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Update of Vapor Extraction System Operation <br /> The vapor extraction system continued to work through the months September, October and <br /> November 1998 Shutdowns occurred for quarterly monitoring (November 12 - 18, 1998) and the <br /> system was shut down on December 19, 1998 The system operated a total of 22629 5 hours (943 <br /> days as of December 19, 1998) Vapor extraction total removed hydrocarbons, as gasoline using <br /> activated carbon as a control was 223 pounds and direct venting to atmosphere of 19 5 pounds, see <br /> Table 2 On October 3, 1997, after concurrence with San Joaquin Valley Air District, the four 110 <br /> gallon vapor scrub units were removed from the treatment system and the offgas from the vapor <br /> recovery system was vented directly to the atmosphere, see Appendix C — Field notes and <br /> Chromatograms Previous vapor extraction removals were controlled by Thermal Oxidation and <br /> removed 74,849 pounds of gasoline range hydrocarbons <br /> Totals of gasoline range hydrocarbons removed by the vapor extraction system are as follows <br /> Thermal Oxidation destruction 74,849 pounds <br /> Carbon Adsorption 223 pounds <br /> Vent to atmosphere 19 5 pounds <br /> Total Removal 75,091 5 pounds or approximately 12,014 5 gallons <br /> Weekly bio-venting of MW-8 and MW-12 was conducted by Lawrence Tank Testing Currentlyth <br /> e <br /> groundwater is too high, no slotted casing is exposed above groundwater at MW 12 to conduct bio- <br /> venting This weekly venting was terminated on December 12, 1998 and has removed a calculated <br /> 5 62 pounds of gasoline range hydrocarbons and a total of 544 pounds of hydrocarbons as gasoline <br /> and CO2 The average flow rate was 50 8 cfrn, with a vapor stream consisting of TPHg of 0 01 mg/L <br /> and CO2 at 1 5%, see Table 3 and Appendix D <br /> ELECTRON ACCEPTORS <br /> Natural Attenuation 1s occurring at this site Field groundwater analysts obtained December 16, <br /> 1997 for Dissolved Oxygen, Nitrate, Sulfate and Ferrous Iron demonstrate that the available oxygen <br /> is being used by microorganisms and a reducing environment has been established at MW2 with the <br /> onset of methogenists During this latest sampling Dissolved Oxygen, Nitrate, Sulfate, Ferrous Iron <br /> and ORP (oxygenation reduction potential) were again measured The following table compares <br /> both Natural Attenuation samplings <br /> 3 R603 Update#55 01/99 <br />