Over the last decade, regulators have accelerated their focus on vapor intrusion risk at hazardous cleanup sites. This has led to new cleanup standards, policies and guidance to evaluate potential risks, environmental investigation requirements for brownfield redevelopments, and the reopening of previously closed remedial actions. Recently, attention has turned from chronic to acute vapor intrusion risk. Although protection of human health is paramount, this recent focus has been plagued with concerns about the validity of the underlying science and a lack of comprehensive guidance from regulators on how to respond. This article explores the evolution of vapor intrusion regulation, particularly developments addressing acute risk, as well as trends in vapor intrusion- related litigation.

Vapor intrusion occurs when vapor-forming chemicals migrate from contaminated soil or groundwater into overlying occupied spaces. Chemicals may collect under structures and infiltrate into buildings. This has been found to occur through cracks in foundations and conduits such as sewers and electric lines. Once inside a building via a completed pathway, concentrations of vapor-forming chemicals may increase and cause health risks. Regulatory attention has focused predominately on volatile organic compounds (VOCs), particularly trichloroethylene (TCE) and tetrachloroethylene (PCE), and their degradant products (e.g., vinyl chloride), as well as petroleum-related constituents like benzene. VOCs historically have been used in a variety of industrial settings, particularly as solvents and for dry cleaning. Given this widespread use, vapor-forming chemicals have been identified at cleanup sites nationwide. Some cleanup sites have been closed by regulators, in the period before attention was focused on vapor intrusion, and in some cases, properties have been transferred or redeveloped. Now, with increased attention on vapor intrusion risk, regulators must grapple with how to address the issue at both active and previously closed cleanup sites.

Regulatory focus on vapor intrusion has evolved over the last 30 years. During the 1980s, regulators were concerned with the risks of radon from natural sources. By the 1990s, attention began to turn to potential chronic exposure risk to vapor intrusion from VOCs and other industrial chemicals. By the early 2000s, regulators increasingly were incorporating vapor intrusion remedial requirements into ongoing cleanups to mitigate potential risk from chronic exposure, while also looking at closed sites to require, in some instances, further investigation and remediation to address vapor intrusion risk not previously evaluated.

The U.S. Environmental Protection Agency’s (EPA) first formal attempt to address vapor intrusion came in November 2002, when the Office of Solid Waste and Emergency Response (OSWER) released draft guidance. That guidance, focusing almost exclusively on chronic risk, languished in draft. In 2009, however, EPA’s Inspector General issued a report critical of the delay. As a result, OSWER reopened the docket for public comment and, in June 2015, issued technical guidance: Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air, OSWER Publication 9200.2-154 (June 2015). The guidance included protocols for vapor intrusion investigations, identified conditions for complete pathways, and provided criteria for response actions where vapor intrusion is determined to pose an unacceptable human-health risk, generally as a result of chronic exposure. EPA specified that the guidance was for use at sites being addressed pursuant to the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and the Resource Conservation and Recovery Act (RCRA) and, under certain circumstances, by state agencies.

EPA further incorporated vapor intrusion evaluations into the site-cleanup process for existing and new cleanup sites. In 2012, EPA issued guidance recommending consideration of vapor intrusion when evaluating remedy protectiveness during the Superfund five-year review process, even if it was not originally considered as part of the selected remedial action. Assessing Protectiveness at Sites for Vapor Intrusion: Supplemental Guidance to the Comprehensive Five-Year Review Guidance, OSWER Directive 9200.2-84 (Dec. 3, 2012). This recommendation has resulted in the identification of vapor intrusion as an issue at some National Priority List sites with long-existing remedial actions, triggering requirements for further investigation and, potentially, new response actions.

