VOCs may be found in soil and groundwater near industrial plants using solvents and in a variety of industrial and commercial processes including chemical manufacturing and petroleum refining.
In September 2011, the Environmental Protection Agency (EPA) announced its final health assessment for trichloroethylene (TCE), a chlorinated hydrocarbon commonly used in industrial degreasing solvent operations such as the cleaning metal parts. The impact will be increased estimated risk levels, lower detection limits not routinely available and modification of remediation strategies in some cases.
Soil, Groundwater and Vapor Intrusion
One of the most significant implications of this assessment will be the need for changes to risk-based corrective action activities at chemical release sites where TCE is a chemical of concern. TCE’s toxicity assessment will lead to increases in risk estimates by a factor of 2 to 9 depending on the calculations used and will most likely lead to more costly cleanup requirements at sites where TCE has been released to soil or groundwater. TCE toxicity values will be evaluated by the EPA when calculating the risk from vapor intrusion as well as in the development of appropriate regulatory standards to limit atmospheric emissions of TCE, a hazardous air pollutant under the Clean Air Act.
One of the EPA’s emerging issues is that of vapor intrusion, such as when TCE vapors move from contaminated groundwater and soil into the indoor air of overlying buildings. The likelihood is that vapor intrusion investigations will be affected when using the new lower screening levels for soil vapor and groundwater since these levels may require more detailed assessments that include indoor air sampling or soil vapor monitoring. In some cases, the EPA has reported TCE levels in indoor air background concentrations from 1.1 (median) to 2.1 (90th percentile) micrograms/m3 in residences not affected by vapor intrusion, values that are higher than the revised levels. Revised indoor air screening levels for TCE may be more difficult to distinguish from background concentrations of TCE without significant technological input.
One of the difficulties in addressing these new toxicity values is that much of the current technology has not been able to detect TCE at the new level prescribed by the EPA, especially in the field. However, mobile instruments such as the Proton Transfer Reaction Mass Spectrometer (PTR-MS) are now available to meet these criteria by sampling VOCs in air concentration down to single parts per trillion levels. Direct air sampling provides microsecond response time. This technology provides both a continuous minute-by-minute record of concentrations throughout the day or an inch-by-inch detailed map of an area of interest.
- Ettinger, Robert A., and Edward L. Strohbehn. “EPA Releases Final Health Assessment of TCE — Results in Lower Screening Levels.” EBA News Alert: 12/21/11 (21 Dec. 2011). 21 Dec. 2012. Web. <http://www.bingham.com/Publications/Files/2011/12/EPA-Releases-Final-Health-Assessment-of-TCE–Results-in-Lower-Screening-Levels>.
- Trichloroethylene Inhalation Toxicity Values and Corresponding Risk Based Indoor Air Concentrations. Tech. US EPA Region 8. Web. 26 Jan. 2005. <http://www.envirogroup.com/TCE_Toxicity_VI_Tech%20Pub_1_26_05.pdf>.
- “Trichloroethylene Toxicological Review and Appendices.” EPA. Environmental Protection Agency. Web. <http://www.epa.gov/iris/supdocs/0199index.html>.
- Vapor Intrusion and TCE Update. Issue brief. US Army Corps of Engineers Environmental and Munitions Center of Expertise. Web. <http://aec.army.mil/usaec/cleanup/workshop/pdfs/08-02.pdf>.