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I CAMBRIA U 1 2004 Receptor Survey: Cambria reviewed Department of Water Resources records and identified four water producing wells within 2,000 feet of the subject site. One of the wells is a municipal well, two are of unknown use, and one is a domestic well. The closest well is the municipal well, located approximately 1,275 feet west(cross-gradient) of the site. No surface water bodies were identified in the survey area. These results are included in our Second Quarter 2004 Groundwater Monitoring Report and Receptor Survey. i Groundwater Monitoring Program: There are currently four groundwater monitoring,wells (MW-1 through MW-4) onsite that are sampled quarterly. Groundwater flow beneath the siteis © predominantly northeasterly. During the second .quarter 2004 sampling event, groundwater samples collected from well MW-1 contained 2,700 parts per billion (ppb) TPHg, 57 ppb benzene, 33 ppb tertiary butyl alcohol (TBA), and 9.3 ppb di-isopropyl ether (D1PE). Well MW-2 contained 300 ppb TPHg. Well MW-3 contained 18 ppb methyl tertiary butyl ether (MTBE) and 5.7 ppb TBA, and well MW-4 contained 0.75 ppb MTBE. Based on the quarterly groundwater monitoring results, S7CEHD requested additional investigation. TECHNICAL RATIONALE FOR PROPOSED SCOPE OF WORT( • Fuel oxygenates have been detected in groundwater collected from site wells located upgradient and cross-gradient of the site USTs and dispensers (MW-1, MW-3, and MW-4). The lateral extent of these oxygenates has not been fully investigated, including in the upgradient direction. Note that the downgradient extent of fuel oxygenates in MW-1 is delineated by data from MW-2. • TPHg has been detected in groundwater samples from wells MW-1 and MW-2. For some of these results, the laboratory has noted that the hydrocarbons reported do not match the laboratory's gasoline standard. Additional research indicated that tetrachloroethene (PCE) and trichloroethene (TCE) may be contributing to these reported TPHg concentrations. The lateral extent of TPHg(and/or PCE and TCE)has not been fully assessed. • There is an active UST case with groundwater monitoring wells located upgradient of the subject site (2315 El Dorado Street, Stockton), and Cambria has not reviewed this site's groundwater data to determine whether it might be a source of the constituents detected in upgradient wells at the subject site. 1641 2