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I i i 17 October 2003 l ' AGE-NC Project No 02-0964 Page 7 of 8 ' The laboratory report (CTEL Lab I D 0304-064-1 to 08, 0304-069-1 to 7 and 0304-087-1 to 4) Quality Assurance and Quality Control(QA/QC) report and chain-of-custody form are included in Appendix B Analytical results of the CPT grab ground water and soil samples are summarized in Tables 1 and 2 4.0. SUMMARY/CONCLUSIONS The following conclusions were drawn from the results of this investigation • The site stratigraphy is composed predominantly of fine-grained soil consisting of silt, clayey ' silt, silty clay and clay, with the exception of five significant sand lenses or layers at depths of approximately 50 feet bsg, between 60 and 75 feet bsg, between 95 and 110 feet bsg, between 120 and 130 feet bsg and between 140 and approximately 160 feet bsg CPT pore I pressure dissipation tests in the sandy silt, sand and gravelly sand indicated that hydraulic conductivities were typical for sand mixtures • TPH-g and BTEX impacted soil was detected at low concentrations at 55 feet bsg, but at • significant concentrations at 78 feet bsg Based on the vertical distribution of contaminants In soil from the present and previous site investigations (Figure 4), AGE delineated two distinct zones of contaminated soil, in fine-grained soil(HU1)at between 30 and 40 feet bsg beneath the Chevron (northeastern-most) former dispenser island, and in fine-grained soil (HU3) at 80 feet bsg The soil contamination at 30 to 40 feet bsg, which included diesel as well as gasoline products,may have originated from the overlying former Chevron dispenser island area However, based on the available data, the source for the deeper contamination at 80 feet bsg is uncertain, the former Standard Oil USTs cannot be ruled out • Petroleum hydrocarbons were detected in grab ground water samples collected from the northeastern portion of the site, in the area of CPT 1, CPT2 and CPT5,to approximately 180 feet bsg Based on the vertical distribution of contaminants in ground water from the present ' and previous site investigations(Figure 5),the highest concentration of contaminants appears to be at between the upper ground water surface at boring A/MW-1 and at 40 and 60 feet bsg in the area of CPT1 and CPT2 The concentrations of contaminants appear to decrease fvertically,towards a minimum in clay-rich fine grained soil at a depth of between 80 and 100 feet bsg However, petroleum hydrocarbons increase again below 100 feet bsg, to high ' concentrations of between 11,000 µg/l and 14,000 ug/l TPH-g at depths of between 120 and 150 feet bsg The vertical distribution of TPH-g concentrations suggests that the primary source of contamination may be the Chevron (northeastern) dispenser island, but does not rule out the former Standard Oil USTs as an additional source i IAdvanced GeoEnvironmental,Inc I