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Concentrations of electrical conductivity in waters from the Mokelumne River are reported to range from 200 to 350 umhos/cm because the relative short distance from watershed source in the Sierra Nevada and Quaternary alluvial terrain the waters traverse (Page, 1986) Temperature and pH concentrations in the monitoring well waters is typical of lit groundwater encountered in the Lodi area (Environmental Forensics Inc, 2002) 2`4 Local Groundwater Flow Direction and Gradient The groundwater surface undulates slightly but has a gentle slope toward S80W with a gradient of 0 00125 (Figure 4) This flow direction and gradient are consistent with published groundwater data from the City of Lodi (Environmental Forensic Investigations, Inc , 2002) and San Joaquin County Department of Public Works (1999) groundwater surface elevations for the North San Joaquin Water Conservation District 25 Petroleum Hydrocarbon Groundwater Plume The areal or horizontal extent of the petroleum hydrocarbon groundwater plume at the site extended throughout the site Isoconcentration maps of TPH-gasoline and benzene in the groundwater are presented as Figures 4 and 5 A review of past groundwater petroleum hydrocarbon concentrations was made and included in the tabulations presented in Table 2 No limit of the petroleum hydrocarbon contamination plume has been identified The past maximum areal extent of the groundwater petroleum hydrocarbon plume as determined from Figures 4 and 5 suggest the site to have a minimum areal extent of approximately 200 by 225 feet (45,000 square feet) Based on review of past analytical data obtained from Geological Audit Service, Inc, 1991 and Booth (1994 a,b,c,d,and e) the highest concentrations of volatile organic compounds (VOC's) at the site are found near PT-MW-3 and within the southern portion of the site It appears that the petroleum hydrocarbon compounds have migrated offsite, most likely to the southwest of the site The extent of the release is currently unknown and undocumented in both the vertical and horizontal extent It is unclear at this time if the site poses a threat to local water supplies Main\D\EnvironmentaE\ParmarTexaco\Reports\13103QSR wpd 4