The following article was originally published on Law360 on August 27, 2014. Posted with permission.

EPA's Concern Over TCE Vapor Intrusion Is Misguided

By Richard C. Coffin, R. Morgan Gilhuly, and J. Tom Boer

On July 9, 2014, the Director of the U.S. Environmental Protection Agency's Superfund Division in Region 9 issued a memo to staff setting an “operational framework” to address “inhalation exposures [to trichloroethylene] in indoor air from the subsurface vapor intrusion pathway” at Superfund sites throughout the region.[1]

The Region 9 policy framework relies upon a June 30, 2014 technical memo[2] prepared by EPA toxicologists summarizing Region 9’s perspective on short-term TCE exposure. In the EPA Memo, Region 9 asserts that there is a significant public health concern associated with very short periods of exposure (i.e., days) to very low concentrations of TCE that migrate from groundwater to indoor air. The EPA Memo states that drastic measures, such as the evacuation of existing buildings, are necessary to protect the public health where short-term exposure to TCE occurs as a result of “vapor intrusion” from groundwater at Superfund sites. The policy announced by the EPA Memo is significant not only because of the controversial toxicology upon which it relies and the drastic measures it purports to require, but also because Region 9 has stated that it is leading a change in policy that will eventually extend nationwide to all Superfund sites, and perhaps to other federal programs as well.[3]

This article reviews the substance of the EPA Memo, the controversial toxicology underlying it, the regulation of TCE exposure in contexts outside the sphere of Superfund and the potential impact and practical consequences of the policy adopted in the memo. We conclude that the EPA Memo is not carefully considered public policy, is inconsistent with other regulations adopted by state and federal agencies and is not supported by the relevant science.

As a result of these issues, and the significant and inconsistent consequences of allowing the policies in the EPA Memo to guide TCE exposure in connection with Superfund remedies in Region 9, EPA headquarters should revisit the policies adopted in the agency's memo. If, after further evaluation, EPA headquarters decides it is appropriate to consider the adoption of short-term exposure standards for TCE vapor intrusion, the agency should do so via a public notice-and-comment process that allows for scientific input from stakeholders nationwide.

EPA Region 9 Policy on Short-Term Exposure to TCE via Vapor Intrusion

The EPA Memo emphasized that “[a]ddressing vapor intrusion at our Superfund sites is one of the top priorities for the Superfund Division,” and provides EPA staff with “interim response action levels” for short-term TCE exposure that are to be used in “making site-specific decisions regarding the investigation of and response to TCE vapor intrusion.”

The policy on short-term exposure to TCE advanced in the EPA Memo is consistent with a Dec. 3, 2013, letter sent by EPA Region 9 to Stephen Hill, Chief of the Toxics Cleanup Division at the California Regional Water Quality Control Board. The December Letter concerned nine Superfund sites in the South San Francisco Bay where the regional board, as opposed to EPA, acts as the lead enforcement agency for the environmental remedy. The December Letter was sent to outline the EPA’s “TCE interim short-term indoor air response actions levels” and recommended that those action levels be incorporated into all vapor intrusion evaluation work plans for the nine South Bay sites. The December Letter implied, but did not explicitly state, that Region 9 expected the regional board to use its enforcement authority under California law to require investigations by responsible parties at the South Bay Sites that were consistent with the guidelines in the December Letter.[4] Taken together, the EPA Memo and December 2013 letter show that EPA Region 9 intends to apply the short-term TCE exposure levels at Superfund sites throughout Region 9.

In setting short-term TCE exposure levels in the EPA Memo and December Letter, EPA Region 9 relies on the September 2011 Toxicological Review of Trichloroethylene in Support of the Integrated Risk Information System (the “2011 IRIS Review”) and concludes that “women in the first trimester of pregnancy” are a particularly sensitive population for TCE short-term inhalation exposure due to the “potential for cardiac malformation to the developing fetus.”[5] In the December Letter, the EPA recognized that the “[s]cientific information on the exact critical period of exposure for this health impact is not currently available,” but proceeded to recommend the TCE action levels for use by the Regional Water Quality Control Board because “general risk assessment guidelines for developmental effects indicate that exposures over a period as limited as 24 hours may be of concern for some developmental toxicants.”[6] The 2014 Memo does not refer to the limitations in the available scientific information for assessing the risks of TCE short-term exposure to sensitive populations.

