Potential impact on decision-making management is substantial.
Memorandum ‘under review’ shortly after release.
Vapor intrusion is an important factor in establishing cleanup goals at many contaminated sites. Oftentimes, the vapor intrusion of trichloroethylene (TCE) is an important risk driver determining remediation alternatives.
As such, an appropriate TCE risk definition has financial significance to the regulated community: remediation costs invariably increase when risk values assigned to TCE are increased. The opposite is also true: remediation costs decrease with decreased TCE risk values. For these reasons, it is crucial that risks associated with TCE vapor intrusion be appropriately defined.
A final TCE toxicity assessment has not yet been issued by the Environmental Protection Agency (EPA). This may be partly due to the fact that the concept of TCE inhalation toxicity has been hotly debated since EPA released its controversial TCE toxicity assessment draft in 2001. Based upon the 2001 draft report, EPA presented an inhalation toxicity factor in the “Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils” (EPA 530-D-02-004, November 2002), and has used this factor to evaluate risks at contaminated federal sites.
Just two months ago (January 15, 2009), EPA’s Office of Solid Waste and Emergency Response (OSWER) released to EPA Regional Administrators a memorandum recommending revised inhalation toxicity factors for the assessment of vapor intrusion risks. The memorandum recommended that:
- EPA Regional Administrators use lower toxicity factors for TCE for cancer effects at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA or ‘Superfund’), Resource Conservation and Recovery Act (RCRA), and other contaminated Federal sites, and that;
- ‘Multiple lines of evidence’ be employed for assessing human health risks for vapor intrusion pathway analyses.
The memorandum, titled, “Interim Recommended TCE Toxicity Values to Assess Human Health Risk and Recommendations for the Vapor Intrusion Pathway Analysis (January 15, 2009 EPA Memorandum)”, could have a potential positive impact on waste generators and developers who are required to evaluate human health risks at contaminated sites.
EPA recommends lower toxicity values for TCE.
According to the memorandum, EPA considers TCE to be less toxic via the inhalation pathway than previously estimated. The Agency has recommended lower TCE toxicity values for evaluating site-specific cancer risks from inhalation or oral exposures. These values were derived by the California EPA (Cal EPA) for use in risk assessments, and the selection of these values is consistent with the 2003 EPA Toxicity Hierarchy.
For assessing TCE carcinogenic effects, the memorandum provides a revised inhalation toxicity factor, which results in an indoor air preliminary remediation goal (PRG) of 1.2 ug/m³ for residential sites (assuming a cancer risk of 1 in 1,000,000). This concentration is 60 times higher than the previous target indoor air concentration of 0.02 ug/m³ that had been used since 2002.
The guidance presented in the memorandum supersedes previous guidance on TCE toxicity values based on OSWER’s “Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils” (EPA 530-D-02-004, November 2002).
The toxicity values presented in the memorandum are appropriate for EPA Regions to assess risks, at least until toxicity values for TCE are available in the Integrated Risk Information System (IRIS) database or until further scientific analysis identifies a more appropriate value. When this happens, EPA cautions that OSWER may review sites to ensure that they remain protective with the revised toxicity values.
EPA recommendations for non-carcinogenic TCE risk.
Non-carcinogenic effects of TCE include neurotoxicity, nausea, drowsiness, and fatigue. For assessing non-carcinogenic effects, OSWER recommends 10 ug/m³ air criterion (NYSDOH) and 600 ug/m³ Chronic Reference Exposure Level (Cal EPA) as Tier 3 toxicity values.
What does this all mean?
Estimated human health risks at contaminated sites may decrease and affect risk conclusions and remediation goals. For example:
- Risk assessments can, and in many cases should, be revised to incorporate USEPA’s recommended toxicity factor.
- If Federal and some state sites impacted with TCE in groundwater, soil vapor, or indoor air are reassessed, the estimated health risks associated with TCE in these media will decrease.
- If established standards are used as comparison values, these standards can be adjusted, thereby increasing screening values for TCE in indoor air, soil vapor and groundwater.
‘Multiple Lines of Evidence’ are required to determine TCE intrusion pathways.
EPA often evaluates inhalation risks from vapor intrusion pathways because they are potentially significant at waste sites. Due to a large number of variables, the Agency found that no single medium should be used to evaluate potential risks above health risk-based levels.
Therefore, in its memorandum, EPA recommends using multiple lines of evidence (e.g., data from multiple media, product inventories, preferential pathway sample data, modeling results, etc.) to evaluate vapor intrusion pathways.
By using this approach, EPA states that project managers are usually successful in determining whether the TCE vapor intrusion exposure pathway is complete and whether any elevated TCE levels in indoor air are likely caused by either subsurface vapor intrusion, an indoor source (i.e., consumer product), or an outdoor source.
The memorandum states that it is often useful to collect and evaluate two or more lines of evidence at the same time. Generally, site conditions determine the number of lines of evidence necessary to provide enough information for decision making.
Status of the new EPA TCE memorandum.
The January 15, 2009 EPA memorandum provides the most recent guidance from the Agency regarding the assessment of inhalation toxicity of TCE. However, EPA informed Roux Associates that the document is now “under review” at its headquarters offices in Washington, DC. While EPA often adheres to its draft guidance documents even when they are under review, the agency recommended that responsible parties contact the EPA Regions for further clarification and interpretation of the recommendations regarding how to proceed at individual sites.
Since the memorandum as it is now written gives the reader the option of selecting different values for TCE preliminary remediation goals, EPA informed Roux Associates that “the Region's input would be necessary even if the memo were not under review.”
Contact Roux.
If TCE is driving risks at your sites, it may be valuable to calculate lower risks or re-derive target cleanup goals. This can be helpful for attaining Site closure, reducing potential for litigation, etc.
Roux Associates’ Risk Assessment Group has extensive experience with vapor intrusion assessments. Should you have any questions regarding the memorandum, or if you would like to explore how we can help you reduce your cleanup costs, please feel free to contact Denise Kmetzo, Senior Risk Assessor, at Roux Associates, at dkmetzo@rouxinc.com or (781) 270-6600.
Notice: ENVIRONMENTAL REVIEW is published by Roux Associates Inc., Islandia, New York. The information contained herein is provided for educational and informational purposes only and should not be taken as technical consulting advice for specific situations, which depends on an evaluation of site-specific factual information. Please direct questions or comments to the Roux Associates professional named in a specific article. Copyright Roux Associates, Inc., 2009.
