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AkNAW <br /> The nearest surface water body is the Stockton Deep Water Channel which trends east to west <br /> and is connected to the Sacramento - San Joaquin Delta The east end of the channel terminates <br /> dust west of the site at Center Street <br /> 1 Previous investigations at the facility show that the unsaturated soils beneath much of the site <br /> consist primarily of clays (CL/CH) from surface to approximately 26 feet below grade with a <br /> ' zone of elastic silt (MH) and clay (CL) to a depth of 36 feet <br /> In the central portion of the site, roughly coincident with the area of the former tank excavation, <br /> the soil is comprised largely of sands A portion of this material may be fill from off-site, <br /> ' placed in the excavation to a depth of approximately 12 feet below grade From approximately <br /> 12 to 26 feet below grade, native sands are dominant The saturated zone from approximately <br /> ' 35 feet to at least 50 feet below grade consists of intercalated clays, silts and sands <br /> Current depth to groundwater at the site, as of May 5, 1992, ranges from 34 14 to 35 73 feet <br /> below grade Groundwater gradient at the site is toward the east - northeast at 0 015 feet per <br /> ' feet or 79 feet per mile (Figure 3) <br /> 4.0 PREVIOUS INVESTIGATIONS <br /> Previous assessments at the facility have identified a petroleum hydrocarbon plume resulting <br /> from the previously excavated product storage tanks, which had been owned and operated by <br /> ' Shell Oil Company A summary of previous consultants and the work conducted by each is <br /> found in RESNA Industries' Remedial Action Plan, dated May 31, 1991 <br /> A total of eight soil borings and three groundwater monitoring wells were drilled and sampled <br />' by Leedshill - Herkenhoff in September 1990 to determine subsurface conditions at the site <br /> (Figure 4) Laboratory analyses of soil samples collected from the soil borings and the <br /> groundwater monitoring wells determined that petroleum hydrocarbons are present largely near <br /> the center and eastern sides of the former storage tank excavation <br /> R070792 TLP 2 <br /> 1 <br />