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' 3.1.1 Feld Analytical Screening And Sampling Rationale <br /> PRC will use field analytical screening to help guide the placement of ground-water <br /> monitoring wells at the site and to estimate the total area of ground-water and soil contamination <br /> ' The PRC Field Analytical Screening and Sampling (FASS) equipment features a mobile hydraulic <br /> sampling system complemented by a laboratory-grade gas chromatograph and a head space analyzer <br /> ' This system will be used to collect and analyze soil gas and ground-water samples in order to <br /> delineate the extent of contamination at the site The advantage of this system is that the data can be <br /> ' collected and analyzed rapidly on site and can then be used to optimize the number and location of <br /> permanent ground-water monitoring wells <br /> 3.1.2 Soil Sampling Rationale <br /> ' One soil boringwill be drilled within the immediate vicinity of the tank excavation to a depth <br /> Y p <br /> ' of approximately 20 feet bgs Placement of the boring in close proximity to the excavation will aid in <br /> determining the extent of contamination in the vicinity of the excavation pit and evaluating the <br /> presence of free product present on the water table near the pit An additional five soil borings will <br /> be drilled to a depth of approximately 20 feet bgs based on field screening data generated by the <br /> ' Geoprobe Split-spoon soil samples will be collected continuously from the boreholes during drilling <br /> Samples for chemical analyses will be collected at a minimum of 5-foot intervals and one sample will <br /> ' be collected as close as possible to the top of the water table All of the borings will be completed <br /> as monitoring wells The well drilled in close proximity to the excavation pit will be installed <br /> immediately downgradient (south-southwest of the UST), given the presumed ground-water flow <br /> ' direction is to the south-southwest The rationale for well placement is discussed in section 3 1 3 <br /> Section 3 4 describes the field methods and procedures to be used during drilling and soil sample <br /> ' collection <br /> SAMPLAN 162 <br /> 044-0162UrATRI-054)6/92 10 <br /> I 1 <br />