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Ms Lori Duncan Project 20805-140 010 May 13, 1999 Page 5 milligrams per kilogram (mg/kg) to below laboratory detection limits BTEX constituents ranged from 220 milligrams per kilogram (mg/kg) to below laboratory detection limits Analytical results are summarized on Table 1 and on Figures 3 and 4 Copies of certified analytical reports (CARS) and chain of custody (COC) documentation are presented in Appendix E The detected petroleum hydrocarbon concentrations are generally highest in the capillary fringe (samples collected at 315 feet bgs) Concentrations attenuate with depth in the water bearing zone In borings AS-1 and AS-3, petroleum concentrations at the base of the borings (56 5 and 66 5 feet bgs, respectively) were limited to total xylenes at concentrations of 0 02 mg/kg or less In boring AS-2, detected concentrations at 615 feet bgs were 3 61 mg/kg for TPHG and 0 036 mg/kg for benzene MTBE was not detected at depths below 36 5 ft bgs in any boring Based on the detected concentrations, and Vttenuation of all hydrocarbon constituents with depth, the vertical soil characterization} appears to be complete I • HydroPunch Sample Analytical Results Dissolved petroleum hydrocarbons were detected in the three samples collected at depths of 64 5 to 69 feet bgs TPHG concentrations ranged from 2,590 to 40,200 µg11 and benzene concentrations ranged from 89 4 to 333 µg11 MTBE was detected at 129 µg11 in sample AS-1 and did not exceed raised etechon limits in the other samples Analytical results are summarized on Table and on Figures 3 and 4 Copies of certified analytical reports (CARs) and chain of custody (COC) documentation are presented in Appendix E These detected concentrations exceed the water table concentrations (Table 3) determined during no-purge sampling of vapor extraction wells The HydroPunch results are suspect because the soil concentrations attenuate with depth and dissolved concentrations typically do not increase with depth The potential for cross-contamination of these samples exists CONCLUSIONS This assessment defined the vertical extent of soil impacts Highest detected impacts are present immediately beneath the former USTs and at the capillary fringe Concentrations attenuate with depth and the vertical extent of impacts are defined to non-detect at 66 5 feet bgs in AS-3 and to low residual concentrations at 615 feet in AS-2 CP\E 1ARCO\0548\REPORTS10548P201 DOC-9811sg 1 ;P"MM& A-5