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the satellites to be turned away from their current areas of focus, CC&V will have to rely <br />entirely on the visual controls that are also re-described below. <br />There are a few "shadows" in the Phase II liner area where coverage by the combination of <br />satellites and ground-based stations will not be adequate for accurate surveying. In these areas, <br />currently anticipated to be 10 percent of the Phase II area, conventional surveying will be <br />performed as the added measure to control dozer-placement at the 2.0 foot thickness. The <br />remaining 90 percent of the liner will be covered by dozers with Drain Cover Fill with the use <br />of the satellite positioning system. <br />Final grade after dozer pushing will be achieved, principally, with motor graders. It will not <br />be necessary to accompany these graders with the same global positioning system as used with <br />dozers because the chance of scraping the liner are almost nil with the grader and because the <br />ground pressure of the grader is minimal. Rather, at the time of this final grading, the final <br />Quality Control and Assurance survey data will be generated to ensure proper thickness. The <br />physical markers on the 50-foot grid will generally be retained until this final grading is <br />essentially complete. <br />The satellite positioning and ground-based survey procedure will rely on apre-placement (of <br />Drain Cover Fill) topographic map established on a grid spacing that possesses sufficient <br />accuracy for areas in which the final thickness of Drain Cover Fill might otherwise be <br />inappropriately reduced. An individual will walk behind or possibly beside the dozer (in any <br />case in safe and close proximity to) that is placing Drain Cover Fill, and will measure the depth <br />relationship to the pre-placement topography and will call out any unacceptable readings directly <br />to the operator of the equipment. If the reading identifies too little Drain Cover Fill, the heavy- <br />equipment (dozer) operator will be notified by the individual with the positioning device and the <br />dozer operator will follow the remedial measures outlined below. <br />The principle of the global positioning system is one of comparing the horizontal and vertical <br />position (northing, Basting, and elevation) determined by stationary reference points and satellites <br />to the pre-placement topography to develop "cut" or "fill" information. <br />The positioning system uses the Trimble "GPS Total Station." It operates within the radio <br />spectrum, allowing use in fog, during precipitation events, or at night. Trimble provides <br />Maxwell-based technology dual-frequency receivers and advanced algorithms which reduce the <br />re-initialization time necessary if contact with the base station and satellites is temporarily lost. <br />The satellites provide a basis for trilateration to establish the position of the receiver. Trimble <br />base stations are positioned on the periphery of the Phase II area as an unattended, omni- <br />directional broadcast hub for known-point, carrier-phase GPS data. This base station allows the <br />use of mobile units that may rove to any location, provided both satellite and base station contact <br />is made. <br />The roving unit is accompanied by the readout device that designates the elevation in terms of <br />"cut" or "fill." The basis for the readout is the comparison between the initial pre-Drain Cover <br />6 <br />