusion risk (which are typically identified in Tier 2 screening), a pVIC is presumed “unlikely.”

Tier 2:  Site-Specific Numeric Screening

The second tier of the ASTM Standard requires comparing the results of environmental sampling at the target property or nearby sites with screening concentrations for vapor intrusion risk. In effect, Tier 2 screening is an expanded Tier 1 “plume test,” with the benefit of additional site-specific data. As with Tier 1 screening, if the site-specific data shows a plume that exceeds a risk-based screening concentration within a critical distance of the target property, a pVIC is presumed; if not, a pVIC is unlikely.

To assemble the additional data, Tier 2 screening may involve either or both of (i) non-invasive analysis of existing sampling data in prior Phase II environmental investigation reports or remediation status reports and (ii) invasive investigations, including direct environmental sampling to assess vapor intrusion risks. The invasive component may be considerably more difficult when off-site sampling is necessary based on the nature and extent of the contamination.

Inherent in Tier 2 screening (and in Tier 1 screening that yields sufficient data) is identification of applicable “risk-based concentrations” or “RBCs.” The ASTM Standard establishes an order of preference: first, “state generic RBCs” if available; then, either “federal generic RBCs” taken from EPA or another federal agency’s guidance, or “site-specific RBCs” developed by the environmental consultant. As mentioned at the outset, many states have published vapor intrusion guidance documents, which differ considerably. Because the ASTM Standard requires the environmental consultant to look to state RBCs first, Tier 2 screening may yield different conclusions about pVICs at identically situated properties located in different states.

Tier 3:  Comprehensive Vapor Intrusion Assessment

Tier 3 assessment is intended to provide a full evaluation of any pVIC at the target property identified in Tier 1 or Tier 2 screening, with one of three outcomes:  a confirmed VIC, no VIC, or a pVIC with “narrowed certainty” regarding its existence, but which is neither a confirmed VIC nor is ruled out by the assessment. In essence, a Tier 3 assessment is focused on proving the negative – i.e., that a suspected or presumed vapor intrusion condition does not exist.

The ASTM Standard describes several “alternative approaches for data collection” in a Tier 3 assessment including direct indoor air sampling or groundwater, soil gas, and/or sub-slab soil gas sampling accompanied by the use of a site-specific “conceptual site model” that allows extrapolation of indoor air impacts. The ASTM Standard states that a health risk assessment using indoor air sampling data can definitively eliminate a VIC from further consideration. In addition, a pVIC identified through Tier 1 or Tier 2 screening may only become a confirmed VIC if the assessment demonstrates “attribution” of elevated indoor air concentrations to a vapor intrusion pathway from subsurface contamination, rather than “background” levels and other indoor sources of contaminants, such as smoking or off-gassing consumer products.

Tier 4:  Mitigation

The ASTM Standard expressly states that “[s]election, design and implementation of appropriate mitigation is beyond the scope of this practice.” It also contemplates, however, that prospective purchasers or sellers of a property with a pVIC may elect to proceed directly to “pre-emptive mitigation measures” rather than undertaking a detailed evaluation to confirm the presence or absence of a VIC. Mitigation may be more economical than further investigation in some cases. Such an approach may be appropriate, for example, where no duty to report a release of hazardous substances to regulatory authorities has yet been triggered, and a mitigation system can be readily incorporated into the building design as part of a new construction project.

The ASTM Standard describes mitigation as falling into one of three categories: (i) institutional controls, such as deed restrictions; (ii) engineering controls, such as source removal or treatment, vapor barriers and venting, pressurization of buildings, or indoor air treatment; and (iii) “intrinsically safe building design” for new structures, such as well-ventilated underground or first-floor parking facilities or vapor barrier systems. The ASTM Standard lists some general advantages and disadvantages of these mitigation approaches based on relative cost, effectiveness, and appropriateness to particular site conditions.

Strategic Considerations

Among the most important considerations to bear in mind are the limited purposes and scope of the ASTM Standard. It is intended primarily as a tool for prospective purchasers, investors, and lenders to supplement their Phase I evaluations with a conservative screening methodology for identifying potential vapor intrusion conditions. The ASTM Standard is not intended as a guide for complying with regulatory requirements for site investigations, so it does not prescribe a systematic methodology for quantifying or resolving an identified vapor intrusion concern. Likewise, it does not address the prospective seller’s interests, for example, in preserving the value of its property or managing any risks arising from the assessment process.

