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e Some hydrocarbon detections in the diesel range shown in Table 3-1 could not be characterized as diesel by the laboratory. Although the _ laboratory methodology does not permit positive identification of these hydrocarbons, they may represent degraded diesel or other naturally occurring organic matter in the soil. During December, soil borings M13-10 through MP-25 were installed and sampled in order to further assess the extent of petroleum hydrocarbon occurrence. Concentrations of diesel and gasoline in excess of 1,000 mg/kg were detected in borings MP-10 and MP-11 at a depth between 40 and 43 feet below grade. These borings were located in the floor of the excavation. Concentrations of diesel and gasoline in excess of 1,000 mg/kg were also detected in boring NM-15 to the not theast of the excavation at a depth 35 feet below grade, decreasing to 19 mg(kg at a depth of 40 feet below grade. A concentration of gasoline in excess of 100 mg/kg was detected in boring MP-18 to the west of the excavation at a depth of 40 feet below grade. Significant concentrations of BTEX were also detected in these samples. The rest of the soil samples had concentrations of diesel and/or gasoline in the two to ten mg/kg range. Figure 3-3 illustrates the extent.of hydrocarbon concentrations in excess of 100 mg/kg(parts per million or ppm.) `~ Ana ;rgl Rvc�ilts of Hy nunrh d oWtorinLrWell Satnnlint Analytical results of hydropunch and monitoring well sampling are presented in Tables 3-1 and 3-2. During November 1990, significant concentrations of diesel and gasoline in groundwater were encountered in borings MP-2, MP-5, and MP-9. Samples collected from the three developed monitoring wells (MPW-1, MPW-2, and MPW-3) also show significant concentrations of gasoline, as well as BTEX (Table 3-2). The highest concentrations of gasoline in n groundwater were in.MPW-.I in the northeast perimeter. of the excavation.. Hydrocarbons in both the diesel and gasoline range in groundwater samples collected from the monitoring wells were characterized by the laboratory as gasoline. During December, groundwater samples were collected from borings MP-12 through MP-25 with a hydropunch in order to further assess the extent of petroleum hydrocarbons in groundwater. Soil borings MP-14,MP-15, and MP-18 were converted to 4-inch-diameter wells for ~� future use as monitoring wells or extraction wells if deemed appropriate. ------------ - ---Figure-3-4--illustrates- the-occurrence-of-gasoline-in--groundwater-- ------------------------ beneath the site. It appears that the highest concentration of gasoline in groundwater (in excess of 100 ppm) occur beneath the excavation and extends to the northeast approximately 100 feet. 3-3