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ENVIRONMENTAL INVESTIGATION REPORT Unocal Service Station No 5886 2701 West March Lane Stockton Califoma. Delta Project No D095-066 ' Page 8 ' 4.4 Geoprobe Installation and Soil and Ground Water Samnlin On September 25 and 26, 1995, a second phase of on-site assessment was performed Twenty-one ' Geoprobes were advanced on-site to a minimum depth of 13 feet bsg, approximately three feet below first encountered ground water Geoprobes GP-11, GP-13, and GP-17 were advanced to 16, 14, and ' 17 feet bsg, respectively Two to three soil samples and one ground water grab sample were collected for chemical analyses from each soil boring Additional soil samples were collected for geologic logging and field screening The methods used to log the soil borings and screen the soil samples in the field is presented in Appendix B Copies of the soil boring logs are presented in Appendix E ' The probes were advanced by Vironex Environmental Field Services of Foster City, California A copy of the boring permit is presented in Appendix A The methods used to advance the probes and collect ' the samples are presented in Enclosure B The locations of the Geoprobes were selected based on the location of the former dispenser islands and the UST locations The sample locations are illustrated in Figure 5, Geoprobe Sample Locations Samples collected from the probes were submitted for chemical analysis based on stratigraphic location, field screening, and discussions with SJCEHD personnel on-site ' Each sample was analyzed for TPH as gasoline, TPH as diesel and BTEX An on-site laboratory was utilized at the request of SJCEHD to perform several of the analyses Additional analyses that could not ' be performed in the field due to the volume of samples submitted for analyses were performed by Sequoia at their Walnut Creek office 4 4 1 Geoprobe Soil Sampling Analytical Results ' Each soil sample selected for chemical analyses was submitted under chain-of-custody documentation to Sequoia for analyses of TPH as gasoline and TPH as diesel using EPA Method 8015 Modified Samples ' were also analyzed for BTEX using EPA Method 8020 Fifty soil samples were submitted for chemical analyses from 21 soil borings One ground water sample was also submitted from each boring for ' analyses RPT160 SJS - L