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' WELL INSTALLATION AND CPT INVESTIGATION REPORT 5400 and 5606 Pacific Avenue,Stockton,Calitomia(CAO NO 5-00707) _ EAI PTOlect No 1232 40 DISCUSSION 41 Distribution of Hydrocarbon Impacted Soil TPH-G, benzene, ethylbenzene and xylenes were not detected in soil borings 1\4W-9 or MW- 27 Toluene was detected in six samples at a maximum concentration of 0 010 mg/Kg (see Table 1) The maximum TPH-G concentration in boring MW-8D was 1,660 mg/Kg at a depth of 50 feet bgs The maximum TPH-G concentration in boring AS-26 was 220 mg/Kg at a depth of 55 feet In these same samples, BTEX were also identified at a maximum concentration of 71 8 Ing/Kg xylenes in MW-8D @ 50 feet The data in Table 1 indicate the highest concentrations of hydrocarbons in soil are between 50 and 60 feet bgs ' 42 Laterally Continuous Silt/Clay Layer The two CPT soundings identified a clay to clayey silt layer extending from approximately 86 feet bgs to the total depth investigated (see Appendix E) These results are similar to the three CPT soundings advanced near the former Robinhood Irrigation Well (RIW) (see EAI, 2000) Data obtained from the two current CPT soundings and the three CPT soundings associated with the RIW all indicate there is a Iaterally extensive silt/clay layer beneath the site This layer begins at approximately 86 feet bgs 1n soundings CPT-MW and CPT-UN and between 86 and 104 feet bgs in the soundings located near the former RIW 4.3 Impact to Deep Ground Water Ground water samples were obtained from CPT borings CPT-MW @ 86' and CPT-UN @ 86' ' Table 2 present the analytical testing results for these two samples No TPH-G of VOCs were detected in boring CPT-UN located on the former Unocal site However TPH-G (7,710 µg/L) and several VOCs at a maximum concentration of 1,230 µg/L (benzene) were detected in the water sample (CPT-MW @ 86') obtained on the former Wards site (see Table 2) BHM WORD 123280191 7 ENVIRONMENTAL AUDIT, INC