Indoor Air Contamination from a Shallow Ground Water VOC Plume – Experience with the Grants Chlorinated Solvents Plume Superfund Site, Cibola County, New Mexico

摘要

The Grants Chlorinated Solvents Plume site is an area of volatile organic compound (VOC)-contaminated ground water. U.S. Environmental Protection Agency Region 6 (USEPA) initiated a Remedial Investigation/Feasibility Study (RI/FS) at the Site in 2002. Chlorinated solvents have been detected in shallow ground water (from 4 to 6 feet below ground surface) at the site. Tetrachloroethene (PCE), trichloroethene (TCE), cis1,2 dichloroethene (cis-1,2-DCE) trans-1,2 dichloroethene (trans-1,2-DCE), 1,1 dichloroethene (1,1-DCE), and vinyl chloride have been detected in concentrations over 50 parts per million in the shallow aquifer. As part of the RI/FS, USEPA evaluated the vapor intrusion pathway. Ground water, soil gas, indoor and ambient air sampling was conducted in and around six residences above the ground water plume plus two selected background locations to determine if the ground water contamination was impacting indoor air. This paper presents the monitoring results along with the attenuation factors calculated from those results. Three rounds of indoor and outdoor air samples and one round of soil gas and groundwater samples were collected from the residences and surrounding areas. Indoor air samples were analyzed using selective ion monitoring and achieved detection limits in the low parts per trillion range. Results ranged from non-detect to 179 micrograms per cubic meter (μg/m3). Soil gas concentrations ranged from non-detect to 95,000 μg/m3. These data were then used to determine the relation between groundwater, soil gas, and indoor air contaminant levels. The soil vapor results generally corresponded with the known dimensions of the chlorinated solvent plume in ground water. The relative trends in ground water and soil gas concentrations may provide information that is useful for selecting soil gas data for calculating attenuation factors.