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0 <br /> soil samples were selected for hydraulic conductivity analysis, two were selected for bacterial <br /> S analysis, and three were selected for total organic carbon and bacterial nutrient analysis The deep <br /> water sample was analyzed on 48-hour rush analysis (rather than 24-hour as originally planned), the <br /> rest were analyzed on standard turnaround <br /> fhe laboratory detected gasoline and the BTEX compounds in the Simulprobe water sample at <br /> concentrations ranging from 411 ppb (TPH-g) to 11 3 ppb(toluene) Therefore, the second boring <br /> was drilled at the location of the proposed monitoring well and was drilled to a depth of 75 feet so <br /> that a dual-completion well could be installed The boring was sampled at 5-foot intervals, and 4 <br /> samples were selected for hydrocarbon analysis (TPH-g, TPH-d, BTEX, and oxygenates),4 <br /> samples were selected for hydraulic conductivity analysis, 2 samples were selected for bacterial <br /> analysis, and 3 samples were selected for nutrient/TOC analysis However, when the boring reached <br /> a depth of 55 feet, a zone of dense, hard, relatively dry silt or clay was encountered that extended <br /> almost without mteruption to the bottom of the boring at 75 feet Hence, the poor aquifer <br /> characteristics of this deep zone implied that it would not yield suitable quantities of water to a <br /> monitoring well and that any contaminated water in the dispenser area would be unlikely to migrate <br /> toward this well even if water could be obtained in suitable quantities Therefore, it was decided to <br /> backfill this boring with grout to the depth of the shallow water zone (55 feet) At the suggestion of <br /> PHSIEHD, the hole was allowed to remain open above that depth, in anticipation that a shallow <br /> monitoring well might be constructed in the near future A well box was placed in the hole and <br /> cemented to prevent surface contamination <br /> Most of the 11 soil samples contained no detectable hydrocarbons Concentrations near the <br /> detection limits for TPH-g and BTEX were Lound at depths of 32 and 75 feet in the first boring, but <br /> none were detected in the second boring and oxygenates were not detected in either boring <br /> Hydraulic conductivities were in the poor to fair range, a reflection of the fact that fine-grained soi <br /> layers make up more than 50%of the volume of sediment above 75 feet Bacterial abundance is <br /> very low, and is below method limits in samples from below the water table, indicating insufficient <br /> oxygen and/or nutrients in the soil Total organic carbon and related data suggest that nutrients are <br /> probably present in sufficient quantities for bacterial growth <br /> Summarizing all laboratory data collected during previous phases of investigation, we conclude that <br /> BTEX compounds are slightly more extensive laterally and vertically than TPH The BTEX plume <br /> is roughly cylindrical in shape, with a radius of approximately 25 feet and a height of 20 feet <br /> Approximately 1,000 cubic yards of soil are probably contaminated with concentrations above <br /> detectable limits We calculate that approximately 125 gallons of gasoline remain in place We see <br /> no need for further delineation of soil contamination <br /> Assessment of the extent of groundwater contamination can probably be completed by installing a <br /> monitoring well in the second boring, which is presently capped but not grouted above 55 feet This <br /> should be done prior to the first-quarter groundwater monitoring event, which has not yet taken <br /> place <br /> 2 <br />