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CLEARWATER <br /> G R O U P <br /> Environmental Services <br /> biodegradation occurs, the rates actually overtake the rate at which petroleum hydrocarbons <br />' released from the sorbed-phase into the dissolved-phase The process that hydrocarbons degrade <br /> often takes place at a first-order kinetics First-order degradation rate can be determined by <br />' evaluating the change of either hydrocarbon concentrations from individual wells or total plume <br /> mass with time, if the plume has been delineated for an extended period of time First-order <br />' degradation rates for the petroleum hydrocarbons beneath this site were estimated by using <br /> historical monitoring data obtained from well MW-1, MW-5B, and MW-8 Concentrations of <br />' TPH-g and benzene measured at these wells were plotted against time as a semi-log function A <br />' degradation rate was determined by fitting a first-order kinetic equation to the plotted data The <br /> fitted curve are presented in Figures 6A, 6B, and 6C, respectively <br />' The estimated first-order degradation rates for TPHg n <br /> g g a d benzene in MW-1 are approximately to <br /> be 0 08 per day and 0 2 per day, respectively (Figure 6A) The semi-log plot for TPHg and <br /> benzene in MW-5B indicates that concentrations of these species in this well are either stabilized <br /> or slowly decreasing with time (Figure 6B) Because monitoring well MW-5B often is located <br /> down gradient of the former UST excavation area, the observed trend in MW-5B suggests that <br /> Eresidual hydrocarbons may exist in the soil or center of the plume is still located up gradient of <br /> MW-5B The observed trend of TPHg. concentration change in MW-8 is similar to that observed <br /> in MW-5B However, benzene shows a decreasing trend The estimated degradation rate is <br /> approximately 0 1 per day <br /> INJECTION WELL AND iSOC SYSTEM INSTALLATION <br /> During the current quarter, Clearwater installed twelve remediation wells (IW-1 through IW-12) <br /> and an oxygen-infusion system ("iSOC") on site Locations of iSOC oxygen infection wells are <br /> Ishown in Figure 7 The iSOC oxygen infusers were installed in each of the remediation wells and <br /> are connected to a central regulated oxygen gas supply The iSOC units are suspended in each <br /> Iwell, approximately 0 5 feet above the bottom, using plastic-lined cord, which is hung from the <br /> • <br /> 4Q/04 Groundwater Monitoring Report 8 <br />