EPA also undertook a toxicological assessment of TCE. EPA’s Integrated Risk Information System (IRIS) system generally recognizes that EPA will use information from an IRIS toxicology review to inform risk management decisions and develop regulations to protect public health. The 2011 Toxicological Review of Trichloroethylene in Support of the Integrated Risk Information System, CAS No. 79-01-6 (Sept. 2011) (IRIS Review) identified a safe level of lifetime exposure (called a “reference concentration”) for TCE, based on a review of studies of chronic health risks. The IRIS Review also found evidence “suggestive of the potential” for short-term exposure to TCE resulting in hazards for women in the first trimester of pregnancy due to potential teratogenic effects, i.e., potential cardiac malformation in developing fetuses. The IRIS Review’s position on potential teratogenic effects associated with short-term TCE exposure, however, was based on a single 2003 study on fetal rats conducted by Paula Johnson, a doctor of veterinary medicine. Paula D. Johnson, et al., Envtl. Health Persp., 111(3): 289–92 (Mar. 2003) (available here) (Johnson Study).

The IRIS Review’s finding that short-term TCE exposures might cause teratogenic risks generated concern from industry, consultants, and other stakeholders about the underlying data used to support the conclusion. For example, in 2012, two respected toxicologists sent a white paper to EPA Headquarters questioning the IRIS Review’s conclusion that TCE is a teratogen. Robert Scofield, D. Env., Principal and Director of the Center for Exposure, Exponent, and Keith Tolson, Geosyntec Consultants, TCE Interim Short-Term Removal Action Level White Paper (Apr. 16, 2012) (on file with authors) (White Paper). The White Paper noted that other federal agencies reviewing the same data did not reach the same conclusion. The authors reviewed all toxicology and epidemiology studies regarding cardiac defects and TCE, and found the majority of scientific studies failed to find a link. Those studies which found a link had well-documented methodological flaws or were based on designs with limited or no value in determining causation. Moreover, the White Paper pointed out that the IRIS Review relied on studies that evaluated chronic, not short-term, exposure. In addition, the White Paper’s authors noted that studies indicating a potential teratogenic effect have not been replicated, even by the same researchers or at doses similar to those in the studies subject to the IRIS Review.

Much of the criticism of the IRIS Review centers on the limitations of the Johnson Study, specifically its “methodology, reported findings, and [] scientific credibility.” White Paper at p. 27 (citing other researchers); see also Letter from Dorothy Rothrock, President, California Manufacturers & Technology Association to Kenneth Olden, Director, National Center for Environmental Assessment, U.S. Environmental Protection Agency (Nov. 26, 2014) (on file with author). In fact, even the IRIS Review recognized the limitations of the study: “The evidence for an association between TCE exposures in the human population and the occurrence of congenital cardiac defects is not particularly strong.” IRIS Review at 4-565. The IRIS Review further notes that the animal data is “not unequivocal” and “lack[s] a clear dose-related response.” Id. Notwithstanding these statements, EPA has rejected criticism of the IRIS Review and defended its conclusions concerning potential acute exposures risks from TCE. For example, in 2015, in response to concerns expressed by the Halogenated Solvents Industry Alliance, EPA stated its position that “information quality concerns were addressed through the IRIS assessment development process . . . [and] are not new.” Letter from L. Kadeli, Acting Assistant Administrator of EPA Office of Research and Development, to Ms. Faye Graule, Executive Director of the Halogenated Solvents Industry Alliance, Inc. (Mar. 19, 2015) (available here). EPA subsequently declined the Halogenated Solvents Industry Alliance’s offer to fund further research into the cardiac issues identified by the Johnson Study.