Region 9, therefore, has adopted a short-term exposure guideline for TCE that assumes there is a teratogenic impact from TCE. The EPA Memo sets short-term exposure levels based on a Hazard Quotient, or HQ, calculated from toxicological conclusions developed from the 2011 IRIS Review, including an additional margin of safety.[7] The short term exposure guidelines require “prompt” (i.e., within weeks) responses to concentrations as low as 2 µg/m3 of TCE in residences and 7 µg/m3 of TCE in commercial buildings for a 10-hour shift. The short-term exposure guidelines require “urgent” responses, including the possibility of evacuation, to concentrations as low 6 µg/m 3 in residences and 21 µg/m3 in commercial buildings for a ten hour shift.

Region 9 also provided a set of recommended, tiered response actions dependent upon the short-term TCE concentrations.[8] In the event that indoor air TCE concentrations related to subsurface vapor intrusion exceed the “prompt response” (HQ = 1) level, the EPA Memo recommends that one or more of the following actions be completed and confirmed within “a few weeks”:[9]

  • increase building pressurization and/or ventilation;
  • seal potential conduits where vapors may be entering the building;
  • treat indoor air (e.g., with carbon filtration or air purifiers);
  • install and operate engineered exposure controls (e.g., subslab/crawlspace or depressurization systems);
  • temporarily relocate occupants.

Footnotes in the EPA Memo and the December Letter state that it is “generally EPA practice to immediately initiate response action” to address concentrations at or above the Urgent Response Level.[10] In other words, it is EPA Region 9 policy that, if TCE concentrations in a residence exceed 6 μg/m3, or if TCE concentrations exceed 21 μg/m3 in a commercial/industrial building with 10-hour work shifts, immediate evacuation may be warranted until the indoor air concentrations of TCE can be reduced to a level below 6 μg/m3 or 21 μg/m3, respectively.[11]

Toxicology Underlying the EPA Region 9 Policy is Controversial

The toxicological assumptions built into the TCE short-term exposure guidelines in the EPA Memo are controversial and are not accepted by a number of respected toxicologists. In April 2012, the responsible parties at the Middlefield-Ellis-Whisman Superfund Site in Mountain View, California provided a white paper on TCE to EPA headquarters that reviewed the 2011 IRIS Review. The white paper was authored by two respected toxicologists[12] and questioned the EPA’s conclusion that the 2011 IRIS Review determined that TCE is a teratogen. The white paper pointed out that neither the EPA nor any other federal agency has concluded that TCE causes teratogenic effects in people.[13] Indeed, the 2011 IRIS Review found that:

The evidence for an association between TCE exposures in the human population and the occurrence of congenital cardiac defects is not particularly strong” [and that the animal data is] “not unequivocal ... [and] include[s] lack of a clear dose-related response” [and] "... cannot be grouped easily by type or etiology."[14]

The white paper reviewed all available toxicology and epidemiology studies regarding congenital cardiac defects and TCE and found that more of the studies found no teratogenic effects than found such effects. Moreover, the studies that found such effects had well-documented methodological flaws or were based on study designs that were of limited or no value in an evaluation of causation.[15] The white paper noted the following regarding the relevant studies:

  • There is no indication in the 2011 IRIS Review that any of the noncancer data referred to in the paper was evaluated for any exposures other than chronic (i.e., lifetime) exposures. However, the December Letter applies the noncancer data to very short exposure periods of less than 24 hours. No peer reviewers evaluated the application of chronic standards to short-term exposures;
  • All "positive" studies in animals were from a single laboratory. That laboratory used a flawed methodology that was criticized by the scientific community, and the positive findings from that laboratory could not be replicated, even by the same researchers. A number of other investigations did not find cardiac teratogenic effects in animals, even at doses similar to those used in the studies that reported finding effects;
  • Several epidemiological studies report no statistically significant association between TCE exposure and cardiac teratogenic effects in humans; and
  • The only epidemiological studies that report teratogenic effects are based on study designs that are of limited value for evaluating a causal relationship.[16]

The white paper pointed out that a number of scientific and regulatory organizations had reviewed the many toxicological and epidemiological studies that evaluated the potential link between teratogenic effects and TCE exposure, and none of the organizations concluded that the studies established a causal link. Therefore, the white paper asked EPA headquarters to conduct a thorough analysis of the available literature and make a formal determination based on the weight of scientific evidence.

