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Second Semiannual 2010 Groundwater Monitoring Report <br /> Former Texaco Service Station <br /> Chevron Site ID 309075 <br /> November 22, 2011 <br /> Nitrate was not detected in the MW-1 groundwater sample, indicating that nitrate reduction likely <br /> was occurring in groundwater in the vicinity of MW-1. The concentration of sulfate in the MW-1 <br /> groundwater sample was lower than sulfate concentrations in groundwater samples collected at <br /> other site monitoring well indicating that sulfate reduction may be occurring in groundwater in <br /> the vicinity of MW-1. Dissolved iron concentrations in groundwater at MW-1 were intermediate <br /> compared with other locations, potentially indicating reaction of dissolved iron with sulfide <br /> produced during sulfate reduction. Methane was not detected in any of the groundwater <br /> samples. The interpretation of more strongly reducing conditions in groundwater in the vicinity of <br /> MW-1 is consistent with the distribution of constituents of concern (COC) in site groundwater. <br /> TPH-GRO has only been detected in groundwater samples collected at MW-1 and may be <br /> providing a source of organic carbon to support microbial activity and more strongly reducing <br /> conditions at this location. <br /> Dissolved TPH-MO Distribution <br /> Concentrations of TPH-MO, with silica gel cleanup, were detected above the laboratory MDL in <br /> the groundwater samples collected from each well in the site monitoring well network. <br /> V <br /> Dissolved TPH-DRO Distribution <br /> Concentrations of TPH-DRO, with silica gel cleanup, were detected above the laboratory MDL <br /> in the groundwater samples collected from three wells in the site monitoring well network. The <br /> detected concentrations do not exceed the water quality objective for diesel-range hydrocarbons <br /> of 100 pg/L. <br /> V <br /> Dissolved TPH-GRO Distribution <br /> One detection of TPH-GRO was reported above the laboratory MDL in the groundwater sample <br /> collected from MW-1. No other detections of TPH-GRO were reported. <br /> Dissolved BTEX Distribution <br /> Concentrations of benzene, toluene, ethylbenzene and total xylenes were not detected above <br /> their respective laboratory MDLs in the groundwater samples collected from the site monitoring <br /> network. <br /> Dissolved MTBE, TBA, DIPS, ETRE, TAME, 1,2-DCA, EDB, Ethanol and Methanol <br /> Distribution <br /> One detection of 1,2-DCA was reported above the California Primary MCL in the groundwater <br /> sample collected from MW-1. No other detections of 1,2-DCA were reported. Concentrations of <br /> MTBE, DIPE, ETBE, TAME, EDB, ethanol and methanol were not detected above the <br /> laboratory MDL in the groundwater samples collected from the site monitoring well network. <br /> Concentration maps of the site are presented as Figures 4 and 5. Concentration versus time <br /> graphs for all wells in the site monitoring well network, except MW-6 and MW-6D, are presented <br /> as Figures 1 through 5 of Attachment I. Wells MW-6 and MW-6D will be included once four <br /> events worth of data has been collected. <br /> g:\aproject\env\chevron\309075\6 deliverables\periodic monitoring\2011\1 sa11\temp pdf\text\309075 1 sa11 gmr fin 11222011.doc 7 <br /> W <br />