Despite questions about the underlying science, federal regulators turned to developing guidance to address short-term TCE vapor intrusion risk. EPA Region 9 was the first to act in response to the IRIS Review when, in June 2014, its toxicologists issued a memorandum with acute TCE exposure thresholds that, if surpassed, would trigger recommended response actions. Technical Memorandum from Gerald Hiatt, Senior Regional Toxicologist, and Daniel Stralka, Regional Toxicologist, EPA Region 9, to Enrique Manzanilla, Director, Superfund Division, EPA Region 9, EPA Region 9 Interim Action Levels and Response Recommendations to Address Potential Developmental Hazards Arising from Inhalation Exposures to TCE in Indoor Air from Subsurface Vapor Intrusion (June 30, 2014) (Technical Memo). For example, the Technical Memo established an “accelerated response” threshold of 2 µg/m3 for residential properties. If the threshold is exceeded, mitigation measures are to be evaluated and implemented within a few weeks. If exposures exceed 6 µg/m3, the threshold for an “urgent” response, mitigation measures should be “immediately” implemented, and any additional exposure should be prevented until concentration levels fall below 2 µg/m3. According to the Technical Memo, evacuation and temporary relocation may be required when the urgent exposure threshold is exceeded.

On July 9, 2014, the EPA Region 9 Superfund Director issued a memorandum adopting the Technical Memo’s guidelines to assist Region 9 staff in “evaluat[ing] and manag[ing] the many issues that arise when investigating or responding to vapor intrusion at a site.” Memorandum from Enrique Manzanilla, Director, Superfund Division, EPA Region 9, to Region 9 Superfund Division Staff and Management, EPA Region 9 Response Action Levels and Recommendations to Address Near-Term Inhalation Exposures to TCE in Air from Subsurface Vapor Intrusion (July 9, 2014) (Region 9 Policy). The Region 9 Policy included short-term action levels for TCE inhalation in indoor air via the vapor intrusion pathway and established urgent response levels, which, if triggered, recommended an “immediate” response.

State regulators have relied upon the Region 9 Policy and IRIS Review to adopt policies addressing short-term TCE exposure. For example, even before issuing its Technical Memo in 2014, EPA Region 9 sent a December 2013 letter to the San Francisco Bay Regional Water Quality Control Board addressing vapor intrusion at state-led Superfund sites. Letter from Kathleen Salyer, Assistant Director, EPA Region 9 Superfund Division, California Site Cleanup Branch, to Stephen Hill, Chief Toxics Cleanup Division, California Regional Water Quality Control Board—San Francisco Bay Region (Dec. 3, 2013). In its letter, EPA instructed the state regulator to use some of the same short-term action levels later identified in the Technical Memo. This was followed, in late 2014 by the same state agency, with the issuance of an Interim Framework for Assessment of Vapor Intrusion at TCE-Contaminated Sites in the San Francisco Bay Region, San Francisco Bay Regional Water Quality Control Board (Oct. 16, 2014) (available here) (Interim Framework). That guidance “provisionally selected residential and commercial/industrial indoor air interim response action levels for TCE that are the same as [those selected in the Technical Memo by EPA Region 9] to determine when to initiate a prompt response action.” Interim Framework at 18.

Other states have proceeded to use the IRIS Review for TCE and follow the approach in the Region 9 Policy. In August 2014, for example, the Massachusetts Department of Environmental Protection issued a fact sheet entitled TCE Toxicity Information: Implications for Chronic and Shorter- Term Exposure that relied upon the IRIS Review to identify short-term exposure action levels for TCE. Exceedances of identified action levels could result in an immediate response action that could include evacuation. More recently, in August 2016, the Ohio Environmental Protection Agency issued its own Guidance Document—Recommendations Regarding Response Action Levels and Timeframes for Common Contaminants of Concern at Vapor Intrusion Sites (Ohio Guidance). The Ohio Guidance set short-term action levels for TCE exposure in indoor air. Similar to the EPA Region 9 Policy, the Ohio Guidance indicates that evacuations may be mandated in circumstances where TCE concentrations exceed specified action levels.

At the national level, EPA continued its prioritization of vapor intrusion risk by issuing a January 9, 2017, rule incorporating a subsurface intrusion component into the hazard-ranking system used to rank cleanup sites for placement on the National Priorities List. 82 Fed. Reg. 2760 (Jan. 9, 2017). That rule, however, was frozen by the new Trump Administration. At the time of this writing, it appears the new administration will allow the rule to take effect, but it remains to be seen how the administration will address vapor intrusion more broadly, particularly whether it will revisit the evaluation of short-term risk.

