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' G eo(v rcaCTechnwcs Inc Page 6 Soil &Groundwater lriwestjgation Report J M Equipment Project No 507 2 July 5,2001 The lab data identified silts as predominant, while the field geologist identified clays as predominant This is not a concern given the difficult), in identifying the demarcation between silt and clay in wet (below the water table)field samples ] ' Y The clayey soils in the upper 20 ft of MW-109 contained prominent field evidence of c.ontainination- odor and staining The 80-foot sample in MW-109 had a faint hydrocarbon odor, and the OVM detected 19 parts per million organic vapors • The deeper soil encountered in SB-109 was a blue/grey to blue/green color so it was difficult to visually determine when drilling had progressed past the contamination 40 CONCLUSIONS AND RECOMMENDATIONS ' Based on our interpretation of the data collected over the course of this subsurface investigation we have reached several conclusions These conclusions are based on the premise that the data we considered, although incomplete, are representative of actual site conditions We acknowledge that there may be undiscovered conditions, which would upon their consideration, change our interpretation and thus our conclusions Our recommendations are based on our knowledge of site conditions and the state of and ' limitations of subsurface investigative technology 4.1 Conclusions Geological Technics Inc , taking into consideration the data obtained during the soil and groundwater investigation, makes the following conclusions I The soil plume is defined laterally (clockwise- from north) by soil borings MW-6, MW-2, MW-8, MW-1, MW-7, SB-6 and MW-10 2 The soil plume is defined vertically by MW-109 3 The majority of the soil contamination present is localized in the near vicinity of the former UST and is present at depths of 10 — 30 feet bgs 4 The soil in the 10 -- 30 feet bgs interval is silty/clayey lithology and not conducive to soil vapor extraction remedial technology 4.2 Recommendations ' Geological Technics Inc intakes the following iecomrnendations based on the conclusions outlined above ® Groundwater monitoring should be performed on a quarterly basis to determine the stability of this plume o Testing for natural attenuating parameters should be included in the monitoring project to determine if biodegradation is mitigating the plume 0 A risk evaluation should be performed to determine if this contamination poses a threat to public health or the environment