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1 <br /> 11.0 MONITORING WELL FATE <br /> ' Upon approval by Regional Water Quality Control Board staff, the five installed ground <br /> water monitoring wells will be abandoned in accordance with California State and San <br /> Joaquin County water well standards. <br /> 12.0 GROUND WATER ANALYTICAL AND ELEVATION DATA <br /> Ground water depth measurements and gradient calculations are presented in each of the <br /> ' ground water monitoring reports. Historical analytical data tables for all monitoring wells <br /> are presented in Appendix C of this report. <br /> t <br /> ' 13.0 MASS CALCULATION FOR SOIL AND GROUND WATER <br /> CONTAMINANTS <br /> ' Based on the results of laboratory analyses of soil samples collected during the initial <br /> investigation and the remedial soil excavation, and current ground water analytical data, a <br /> calculation of the mass of residual contaminants has been made. Because of the minimal <br /> volume of both soil and ground water contamination, assumptions have been made <br /> regarding the maximum extent of contaminant migration. <br /> 13.1 Soil Contaminant Mass Calculation <br /> ' Following the completion of the remedial soil excavation, soil sample analytical data <br /> were evaluated to determine the mass of gasoline removed from the subsurface. Sidewall <br /> soil sample data were also evaluated to estimate the mass of gasoline remaining in the <br /> ' subsurface at the site. Because averaged values were used, the calculations are believed <br /> to be accurate but necessarily represent a range in terms of percentage of mass removed <br /> versus that remaining. <br /> 1 <br /> Based on the results of-,the remedial excavation soil sampling, the average gasoline value <br /> is 6,128 mg/Kg. Using an excavated soil volume of 1,522 cubic yards, a total gasoline <br /> mass of approximately 11,450 Kg, roughly equivalent to 4,000 gallons, are calculated to <br /> have been removed from the subsurface. <br /> ' 13.2 Ground Water Contaminant Mass Calculation <br /> ' The ground water contaminant plume is believed to cover an area of approximately 3,900 <br /> square feet, with a vertical thickness of 8 feet. With an estimated soil porosity of 30%, <br /> this soil volume contains approximately 70,000 gallons of ground water. Prior to <br /> American Geological Service, Inc. <br /> ' CA95DE-029 15 <br />