The following are additional practical issues that prospective buyers and sellers should consider before commissioning, permitting, or interpreting a VIA under the ASTM Standard.

  • Retain environmental consultants with specialized vapor intrusion experience to conduct VIAs. In Appendix X2, the ASTM Standard stipulates that, in addition to the requirements stated in ASTM E 1527, “the environmental professional conducting a VIA should be knowledgeable and/or experienced specifically in the conduct of vapor intrusion investigations.” If vapor intrusion is likely to be an issue, both the prospective seller and buyer have an interest in ensuring that the consultant conducting the VIA has successfully completed vapor investigations and mitigation measures in comparable circumstances and is well aware of current regulatory guidance and practice in that state.
  • Define and plan how to respond to the results of the VIA. The ASTM Standard specifically states that the VIA need not proceed sequentially through the four tiers of potential investigation and mitigation activities. The prospective seller and buyer have an interest in determining at the outset what the scope and sequence of activities will be, and how the interim and final conclusions will be reached and communicated. It may be preferable, for example, to include soil vapor testing as part of a planned Phase II investigation, rather than to rely on the Tier 1 and 2 screening measures outlined in the ASTM Standard. Issues of particular sensitivity to a prospective seller will be whether indoor air testing will be conducted and whether the results of any testing conducted will become reportable to regulatory authorities, tenants, or employees.
  • Tier 1 and Tier 2 are conservative screening methods that may result in a presumption of a potential vapor intrusion condition that does not exist.  The ASTM Standard is useful as a screen to eliminate concerns regarding the many properties with no potential vapor intrusion issues, but not as a tool to make difficult cost judgments for properties with potential problems. Accordingly, the ASTM Standard casts a wide net in Tier 1 screening, requiring consideration of most contaminated sites within one-third of a mile from the target property and other contaminated sites up to one mile hydrogeologically upgradient from the target property. Once a contaminated site is identified in these areas of concern, a VIC is presumed unless proven, through more burdensome investigations, not to exist. To reach the conclusion that a pVIC is unlikely, Tier 2 or 3 work must generate sufficient data, potentially including off-site sampling results, to determine that there is no likely pathway from the off-site property to the target property.
  • The ASTM Standard does not establish a protocol for completing an investigation that complies with applicable regulatory standards. The ASTM Standard repeatedly cautions the user and the environmental professional that “available regulatory and technical guidance documents for vapor intrusion contain disparate and often conflicting recommendations for data needs, data collection methods, and screening or evaluation criteria.” It is not the intent of the ASTM Standard to reconcile those requirements. The ASTM Standard likewise states that it is not intended to be used as a basis for determining whether a vapor intrusion exposure pathway is complete or may pose an unacceptable risk to human health, as those also are questions that can be determined only with reference to applicable regulatory standards.
  • Beware of the ASTM Standard’s express limitations. One apparent goal of the ASTM Standard is to create some protection for environmental consultants against claims that they failed to identify and disclose potential vapor intrusion risks during a Phase I or that a limited VIA failed to meet “good commercial and customary practice.” Tier 3 assessments and Tier 4 mitigation are expressly outside the scope of the ASTM Standard and require separate scopes of work based on applicable regulatory requirements. In negotiating access terms with prospective sellers or terms of engagement with environmental professionals, it is not enough, therefore, simply to prescribe a “vapor intrusion assessment completed in accordance with ASTM E 2600.”


The ASTM Standard creates a new category of environmental assessment – the ASTM-compliant vapor intrusion assessment. Users of such VIAs can now point to an ASTM standard practice as evidence that they followed a standard of reasonable care in assessing potential vapor intrusion issues at the property they are selling, purchasing, or financing. The scope and intended purposes of the ASTM Standard, however, are narrowly circumscribed. Before commissioning or permitting any work to assess potential vapor intrusion, it is imperative that a prospective buyer or seller carefully consider the kind and extent of the investigation to be conducted, the results that will be generated, and the lasting economic and legal ramifications that any such results may entail.