NYDOH Lowers PCE Recommended Action Level For Vapor Intrusion

The New York State Department of Health (NYSDOH) recently reduced its air guideline value for PCE from 100 to 30 micrograms per cubic meter of air (30 mcg/m3). Three other ways of expressing the new guideline are 0.03 milligrams per cubic meter of air (0.03 mg/m3), 4.4 parts per billion (ppb) or 0.0044 parts per million (ppm)

The guideline of 100 mcg/m3 was issued in 1997 and had been based on toxicological data available at the time. In 2012, EPA completed a new PCE risk assessment and recommended a chronic reference concentration (Rfc) 40 mcg/m3 for the non-cancer risk and 4 mcg/m3 a cancer risk of one-in-one million (10-6 ) based on  continuous, lifetime exposure. EPA has established regional screening levels (SLs) to help identify areas, contaminants, and conditions that require further federal attention at a particular site. Sites where contaminant concentrations fall below SLs generally do not require further action or study  so long as the exposure assumptions at a site match those taken into account by the SL calculations. Sites where contaminants exceed the SLs do not necessary require cleanup but will likely undergo further investigation. For PCE,  EPA’s indoor air concentration screening level  residential buildings is 9.4 ug/m3 for the one-in-a-million (10-6) excessive cancer risk and 42 ug/m3 for the non-cancer risk. For commercial / industrial buildings the new range is 47 ug/m3 (cancer) to 180 ug/m3 (non-cancer).

Because it has been the past practice of NYSDOH to set its air guideline values at or less than a RfC, the agency reduced its guideline to 30 mcg/m3. Note that the estimated excess cancer risk associated with lifetime, continuous exposure to 30 mcg/m3 is about one-in-one-hundred thousand (10-5). In contrast, California has adopted a .41 ug/m3 threshold for PCE.

NYSDOH has developed two decision matrices to provide guidance about actions that should be taken to address current and potential exposures related to soil vapor intrusion. Actions recommended in the matrix are based on the relationship between sub-slab vapor concentrations and corresponding indoor air concentrations PCE has been assigned to matrix 2.

NYSDOH has emphasized that the air guideline value are not a bright line test and that exposure to levels above but near the guideline will not cause health effects in most, if not all, people.  However, the practical effect of the change will be that mitigation may now be recommended for PCE concentrations  exceeding 30 mcg/m. More information is available at: http://www.health.ny.gov/environmental/chemicals/tetrachloroethene/index.htm.