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<br /> Ms. Margaret Lagorio
<br /> ' October 14, 2004
<br /> Page 2
<br /> ' direction for zone B was generally east-northeast with an average hydraulic gradient ranging from
<br /> approximately 0.001 ft/ft to 0.009 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 east-northeast with an
<br /> ' average hydraulic gradient of approximately 0.005 ft/ft. Copies of the groundwater sampling
<br /> information sheets are included as Attachment B.
<br /> Quarterly Groundwater Sampling and Analytical Results
<br /> Groundwater samples were collected from site wells on August 16 through August 20, 2004. The
<br /> ' groundwater samples were submitted to Califomia 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 (ETRE)
<br /> using EPA Method 8260B.
<br /> '. Cumulative groundwater sampling analytical results are summarized in Table 1 through
<br /> Table 6. Dissolved concentrations of benzene, TPHg, and MtBE for zone A, B and C in third
<br /> 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 /> ' TPHg Concentration Trends
<br /> • TPHg concentrations decreased in wells U-11, U-16, U-17, U-22 through U-26 and
<br /> ' piezometer NP-1-22 since the last sampling event.
<br /> • TPHg concentrations in wells U-1, U-2, U-3, U-12, U-13, U-19, U-20 and piezometer
<br /> NP-2-60 and NP-2-116 increased since the last sampling event.
<br /> TPHg concentrations remained below laboratory reporting limits in the remaining wells and
<br /> piezometer NP-2-22.
<br /> Benzene Concentration Trends
<br /> Benzene concentrations decreased in wells U-1, U-5, through U-9, U-11, U-15, U-16, U-17,
<br /> U-19 through U-26 and piezometers NP-1-22 and NP-1-65 since the last sampling event.
<br /> • Benzene concentrations in wells U-2, U-3, U-4, U-10, U-12, U-13, U-14 and piezometers
<br /> NP-2-60 and NP-2-116 increased since the last sampling event.
<br /> • Benzene concentrations remained below laboratory reporting limits in the remaining wells
<br /> ' piezometer NP-2-22.
<br /> • J:1Projects10694010187-3251FinaRReportsl3rd Qtr04-QMR RSR10187 3rd Qtr04-QMR RSR.doc
<br /> ' Celebrating 35 Years of Excellence in Environmental Services
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