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' Closure Report 12 <br /> • Golden Grain Manteca Bean Facies ,299 Moffat Boulevard,Manteca,Cahforn�a July 16,1996 <br /> a present system groundwater Influent TPH-g concentrations below detection limit, a <br /> ' decrease of 100% <br /> ■ Initial soil vent gas concentrations approximately 3,500 ppmv TPH-g <br /> present sod vent gas concentrations 0 ppmv TPH-g <br /> R total mass of petroleum hydrocarbons removed by the remediation system to date is <br /> ' approximately 3,450 pounds <br /> 3 3.1 Soil Vapor Extraction <br /> Approximately 3,450 pounds of petroleum hydrocarbons have been removed from the subsurface <br /> soil and groundwater since the start of operation of the treatment system Of that total mass, <br /> ' approximately 3,440 pounds of hydrocarbons have been removed from the vadose zone soil The <br /> mass removed estimates were calculated using flow rates and Influent concentrations During the <br /> first two and one-half years of system operation, 99 9 percent of the total mass removed was <br /> extracted Over the past year and a half, virtually no mass(< 1%) of petroleum hydrocarbons has <br /> been removed Table 7 presents the mass of petroleum hydrocarbons removed by each of the <br /> systems by quarter since the beginning of operation, and graphical representation of the mass <br /> removal is included In appendix D The large difference in hydrocarbon removal between the soil <br /> and groundwater media is typical for the treatment technologies utilized at the site As discussed in <br /> ' previous sections of this report, various system modifications were made during the past year to <br /> maximize removal of hydrocarbons present in the subsurface While all of the modifications were j <br /> appropriate and technically sound, no additional hydrocarbon mass removal resulted from the <br /> changes <br /> Since the beginning of sod vapor extraction system operation, the hydrocarbon removal efficiency <br /> has been at least 97 percent, except for three occasions, when the removal efficiency was 96 <br /> percent In order to calculate the hydrocarbon removal efficiencies,the influent and effluent vapor <br /> concentrations were measured weekly during normal operating conditions with a portable flame <br /> Ionization detector(FID) Weekly influent and effluent FID readings from the sod vapor extraction <br /> ' system have been presented in the site quarterly status reports since the start of the remediation <br /> system operation <br /> 42(120213 CR <br /> FLUOR DANIEL GTI <br /> i <br />