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QUARTERLY GROUND WATER <br /> MONITORING AND SAMPLING REPORT <br /> for <br /> Former Mobil Station 04-NP4 <br /> 2375 Tracy Boulevard <br /> Tracy, California <br /> June 26, 1992 <br /> INTRODUCTION <br /> This report presents results of March 1992 quarterly ground water monitoring and sampling <br /> performed by Alton Geoscience at former Mobil Station 04-NP4, 2375 Tracy Boulevard, <br /> Tracy, California The site is currently an operating BP Oil Company station A site vicinity <br /> map is shown in Figure 1 <br /> In 1986, four underground storage tanks (USTs) were removed from the site Detectable <br /> concentrations of petroleum-range hydrocarbons were present in the subsurface Kaprealian <br /> Engineering, Inc (KEI) subsequently installed Monitoring Wells MW-1 through MW4 In i <br /> 1987, KEI installed an additional four wells, MW-5 through MW-8 Alton Geoscience was <br /> retained by Mobil Oil Corporation in 1990 to perform a supplemental site investigation As <br />. part of the continuing site characterization, another four monitoring wells, AMW-1 through <br /> AMW-4, were installed In May 1992, Alton Geoscience installed and brought online an <br /> ground water automatic recovery and treatment system (ARS), as shown in Figure 2 <br /> Information pertaining to past activities, based on reports prepared by KEI and Alton <br /> Geoscience, is included in Appendix A. <br /> FIELD PROCEDURES <br /> On March 25, 1992, Alton Geoscience monitored and sampled ground water Monitoring <br /> Wells AMW-1 through AMW-6 and MW-1 through MW-8. Ground water morutonng and <br /> sampling were in accordance with the guidelines of the California Regional Water Quality <br /> Control Board, Central Valley Region (RWQCB), and the San Joaquin County Public <br /> Health Services (SJCPHS) Alton Geoscience ground water monitoring and sampling <br /> protocol is presented in Appendix B Ground water field survey forms presenting field <br /> measurements and observations are presented in Appendix C. <br /> Ground water samples collected from the 14 wells were analyzed for total petroleum <br /> hydrocarbons as gasoline (TPH-G) and benzene, toluene, ethylbenzene, and total xylenes <br /> (BTEX) MW-3 was not sampled because of the presence of free product Ground water <br /> samples were analyzed at Sequoia Analytical Laboratory of Concord, California. Official <br /> laboratory reports and chain of custody records are included in Appendix D <br /> 1 <br />