The Evolving Regulation of Tce Vapor Intrusion Issues

• Jurisdiction: United States,Federal,California
• Author: by Ben Clapp, Don J. Frost Jr. and Stacy E. Kray
• Publication year: 2016
• Citation: Vol. 25 No. 2

THE EVOLVING REGULATION OF TCE VAPOR INTRUSION ISSUES

by Ben Clapp,^* Don J. Frost Jr.^** and Stacy E. Kray^***

Ben Clapp

Don J. Frost Jr.

Stacy E. Kray

Over the past five years, multiple U.S. Environmental Protection Agency ("EPA") Regions and numerous state environmental agencies have imposed stringent new action levels to address human health risks relating to inhalation of trichloroethylene ("TCE") as a result of vapors intruding into indoor air from subsurface contamination. Because the new action levels are significantly more aggressive than historical regulatory thresholds, these developments could have long-lasting repercussions regarding current and future remedial investigations, and could alter the risk profile of sites that previously received regulatory closure. In addition, the new action levels differ among the various agencies in California, which has created much confusion in the regulated community.

Drawing of the interior view of a house sitting above contaminated ground water with vapors rising through the soil into and around the house.
Image description added by Fastcase.

Figure 1: Vapor intrusion into a residence. Graphic courtesy of U.S. EPA.

I. DEVELOPMENT OF REVISED TCE RESPONSE ACTION LEVELS

TCE is a volatile organic compound that is considered carcinogenic.¹ For many years, it was widely used as a solvent in manufacturing and other industrial operations. The most recent changes to TCE regulation result from evidence that even very low levels of TCE exposure may also present non-carcinogenic risks to human health.² These risks have raised regulatory concern about possible inhalation of TCE vapors migrating into indoor air from contaminated soil and groundwater beneath building foundations.

The current approach for TCE regulation dates back to 2011, when EPA released its Toxicological Review of Trichloroethylene in Support of the Integrated Risk Information System ("TCE IRIS Assessment").³ The TCE IRIS Assessment established a non-cancer inhalation toxicity value for TCE ("Reference Concentration") of 2 micrograms per cubic meter (µg/m³).⁴ The Reference Concentration is an "estimate . . . of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime."⁵ Relative to previously issued TCE toxicity values, a 2 µg/m³ Reference Concentration is extremely stringent. For example, the California Office of Environmental Health Hazard Assessment published a chronic reference level for TCE that is 300 times more lenient - at 600 µg/m³.⁶ The primary basis for the Reference Concentration is a disputed 2003 study that reported a dose-response relationship between consumption of TCE in drinking water by pregnant rats and cardiac defects in rat fetuses (the "Johnson Study").⁷

EPA's reliance on the Johnson Study has proven controversial. Critics contend that the methods employed in the study were flawed and that the results have not been replicated by other labs despite various attempts to do so.⁸ In February of 2016, EPA denied an industry request for reconsideration of the Reference Concentration under the Information Quality Act.⁹ It remains to be seen whether critics of the TCE Reference Concentration will initiate any other legal challenges relating to the standard.

Following the release of the TCE IRIS Assessment, multiple EPA Regions and a number of state agencies revised their response action levels for addressing TCE vapor intrusion at contaminated sites ("RALs"). Most notably for California lawyers, EPA Region 9 released a two-tiered operational framework in 2014 for addressing TCE vapor intrusion at all Region 9 Superfund sites (the "Region 9 Superfund Framework").¹⁰ The framework adopted the TCE IRIS Assessment's 2 µg/m³ Reference Concentration as an "accelerated" residential RAL, and accelerated commercial/industrial RALs of 8 µg/m³ for an 8-hour work day and 7 µg/m³ for a 10-hour work day. Accelerated response actions contemplate that all response work be completed and confirmed within a few weeks.

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The Region 9 Superfund Framework also established "urgent" residential RALs of 6 µg/m³ and urgent commercial/industrial RALs of 24 µg/m³ for an 8-hour work day and 21 µg/m³ for a 10-hour work day. "Urgent" response actions contemplate that all response work will be initiated immediately and completed and confirmed within a few days. An urgent response action can include the temporary evacuation of impacted buildings to prevent additional exposure.

EPA Region 9 TCE Response Action Levels

Media	Units	Accelerated Response	Urgent Response
Indoor Air Residential	µg/m³	2	6
Indoor Air Commercial/Industrial	µg/m³	8*/7**	24*/21**

* Based on 8-hour workday.

