A field study was conducted at a former gasoline service station in Cincinnati, Ohio to remediate groundwater contaminated with dissolved benzene, toluene, ethylbenzene, and xylenes (BTEX). The site was operated as a gasoline service station until operations ceased in the late 1970’s. The underground storage tanks (USTs) were removed in 1981. The former USTs were located near the center of the site, and a former gasoline dispenser was located northeast of the USTs (Figure 1). A total of seven groundwater monitoring wells, MW-1 to
MW-7, were installed at the site between May and October 1996 for site assessment activities. Soil samples were collected during the installation of the wells, and groundwater samples have been collected from each well.
The geology of the site consists of silty clay from surface grade to depths ranging from 8 to 12 feet (2.4 to 3.7 m) below ground surface. The soil grades into silt with variable amounts of sand below the silty clay from 12 to 29 feet (3.7 to 8.8 m), then the soil grades back into silty clay from 29 feet to 31 feet (8.8 to 9.5 m), the greatest depth sampled at the site. The former UST pit consists of silty clay fill material with some gravel and large concrete fragments. The monitoring wells are screened through the bottom of the silty clay layer into the saturated silt and sand layers. Groundwater generally flows to the southwest, parallel to the road, with a hydraulic gradient of 0.05 feet per foot (Figure 1).
FIGURE 1. Site Plan showing site features and monitoring well locations.