CHARACTERIZING DNAPL CONTAMINATION AND VAPOR INTRUSION IN DAYTON, OHIO

Vapor intrusion originating from volatile organic compounds (VOCs) represents a growing concern for toxic chemical exposure to the public. A former manufacturing site in Dayton, Ohio has experienced soil and groundwater contamination due to leakage from underground storage tanks containing trichloroethylene (TCE), perchloroethylene (PCE), and chloroform. Increased levels of VOC vapor concentrations were detected in the vicinity of the site leading to an investigation by the Ohio EPA and US EPA. For this study, geologic well-log, hydraulic head, and contaminant (TCE, PCE, chloroform) concentration data obtained at 13 groundwater monitoring wells were analyzed to characterize geologic and hydrogeologic settings of the aquifer, and patterns of groundwater flow and contaminant migration within the contaminated aquifer were also derived using this information. In addition, 24 soil samples and 30 soil vapor data collected throughout the study area were analyzed to characterize distributions of organic vapor in the unsaturated zone.

The study site is underlain by an approximately three-meter thick layer of unsaturated sand and gravel layer above the primary aquifer (comprised of sand and gravel) separated by a meter-thick layer of clay. Primary direction for groundwater flow and contaminant migration in the sand and gravel aquifer is to the southeast towards a river where other residences are located. The VOC contamination is most severe where three of the former underground storage tanks were located with soil vapor concentrations of up to 8,100 ppbv (parts per billion per volume of air) of chloroform and 7,700 ppbv of TCE. Dissolved concentrations in groundwater samples were as high as 370 μg/L for chloroform and 150 μg/L for PCE. Results of this study may provide insight into further developing mechanisms in identifying vapor intrusion in residential homes resulting from sub-surface contaminant sources.