** Based on 10-hour workday.

EPA Region 9 had previously signaled its intention to adopt more stringent TCE RALs in a letter issued in December of 2013 ("2013 Region 9 South Bay Letter") to the California Regional Water Quality Control Board - San Francisco Bay Region (the "SF RWQCB"), in which Region 9 provided recommended guidelines for addressing vapor intrusion at nine Superfund sites being remediated in the South San Francisco Bay Area under SF RWQCB oversight ("South Bay Superfund Sites"). The letter included a recommendation that the SF RWQCB incorporate the revised TCE RALs.¹¹ In addition, the letter required indoor air testing at all properties overlying groundwater with concentrations of TCE at or over 5 µg/L.

EPA Region 3, while not having promulgated official TCE RALs for indoor air, has demonstrated a similar approach to EPA Region 9 by requiring the evacuation of two U.S. Navy buildings with indoor air levels in excess of an "ad hoc" response action level of 27 µg/m³.¹² Separately, in 2012, EPA Region 10 issued toxicity values for TCE in indoor air at Superfund and RCRA cleanup sites, recommending that for residential settings the average TCE exposure over any 21-day period not exceed the 2 µg/m³ Reference Concentration, and that for industrial/commercial settings the average TCE exposure over any 21-day period not exceed 8.4 µg/m³.¹³ At the national level, in August 2014, EPA's Director of Superfund Remediation and Technology Innovation issued a memorandum to the Regional Superfund Division Directors encouraging the use of the 2 µg/m³ Reference Concentration from the TCE IRIS Assessment to support early or interim action at Superfund sites.¹⁴

A number of state and local environmental agencies have also adopted or revised TCE RALs based on the TCE IRIS Assessment, with Alaska following the lead of Region 10 and Massachusetts, New Jersey, Connecticut, Minnesota and New Hampshire adopting similar approaches. In contrast, Indiana has publicly indicated that it will not follow the TCE IRIS Assessment, concluding that an accelerated response for TCE indoor air exposures is not scientifically supported.¹⁵ California's response is discussed below.

II. IMPLEMENTATION OF NEW TCE STANDARDS AT SOUTH BAY SUPERFUND SITES AND BEYOND

A. Use of New Standards at South Bay Superfund Sites

Recent events at the South Bay Superfund Sites demonstrate some of the possible impacts to responsible parties from the changes in TCE action levels. After the 2013 Region 9 South Bay Letter was issued, the SF RWQCB issued specific directives to potentially responsible parties ("PRPs") for the South Bay Superfund Sites requiring them to revise previously approved workplans to incorporate EPA recommendations from the 2013 Region 9 South Bay Letter (the "SF RWQCB South Bay Directives"), including adhering to Region 9's RALs and requiring vapor intrusion studies on all off-site properties overlying areas of shallow-zone groundwater contamination at or over 5 µg/L of TCE.¹⁶

In 2014, PRPs at the South Bay Superfund Site submitted petitions for review to the State Water Resources Control Board ("SWRCB"). The PRPs asserted, among other things, that (i) the new TCE RALs were not legally binding because they had not been adopted as regulation or official guidance by EPA, SWRCB, or any other agency;¹⁷ (ii) the RALs were invalid because they were applied in contravention of the SF RWQCB's previously published vapor intrusion standards;¹⁸ (iii) the SF RWQCB South Bay Directives' requirement that the workplans include vapor intrusion evaluation of all buildings overlying the 5 µg/L TCE shallow groundwater contour was arbitrary and capricious and not supported by the best available science;¹⁹ and (iv) the SF RWQCB's reliance on standards imposed by the 2013 Region 9 South Bay Letter was improper at the South Bay Superfund Sites because they were inconsistent with the final remedy adopted by SF RWQCB and EPA for the facilities at issue.²⁰ To date, SWRCB has not issued any substantive ruling on these petitions.

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B. SF RWQCB Draft Interim Framework & DTSC Human Health Risk Assessment Note

Since it issued the South Bay Directives, the SF RWQCB has sought to expand its implementation of new TCE vapor intrusion standards. In October of 2014, the SF RWQCB issued its Draft Interim Framework for Assessment of Vapor Intrusion at TCE-Contaminated Sites in the San Francisco Bay Region ("SF RWQCB Interim Framework").²¹ The SF RWQCB Interim Framework "provisionally" adopts the EPA Region 9 TCE RALs and endorses approaches to sampling both residential and commercial buildings as set forth in the Region 9 Superfund Framework.²²

Importantly, however, the SF RWQCB Framework does not adopt EPA's directive in the 2013 Region 9 South Bay Letter that indoor air sampling be conducted in all buildings overlying 5 µg/L TCE in groundwater.²³ Instead, SF RWQCB announces "Trigger Levels" for TCE in soil gas and groundwater samples.²⁴ Trigger Levels are "concentrations in environmental media that prompt prioritization of indoor air sampling."²⁵

For soil gas, the Trigger Level is 1,000 µg/m³ for residential properties and 8,000 µg/m³ for commercial/industrial properties. For groundwater, the...