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I <br /> Io Groundwater flow at the site, measured in November and December 1995, was to the <br /> southwest and south-southwest <br /> o Monitoring well MW 1 is located downgradient of the former tankpit and within five feet <br /> of the former excavation limit <br />' No petroleum hydrocarbon groundwater contamination exists at the site The release from the <br /> former UST has not impacted groundwater <br /> Soil <br /> o Residual soil contamination following overexcavation of the tankpit in 1990 was most <br /> pronounced along the southwestern wall of the excavation <br /> o Exploratory soil borings installed in 1990 identified low levels of residual soil <br /> contamination, prunarily between the depths of 22 and 32 feet Benzene concentrations <br /> did not exceed 1 part per million in any sample <br /> Io Soil borings installed in 1992 and 1994 demonstrated that significant reductions in <br /> residual contaminant concentrations had occurred during the intervening years The <br /> Ihighest benzene concentration recorded was 0 08 ppm <br /> o Soil samples collected from boring SB11MW1 during the current phase of investigation <br /> were not found to contain any detectable concentrations of petroleum hydrocarbon <br /> analytes This boring was installed within five feet of the southwest wall of the former <br /> Itankpit <br /> o Biological and physical analyses of soil samples collected during the current investigation <br /> indicate <br /> • Sufficient nutrients are present in the upper clayey silt horizon (0 to 28 ft) to <br /> support active colonies of hydrocarbon degrading bacteria Colony forming <br /> bacteria were present in the soil <br /> • The upper clayey silt horizon has high adsoption potential (low leaching potential) <br /> as indicated by an organic carbon content of 17% and an extremely low vertical <br /> hydraulic conductivity of 9 x 10-1 cm/sec This unit, in which residual <br /> hydrocarbons were previously identified, would not be expected to yield those <br /> hydrocarbons readily to vertical transport <br /> I • The lower clayey silt horizon (40 to 50 ft) has a moderately low organic carbon <br /> content and would be expected to have an extremely low vertical permeability, <br /> similar to the upper clayey silt unit This unit should function as a very effective <br /> barrier to vertical transport to groundwater <br /> groundzelnormaclsurnrepor 95 7 <br />