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n p meg ' a s_ - ;� Y <br /> . e ua �`T ..Jr ' t. .." ., u`" <br /> _,ry �`* Win,a?" ri3".z-.` r^� �" 'PER, 'r+ � ��:x � rt. <br /> ri^a.�a r^r�r - .��..� �s r_^rc'� � i"]�; .rz <br /> f a <br /> �p <br /> x} <br /> QUARTERLY GROUND WATER <br /> MONITORING AND SAMPLING REPORT <br /> for <br /> Pos.-mer Mobil Service Station 10--NP4 <br /> 2375 Tracy Boulevard <br /> Tracy, California <br /> INTRODUCTION <br /> This report presents the results and findings of the recent <br /> quarterly ground water monitoring and sampling activities <br /> performed by Alton Geoscience, Inc. at former Mobil Service <br /> Station 10-NP4, located at 2375 Tracy Boulevard, Tracy, <br /> California. The site location is presented in Figure 1. <br /> PROJECT BACKGROUND <br /> The former Mobil oil service station site is presently a BP <br /> oil service station, located at 2375 Tracy Boulevard, Tracy, <br /> California. <br /> In August 1986, four underground storage tanks were removed <br /> from the site. Three grab samples of water collected from <br /> + the gasoline tank excavation cavity were composited and <br /> analyzed. Analytical results of the composited water sample <br /> indicated the presence of Total Petroleum Hydrocarbons as <br /> Gasoline (TPH-G) at a concentration of 30 ppm. Benzene, <br /> toluene, and xylene (BTX) constituents were detected at <br /> concentrations of 1.6, 3_0, and 5.3 ppm, respectively. <br /> Analysis of one soil sample collected from the wall of the <br /> waste oil tank excavation cavity resulted in TPH-G <br /> concentrations of 61 ppm. BTX constituents, polychlorinated <br /> biphenyls (PCBs) and halogenated volatile organic compounds <br /> (HVOC) were not detected above reported detection limits. <br /> Analysis of a soil sample collected from the excavated area <br /> of the gasoline product line revealed TPH•-G concentrations of <br /> 2 ppm and BTX concentrations of 0.22, 0.34, and 0.29 ppm, <br /> respectively. <br /> Following the tank removal and replacement, Kaprealian <br /> Engineering, Inc. (KEI) , installed four ground water <br /> monitoring wells onsite (MW-1, MW-2, Mw-3, and MW-4) . Ground <br /> - --- <br /> water--sample--analysis--revealed_-detectable concentrations of <br /> hydrocarbon constituents in the samples from MW-3 an - <br /> only. In January 1987, KEI installed four additional ground <br /> water monitoring wells (MW-5, MW-6, MW-7, and 14W-8) . Soil <br />