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EDCV. <br /> B-207-2,2333= <br /> Margaret Lagorio <br /> ' April 26, 2004 <br /> Page 2 <br /> ' construct the groundwater elevation contour map included as Figure 4. The groundwater flow <br /> direction for zone B was generally northeast with an average hydraulic gradient of approximately <br /> 0.005 ft/ft. <br /> ' Groundwater measurements from wells screened in zone C (U-10, U-12, U-15, U-17, U-19, U-21, <br /> U-23, U-25, U-26, NP-1-111 and NP-2-116), and wells screened in zone C at the former Vintage <br /> ' Car Wash site, were used to construct the groundwater elevation contour map included as <br /> Figure 5. The groundwater flow direction for zone C was generally northeast with an average <br /> hydraulic gradient of approximately 0.005 ft/ft. Copies of the groundwater sampling information <br /> ' sheets are included as Attachment B. <br /> Groundwater Sampling and Analytical Results <br /> ' Groundwater samples were collected from site wells between February 16 through 18, 2004. .The <br /> groundwater samples were submitted to California Laboratory Services (CLS) in Rancho <br /> Cordova, California for analyses of benzene, toluene, ethylbenzene and total xylenes (BTEX) by <br /> EPA Method 8021, total petroleum hydrocarbons as gasoline (TPHg) by EPA Method 8015 <br /> —Modified, and fuel oxygenate compounds: methyl tertiary butyl ether (MtBE), tertiary-amyl methyl <br /> ether (TAME), tert butanol (TBA), diisopropyl ether (DIPE), and ethyl tertiary butyl ether (ETBE) <br /> using EPA Method 82606. <br /> Cumulative groundwater sampling analytical results are summarized in Tables 1 through 6. <br /> Dissolved concentrations of benzene, TPHg, and MtBE in groundwater for first quarter 2004 are <br /> presented in Figure 6 through Figure 8. Copies of the groundwater sampling information sheets <br /> are included in Attachment B. Laboratory analytical results with chain-of-custody <br /> 1 documentation are included in Attachment C. <br /> No sample was collected from monitoring well U-14, as there was an obstruction in the well. <br /> Laboratory analytical results reported toluene at a concentration of 0.69 micrograms per liter <br /> (µg/L) in a trip blank submitted and analyzed for quality assurance (QA). Toluene was not <br /> reported in other samples submitted by ENSR for this sampling event. <br /> Ozone Microsparge System Description <br /> ' The Ozone system consists of groundwater treatment via C-SpargeTM panels installed at the <br /> site. Each C-SpargeTM system includes an ozone generator, air compressor, and a <br /> _programmable timer/controller. The C-SpargeTM system utilizes ozone microsparging: a <br /> ' process where ozone is entrained in air and introduced into groundwater. The ozone/air <br /> mixture is injected at rates of 2 - 6 cubic feet per minute through specially designed sparge <br /> points to create "microbubbles." As these microbubbles rise within the column of water, <br /> ' dissolved volatile organic compounds (VOCs) including petroleum hydrocarbons are oxidized. <br /> The system cycles between 16 micro-sparge points and injects an ozone/air mixture into wells <br /> SP-1A&B, SP-1 C, SP-2A, SP-26, SP-3A, SP-313, SP-3C, SP-4A, SP-4B, SP-5A, SP-513, SP-5C, <br /> SP-6A, SP-66 and SP-6C. Ozone sparge wells are located in the areas of highest dissolved <br /> J:IProjects10694010187-3251Final\Reportsllst Qtr 04-QMR RSR10187 1st Qtr 04-QMR RSR.doc <br /> ' '" 35 Years of Excellence in Environmental Services <br />