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4 <br /> QUARTERLY GROUND HATER <br /> F MONITORING AND SAMPLING REPORT <br /> for <br /> Mobil oil corporation <br /> Former Mobil Oil Bulk Plant 03-343 <br /> 500 East arantline Road <br /> Tracy, California <br /> Marcb 26, 1992 <br /> INTRODUCTION <br /> This report presents the results of the February 1992 quarterly <br /> ground water monitoring and sampling event performed by Alton <br /> Geoscience at former Mobil Oil Bulk Plant 03-343 , <br /> 500 East Grantline Road, Tracy, California. The site is <br /> presently a fenced, vacant lot. Adjacent properties are either <br /> vacant or commercial and industrial developments. A site <br /> vicinity map is shown in Figure 1 and a site plan in Figure 2. <br /> In August 1988, Mobil Oil Corporation abandoned the former bulk <br /> storage and distribution plant. All structures were removed from <br /> the property including one underground gasoline tank and four <br /> aboveground diesel fuel storage tanks, shown in Figure 2. <br /> Following removal of the underground gasoline storage tank, <br /> analyses of soil and ground water samples detected the presence <br /> of total petroleum hydrocarbons (TPH) , and benzene, toluene, <br /> ethylbenzene, and total xylenes (BTEX) . <br /> In April 1990, Alton Geoscience drilled 48 exploratory soil <br /> borings in a grid pattern to characterize hydrocarbon <br /> concentrations in situ. In July 1990, approximately 6, 100 cubic <br /> yards of soil were excavated as a remedial measure to remove and <br /> properly dispose of hydrocarbon-affected soil onsite to the <br /> greatest possible extent. <br /> Eight monitoring wells were installed between September 26, 1990 <br /> and May 1, 1991, to evaluate the possible impact of hydrocarbons <br /> on ground water, both on and offsite. Ground water monitoring <br /> and sampling began on a regular basis on August 21, 1991. <br /> Chronological details are presented in Appendix A, Project <br /> Background. <br /> FIELD PROCEDURES <br /> On February 21, 1992 , Alton Geoscience performed ground water <br /> monitorina and sampling of Monitoring Weiss nw_1 through AT:--S i <br /> accordance with the guidelines of the Regional Water Quality <br /> Control Board, Central Valley Region (RWQCB) , and the San Joaquin <br /> 1 <br />