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December 8, 1993 Working to Restore Nature <br /> ARCO Station No 760, Lodi, California <br /> Reporting Results of Analyses <br /> Hydrocarbon constituents in soil samples are reported in units of parts per million <br /> Hydrocarbon constituents in groundwater samples are reported by the laboratory in units <br /> of parts per billion (ppb) The maximum contaminant levels listed in Title 22 of the <br /> California Code of Regulations for benzene, ethylbenzene, and total xylene isomers in <br /> drinking water are 10, 680, and 1,750 ppb, respectively The action level established by the <br /> California Department of Health Services for toluene is 100 ppb To conform with the <br /> laboratory reports, we report groundwater chemical data in units of ppb <br /> Evaluating the Groundwater Flow Direction and Gradient <br /> The elevations and positions ("x" and "y" lateral coordinates) of the monitoring well are <br /> surveyed by a licensed land surveyor with respect to a local datum that references the <br /> elevation according to mean sea level The elevation of the monitoring wells are measured <br /> within 0 01 foot of the local datum. The horizontal distances are measured to the nearest <br /> 01 foot The elevations are to be taken to either a notch or an arrow to be marked on the <br /> top edge of the well casing <br /> The groundwater elevation for each monitoring well is calculated by subtracting the depth <br /> to water from the wellhead elevation The groundwater elevation information is used to <br /> construct a potentiometric surface map, which 1s used to evaluate the direction of <br /> groundwater flow and the magnitude of the groundwater gradient <br /> 0913ccar <br /> ' 3WMS-10 <br />