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Irl APPENDIX A ADDITIONAL SITE ASSESSMENT On July 24, 1996, the following activities were performed to evaluate the extent of petroleum hydrocarbons west of the former service station and to provide further vapor extraction capability within and beneath the former UST complex An EMCON field geologist observed Woodward Drilling of Rio Vista, California, drill four soil borings (B-22 through B-25) The borings were converted to vapor extraction wells VW-10 through VW-13 and were drilled to a depth of 26 feet below ground surface (bgs) The locations of the soil borings and vapor wells are shown on Figure 4 Groundwater was not encountered during drilling actnnties EMCON's field procedures are presented in Appendix B Samples were obtained at approximately 5-foot intervals for possible laboratoiy analyses and to characterize the geology beneath the site Samples were logged using visual and manual methods and classified according to the Unified Soil Classification System Sediments encountered are shown on the logs of borings (see Appendix C) Drill cuttings were stockpiled on site and covered with plastic sheeting On April 24, 1996, an EMCON geologist collected sod samples (one composite of four samples) from the stockpiled soil for analyses to evaluate disposal options At ARCO's request, the drill cuttings were transported by Dillard Trucking of Byron, California, to the BFT landfill in Livermore, California, for disposal. Select soil samples collected from the wells and samples from the stockpiled soil were analyzed for TPHG using U S Environmental Protection Agency (USEPA) Method 503018015, BTEX using USEPA Method 503018020, and methyl-tert-butylether (MTBE) using USEPA Method 8020 In addition, the stockpile composite soil sample was analyzed for total lead Samples were analyzed at Sequoia Analytical in Sacramento, California (California Department of Health Services, Hazardous Waste Testing Laboratory, Certification No 1624) Laboratory analytical results and chain-of-custody records are presented in Appendix D Residual hydrocarbons were detected in soil samples collected from all borings TPHG concentrations ranged from below laboratory detection limits to 730 parts per million (ppm) Benzene concentrations ranged from below laboratory detection limits to 0 22 ppm MTBE concentrations were below laboratory detection hmits in soil samples analyzed from the borings Results of the laboratory analyses are presented in Table A-1 Although hydrocarbons were detected in the soil sample collected near the former dispenser island, hydrocarbons do not appear to extend beyond 21 feet bgs in the vicinity of the former dispenser udand SAO N\PJ"805 08051460 7CS-96Nc1b 1 A-1 Rev 0 10/25196