Neither EPA headquarters nor Region 9 responded to the white paper before Region 9 issued the December Letter and the EPA Memo. Instead, despite the limitations in the underlying science, Region 9 has forged ahead with issuance of the EPA Memo. Further, Region 9 has shown that it will immediately seek to implement the short-term TCE exposure levels at Superfund sites within its jurisdiction by issuance of the December Letter applying the short-term TCE exposure guidelines to nine Superfund sites in Northern California. All of these actions are being taken by EPA Region 9 notwithstanding the lack of a uniform policy or nationwide standard equally applicable to all of the approximately 1,300 Superfund sites in the U.S.

Regulation of TCE Outside the Context of Superfund

TCE is a solvent still used in some occupational settings.[17] As a result, short-term exposure to TCE is already regulated in a number of contexts by state and federal worker safety laws and worker safety organizations. For example, the U.S. Occupational Safety Health Administration, California Division of Occupational Health, National Institute for Occupational Safety and Health and American Conference of Governmental Industrial Hygienists all set limits for exposure to TCE in employment settings.

The standards set by OSHA and Cal/OSHA are referred to as permissible exposure levels. The NIOSH standards are referred to as recommended exposure levels. RELs are based on 10-hour time-weighted averages during a 40-hour workweek unless otherwise indicated. ACGIH standards are referred to as threshold limit values. TLVs are provided for recommended time-weighted eight-hour averages, also designated as “TWAs,” short-term exposure levels, designated as “STELs,” and ceiling concentrations allowed in an eight-hour time period, designated as “C” levels. All of the OSHA, Cal/OSHA, NIOSH and ACGIH standards are intended to protect workers exposed to TCE at their place of employment. The standards are set based on each entity’s evaluation of relevant toxicology; in some instances the same toxicology that was the basis of the 2011 IRIS Analysis.[18]

Unlike Region 9’s conclusions regarding short-term exposure to TCE, the other agencies that set standards for short-term exposure to TCE set the permissible exposures orders of magnitude higher than the standards set in the EPA Memo and the December Letter. For example, the short-term exposure level for TCE under federal OSHA regulations is 537,000 µg/m3 for an eight-hour shift — 59,666 times greater than the short-term exposure standard set by the EPA Memo. Similarly, the Cal/OSHA regulations set a TCE exposure level of 53,700 µg/m3 for an eight-hour shift — 5,966 times greater than the short-term exposure standard set by the EPA Memo.[19]

The occupational standards create extreme inconsistency between acceptable “environmental” and worker exposures to TCE. If a worker in California works with TCE in his/her workplace, he/she could be exposed to 53,700 µg/m3 of TCE as an eight-hour average for every workday and be “protected” by all applicable state and federal standards for worker safety. However if the same worker was exposed to 8 µg/m3 of TCE as a result of vapor intrusion from groundwater, Region 9 would require a remedy at that workplace within “weeks” and would require a remedy “immediately” (i.e., evacuation of the workplace) if the worker was exposed to 24 µg/m3 of TCE as a result of vapor intrusion from groundwater.

In other words, the EPA Memo could require the evacuation of a workplace based on a one-day exposure to TCE in indoor air from vapor intrusion, where that exact same workplace would be considered safe for long-term exposure to TCE for workers by all applicable workplace safety laws at concentrations 5,966 times greater. The disparity in these standards is stark, is not justified by any technical or scientific analysis in the EPA Memo or otherwise, and makes no sense.

Potential Impact of the EPA Memo

The potential impact of the EPA Memo is hard to overstate. There are approximately 1,319 Superfund sites in the U.S. According to ATSDR, TCE has been detected at over 800 of them.[20] A substantial change in the EPA’s policy regarding investigation or remediation of TCE would have a dramatic impact at these sites. And, of course, there are many other sites contaminated with TCE that are not Superfund sites but are instead being investigated and cleaned up under state supervision. If a change in EPA policy resulted in changes in state policies as well, the impact of the change would be multiplied.

