ARCHIVED REPORTS_MONITORING WELL INSTALLATION REPORT - SITE ASSESSMENT WORK PLAN

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' • Historical Background: River City Petroleum and Connell Motor Lift Truck ' Page 12 of 13 monitoring well borings throughout the former UST area. The TPH-g highest impact to soil ' near the water table and below the water table to a depth of 75 feet bsg occurs in the UST area. A smear zone of five feet of saturated soil contamination is documented at the wells east of the dispenser area, west under the building, where the smear zone of saturated, ' impacted-soil expands to ten or fifteen feet in thickness. The aerial extent of the soil contamination in the vadose zone is defined to the west of the former UST area. ' TPH-g and BTEX compounds were detected in ground water samples collected directly west of the dispenser island at maximum concentrations of 197,000 gg/l and 18,000 µg/1 (benzene). Relatively significant concentrations of TPH-g and BTEX compounds were ' detected in ground water samples collected directly east of the former dispenser island,in the shallow ground water and towards the west under the building at the site. ' TPH-g and BTEX compounds were also detected in deeper ground water samples collected from wells within the building on the site and each of the deep CPT samples near well MW-1, inexplicably increasing or remaining at stable concentrations with depth, and migrating towards the west from the former UST area. • The vertical and the lateral extent of TPH and BTEX previously had been defined by • monitoring well samples collected at MW-34.However,a deep CPT grab-sample collected from beneath the former dispenser area leak, indicated dissolved contamination and the possible presence of a non-aqueous phase liquid plume near the depth of 225 feet bsg,based ' on increasing vertical contamination(see Figure 3). DISTRIBUTION OF 1,2-DCA • A release of 1,2-DCA mostly likely occurred from dispenser line releases. However no samples from the UST removal or soil borings until the most recent had been analyzed for this compound. ' • Five soil samples collected from below the former UST area, from a boring for a deep well installation have detections of 1,2-DCA. These sample were collected from between sixty- five and eight-five feet bsg. The true distribution of 1,2-DCA within the vadose zone is ' uncertain. Once released to the subsurface,the 1,2-DCA contaminant migrated to a vertical depth of approximately 85 feet bsg at the former UST area. The 1,2-DCA, has physical properties (readily higher vapor pressure, low Henry's Law Constant and higher aqueous ' solubility or the tendency to remain dissolved) which cause the highest impact to site to remain in the dissolved phase. 1,2-DCA is the most widespread contaminant released at the ' site. 1,2-DCA extends vertically to a depth of 225 feet bsg based on deep CPT grab ground water samples, at concentrations of 100's,while lower concentrations in the 10's,remain at the depth of 150 feet bsg in the former UST area. Advanced GeoEnvironmental,Inc. i