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L A M B R I A Mr.Jeffrey Wong April 20,2006 PREVIOUS WORK 2003 Well Installation: During January 2003, KHM Environmental Management, Inc. (KHM)of San Jose, California installed four groundwater monitoring wells (MW-1 through MW-4) as part of Shell's voluntary Groundwater Assessment Program (GRASP). Soilsampleswere collected from MW-1. No total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and xylenes (BTEX), or fuel oxygenates were detected in these samples. Soil samples from the other wells were not analyzed. KHM documented these activities in their - © May 1, 2003 GRASP Site Assessment Report. 2004 Receptor Survey: Cambria reviewed Department of Water Resources (DWR) records and identified four water-producing wells within 1/2 mile of the subject site. Two of the wells are municipal wells, and two are.of unknown use. The,closest well is a municipal well located approximately 1,275 feet west (cross-gradient) of the site.'I The second municipal well was installed in 1926 and could not be located in the field. DWR logs indicate that one of the unknown wells may be holes for an elevator shaft. No wells are located downgradient of the site. No surface water bodies were identified in the survey area.' Cambria's July 22, 2004 Second Quarter 2004 Groundwater Monitoring Report and Receptor Survey includes these results. i Figure 1 shows the well locations. The Geotracker database.also lists two wells at St. Joseph's i Hospital. The hospital is located approximately 1/2 mile southeast of the subject site. 2005 Site Conceptual Model (SCM): On November 2, 2005, Shell submitted an SCM which recommended continued coordinated groundwater monitoring with the Castle Motors site located upgradient of the subject site''at 2320 El Dorado Street and installing groundwater monitoring wells downgradient of Shell's at USTs. Groundwater Monitoring Program: There are currently four groundwater monitoring wells (MW-1 through MW-4) on site that are sampled quarterly. Groundwater flow beneath the site is predominantly northeasterly. During the first quarter 2006 sampling event, groundwater samples collected from well MW-1 contained 3,500 parts per billion'(ppb) TPHg, 65 ppb benzene, and 69 ppb tertiary-butyl alcohol (TBA). Well MW-2 contained 360 ppb TPHg and 0.87 ppb benzene. Previously, the.laboratory has noted the presence of tetrachloroethene (PCE) and trichloroethene (TCE) in wells MW-1 and MW-2. Wellr,MW-3 contained 2.6 ppb methyl tertiary-butyl ether(MTBE) and 9.2 ppb TBA,and well MW-4 contained 3.0 ppb MTBE. Starting with the second quarter 2005 event, groundwater monitoring has been coordinated with the Castle Motors site located across.El Dorado Street (upgradient) at 2315 North El Dorado Street in Stockton. 2 i I f