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Slightly different su veying techniques were used for the June 1981 survey <br /> of the five control point (TP-serles) and the three surveys of the nine <br /> subsidence monitoring pot is (MC-serles). <br /> a; 3.1 Control Survey <br /> The surveyof the flv� TP-serles control <br /> points was performed in June 1981 <br /> T <br /> under the direction of Mining•& Subsidence Engineering Company by Claycomb <br /> Engineering Associates, i c. This control survey was performed to an accuracy <br /> equivalent to a Second Order, Class 11 survey. <br /> Horizontal and vertic;l 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 measut�Ing device (EDM). <br /> The method of the control survey involved a closed traverse tied Into the <br /> = existing mine coordinate ystem. Horizontal and vertical angles were measured <br /> in both the erect and Inverted aspects. Six sets of inverted and erect Internal <br /> x <br /> angles were measured at a ch traverse station. Three slope distance <br /> measurements were obtained at each traverse point. These were averaged to ! <br /> provide the slope distanc$ value to the nearest 0.01 ft. <br /> A closed traverse was utilizedto allow for Internal angle triangulation and., <br /> w. <br /> elevation closure to prov�de 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 Or er, 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 />