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' U-Haul#709-5o Additional Site Characterization Blaes Environmental hydrocarbon Y plume in groundwater was centered near monitoring well MW-4 Benzene concentrations in samples from each of the six monitoring wells(Mw-1 through MW-6)exceeded the California action level ' SOTA was contracted by U-Haul in 1995 to conduct further assessment of groundwater conditions with the installation of one on-site and one off-site groundwater monitoring well These monitoring wells (MW-7 and MW-S) were included in the quarterly monitoring program in October 1995 Results of the October 1995 quarterly monitoring and sampling event indicated that the depth to groundwater was between ' approximately 63 to 66 feet bgs and the groundwater flow direction was toward the southwest Analytical results indicated that hydrocarbon concentrations exceeded California action levels in groundwater samples from five of the seven on-site monitoring wells (Table 2) Results also indicated that elevated hydrocarbon concentrations were present in groundwater from the off-site monitoring well MW-7 Between November 1994 and September 1997, SOTA conducted groundwater monitoringat the site During this period, the screen intervals of the on-site monitor wells became submerged(Tables 2 and 3) 1 25 LITE aEQLQ!Liy The subject site is located in the northern portion of the San Joaquin Valley, which is bound to the west by the coastal ranges and to the east by the Sierra Nevada Mountains The San Joaquin Valley is a broad ' elongated valley that is crossed by many meandering rivers and streams that drained the western slopes of the Sierra Nevada Mountains These drainages are now channelized and diverted into canals to provide ' water and prevent flooding Prior to being channelized, these fluvial systems would Periodicallyoverflow and flood the valley ow I The local subsurface geology of the site consists of poorly sorted sands and silty sands with interbedded silts, clayey sands, and clay The occurrence of these near surface sediments are characteristic of fluvial and over-bank flood deposits, which are typical of the San Joaquin Valley The nearest fluvial system to the site Iis the Calaveras River, located approximately a mile north of the site The nearest water body is the Stockton Diverting Canal, which is approximately one-half mile north of the site Based on soil sampling conducted in January 2000, soil beneath the site consists of silty sand, silt, sand, clayey sand, and clay The logs of exploratory soil borings (Appendix B) include a description of soil samples collected from the direct-push boreholes and soil borings Based on the soil descriptions, interpretation, and the correlation between the sample points, Blaes Environmental created two cross- 5