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16 October 1996 AGE-NC Project No. 95-0165 f Page 2 of 6 California. The valley is a nearly flat, elongate trough trending northwest and southeast for approximately 450 miles. The valley is enclosed by the granitic Sierra Nevada Mountains on the east and the sedimentary and metamorphic Franciscan Coast Range on the west. The surficial and upper several thousand feet of subsurface layers consist primarily, of unconsolidated and consolidated L_ alluvial and flood plain sheet deposits(predominantly sand; silt and clay) of Quaternary age, which, was derived from the Sierra Nevada Mountains.Beneath the upper sedimentary deposits lies a thick sequence of marine deposits of Mesozoic age,which in turn is underlain by a pre-Jurassic complex of igneous and metamorphic rock. Regional,flow direction of the ground water in the area of the site- is west to southwest. However, flow direction can vary locally and seasonally. La, 2.4, REMOVAL OF UNDERGROUND STORAGE TANKS Three underground storage tanks (USTs), dispenser islands;and associated piping were removed . from the site in January 1995. After removal of the tanks, soil"samples were collected from beneath L, each former UST invert. Samples collected from beneath the northern-most tank contained- detectable concentrations of petroleum hydrocarbons. Soil was.then excavated to sixteen feet below surface grade (bsg). Soil removed from the excavation was stockpiled east of the former UST area. . Soil samples were also collected beneath the dispenser islands and piping. Laboratory analysis of two soil samples indicated that hydrocarbon-impacted soil was present near the northern dispenser islands. Analytical results of soil samples collected following the UST removal are,inciuded in Table 1. The laboratory report and chain-of-custody are included as Appendix A. 3.0. SITE ASSESSMENT AND ]ZEMEDL ATION 3.1. EXCAVATION OF HYDROCARBON-IMPACTED SOIL On 06 February 1995, approximately seventy-five cubic yards of hydrocarbon-impacted soil were removed from the northern portion of the former UST area. The excavation extended to approximately thirty-one feet bsg. Additionally, soil was removed from two areas near the original LOW - - dispensers,.immediately north and northeast of the former_USTs.One soil sample was collected from the floor of the UST 'excavation (sample NBA); two soil samples were collected from the dispenser/piping areas (samples D-1 and D-2). Total petroleum hydrocarbons quantified as gasoline (TPH-g)were detected in sample NB-1 at a concentration of 240 milligrams per kilogram: mg/kg (parts per million, ppm); benzene, toluene, ethyl benzene and xylenes(BTE&X)were detected at concentrations of 0.12 ppm, 3.0 ppm, 1.5 ppm and 21 ppm, respectively. Petroleum hydrocarbons were not detected in the samples from the ' s