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' Ceofogrca(Technws Inc Page 7 <br /> Soil&Groundwater Investigation Report <br />' J M Equipment <br /> Project No 507 2 <br /> June 9, 1999 <br /> Our recommendations are based on our knowledge of site conditions and the state and <br /> limitations of subsurface investigative technology <br />' 4.1 Conclusions <br /> Geological Technics Inc , taking into consideration the data obtained during the April 1999 <br />' soil and groundwater investigations, makes the following conclusions <br /> Subsurface Investigation <br /> The following conclusions are made based on our professional interpretation of the field <br />' observations made during the completion of the soil borings, well installation, and soil and <br /> groundwater sample test data <br />' 1 Since the contamination in most boreholes was not detected until a depth of <br /> approximately 20 feet, SB-1 and SB-5 were probably not drilled deep enough to <br /> encounter the soil and groundwater plume <br />' 2 The soil plume appears to be defined vertically by SB- 109 Even though the soil samples <br /> collected at the 50, 60 and 70 foot intervals showed low levels of BTEX compounds they <br /> are most likely a result of the samples coming into contact with the highly contaminated <br /> shallow waters in the borehole To confirm this a SimulProbe sampling tool would have <br /> to be used to resample these intervals <br /> 3 The soil plume appears to be defined to the northeast at MW-6, however the groundwater <br /> samples from MW-6 show the presence of BTEX and TPH-G <br /> 4 The groundwater plume appears to be defined to the northeast and southeast by MW-1 <br /> and MW-2 <br /> 5 Groundwater gradient is N41°E at 0 0027 ft/ft <br /> 4.2 Recommendations <br /> Geological Technics Inc makes the following recommendations based on the conclusions <br /> outlined above <br /> • Groundwater monitoring should be performed on a quarterly basis for one year to <br /> I determine the stability of this plume <br /> • Testing for natural attenuating parameters should be included in the monitoring project to <br /> determine if biodegradation is mitigating the plume <br /> • A risk evaluation should be performed to determine if this contamination poses a threat to <br /> Ipublic health of the enviromnent <br /> r <br /> i <br />