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' Pombo Ranch Facility May 2006 <br /> Site Closute Report <br /> the extent of the xylene contamination are shown in Figure 30 and Figure 31. <br /> A ximately 0.9 pounds of MTBE was removed by the remedial excavation. Residual <br /> \gasoline contamination was not detected in the confirmation soil samples in the <br /> 2 �c vation sidewalls. Post excavation MTBE contamination is shown in Figure 32. <br /> Trace concentrations of MTBE and gasoline range petroleum hydrocarbons were detected <br /> in wells MW4B and MWS respectively. An estimated 0.5 pounds of gasoline and 0.1 <br /> pounds of MTBE remain present in the groundwater. Mass balance calculations for the <br /> ' residual groundwater contamination are attached in Appendix B. <br /> ' 4.0 CONCLUSIONS & RECOMMENDATIONS <br /> Approximately 212 pounds of petroleum hydrocarbons including 9.8 pounds of aromatic <br /> compounds and fuel additives were removed from the shallow soil at the Pombo Ranch <br /> site. Gasoline and MTBE contamination in groundwater show significant reductions as a <br /> ' result of the remedial excavation. Residual gasoline and MTBE groundwater <br /> contamination is present in two of the down gradient wells. MTBE is present in well <br /> MW4B at a concentration of 1.2 ug/l, below the maximum contaminant level (MCL) of <br /> ' 13 ug/l and the secondary MCL and taste and odor threshold of 5 ug/l. Gasoline <br /> hydrocarbons are present in well MW5 at a concentration of 60 ug/l which is above the <br /> taste and odor threshold water quality goal of 5 ug/l. <br /> ' A Department of Water Resources Well records search for all wells within a 2000-foot <br /> radius of the site did not identify any wells within the 2000 foot search area. Records for <br /> several wells were reported in the northwest quarter of section 30 Township 2 South 1 <br /> ' Range 5 East. There were no well completion reports on file for the three domestic wells <br /> located up gradient to the release. The residual gasoline contamination does not pose a <br /> ' threat to the existing wells or other receptors and will continue degrade and attenuate <br /> over time. Additional corrective action on this site is not warranted. A No Further Action <br /> determination should be issued for the Pombo Ranch 24100 S. Lammers Road, Tracy site <br /> 1 <br /> 10 <br /> 1 � <br />