Evaluating the vapor intrusion to indoor air exposure pathway public health consultations for the Chillum Perchlorethylene site, Chillum, Maryland

[Objectives] Agency for Toxic Substances and Disease Registry (ATSDR) reviewed indoor air and active soil vapor sampling data collected for the Chillum site to evaluate public health implications associated with inhalation exposure. [Methods] The first component of the evaluation involved a screening process that identified vapor intrusion as the potential exposure pathway and the contaminants of concern (COC). The second component of the evaluation employed a weight-of-evidence approach that integrated estimates of likely exposure with information about the toxicology and epidemiology of the COC. [Results] The contamination at this site consists of a mixed gasoline and perchloroethylene (PCE) groundwater plume. The primary route of human exposure was inhalation of potentially contaminated indoor air through vapor intrusion. Over 250 active soil vapor samples and 50 indoor air samples were collected and analyzed for selected volatile organic compounds (VOCs). COG include PCE, benzene, and methyl tertiary butyl ether (MTBE),,and other VOCs. PCE soil vapor concentrations ranged from non-detectable to 4,600 mu g/m(3) and indoor air concentrations ranged from non-detectable to 41.4 mu g/m(3). Benzene soil vapor concentrations ranged from non-detect to 160 mu g/m(3) and indoor air concentrations ranged from non-detectable to 13.2 mu g/m(3). MTBE soil vapor concentrations ranged from non-detectable to 3,788 mu g/m(3) and indoor air concentrations ranged from non-detectable to 25.2 mu g/m(3). The Spearman rank-order correlation coefficient indicated no direct relationship between PCE soil vapor and indoor air concentrations. However, not enough data are available to test the correlations between indoor air concentrations and soil-vapor concentrations of benzene and MTBE. [Conclusion] All indoor air VOC concentrations detected at the site are at levels unlikely to cause adverse, noncancer health effects for acute, intermediate, and chronic exposures. There is no direct relationship between soil vapor and indoor air concentrations. The limited available data indicated soil vapor intrusion is either not occurring, or occurring at a de minimus rate that poses no adverse health effect in the community. ATSDR categorizes this site as posing no apparent public health hazard. This means human exposure to contaminated indoor air could be occurring, could have occurred in the past, or could occur in the future, but such exposure is not expected to cause any adverse health effects.