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Slightly different surveying techniques were used for the June 1981 survey <br /> of the five control points (TP-serles) and the three surveys of the nine <br /> �7 subsidence monitoring points (MC-serles). <br /> 3.1 Control Survey <br /> The survey of the five TP-serles control points was performed in June 1981 <br /> 4 <br /> under the direction of Mining*& Subsidence Engineering Company by Claycomb <br /> Engineering Associates, inc. This control survey was performed to an accuracy <br /> equivalent to a Second Order, Class 11 survey. <br /> Horizontal and vertical angles were measured to the nearest 1 second with a <br /> Wild T-2 theodolite. Slope distances were measured with a Topcon DMC-2 <br /> electronic distance measuring device (EDM) . <br /> The method of the control survey involved a closed traverse tied into the <br /> existing mine coordinate system. Horizontal and vertical angles were measured <br /> in both the erect and inverted aspects. Six sets of Inverted and erect Internal <br /> angles were measured at each traverse station. Three slope distance <br /> measurements were obtained at each traverse point. These were averaged to <br /> provide the slope distance value to the nearest 0.01 ft. <br /> A closed traverse was utilized to allow for Internal angle triangulation and .. <br /> elevation closure to provide further accuracy for the control survey. <br /> 3.2 Subsidence Monitoring Surveys <br /> Subsidence monitoring surveys were performed In August 1981 , July 1982 and <br /> August 1983. Subsidence monitoring surveys of the MC-serles points were <br /> performed within Third Order, Class II accuracy limits. <br /> Horizontal and vertical angles were measured to the nearest 1 second with a <br /> Wild T-2 theodolite. Slope distances were measured with a Wild D13-S <br /> 2 <br />