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Project No S8100-06-11B April 19, 1996 ' 4.0 WVESTIGAT VE RESULTS ' 4 1 Site Geology The alluvial deposits encountered during the investigation generally consisted of clayey silts, silty clays, silty sands,and poorly graded sands Fine grained soil layers consisting of stiff, brown to olive- brown, silty clays and clayey silts with interbedded dense, tan-brown, silty sands extend to depths of approximately 18 3 meters (60 feet) bgs These fine grained soil layers overly the coarser grained soils comprised of medium dense, cohesionless, fine to medium grained sands Saturated soils were encountered within this sand unit A generalized cast-west trending geological cross section is presented as Figure 3 Copies of boring logs and well completion diagrams are included in Appendix B ' 42 Site Hydrogeology The groundwater elevations measured on February 5, 1996 ranged from -12 35 to -12 60 meters (- 40 54 to -4131 feet) below MSL, or approximately 18 9 meters (62 feet) bgs The February 1996 ground water elevations were variable and inconsistent with previous monitoring data, consequently, ' an additional groundwater monitoring event was performed on April 11, 1996 and groundwater elevations ranged from -12 07 to -12 18 meters (-39 62 to -39 95 feet) below MSL, or approximately 18 6 meters (61 feet) bgs The groundwater flow direction generally trends towards the west at a gradient of 0 001 A cumulative summary of groundwater elevation measurements is presented on Table III Groundwater elevation contours and the groundwater flow direction and gradient on April 11, 1996 are depicted on the Groundwater Elevation Map,Figure 4 43 Soil Analytical Results Soil samples collected during the site investigation from borings SB-3, MW-9 through MW-12, and VW-2 were tested for the presence of TPHg, TPHd, and BTEX Soil samples collected at the capillary fringe and the sample with the highest TPHg and/or BTEX concentration from each boring ' were further tested for MTBE Cumulative analytical results for soil samples collected during the site investigation are summarized on Table 11 Laboratory reports and chain-of-custody records are presented in Appendix E In the perimeter borings, MW-9 through MW-12, TPHg, TPHd, BTEX, and MTBE were not detected above the laboratory test method detection limits, with the exception of 31 mg/kg TPHg (MW9-8) at ' 12 2 meters(40 feet)bgs and 0 11 mg/kg total xylenes(MW 11-15)at 22 9 meters(75 feet)bgs TPHg, TPHd, and BTEX were not detected above the laboratory test method detection limits in soil ' collected beneath the former pump island in boring SB3 Boring VW-2, located adjacent to the former UST excavation and former pump island, contained petroleum hydrocarbons identified as TPHg and BTEX TPHg was detected between the depths of 7 9 to 18 6 meters (26 to 61 feet) bgs with a maximum concentration of 550 mg/kg at 14 0 meters (46 feet) The maximum BTEX concentrations were detected at 15 5 meters (51 feet) bgs at i8 i