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p Appendix A - Historical Background River City Petroleum and Connell Motor Lift Truck Page 13 of 14 possible presence of a non-aqueous phase liquid plume near the depth of 225 feet bsg,based on increasing vertical contamination 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 Laterally, 1,2-DCA extends into almost every well on-site, at low concentrations west and south Significant concentrations are detected in the wells established directly west of the former UST area, lower concentrations in the magnitude of the 10's are present in the wells established in the western end of the building and further west of the building The 1,2-DCA is defined at 200 feet west, at 150 feet north and 120 feet south by CPT samples, monitoring well data and at 100 feet east of the site, mostly through monitoring well sampling and soil boring samples 1,2-DCA was detected in samples at concentrations ranging from 4 2 gg/1 to 1,600 µg/l, which are above the MCL of 0 5 gg/1 for drinking water The investigations to date suggest that the source of the 1,2-DCA is the former UST site • The vertical extent, and the lateral extent between intermediate- and deep-screen ground water depths, of 1,2-DCA have not been defined Advanced GeaEnviranmental,Inc