Eleven years after releasing an initial draft, EPA has finally issued for public comment its proposed vapor intrusion guidance documents: the “Final
Guidance for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Sources to Indoor Air” (VI Guidance) and the “Guidance for Addressing
Petroleum Vapor Intrusion at Leaking Underground Storage Tank Sites” (Petroleum VI guidance). While providing more certainty as to how to investigate and
assess vapor intrusion, the guidance could significantly increase remediation costs, add more uncertainty to business transactions and cause regulators to
reopen sites where cleanup had previously been declared closed.
The 196-page VI Guidance will be applicable to Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), Resource Conservation and
Recovery Act (RCRA) and brownfield grant sites. As the guidance is meant to comply with the National Oil and Hazardous Substances Pollution Contingency
Plan (NCP), it provides for a detailed and through investigation of the potential for vapor intrusion. The highlights of the VI Guidance are as follows:
- VI Concerns. The guidance notes that there must be three conditions present at a minimum for there to be a VI risk:
- Source of vapor-forming chemicals in the subsurface;
- Buildings present or could be constructed in the future; and
- A pathway between the source and the building.
- Conceptual Site Model (CSM). The guidance suggests that the starting point for assessing VI concerns is with the CSM, consisting of:
- Nature, location and spatial extent of vapor-forming chemicals in subsurface;
- Location, use, occupancy and basic construction of existing and future buildings;
- Current understanding of hydrologic and geologic setting; and
- Known or suspected preferential pathways for vapors.
- Initial Screening. Evaluate existing sampling data for reliability and quality and compare to screening criteria using EPA’s separate Vapor Intrusion
Screening Level (VISL) Calculator:
- The VISLs are risk-based “screening level” concentrations that are, for carcinogenic chemicals, based on an extremely conservative (i.e., extremely
protective) cancer risk level of one in one million.
- EPA emphasizes, however, that the VISLs are not response action levels or cleanup standards and that exceedances do not establish that vapor
intrusion will pose an unacceptable health risk.
- Rather, professional judgment must be used when applying the VISLs.
- VI Investigation. As previously noted, the guidance provides for a very detailed investigation:
- Confirm CSM information;
- Accumulate “multiple lines of evidence,” including sampling of various forms of subsurface media;
- Provide for multiple rounds of sampling, including soil gas from various depths;
- Complete groundwater sampling from wells screened for sampling from upper portion of aquifer;
- Provide for sub-slab sampling, but advocate for indoor air sampling;
- Allow for modeling but only “when suitably constructed, documented and verified” and not as the only “line of evidence” to screen out a site; and
- Note concerns for sampling near slab as being different physical conditions from under a building:
- Initial investigation area extends into a 100-foot buffer vertically and horizontally from the plume edge (e.g., limits of exceedance of
drinking water standard in groundwater plume). Some exceptions to the buffer include:
- landfill methane;
- concentrated volatile chemicals; and
- natural gas transmission lines.
- Risk Assessment:
- Weighing site-specific lines of evidence.
- Assessing the lines of evidence.
- Evaluating whether the VI pathway is complete.
- Conducting a risk assessment:
- At this stage for carcinogens response action is generally not warranted if the aggregated (adding the cancer risk level for multiple
vapor-forming chemicals, if present) cancer risk level exceeds one hundred per million.
- Remediation/Mitigation Measures:
- Pre-emptive type mitigation measures such as installing a radon-type system or vapor barriers are considered “interim measures” and will still
require source remediation.
- Indoor air sampling will be necessary to confirm adequacy of abatement/remediation measures.
- An operation and maintenance plan will be necessary to assure proper system operation.
- Community Involvement: Extensive discussion of interaction with community on issues at each stage of the process.
Petroleum VI Guidance.
The 2002 VI Guidance only applied to nonpetroleum releases, so the issuance of the Petroleum VI Guidance specifically applicable to petroleum releases will
have a material impact on how such releases are assessed and remediated. However, the Petroleum VI Guidance only applies to releases from petroleum
underground storage tanks. VI concerns related to releases from aboveground storage tanks, pipelines, and terminals and refineries are not covered. The
highlights of the Petroleum VI Guidance are as follows:
- Chemicals of Concern: In addition to the traditional chemicals found in petroleum products (such as benzene, toluene, ethylbenzene and xylene), the
Petroleum VI guidance also requires that vapor risks associated with gasoline additives (such as MTBE) and chemicals that develop from biodegradation
of petroleum in soil and groundwater (such as methane) also be considered.
- Screening Out Sites:
- Step 1: Lateral Inclusion Zone
- In determining whether or not vapor or indoor air sampling is required at a site, the Petroleum VI Guidance first requires that the “full
extent and location of the contamination” be determined followed by the development of a conceptual site model (similar to the VI Guidance).
- Following this, the “lateral inclusion zone” — “the area surrounding a contaminant mass through which petroleum vapors may travel, intrude into
buildings and potentially pose a threat to human health and the environment” — is determined.
- Further vapor intrusion investigation is not required at any building outside the “lateral inclusion zone.”
