Vapor intrusion (VI) is the term used for gas vapors migrating from subsurface sources into structures where people live, work and gather. Vapor intrusion generally occurs when there is a migration of volatile chemicals, such as from petroleum, solvents or volatile dry cleaning chemicals, from contaminated groundwater or soil into an overlying building. In certain extreme cases, the vapors may accumulate in occupied buildings to levels that may pose near term safety hazards (e.g., explosion), acute health effects or aesthetic problems (e.g. odors). In most cases, however, the levels are low and concerns are whether long-term exposure to the low levels of vapors can present a risk of chronic health impacts. Vapor intrusion can sometimes be difficult to identify due to the use of similar substances in the buildings such as paints or cleaners. When it is discovered, it can be a big “surprise” to landowners because suddenly the landowner may have liability for conditions that occurred on the property many years ago or that may be emanating from offsite.

It was not until about 10 years ago that the chronic effects of vapor intrusion received attention from the U.S. Environmental Protection Agency (EPA), starting with issuance of draft guidance in 2002.[1] EPA quickly realized that the study of VI is extremely complex. Because of these complexities, it has taken the EPA years to update its draft 2002 VI guidance document. On April 15, 2013, EPA finally issued draft vapor intrusion guidelines for public comment. EPA issued two draft guidelines: (1) Office of Underground Storage Tanks (OUST) Vapor Intrusion Guidelines; and (2) Office of Solid Waste and Emergency Response (OSWER) Vapor Intrusion Guidelines. The first document addresses petroleum contamination from regulated underground storage tank (UST) sites. The second guidance document covers all other vapor intrusion sites, although it specifically states that the OUST document may be used for petroleum releases not expressly covered in its scope (e.g., petroleum released from unregulated USTs, aboveground storage tanks (ASTs), etc.). These documents may be found at http://www.epa.gov/oswer/vaporintrusion/index.html .

EPA’s 2002 draft VI guidelines were never finalized as the science of vapor intrusion continued to advance. Meanwhile, the states tried to fill in the gaps, leading to a patchwork of requirements, with some states having detailed requirements and others having none. In addition, groups such as the Interstate Technology & Regulatory Council (ITRC), a public-private coalition, and the American Society of Testing and Materials (ASTM) developed guidelines and standards for evaluating vapor encroachment. The combination of EPA’s stagnant guidelines, the variety of state guidelines, the ASTM standards and the ITRC Guidelines, created an uncertainty for the regulated community. Where one state may require significant vapor intrusion corrective actions, another may require nothing at all. It is anticipated that the 2013 draft guidance will ultimately result in nationally consistent standards and bring greater predictability to the regulated community. Of course, the increased standards will also bring greater complexity and potentially greater costs.

The EPA Draft Guidelines may have significant impacts on how contaminated sites are assessed and remediated in the future. The guidelines are highly prescriptive, providing the framework that EPA believes is appropriate for vapor intrusion assessment and mitigation, along with some flexibility on evidence to use in the assessment of vapor intrusion risks. EPA encourages the use of “multiple lines of evidence” to assess the vapor intrusion pathway and the risks presented. Some of these “multiple lines of evidence” include soil, groundwater, sub-slab sampling, and it is anticipated that not all of the multiple pathways will need to be evaluated in every situation. EPA also emphasizes that temporal and spatial variability are important factors for how VI affects structures. As a result, multiple samples must be obtained to get a VI pathway snapshot, with some re-sampling over time to fully understand the VI problems at a site. This sampling will be time-consuming and expensive, adding costs to a project.[2] EPA continues to push that the goal is to develop a permanent remedy (i.e., site cleanup by removal or other measures to address the contaminants) and it considers VI mitigation as only an interim measure. Vapor mitigation comes in several forms. In some cases, a chemical vapor-resistant barrier may be installed to prevent chemical gas migration into the building. Other methods include venting of the soil gas from underneath the building foundation to allow the gases to vent to the atmosphere, instead of entering the building. Another form of mitigation includes the use of fans that apply suction to the soils beneath the foundation and the chemical vapors are exhausted from a small exhaust pipe. The goal of each method is to prevent inhalation exposure hazards within buildings.

There are a number of issues raised by the Agency guidelines:

1. Both draft guidelines require a data-intensive study of the VI pathway during the site assessment. This will substantially increase the costs of site assessment at sites with a VI risk.

