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C?eologmil recknus 144 Page 5 ' Yd Quarter 2001 Groundwater Monitonng Report Project No 507 2 November 6,2001 ' 0 Wells MW-4 MW-5 and MW-9 contained 58 560 and 800 u /l 1 2 DCA respectively r g p These wells contain elevated levels of TPH-G but were previously non-detect for 1,2 ' DCA for the June event • Well MW-9 contained 88 ug/1 ethanol ' • 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 • Oxidation-Reduction Potential (ORP) was measured (Table 4) and the results suggests ' that ten of eleven 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 September 17, 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 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