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1 - <br /> E11�� <br /> • Ms. Margaret Lagorio <br /> February 11, 2005 <br /> Page 2 <br /> ' direction for zone B was generally east-northeast with an average hydraulic gradient ranging from <br /> approximately 0.005 fUft to 0.006 ftlft. <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 east-northeast with an <br /> average hydraulic gradient of approximately 0.004 fUft. Copies of the groundwater sampling <br /> information sheets are included as Attachment B. <br /> ' <br /> Quarterly Groundwater Sampling and Anal3dicall Results <br /> ' Groundwater samples were collected from site wells on November 16 through <br /> November 18, 2004. The groundwater samples were submitted to California Laboratory Services <br /> (CLS) in Rancho Cordova, California for analyses of benzene, toluene, ethylbenzene and total <br /> ' xylenes (BTEX) by EPA Method 8021, total petroleum hydrocarbons as gasoline (TPHg) by EPA <br /> Method 8015 Modified, and fuel oxygenate compounds: methyl tertiary butyl ether (MTBE), <br /> tertiary-amyl methyl ether (TAME), tert butanol (TBA), diisopropyl ether (DIPE), and ethyl tertiary <br /> liebutyl ether (ETBE) using EPA Method 82608. <br /> Cumulative groundwater sampling analytical results are summarized in Table 1 through <br /> ' Table 6. Dissolved concentrations of benzene, TPHg, and MTBE for zones A, B and C during <br /> fourth quarter 2004 are presented in Figure 6 through Figure 8, respectively. Copies of the <br /> groundwater sampling information sheets are included in Attachment B. Laboratory analytical <br /> results with chain-of-custody documentation are included in Attachment C. <br /> ' TPH_q Concentration Trends <br /> ' • TPHg concentrations decreased in zone A wells (U-1 through U-3), zone B wells (U-13, U- <br /> 16, U-20 and U-24) and piezometers (NP-1-65, NP-2-60 and NP-2-116) and zone C wells <br /> (U-12, U-17, U-19 and U-21) since the last sampling event. <br /> ' • TPHg concentrations did not increase in any sampling locations since the last sampling <br /> event. <br /> • TPHg concentrations remained below laboratory reporting limits in the remaining wells and <br /> ' zone A piezometers (NP-1-22 and NP-2-22) and zone C piezometer (NP-1-111). <br /> Benzene Concentration Trends <br /> ' • Benzene concentrations decreased in zone A wells (U-1 through U-5, U-7, and U-8), zone B <br /> wells (U-14, U-20 and U-22) and piezometers (NP-1-65 and NP-2-60), and zone C wells <br /> ' (U-10, U-12, U-17, U-21 and U-23) and piezometer (NP-2-116) since the last sampling <br /> event. <br /> ' JAProjectsl0694014187-325lWorkinglReports10187 4th Qtr 04-QMR RSR.doc <br /> ' Celebrating 35 Years of Excellence in Environmental Services <br />