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