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1 Project No S8100-06-1IA June 29, 1995 40 INVESTIGATIVE RESULTS ' 4 1 SITE GEOLOGY AND HYDROGEOLOGY Site Geology The entire area within the project boundaries was covered with asphalt and an approximate 0 3 meter(one foot) thick section of road base materials consisting of sandy fine to coarse grained gravels 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, cohesion less,fine to medium grained sands Saturated soils were encountered within this sand unit A stiff clay was encountered beneath the saturated sand layer in MW-6, MW-7, and MW-8 at depths ranging from 21 3 to 22 9 meters (70 to 75 feet) bgs This clay unit was not encountered to MW-4, MW- 5 or VW-1 Generalized north-south and east-west trending geological cross sections are presented as Figures 3 and 4, respectively Copies of boring logs and well completion diagrams are included in Appendix B i Site Hvdrogeology The groundwater elevations measured within the project area on May 2, 1995 ranged from 12 99 to 13 01 meters (42 57 to 42 69 feet) below MSL, or at a depth of approximately 19 5 meters (64 feet) bgs The groundwater flow direction generally trends from southwest to northeast with a gradient ranging from approximately 0 0002 to 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 May 2, 1995 are depicted on the Groundwater Elevation Map, Figure 5 ' 42 SOIL ANALYTICAL RESULTS Soil samples collected from borings MW-4 through MW-8, and VW-i were tested for the presence of TPHg, TPHd, and BTEX Cumulative analytical results for soil samples collected during the site ' investigation are summarized on Table II Laboratory reports and chain-of-custody records are presented in Appendix E TPHg and TPHd was detected in vadose zone soil at a depth of 13 7 meters (45 feet) in MW-5 at concentrations of 17 mg/kg and 12 mg/kg, respectively TPHg was detected in the capillary fringe in VW 1-12 at a depth of 19 8 meters (65 feet) at a concentration of 1 3 mg/kg VW-1, located to the former UST excavation, contained concentrations of benzene, toluene, and total xylenes in the vadose zone and capillary fringe between the depths of 13 7 and 21 2 meters (45 and 69 5 feet) bgs The maximum concentrations detected were 0 13 mg/kg benzene, 0 061 mg/kg toluene, and 0 013 mg/kg total xylenes, respectively 8