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