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' eo(o icu(Tec(imcs Inc 4 � g Page Groundwater Monztornig Report Project No 507 2 March 30, 2001 ' • Wells 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/l TAME, respectively Gasoline oxygenates, DIPE, ETBE and TBA, are not present in any of the groundwater samples • The levels of MTBE present are consistent with past events, however the TAME concentrations have not been previously recorded This may be due to the elevated detection limits in wells MW-4, MW-5 and MW-9 1 • The groundwater gradient is relatively flat and the direction of groundwater flow has varied 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 0 Oxidation-Reduction Potential (ORP) was measured (Table 3) 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 MW-3, MW-2 and MW-1 The plume has not been defined laterally to the west, northwest, or southwest, nor has it been defined vertically GTI has submitted a work plan to address the definition of the lateral and vertical extent of the plume, which has been approved by San Joaquin County PHS/EHD, and the USTCFP has approved the cost of the project 1 3.0 LIMITATIONS ' This report was prepared in accordance with the accepted standards and practices of the field of environmental 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