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Margaret Lagorio <br /> ' July 19, 2004 <br /> Page 2 <br /> ' direction for zone B was generally east-northeast with an average hydraulic gradient of <br /> approximately 0.01 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, and NP-1-111), and wells screened in zone C at the former Vintage Car Wash <br /> site, were used to construct the groundwater elevation contour map included as Figure 5. The <br /> groundwater flow direction for zone C was generally east-northeast with an average hydraulic <br /> ' gradient of approximately 0.005 ft/ft. Copies of the groundwater sampling information sheets are <br /> included as Attachment B. <br /> ' Quarterly Groundwater Sampling and Analytical Results <br /> Groundwater samples were collected from site wells between April 19 through 21, 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 8260B. <br /> Cumulative groundwater sampling analytical results are summarized in Tables 1 through 3. <br /> Dissolved concentrations of benzene, TPHg, and MtBE in groundwater for second quarter 2004 <br /> are presented in Figure 6 through Figure 8. Copies of the groundwater sampling information <br /> sheets are included in Attachment B. Laboratory analytical results with chain-of-custody <br /> documentation are included in Attachment C. <br /> ' No samples were collected from monitoring well U-14 or piezometers NP-1-22, NP-1-65, <br /> NP-1-111, and NP-2-116 as there were obstructions in the wells. <br /> ' TPHg Concentration Trends <br /> • TPHg concentrations decreased in wells U-3, U-10, U-13, and U-18 through U-21 since the <br /> ' last sampling event. <br /> TPHg concentrations in wells U-1, U-11, U-12, U-16, U-17, U-22 through U-26, and <br /> piezometer NP-2-60 increased since the last sampling event. <br /> ' • TPHg concentrations remained below laboratory reporting limits in piezometer NP-2-22. <br /> Benzene Concentration Trends <br /> ' • Benzene concentrations decreased in wells U-3, U-4, U-8, U-13, U-17, U-19 through U-21, <br /> and piezometer NP-2-60 since the last sampling event. <br /> ' • Benzene concentrations in wells U-1, U-2, U-7, U-10 increased since the last sampling <br /> event. <br /> • • Benzene concentrations remained below laboratory reporting limits piezometer NP-2-22. <br /> ' J:4Projects10694010187-3251FjnallReportsVnd Qtr04-QMR RSM0187 2nd Qtr04-QMR RSR.doc <br /> ' Q over 30 Years of Excellence in Er?wanrnental Services <br />