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Kennedy/Jenks Consultants <br /> 6.6.2 Groundwater <br /> During the subsurface characterization activities summarized herein, groundwater was <br /> encountered at depths of 13 to 15 feet bgs in OU-2, and slightly deeper in OU-5. Based upon <br /> water level data from the groundwater monitoring wells previously located in OU-1, the <br /> groundwater flow direction is believed to be north to northwest. <br /> Several metals were detected in unfiltered reconnaissance samples at concentrations <br /> exceeding analytical reporting limits, and in some cases, MCL values. In the absence of other <br /> regulatory or <br /> risk-based values, MCLs were used as comparison values, however it is not clear that <br /> groundwater beneath the site is considered a potential source of drinking water. Moreover, the <br /> groundwater samples were not filtered prior to analysis, so that metals associated with <br /> suspended solids in the water sample also contributed to the measured concentrations of <br /> metals. <br /> Although elevated concentrations of lead and arsenic were present in numerous shallow soil <br /> samples, the data suggest that the lead and arsenic concentrations in soil typically decrease <br /> with increasing depth. In summary, metals are not considered chemicals of further interest in <br /> groundwater beneath the former Railyard. <br /> Based upon the analytical results from 18 reconnaissance groundwater samples collected and <br /> analyzed for VOCs during the recent subsurface characterization activities, VOCs, including <br /> BTEX and MTBE, are not considered chemicals of further interest in groundwater. <br /> The shallow groundwater beneath portions of the former Railyard, including the western portion <br /> of OU-5, the western portion of OU-2, and the southwestern portions of OU-3 and OU-4 <br /> contains elevated concentrations of TPH. <br /> The western extent of TPH in groundwater beneath the western portion of OU-5 has not been <br /> characterized. Future analysis of groundwater samples for TPH should include laboratory <br /> preparatory steps of filtration and/or silica gel cleanup prior to chemical analysis. This will assist <br /> in characterizing the concentration of TPH that is dissolved in groundwater. <br /> DRAFT Phase I Remedial Investigation Report Page 46 <br /> Former Tracy Railyard, Tracy, California <br /> g:\is-group\admin\job\05\0565777.18_uprr\09-reports\ri rpNext.doc <br />