- Step 2: Vertical Separation Distance:
- For buildings within the “lateral inclusion zone,” the depth and concentration of the contamination is then compared to the Petroleum VI
Guidance’s “vertical separation distance.”
- For sites with lower levels of contamination (less than 10 mg/kg of benzene and 250 mg/kg total petroleum hydrocarbons in soil and less than 5
mg/kg of benzene and 250 mg/kg total petroleum hydrocarbons in groundwater), if there is at least six feet of clean soil between the bottom of
the building’s foundation and the contamination, no further vapor intrusion investigation is required.
- If the contaminant levels exceed these thresholds (which is likely the case when a light nonaqueous phase liquid, or LNAPL, is present), the
separation distance must be at least 15 feet.
- Ongoing Groundwater Monitoring:
- Since groundwater levels and groundwater plumes can change over time, a single sampling event is not sufficient for determining that further vapor
intrusion investigation is not required.
- The Petroleum VI Guidance states that “periodic monitoring and sampling over more than one annual cycle is generally needed” but does not state how
much sampling is actually needed.
- Site-specific Factors: **
- Certain site-specific factors may require further investigation even if a building is outside the lateral inclusion zone or the vertical separation
distance is met.
- These factors include conditions that would impede natural biodegradation in the soil or groundwater (such as very dry soil or very large buildings
or large areas with extensive impermeable surfaces) or preferential pathways for vapor migration (such as utility lines).
- Modeling Falls Out of Favor:
- Historically, the regulated community relied on computer models (most notably the Johnson & Ettinger) to determine whether a certain
contaminant concentration in soil or groundwater posed a vapor intrusion concern.
- The Petroleum VI Guidance shows a distinct dislike for such models, saying that they should be used only when based on site-specific information
and should not be the soil basis for screening out sites from further investigation.
While EPA could change aspects of the two guidance documents, the current versions present numerous potential issues and questions:
- The VI Guidance is designed for the most stringent remediation sites requiring multiple rounds and types of sampling, and does not adapt well for due
diligence where time is limited.
- Treating pre-emptive mitigation measures as “interim solutions” runs counter to state voluntary and brownfield programs where such measures are used in
combination with restrictive covenants to assure maintenance of the systems, so the impact on state programs is unclear.
- Many states have already developed guidance for addressing vapor intrusion; it is uncertain how EPA’s guidance will interplay with state programs.
- The excessive push for indoor air sampling runs counter to potential liability issues faced by owners or operators.
- Although the VI Guidance is intended for use by EPA in evaluating sites in regulatory programs, it will almost certainly be used as a standard of care
both for transactions and in private tort litigation.
- Plaintiffs in citizen suits under the Resource Conservation and Recovery Act may attempt to use VISLs to establish “imminent and substantial
endangerment” in spite of EPA’s cautionary notes about their use as screening levels only.
- Similarly, plaintiffs in negligence or nuisance actions may attempt to establish elements of those causes of action by using VISLs.
- The risk of citizen suits or common law tort actions may be increased by EPA’s emphasis on community involvement.
- The VI Guidance emphasizes the need to obtain detailed information on off-site source of potential VI, including conducting file reviews that will
increase the costs and time necessary for completing a Phase I as such requirements are incorporated into the ASTM standard.
- Certain statements in the VI Guidance are sure to cause problems for the regulated community and those looking to the guidance for assistance on other
matters, such as “[n]on-detect results for soil samples cannot be interpreted to indicate the absence of a subsurface vapor source.”
- How much data is needed? Under many state cleanup programs, as few as three soil samples and one groundwater sample are sufficient to obtain a
no-further-action determination at a petroleum underground storage tank site. The Petroleum VI Guidance clearly requires much more sampling. However,
it does not clearly specify how much more. Such uncertainty leaves a regulated party at the mercy of a regulator who wants and can now legally justify
getting as much information as possible.
- Will sites be reopened?
- EPA notes in the VI Guidance that VI will be re-valuated in Superfund 5 year reviews where contaminants remain on site “even if vapor intrusion was
not addressed as part of the original remedial action.”
- Over the last several years, states have implemented risk-based cleanup programs for releases from petroleum underground storage tanks, which have
allowed property owners to get no further action determinations without having to determine the full extent of contamination or do any cleanup,
especially if they were willing to put a deed restriction on the property prohibiting residential development and the use of groundwater. Many of
these sites may not meet all the Petroleum VI Guidance’s requirements, such as those for lateral exclusion zones or vertical separation distances.
- So will state agencies reopen “closed” leaking underground storage tank sites and require further vapor intrusion investigation? What about sites
in other state programs? If that happens, will loan covenants be violated or indemnification provisions in purchase and sale agreements be
Conclusion. The issuance of the two guidance documents is a material milestone in the vapor intrusion area, but how the guidance will be further amended and adapted for state programs and due diligence in purchases, leases and loans involving real property as well as the redevelopment itself remains to be seen. Similarly, how the guidance will be used, or misused, in environmental and tort litigation is uncertain. For more information please contact Jim Thornhill, Benne Hutson or Don Anderson.