Acute Vapor Intrusion

A variety of critical questions are raised by EPA and the states’ continued focus on acute vapor intrusion risk. First, and foremost, are the questions—addressed above—about the strength of the IRIS Review’s technical basis for short-term TCE vapor intrusion risks. This is not just an academic issue; vapor intrusion policies, including those flowing from the IRIS Review, are driving cleanup goals and requiring a substantial investment of funds by regulators and industry. For example, the Michigan Department of Environmental Quality requested an additional $2.6 million in its fiscal year 2018 budget to address vapor intrusion and recently reported that as many as 4,000 sites may require further assessment for vapor intrusion risk. Beth LeBlanc, As vapor intrusion concerns emerge, EPA tests Lansing homes, Lansing St. J. (Mar. 3, 2017) (last visited June 13, 2017).

There are other procedural and practical concerns with EPA’s approach. EPA Headquarters has declined to take a national approach on vapor intrusion risk, perhaps including a formal rulemaking process that would include public comment, instead allowing the regions to develop independent policies. The Region 9 Policy was issued as guidance and had neither the benefit of public comment nor peer review. EPA’s position has been that the Region 9 Policy is not binding and, rather, only provides guidance to be applied by EPA in making site-specific decisions. This reasoning, however, is belied by the implications of the policy. First, state agencies are relying on the document as the only federal policy applying the IRIS Review by providing short-term action levels and recommended responses. As such, the “guidance” document is driving decision making at the state level. Furthermore, adoption of those thresholds by state agencies may effectively become a binding standard at some sites as an applicable or relevant and appropriate requirement pursuant to Section 121(d) of CERCLA.

In addition, the recommendation in the Region 9 Policy specifies “immediate” action if certain short-term exposure thresholds are exceeded. An immediate response, however, cannot provide time for further regulatory decision making and public processes like those associated with issuance of a record of decision or the adoption of standards via implementation of a time-critical removal action. In the event of an exceedance of short-term thresholds, available evidence and practice indicates EPA would seek an immediate response and, if property owners are not cooperative, likely turn to state or local agencies with emergency authorities for assistance. As a result, the Region 9 Policy is functioning more as a formal regulation than a tentative guide to future agency decision making. This is an inappropriate use of agency guidance. See, e.g., McLouth Steel Prods. Corp. v. Thomas, 838 F. 3d 1317, 1320–21 (D.C. Cir. 1988) (“to be exempt from legislative rulemaking requirements a policy statement must be tentative and not intended to be binding”).

The thresholds in the Region 9 Policy are also inconsistent with permissible exposure levels (PEL) adopted by the Occupational Safety and Health Administration (OSHA) for worker exposure to TCE. For an eight-hour workday in a commercial building, EPA would require a remedy within “weeks” for TCE exposures above 8 µg/m3 and “immediately” at 24 µg/m3. In contrast, OSHA’s exposure limit for workers exposed to TCE is orders of magnitude greater, at 537,000 µg/m3. This inconsistency could lead to absurd results. For example, a workplace using TCE could have permissible indoor-air contamination levels below OSHA’s PEL, but orders of magnitude above EPA’s thresholds. If a release from those operations causes a plume of groundwater contamination, and downgradient vapor intrusion, EPA’s policy could require an “immediate” response for those downgradient buildings, while no action would be required for the workers exposed to a greater TCE concentration. Although EPA indicated that OSHA may revisit the TCE PEL, two years have passed without any action taken. This discrepancy calls into question the reasonableness of the action levels, and proposed responses, in the Region 9 Policy.

Finally, EPA has failed to identify how an “immediate” response action would be implemented if an acute TCE threshold is exceeded. The EPA Region 9 Policy recommends evacuations if TCE concentrations exceed certain thresholds in indoor air. The policy, however, provides no basis for EPA’s authority to require evacuations or guidance detailing how to orchestrate such evacuations. Publicly stating an evacuation may be necessary to protect human health, but failing to provide implementing instructions increases risks and uncertainties for the public, property owners, municipalities, and industry.

