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1 <br /> i Treadwell&Rollo <br /> 1 an Omnidata data recorder that automatically stores TC values. The TC method was used to <br /> determine conductivity variations that may indicate the presence of USTs and other buried debris <br /> ' and objects. <br /> 1 3.1.1.3 Ground Penetrating Radar (GPR) <br /> 1 The GPR method provides a continuous, high resolution cross-section depicting variations in the <br /> electrical properties of the shallow subsurface. The system operates by continuously radiating an <br /> 1 electromagnetic pulse into the ground from an antenna as it is moved across the surface. When <br /> the pulse encounters a metal object, a signal is reflected that is received by a transducer at the <br /> 1 surface and is printed in cross-section on a recorder. A Geophysical Survey Systems, Inc. SIR-2 <br /> Subsurface Interface Radar System equipped with a 500 megahertz transducer was used to <br /> 1 perform this survey. The GPR generally provides higher target definition than VMG or TC and <br /> is not significantly affected by close proximity to above ground structures, vehicles, or <br /> 1 equipment. <br /> 1 3.1.2 Direct Push Method <br /> The direct push technologies used during this investigation involved pushing soil or groundwater <br /> 1 samplers into the ground to collect samples or to make a boring for installing temporary well <br /> casing. Three types of direct push drilling rigs were used during the project. The direct push <br /> 1 method produces no cuttings at the surface during the sampling process and allows grout to be <br /> tremied through the casing to close the borings. <br /> 3.1.2.1 Geoprobe Model 5400 <br /> The Geoprobe Model 5400 is a hydraulically-powered,percussion/probing machine designed <br /> specifically for use in environmental investigations. It relies on a relatively small amount of <br /> static (vehicle) weight combined with percussion to advance samplers. A hollow steel rod with <br /> 1 an attached Macrocore sampling device is advanced into the soil using a hammer that produces a <br /> force of 345 foot-pounds. The Macrocore used in this investigation was 4 feet in length and <br /> ' 5 <br /> 1 25970119.DGD 13 December 1999 <br />