Recent changes to EPA risk values for trichloroethylene (TCE) and perchloroethyle (PCE) have raised the bar for listing sites contaminated with these constituents as the final risk values for these constituents are weaker than values that U.S. EPA had previously used to score hazardous waste sites. The new risk values are now reflected in U.S. EPA's Superfund Chemical Data Matrix (SCDM). The toxicity factor for TCE dropped from 10,000 to 1,000 and the TCE drinking water benchmark value changed from .21 ug/l to 1.0 ug/l. For PCE, the cancer risk level increased by a factor 20.
The effect of these revised values on the site scoring process can be dramatic. For example, U.S. EPA recently rescored a site in Leeds, Maine using the new values and the score dropped from 50 to 32.92 (the site was still eligible for listing since the listing threshold is 28.5). However, under the old system, 17 residents were documented to be drinking contaminated water from several wells; based on the new scoring, only two wells were above the threshold.
Please click here to go to the SCDM website for further information on the recent changes to U.S. EPA's NPL scoring matrix.