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Human Health Risk Assessment <br /> Former Mobil Oil Bulk Plant 04-343 <br /> 500 East Grant Line Road <br /> Tracy, California <br /> 1.3.3 Proposed Final Remediation Plan <br /> The final remediation plan outlined below addresses hydrocarbon-affected soil and low-level <br /> dissolved-phase hydrocarbon concentrations in ground water. In addition, this approach <br /> evaluates potential human health risks associated with the presence of residual petroleum <br />' hydrocarbons in the subsurface. <br />' A review of proven remediation technologies commonly used for treatment of hydrocarbon- <br /> affected soil and ground water, including the advantages and disadvantages of each technology, <br /> ' is presented in Appendix A. <br /> 1.3.3.1 Fluid-Level Monitoring and Ground Water Sampling <br /> The quarterly fluid-level monitoring and ground water sampling program will continue at this <br /> ' site. Field and laboratory data will be used to assess the ground water gradient and the lateral <br /> extent of the dissolved-phase hydrocarbons. <br /> Fluid levels will be measured in the monitoring wells prior to sample collection to confirm the <br /> absence of liquid-phase hydrocarbons. Fluid levels are monitored in the wells using an <br /> electronic interface probe with conductance sensors. The presence or absence of liquid-phase <br /> hydrocarbons is verified using a hydrocarbon-reactive paste. The depth to liquid-phase <br /> hydrocarbons and water is measured relative to the well box top or top of casing. Well box or <br /> ' casing elevations are surveyed to within 0.02 foot relative to a county or city bench mark. In <br /> ' the event that the liquid-phase hydrocarbons are observed in any monitoring wells, the well(s) <br /> will be pumped out manually. <br /> ' Prior to sampling, monitoring wells will be purged of three to four casing volumes, until pH, <br /> temperature, and electroconductivity parameters have stabilized. Ground water samples will be <br /> collected by lowering a 1.5-inch-diameter,bottom-fill,disposable, polyethylene bailer just below <br /> the air/water interface in the well. The samples will be transferred from the bailer to <br /> zero-headspace, 40-milliliter and 1-liter glass containers fitted with Teflcn-sealed caps. Samples <br /> will be inverted to ensure that entrapped air is not present. Sample labels will include the <br /> 30-0136-11 <br /> 1-14 <br />