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1 <br /> a <br /> A S S O C I AT E S I N C . <br /> RESULTS OF INVESTIGATION <br /> Site Geology <br /> Native sediments encountered in soil boring SBI during field activities indicate that the upper 6 <br /> feet of the soil column consists primarily of organic soil that was used as backfill material. Soils <br /> om-between-approximately-6-5-tv 1-0-feet bgs-and 21-5-to 25-feet-bgs-consist-of-silt-and elastic <br /> silt. Soils from between 21.5 to 25 feet bgs and 31.5 to 35 feet bgs consist of lean clay. Soils <br /> from between 31.5 to 35 feet bgs and 36.5 to 40 feet bgs consist of elastic silt. Soils from <br /> between 36.5 to 40 feet bgs and 41.5 feet bgs, the maximum depth explored, primarily consisted <br /> of lean clay. Groundwater was encountered at approximately 40 feet bgs during drilling activities. <br /> Analytical Results <br /> Petroleum hydrocarbon constituents were detected in soil samples collected from boring SBI. <br /> The highest reported constituent concentrations were observed in the soil sample collected at 5.5 <br /> feet bgs. The highest concentrations of petroleum constituents at this depth include TPHd (5,800 <br /> mg/kg), TPHg (400 mg/kg), 1,2,4-trimethylbenzene (16 mg/kg), and 1,3,5-trimethylbenzene (6 <br /> mg/kg). The petroleum hydrocarbons appear to attenuate rapidly with depth as indicated greatest <br /> . by soil sample from 35.5 feet bgs, which contained only trace levels of isopropylbenzene (0.006 <br /> mg/kg), 1,2,4-trimethylbenzene (0.014 mg/kg), and 1,3,5-trimethylbenzene (0.013 mg/kg). Trace <br /> amounts of petroleum hydrocarbon constituents were also detected in the groundwater sample <br /> collected from soil boring SBI. Analytical results are summarized in Table 1 and laboratory data <br /> sheets are contained in Attachment 3. <br /> SUMMARY <br /> Soil and groundwater appear to be impacted by petroleum hydrocarbons. The highest <br /> concentrations of petroleum hydrocarbons in soil are present in the backfill material between 5.5 <br /> and 10.5 feet bgs. Petroleum affected soil at this site generally attenuates rapidly with depth with <br /> low concentrations of petroleum hydrocarbons detected in the groundwater. Based on the <br /> available data, the horizontal and vertical extent of soil and groundwater contamination has not <br /> been defined. ATC Associates recommends further investigation to define the horizontal and <br /> vertical extent of soil and groundwater contamination. Once that has been completed, a Problem <br /> Assessment Report can be prepared to determine if active remediation will be necessary. <br /> w:117295\reportstisum.doc 3 <br />