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r • • <br /> Meeting Minutes for Stockton Former MGP Site Project <br /> October 11, 1996 <br /> Offices of DTSC, Sacramento <br /> Attendees: <br /> 1.0 Objectives <br /> Liz Dodge reviewed the objectives and agenda for this meeting. The objectives of the meeting <br /> were: <br /> 1. to discuss and agree on parameters of VLEACH model <br /> 2. to discuss groundwater model parameters and preliminary results. <br /> Tricia Sullivan requested adding to the agenda a discussion of the information she collected on <br /> underground water and sewer lines and gas holder construction. <br /> 2.0 Parameters for VLEACH analysis <br /> Fritz Carlson reviewed the results of the sensitivity analysis performed on the VLEACH input <br /> parameters. The following parameters were used in the sensitivity analysis: <br /> • Recharge rate (assumed typical value of 1% of precipitation and sensitivity analysis value <br /> of 2%) <br /> • Moisture content (typical value is equal to the mean of 134 site samples, sensitivity value <br /> is equal to the lower bound of the 95% confidence interval) <br /> • Foc (typical value is equal to the geometric mean of 78 site samples, sensitivity value is <br /> equal to the lower bound of the 95% confidence interval) <br /> • Porosity (assumed typical value of 0.4 and sensitivity analysis value of 0.49) <br /> Increasing the recharge did not significantly affect the results. Lowering the moisture content <br /> and Foc resulted in faster transport of the COCs. Increasing the porosity resulted in the <br /> greatest increase in the transport of the COCs. The sensitivity of the porosity may be an <br /> artifact of the model and may not represent actual conditions. Further evaluation of this result <br /> is being conducted. PG&E will also evaluate whether Shelby tubes, in conjunction with the <br /> geoprobe, can be used to collect site-specific porosity data during the next field investigation. <br /> The sensitivity analysis did not result in order of magnitude variations. When all the <br /> parameters are varied in the conservative direction (the super run), benzene concentrations are <br /> about 50 percent higher and naphthalene concentrations are about 3 times higher. <br /> It was agreed that the parameters used in the VLEACH model are acceptable. Both the <br /> typical and "super run"scenarios will be used in evaluating areas for remediation. <br /> 3.0 Groundwater Mixing Cell Model <br /> 1 <br />