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<br /> • Ms. Margaret Lagorio
<br /> ' May 4, 2005
<br /> Page 2
<br /> construct the groundwater elevation contour map included as Figure 4. The groundwater flow
<br /> direction for zone B was generally east-northeast with an average hydraulic gradient of 0.004.
<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 S. The groundwater flow direction for zone C was generally east 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 /> ' Quarterly Groundwater Samplina and Analytical Results
<br /> ' Groundwater samples were collected from site wells on February 14 and February 15, 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, for total petroleum hydrocarbons as gasoline (TPHg) by EPA Method 8015
<br /> Modified, and for fuel oxygenate compounds. methyl tertiary butyl ether (MTBE), tertiary-amyl
<br /> methyl ether (TAME), tert butanol (TBA), diisopropyl ether (DIPE), and ethyl tertiary butyl ether
<br /> ' (ETBE) using EPA Method 8260B. Additionally, samples collected from monitoring wells U-2,
<br /> U-3, U-6, U-12 through U-14, U-20, U-21, and piezometers NP-1-65, NP-2-60, and NP-2-116
<br /> were analyzed for nitrate and sulfate by EPA Method 300.0, for methane by EPA Method TQ-3
<br /> GC, and for ferrous iron by EPA Method SM3500-Fe D.
<br /> Cumulative groundwater sampling analytical results are summarized in Table 1 through
<br /> 9 p g Y 9
<br /> Table 6. Dissolved concentrations of benzene, TPHg, and MTBE for zones A, B and C during
<br /> ' first quarter 2005 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 /> TPHa Concentration Trends
<br /> • TPHg concentrations decreased in zone A wells U-1 and U-3, in zone B wells U-13 and
<br /> U-20, and piezometers NP-1-65 and NP-2-60, and in zone C wells U-12, U-17, U-19, U-21,
<br /> and U-23, and piezometer NP-2-116 since the last sampling event.
<br /> • TPHg concentrations increased in wells U-2 (zone A), U-23 (zone C), and U-24 (zone B)
<br /> since the last sampling 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 in zone C piezometer (NP-1-111).
<br /> Benzene Concentration Trends
<br /> • Benzene concentrations decreased in zone A wells U-1, U-3, and U-11, zone B wells U-13,
<br /> U-18, U-20 and U-22, and piezometer NP-2-60, and in zone C wells
<br /> U-12, U-15, U-17, U-19, and U-21 since the last sampling event.
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<br /> Celebrating 35 Years of Excellence in Environmental Services
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