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' eo10 ua(Tec/intcs Inc e 5 Pa � B g Groundwater Mon,tonng Report Project No 507 2 l June 19, 2001 ' • Well,; MW-5, MW-6 and MW-9 contained 290, 5 1 and 400 ug/1 MTBE, respectively Wells MW-4, MW-5 and MW-9 contained 130, 450 and 400 ug/I TAME, respectively ' Gasoline oxygenates, DIPS, ETBE and TBA, are not present in any of the groundwater samples • The groundwater gradient is relatively flat and the direction of groundwater flow has vatted during the course of the investigation The site is quite close to the San Joaquin River and tidal fluctuations might be responsible for the observed changes in ' groundwater direction • Oxidation-Reduction Potential (ORP) was measured (Table 4) and the results suggests that all of the wells are either in the core of the contamination plume or are immediately ' down gradient of the plume and are within the halo of reaction depleted water caused by biodegradation of the contaminants ' The lateral extent of the contamination plume is defined to the east, northeast and southeast by wells MW-3, MW-2 and MW-1, respectively The plume is defined to the northwest and southwest by wells MW-10 and MW-7, respectively Figure 7 is a contour map indicating ' the wells' TPH-G concentrations on June 1, 2001 The vertical extent of the plume will be defined by MW-109 with additional monitoring 3.0 LIMITATIONS This report was prepared in accordance with the accepted standards and practices of the field of envitonmental geology, groundwater hydrology and good business practices It ' should be recognized that definition and evaluation of environmental conditions is a difficult and an inexact science Judgments leading to conclusions and recommendations are generally made with an incomplete knowledge of the site-specific conditions present ' The tasks proposed and completed during this project were reviewed and approved by the local regulatory agency for compliance with the law No warranty, expressed or implied, is ' made 1 ,1