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New TCE Toxicity Values: So What Does this Mean for Groundwater and Vapor Assessment?

Author: The Author
Date: October 5, 2011

This blog post was contributed by REGENESIS CEO Scott Wilson

USEPA Announces final toxicity values for TCE

As most of you are probably aware, the USEPA announced last week that the agency has completed its Final Health Assessment for Trichloroethylene (TCE). In short, this means that the agency has performed an in-depth study of the health hazards posed by the chemical which is often found as a groundwater and soil contaminant at dry cleaner sites, manufacturing facilities and the like. The results of the study have formally characterized the chemical as a human carcinogen and a non-carcinogenic health hazard… no big surprise to those of us involved in groundwater and soil remediation. Here is a link to the official press release in case you didn’t catch it.  If you are interested in the toxicological details here are the established reference doses (RfD)/concentrations (RfC) for TCE:

Chronic Oral RfD Assessment: 0.0005 mg/kg/day
Chronic  Inhalation RfC Assessment: 0.002 mg/m3
Carcinogenicity Assessment: Carcinogenic by weight of evidence (mutagenic mode of action kidney tumor)

For further details on the assessment and references go to the USEPA’s Integrated Risk Information System (IRIS) database.

So How Does this Impact Groundwater and Vapor Assessment?

When I saw the USEPA press release announcing the Final Health Assessment for TCE the first thing I asked myself was, “So how does this impact the sites around the U.S. known to contain TCE in soil, groundwater and soil vapor?” After a bit of research it appears to me that there will in fact be some impact… but not right away.

First we have to realize that current federal cleanup standards for TCE in groundwater are based upon Maximum Concentration Limits (MCLs) which were established decades ago by the Office of Water. These MCLs (i.e. 5.0 ug/l) were based primarily upon limits of analytical methods in use at the time rather than toxicological risk.

Currently when establishing cleanup goals for regions within U.S., the USEPA takes the MCL and adjusts the value taking into consideration toxicological risks and physical characteristics inherent within the region and comes up with a Regional Screening Level (RSL).

Now that we have the USEPA established Final Health Assessment Values for TCE, there is a shift underway to re-evaluate the current RSLs. Already, an RSL Working Group has been underway at USEPA headquarters reviewing the impact the newly published Assessment Values will have on RSLs for TCE.

Of particular interest is the impact the newly published Final Health Assessment Values will have on vapor limits (not currently based upon MCLs). Word on the street is that the RSL Working Group has been focusing on this with preliminary thoughts for USEPA Region 9 of 0.5ug/m3 for carcinogenic RfC and 2.0 ug/m3 for non-carcinogenic RfC.

As far as timing of new RSL adoption, I have been told that historically this has been a rather slow process- say 2 to 3 years or so. However, movement in convening the RSL Working Group and talk of having already generated preliminary values for vapor indicate the timeframe for Trichloroethylene RSL adoption could be much sooner. I’ll keep you posted on what develops.