Yet, despite the significant impact that a change in EPA policy regarding TCE cleanup might have, the procedures the EPA employed to develop the short-term exposure levels set forth in the EPA Memo have not provided any opportunity for public input or peer review.[21] The EPA has not developed the recommendations and requirements in the EPA Memo as a regulation, or even as a formal guidance document. The action levels in the EPA Memo were never published for public comment before being issued, and there have been no hearings or public meetings held to discuss the standards. As we note above, the standards that Region 9 seeks to apply via the EPA Memo differ by orders of magnitude from existing occupational and other standards. New standards that differ so dramatically from existing standards suggest the need for public notice and an opportunity for public input.

The short-term TCE exposure levels in the EPA Memo are already being applied to specific sites as evidenced by the December Letter. The fact that the December Letter was issued by a single region of the EPA and is being applied only to selected sites also raises questions of selective enforcement and unfairness. The December Letter has been directed to less than a dozen sites. If, as the EPA suggests in the December Letter and the EPA Memo, the risks from exposure to TCE vapor over very short time frames are so significant that buildings must be evacuated to prevent harm to human health, then it is impossible to justify taking action in one EPA region while simultaneously ignoring similar risks outside of Region 9. The disparity in treatment begs the question why the EPA has not proposed national guidance, applicable to all sites, subject to public notice and comment.

The result of the haphazard development of short-term TCE exposure action levels will be a confusing welter of inconsistent standards for all of the different parties involved at affected sites. For example, at the nine Northern California sites addressed in the EPA’s December Letter, the responsible parties are required to implement remedies that are recorded in Superfund Records of Decision applicable to each site. These RODs, which were published decades ago, of course make no mention of the standards that EPA Region 9 purports to implement via the December Letter or the EPA Memo. So far, the EPA has sought to rely on the state to require compliance with the December Letter at the Northern California sites, but that strategy is not consistent with Comprehensive Environmental Response, Compensation, and Liability Act procedure, which does not allow a significant change in the remedy without a public notice and comment procedure.

Finally, commercial building owners within EPA Region 9 will now be subject to confusing and conflicting standards. Those whose facilities are within the boundary of a TCE groundwater plume may be asked to undergo significant disruptions for investigation and remedial activities, and even to evacuate their premises, despite having a concentration of TCE hundreds of times less than the permissible exposure level for workplace exposure. Meanwhile, building owners a few blocks away may be told that the same concentrations in indoor air do not require any measures, much less extreme measures such as evacuation. These conflicting standards are likely to sow confusion among the media and general public over safe exposure levels at Superfund sites and elsewhere.

Some Practical Consequences of the Short-Term TCE Exposure Standards Set by the EPA Memo

The new EPA policy will have significant consequences immediately, beginning with the Northern California Superfund sites specifically identified in the December Letter. Property owners, employers and tenants in the historic center of semiconductor activity in Northern California are now asking Region 9 to explain its position and the implications of the new short-term TCE exposure policy for hundreds of thousands of workers who are employed in Silicon Valley.[22] For the most part, Region 9’s response has been to broadcast its new policy without either careful or considered explanation of the limits of the toxicology upon which Region 9 relies or any concerted effort to address the concerns of potentially affected property owners, employers and tenants. As a result, property owners, employers and tenants are left with more questions than answers.

Meanwhile, the environmental consulting community has seized on the EPA Memo and December Letter as a marketing opportunity. Even before issuance of the EPA Memo in July, numerous consultants organized seminars on the standards set in the December Letter with headlines like: “EPA has determined that low level TCE exposures for women in their first trimester of pregnancy can lead to serious birth defects for their children.”[23] Another consultant generated an article in the Mountain View Voice newspaper, where the consultant advised a reporter that it has mapped plumes of chemicals of concern in the Silicon Valley from various government sources and made the map available on various social media.[24] The article then quotes the principal of the consultant firm saying: "He also suggested that indoor air testing was the only way for people to be sure about health risks, and recommends a [do it yourself] air test kit he sells on his site."

In short, unintended consequences from the EPA Memo and December Letter are already surfacing.