How EPA will address vapor intrusion acute exposure requiring “immediate” response actions, therefore, remains uncertain and raises a host of practical questions. It is unclear, for example, how EPA would order or coordinate an evacuation. For example, although EPA may have leverage to request that a responsible party vacate its own building, this avenue will be foreclosed where responsible parties no longer own the relevant property or where a groundwater plume has extended off-site under properties owned by others. The situation will only be more complicated where multiple responsible parties may be involved. There also is substantial uncertainty over how costs for any evacuation required by EPA would be covered, particularly where properties are not owned by a responsible party acting under regulatory oversight. Additionally, given that the only claimed scientific evidence of short-term exposure risk is for women of child-bearing age, it remains unclear whether EPA has a reasonable legal basis to require evacuation of others solely on the basis of acute exposure.

Evacuations and temporary property closures already have occurred as a result of TCE vapor intrusion. For example, a public school in El Cajon, California, was shut down for the 2015–2016 academic year amid concerns about TCE vapor intrusion from a groundwater plume. Public schools in Winston-Salem, North Carolina, and Millis, Massachusetts, were closed in 2015 and 2016, respectively, due to similar concerns. In 2016, an evacuation was ordered at two Navy office buildings in Yorktown, Virginia. These cases involved publicly owned buildings, where it was feasible for regulatory agencies to implement property closures independently. Yet, private party evacuations may become more commonplace as state agencies adopt response action levels similar to those in the EPA Region 9 Policy and investigate vapor intrusion more regularly. Last year, the San Francisco Bay Regional Water Quality Control Board, which was an early adopter of the same Region 9 acute-exposure thresholds, required a coffee freeze-drying facility to implement response measures at its property, including relocating employees after vapor intrusion was identified above action levels.

Matters will be much more complicated in scenarios where a groundwater plume causes a vapor intrusion risk to buildings owned by private, non- potentially responsible parties. EPA, and even some state agencies, may not have authority to require an “immediate” evacuation or to otherwise shut down a building. And, as noted above, even where such authority can be identified, perhaps via concurrence from local health agencies, EPA has failed to prepare clear procedures for implementing an evacuation. The absence of such procedures creates substantial uncertainty and risk. If EPA reasonably expects to require evacuations (or request other agencies to require evacuations), a failure to prepare necessary procedures and processes in advance might be deemed arbitrary and capricious. This failure could delay otherwise necessary evacuations and also result in a web of potential legal claims for business interruption, negligence, property damage, and personal injury in the event of a poorly implemented response by regulators.

Evolving Regulatory Landscape

The evolving regulatory landscape concerning vapor intrusion has created a heightened litigation risk for potentially responsible parties and other property owners. Plaintiffs, for example, are turning to federal RCRA citizen suits to pursue vapor intrusion claims. Although plaintiffs cannot collect punitive damages, RCRA can be an attractive tool because it allows for injunctive relief to require remediation and may allow for the recovery of attorneys’ fees. Thus far, however, courts have been split on a number of the key issues associated with these cases.

To proceed with a RCRA claim, plaintiffs must show that contamination presents “an imminent and substantial endangerment to health or the environment.” 42 U.S.C. § 6972(a)(1)(B). Courts have not, however, developed a uniform approach on what is required to meet this threshold in the vapor intrusion context. Some courts have held there must be actual exposure for a plaintiff to sustain a claim. For example, in Newark Group, Inc. v. Dopaco, Inc., No. 2:08-cv-02623 (E.D. Cal. Apr. 1, 2010), the court required more than proof of high groundwater contamination levels and the migration of a plume onto neighboring properties to sustain RCRA claims, finding that “[s]omeone has to actually be exposed to vapors.” Similarly in SPPI-Somersville, Inc. v. TRC Companies, 04-2468, 2009 WL 2612227 (N.D. Cal. Aug. 21, 2009) (SPPI), the lack of development on contaminated properties precluded a finding of an imminent and substantial endangerment because there was no threat of exposure. In contrast, in Sisters of Notre Dame v. Garnett-Murray, 010-01807, 2012 WL 2050377 (N.D. Cal. Jun. 6, 2012), the court held that the lack of a complete vapor intrusion pathway did not preclude a finding of an imminent and substantial endangerment where the plaintiffs established that a threat of vapor intrusion was present.

