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1 3 CONFIRMATION SOIL BORINGS Delta Environmental Consultants, Inc (Delta) drilled confirmation soil borings at the subject site ' on 26 and 27 August 1999 The Iocations of the confirmation soil borings are shown in Figure 2 This work was performed in part to assess the effectiveness of the soil vapor extraction system in the removal of petroleum hydrocarbons from impacted soil, and to assess the area southeast of the former UST basin This work was conducted in accordance with EA's Work Plan for Confirmation Soil Borings in Support of a Request for Case Closure (EA 1998), and the work plan approval letter from the Public Health Services of San Joaquin County Environmental Health Division (Appendix A) A copy of the permit for the borings, acquired prior to field work, is also included in Appendix A t31 SOIL BORING DRILLING AND SAMPLING On 26 and 27 August 1999, Delta supervised Vironex Environmental Services of Hayward, California, during the advancing of five geoprobe soil borings (SB3 through SB7) to depths of approximately 50 feet bgs Soil samples were collected from each soil boring at a minimum of 5- foot intervals and at changes in lithology to the total depth of the borings Soil samples were screened every 5 feet using a photoionization detector (PID) Soil samples were classified using the Unified Soil Classification System and recorded on the soil boring logs On 26 and 27 August 1999, groundwater grab samples were collected from SB3 through SB7 Upon completion, the borings were backfilled with neat cement slurry (grout) using a tremae pipe, and surfaces were finished with concrete Field methods and procedures used by Delta during the installation of these borings are summarized in Appendix C Copies of the soil boring logs with lithologic descriptions are presented in Appendix D The locations of the soil borings are shown in Figure 2 3.2 SOIL SAMPLE ANALYTICAL RESULTS Selected soil samples collected from borings SB3 through SB7 were submitted under chain-of-custody to Sequoia Analytical in Petaluma, California Samples were submitted for analysis of benzene, toluene, ethylbenzene, and total xylenes (BTEX) and methyl tertiary butyl ether (MTBE) using EPA Method 8020 Modified, and for TPH-g using EPA Method 8015 Modified In addition, oxygenates, 1,2-dibromoethane (EDB), and 1,2-dichloroethane (1,2-DCA), and methanol were analyzed for using EPA Methods 8260B and 8015 Modified, respectively Soil sample analytical results are summarized in Table 2, and on Figure 6, and a copy of the laboratory analytical report and chain-of-custody documentation is included in Appendix E Oxygenates, EDB, and 1,2-DCA were not detected above laboratory reporting limits in any of the soil samples submitted for analysis TPH-g was detected in soil samples SB5-36, SB6-36, and SB7-I6 at 14,300, 0 501, and 832 milligrams per kilogram (mg/kg), respectively Benzene was detected in soil sample SB5-36 at 3 81 mg/kg The soil samples collected from soil borings SB-5 and SB-6 at 36 feet bgs were collected from below the groundwater surface, as the average depth to groundwater across the site on 30 July 1999 was approximately 26 feet bgs F%piejects17013'MaslenlVp\Closnie l 10010137cneet doc 7