The EPA Memo is not carefully considered public policy and the short-term TCE exposure levels imposed by Region 9 should be reconsidered by EPA headquarters. If there is a legitimate weight of scientific evidence that supports the standards articulated in the EPA Memo, those standards should be applied to all Superfund sites where TCE is a chemical of concern and EPA headquarters should demonstrate leadership by applying that policy nationwide and fairly. However, the EPA has not done the necessary analysis to conclude that the weight of scientific evidence supports the exposure levels set by the EPA Memo. If, as suggested in the April 2012 White Paper, the weight of scientific evidence does not support the standards articulated in the EPA Memo, the EPA's headquarters should demonstrate leadership and rescind its memo and the December Letter and initiate the development of standards based on sound science, subject to appropriate public notice and comment.

Richard Coffin is a founding partner and R. Morgan Gilhuly and J. Tom Boer are partners in Barg Coffin Lewis and Trapp's San Francisco office.

The opinions expressed are those of the author(s) and do not necessarily reflect the views of the firm, its clients, or Portfolio Media Inc., or any of its or their respective affiliates. This article is for general information purposes and is not intended to be and should not be taken as legal advice.

[1] Memorandum re: EPA Region 9 Response Action Levels and Recommendations to Address Near-Term Inhalation Exposures to TCE in Air from Subsurface Vapor Intrusion from Enrique Manzanilla, Director Region 9 Superfund Division to Region 9 Superfund Division Staff and Management (July 9, 2014).

[2] Memorandum re: 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, from Gerald Hiatt to Enrique Manzanilla (June 30, 2014) (“EPA Toxicological Memo”).

[3] In June 2014, EPA issued a TSCA Work Plan Chemical Risk Assessment for TCE (“2014 TSCA Assessment’) based on the same toxicological assessment underlying the EPA Memo. See

[4] Region 9 was not in a position to require immediate investigations itself because addressing vapor intrusion was not part of the approved remedy under CERCLA at the nine sites.

[5] EPA Memo at p. 1.

[6] December Letter at p. 4.

[7] December Letter at p. 3.

[8] EPA Memo at p. 4.

[9] December Letter at p. 4.

[10] December Letter at footnote 2; EPA Memo at footnote 4.

[11] The eight hour shift concentrations for commercial buildings adopted by the EPA Memo are 8 µg/m3 for “prompt” response and 24 µg/m3 for “urgent” response.

[12] TCE Interim Short-Term Removal Action Level White Paper, authored by Dr. Robert Scofield D. Env., Principal and Director of the Center for Exposure, Exponent and Dr. Keith Tolson, Geosyntec Consultants (April 17, 2012).

[13] As indicated in Footnote 3 above, on June 25, 2014, EPA released its 2014 TSCA Assessment. The 2014 TSCA Assessment restates that the fetal cardiac studies relied upon in the 2011 IRIS Review are “controversial,” “have not been replicated in other animal or human studies. . .” and “comments from the public and the peer review panel” objected to reliance on the studies. Nonetheless, the 2014 TSCA Assessment concluded that the studies are “adequate to use in hazard identification.” 2014 TSCA Assessment at p. 98.

[14] 2011 IRIS Review at 4-565.

[15] White Paper at p. 12, et seq.

[16] White Paper at p. 12, et seq.

[17] 2014 TSCA Assessment.

[18] OSHA acknowledges that many of its standards are outdated and may not be protective. As a result, OSHA defers to Cal/OSHA, NIOSH and ACGIH as more protective and up to date.

[19] The OSHA regulation is 100 ppm of TCE in air. The Cal/OSHA regulation is 10 ppm of TCE in air. 1 “ppm” of TCE in air translates into approximately 5,370 µg/m3 of TCE assuming a standard temperature and pressure.

[20] ATSDR, Tox FAQs for Trichloroethylene,

[21] Indeed, on June 25, 2014 members of the Senate Committee on Environment and Public Works wrote the Assistant Administrator of EPA to question EPA’s reliance on questionable toxicology in the 2014 TSCA Assessment. That same questionable toxicology was relied upon in the EPA Memo.

[22] The 2014 Silicon Valley Index indicates that over 1.4 million people are employed in the Silicon Valley as of mid-2013. 2014 Silicon Valley Index, Silicon Valley Institute for Regional Studies and Silicon Valley Community Foundation, at p. 6.

[23] See, e.g., Groundswell Technologies Spring 2014 Newsletter.

[24] Mountain View Voice article Local company's toxic plume map causes alarm (May 22, 2014).