Courts also are split on whether RCRA citizen suits are permitted where the government is implementing a cleanup. In SPPI, the Northern District of California found “no basis for the relief plaintiffs seek because the contamination is already being addressed by the [California Department of Toxic Substances Control].” SPPI at *15. Other courts have allowed such suits to proceed. In Forest Park National Bank & Trust v. Ditchfield, 881 F. Supp. 2d 949 (N.D. Ill. 2012), the court found no evidence the suit would interfere with relevant government action and allowed the suit to proceed because it sought “to jumpstart a nonexistent cleanup action.” 881 F. Supp. 2d at 972. The determinative issue for courts, therefore, may be less whether there is government involvement and more whether government action is actively addressing an actual or threatened imminent and substantial endangerment.

Plaintiffs are advantaged further if a court permits class action certification for vapor intrusion claims, for example, where there is an allegation that multiple buildings in an area are impacted. Courts are split, however, on whether such certification is appropriate. To evaluate whether class certification will be allowed, courts focus on whether common questions of liability or damages among the class members will predominate over individual questions. Some courts have found the common questions to predominate in the vapor intrusion context. For example, in Mejdrech v. Met-Coil Systems Corp., 319 F.3d 910 (7th Cir. 2003), the Seventh Circuit affirmed certification for the purpose of determining whether the defendant caused the contamination in question. Individual class members’ injuries and damages, however, were to be reserved for individual hearings. In contrast, in the more recent Ebert v. General Mills, 823 F.3d 472 (8th Cir. 2016), the Eighth Circuit denied class certification. The court held it was necessary to examine the properties individually to determine whether the alleged contamination threatened each property, and if so, whether the contamination is “wholly, or actually, attributable” to the defendant in each instance. Those issues, the court held, predominated over the common questions of liability. 823 F.3d at 479.

Although RCRA claims may provide a basis for federal question jurisdiction, common law claims also appear frequently in the vapor intrusion context. Claims are frequently made for property damage (usually in the form of diminution of property value) and for business interruption. Nuisance and trespass claims also are common. In contrast, personal injury claims arising from vapor intrusion rarely appear in publicly reported cases. The reasons for this are uncertain; it could be because few injuries are associated with vapor intrusion, such claims have been rapidly settled out of court, or because the complexity of proving causation has deterred litigation.

If regulatory agencies continue to adopt and implement short-term vapor intrusion policies, an uptick in private lawsuits alleging common law claims concerning property damage, business interruption, and even personal injury, as well as RCRA citizen suits, also is to be expected in response to increased cleanup requirements and short-term response actions.


Increased attention to short-term vapor intrusion exposure risk by regulators likely will continue. Further evaluation of the science underlying the findings presented in the IRIS Review may be pursued by EPA under the new administration or independently by stakeholders, which could result in the redrafting of documents such as the EPA Region 9 Policy. Absent a reconsideration of these policies, it is incumbent upon regulatory agencies to develop clear implementation guidance for urgent and immediate response actions. EPA also should evaluate further whether the types of response actions identified in the EPA Region 9 Policy are reasonable and contain clearly identified legal bases.

In the meantime, stakeholders should be prepared to respond to short-term risks where exposures exceed thresholds and incorporate vapor intrusion mitigation measures into site cleanup plans. Concomitantly, the continued attention to vapor intrusion makes it likely that private lawsuits alleging RCRA and common law claims will continue. Due to the limited case law in this area, courts are likely to be called upon to provide litigants with more insight into adjudication of these claims.


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