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1 18 February 1997 AGE-NC Project No 95-0104 Page 2 of 22 Samples • On 14 January 1992, ground water elevations were reported to have decreased below the screen interval of MW-1 • In December 1992, ground water monitoring well MW-2 was installed southwest of the former UST area, to a total depth. of 110 feet Petroleum hydrocarbons were not detected in soil samples collected during the construction of MW 2, however, benzene and halogenated volatile organic compounds (HVOCs) were detected in the initial ground water samples Analytical results of soil and ground water samples are summarized in Tables 1 and 2, respectively • On 29 and 30 September 1993, ground water monitoring wells MW-3 and MW-4 were installed down-gradient of the former UST area to total depths of 100 and 105 feet, respectively Petroleum hydrocarbons were not detected in selected soil samples, however, HVOCs (bromomethane) were detected at low concentrations in soil samples from MW-4 IAnalytical results of soil and ground water samples are summarized in Tables I and 2 • On 4 April 1994, soil vapor extraction well VW-I was installed within the former UST • excavation to a total depth of 80 feet bsg TPH-g was detected in soil samples from VW-1 Analytical results of soil samples are summarized in Table I • On 06 March 1995, an eight-hour soil vapor extraction pilot test was performed to provide feasibility data prior to initiation of a full-scale remediation system Analytical results of vapor samples collected during the pilot test are summarized in Table 3 - Analytical Results Of Vapor Samples Additional background information is summarized in numerous Quarterly Reports submitted to PHS- EHD (prepared by Geological Audit Services Inc and AGE) between 1992 and 1996 23 REGIONAL GEOLOGICAL/HYDROGEOLOGICAL SETTING The subject site is located in the eastern portion of the Great Valley geomorphic province of California The valley is a nearly flat, elongate trough trending northwest and southeast for approximately 450 miles The valley is enclosed by the igneous Sierra Nevada on the east and the sedimentary and metamorphic Coast Ranges on the west The surficial and upper several hundred feet of subsurface sedimentary layers consist of a great thickness of predominantly unconsolidated alluvial and floodplain deposits (dominantly sand, silt, and clay) of Quaternary age, which are derived from the predominantly granitic mountains of the Sierra Nevada Beneath the upper sedimentary deposits lie a thick sequence of marine deposits of Mesozoic age These units are underlain by a pre-Jurassic complex of igneous and metamorphic basement rock I