2. Most states have a leaking petroleum underground storage tank fund to assist with the cleanup of petroleum contaminated sites. The OUST document specifically states that the assessment of VI is considered part and parcel with the UST regulatory requirements for suspected releases and confirmed releases. Thus, it appears that the guideline will affect UST closures, site assessments and cleanups. However, the OUST document does not address how the states will use their trust funds to assess and mitigate petroleum vapor intrusion. If addressed, the substantial costs could have significant impact on a state’s ability to keep its fund solvent.

3. EPA’s emphasis on permanent remedies and its view that VI mitigation as an “interim solution” may conflict with current policies of state programs, which may allow VI mitigation as a permanent solution for a release at a site.

4. A legal issue that may be destined for the courts is whether OSHA or EPA has jurisdiction over indoor air standards for the occupational environment.

5. EPA developed these guidelines over the years based primarily on its experience managing contaminated sites that affected residences. The VI issues for the residential setting clearly are distinct from those in the industrial or even commercial setting. Thus, application of the guidelines for non-residential settings must be carefully monitored for overly conservative assumptions that increase project costs with little to no additional benefit.

6. Recent studies for TCE, a typical industrial solvent and dry cleaning chemical, have led EPA to consider much more stringent “short-term exposure limits” for that chemical. If EPA proceeds with this approach, the decision may lead to the reopening of previously-closed sites. In addition, EPA may subject additional chemicals to tighter standards in the future.

Perhaps the issue of greatest concern is how these standards will be used to address sites that have been closed for many years. It is predicted that the latent discovery of vapor intrusion may trigger parties to debate and litigate over whether cleanup orders and decrees should be reopened. Such reopeners may mean additional cleanup liabilities for parties who previously cleaned up a site or otherwise settled their liability with regulatory agencies. Whether such sites can be reopened will be a significant legal issue, especially where orders or decrees specifically limit such reopening. An example of concerns with reopening sites comes  in New York, a state that has already taken a hard look at vapor intrusion, where more than 400 sites have been reopened to consider VI problems and, of those, 74 were determined to require additional action (as of January 2013).

VI has been listed as one of the top 10 environmental concerns of lenders and general counsel. Companies and other entities that learn of a volatile and toxic chemical at or near its property should obtain legal advice. This concern is even greater where a property has undergone cleanup years ago and has been “closed” by the regulatory agency. In addition, concerns are presented by the risk of “toxic tort” or similar lawsuits as awareness of the risks of vapor intrusion increase, raising concerns of the building occupants. This may create additional toxic tort fodder for creative plaintiff lawyers.

Kilpatrick Townsend remains vigilant in its monitoring of vapor intrusion issues, counseling its clients to thoughtfully consider vapor intrusion issues when they arise.


For more information on vapor intrusion:

“N.C. Attorneys Beware (or Be Aware): Vapor Intrusion is Changing the Rules,” N.C. Bar Association, Environment, Energy & Natural Resources Section, Newsletter, February 8, 2013, available at http://www.kilpatricktownsend.com/en/Knowledge_Center/Publications/Articles/2013/02/N.aspx 

"Attorneys Beware: RCRA Is Rapidly Becoming a Powerful Tool for Vapor Intrusion Litigation,” BNA Daily Environment Report, September 2012, available at http://www.kilpatricktownsend.com/en/Knowledge_Center/Publications/Articles/2012/09/Attorneys_Beware.aspx 

Construction Law Update 2013, New Developments In Environmental Law and Regulation chapter, Aspen Publishers, May 2013, (includes a section on vapor intrusion) available at http://www.aspenpublishers.com/ 

Cleaning Up Our Act: New Developments in Environmental Law – 2013 Environment, Energy & Natural Resources Section Annual Meeting and 25th Anniversary, Indoor Air Quality/ Vapor Intrusion, Apr. 26, 2013, manuscripts and presentation available at https://www.ncbar.org/cle/bookstore/13513      


[1] The 2002 draft guidance is generally considered the first EPA draft guidance, but it technically superseded the draft RCRA Supplemental Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway issued just one year earlier.

[2] As a result, in some cases, owners and operators of certain buildings may decide on a cost benefit analysis that preemptive mitigation of vapor intrusion for a building, especially for new construction, is desirable and may prevent time delays. For example, in some cases, preemptive mitigation may be more cost-effective, avoid undesirable time delays and head off any claims of any risk presented by VI in the building.

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