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1 <br /> In order to ensure that critical subsurface utilities would not interfere with the investigation, <br />' Tetra Tech implemented a utility clearance program A geophysical survey was conducted to <br /> trace the locations, and estimate the burial depths of the utilities Outlines of utilities were <br /> located using electro-magnetic detectors (EM), ground penetrating radar (GPR) and other <br />' methods Information derived from the geophysical survey was used to outline all utility <br /> locations and, accordingly, mark all final boring locations <br />' 3.3 Drilling <br />' The soil boring program was implemented on February 6, 1995 SJCPHS officials were <br /> notified in advance of the scheduled investigation activities to coordinate appropriate <br /> inspections Photo--documentation of the drilling program is presented in Appendix A <br /> Seven of the eight soil borings were completed using a truck-mounted drill rig with eight inch <br /> diameter hollow-stem augers Each boring was drilled vertically, with the exception of boring <br />' B-9, which was drilled at a 30° angle to circumvent local utility lines Relatively undisturbed <br /> soil samples were collected by driving a split spoon sampler past the bottom of the augers that <br /> had been advanced to the sampling depth <br /> Due to access limitations, boring B-10 was drilled manually using standard hand auger <br /> equipment The boring was drilled in the utility control yard located to the north of the <br /> bunker fuel UST B-10 was drilled to a total depth of 15 feet bgs <br /> Following completion of each borehole, a bentonite or concrete slurry was used as backfill <br />' All drill cuttings and non-retained samples were placed in 55-gallon drums Decontamination <br /> and steam-cleaning water was also stored in 55-gallon drums The drums were stored on site <br />' pending characterization for proper disposal <br /> 3.4 Soil Sampling <br /> 34 1 Sampling Sequence and Methodology <br />' <br /> During the completion of each boring, soil samples were collected at discrete depth intervals <br /> s <br /> for geological observation and on-site screening Samples for chemical analysis were collected. <br /> at 5-foot depth intervals to the maximum depth of each boring (15 to 25 feet) <br /> TETRA TECH Stockton Developmental Center,Phase II Site Investigation Report Page 9 <br /> 1 <br />