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1 <br /> CreologccalTecluucslnc Page 5 <br /> 1"Quarter 2002 Groundwater Monitonng Report <br /> Project No 507 2 <br /> June 17,2002 <br />' • Figures 4 and 5 indicate a previously inverse relationship between groundwater <br />' elevation and contaminant concentrations in wells MW-9 and MW-5 respectively <br /> These two parameters have demonstrated parallel slopes for recent events In Figure 4, <br /> the inverse trend was consistent for well MW-9 for the first four monitoring events, but <br /> since the March 2001 event the relationship has been parallel In Figure 5, the inverse <br /> trend was constant for MW-5 for the first five monitoring events, but since the January <br /> 2001 event the relationship has been parallel <br /> • Figure 6 indicates an inconsistent relationship between groundwater elevation and <br /> contaminant concentrations in well MW-6 The relationship has been direct for the last <br /> three events <br /> • Wells MW-4, MW-5 and MW-9 respectively contained 58, 560 and 800 µgli 1,2 DCA <br /> for the September 2001 event These wells did not contain 1,2 DCA above detection <br /> limits for the December 2001 and February 2002 events It is noted that these wells <br /> contain elevated levels of TPH-G and therefore detection limits for 1,2 DCA were <br /> elevated <br />' • Well MW-5 and MW-9 contained 14 and 21-lig/l ethanol respectively <br /> • The groundwater gradient is relatively flat and the direction of groundwater flow has <br /> varied during the course of the investigation The site is quite close to the San Joaquin <br /> River and tidal fluctuations might be responsible for the observed changes in <br /> groundwater direction <br /> o Oxidation-Reduction Potential (ORP) was measured (Table 4) and the results suggest <br /> that all of the wells sampled are either in the core of the contamination plume or are <br /> immediately down gradient from the plume and are within the halo of reaction depleted <br />' water caused by biodegradation of the contaminants <br /> • Figure 7 is a contour map indicating the TPH-G concentrations on February 26, 2002 <br /> The groundwater plume is localized in the vicinity of the former UST excavation <br /> 1 <br /> 3.0 CONCLUSIONS AND RECOMMENDATIONS <br /> Conclusions <br />' 1 Elevated concentrations of BTEX, TPH-G and MTBE are present in a laterally limited <br /> groundwater plume <br /> 2 The MTBE and 1,2 DCA plumes are minor in comparison to the BTEX and TPH-G <br />' plumes <br /> 3 The lateral extent of the contamination plume is defined to the east, northeast and <br /> southeast by wells MW-3, MW-2 and MW-i respectively <br /> 4 The plume is defined to the northwest and southwest by wells MW-10 and MW-7 <br /> respectively <br /> 5 The BTEX/TPH-G groundwater contamination plume may be defined by MW-109 with <br /> additional monitoring, if the concentrations decrease <br /> 6 The groundwater gradients flow to the northeast or east with relatively flat slopes <br />