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1 <br /> E11��t® <br /> Ms Margaret Lagono <br />' July 16, 2004 <br /> Page 3 <br />' SP-31B) Ozone sparge points introduce ozone into the areas of highest dissolved VOC <br /> concentrations near the eastern property boundary of the Unocal site Each sparge point has a <br /> dedicated line and is connected to the system by LDPE tubing The LDPE tubing runs through <br /> 1 Schedule 40 PVC conveyance piping for added protection <br /> Ozone Microsparge System Operation <br /> 1 The schedule was initially set to cycle through each sparge point 18 times per day, for nine <br /> minutes per point per cycle There is an eight-minute rest period between cycles The <br /> programmable timer/controller is varied during the quarter to provide more treatment to selected <br /> 1 areas <br /> Ozone Microsparge System Status <br /> 1 System operation began on August 14, 2002 System effectiveness is monitored by assessing <br /> monthly concentrations of dissolved oxygen (D O ) and monthly analysis of groundwater from <br /> 1 monitoring wells MW-2, MW-10, and MW-11 and piezometer well NP-1 Wells MW-2, MW-10, <br /> MW-11, and NP-1 are located adjacent to the eastern property boundary of the site (Figure 2) <br /> and are within the zone of influence of one or more sparge points Well MW-2 is screened from <br /> 20 to 50 feet below ground surface (bgs) Wells MW-10 and MW-11 are screened from 50 to 60 <br /> feet bgs Well NP-1 is screened from 85 to 90 feet bgs A summary of D O concentration data <br /> is presented in Table 3 Concentrations of TPHg and benzene versus time and TPHg versus <br /> 1 depth to water in wells MW-2, MW-10, MW-11, and NP-1 are depicted graphically in <br /> Attachment D <br /> Effectiveness of Ozone Microsparge System <br /> 1 Quarterly groundwater samples were submitted for analyses of BTEX by EPA Method 8021, <br /> TPHg by EPA Method 8015 Modified, and fuel oxygenate compounds MtBE, TAME, TBA, DIPE, <br />' and ETBE using EPA Method 82606 Additionally, groundwater samples were analyzed for <br /> lead scavengers, EDB, and 1,2-DCA, using EPA Method 82608 <br /> 1 Monthly groundwater samples are collected from wells MW-2, MWA 0, MWA 1 and piezometer <br /> NP-1 to further assess the effectiveness of the system Monthly samples were collected on May <br /> 21, 2004 The samples were submitted for analysis of BTEX by EPA Method 8021 and TPHg by <br /> 1 EPA Method 8015M A summary of analytical results including the monthly sampling events is <br /> included in Attachment D as Table 1 <br />' Discussion <br /> Analytical results from well MW-2 and MW-15 indicate that the ozone microsparge system <br /> 1 appears to be effective as evidenced by the overall decreasing petroleum hydrocarbon <br /> concentrations Increases were observed in petroleum hydrocarbon concentrations in wells <br /> . MW-3, MW-6, MW-10, MW-11, MW-12, MW-14, MW-16, and MW-18 through MW-21 These <br /> increases in hydrocarbon concentrations are most likely due to desorption of hydrocarbons from <br />' J 1prolects106940059-357TinailReportsl2nd Qtr 04-QMR R5R12nd Qtr 04-QMR doc <br />' E Over 30 Years of Excellence in Environmental Services <br />