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• In addition to the subsidence monuments. six survey control monuments <br /> are positioned at strategic locations outside the area of Influence of <br />proposed mining activities. These points are positioned to provide max- <br />imum visibility to various monument lines. The coordinates and eleva- <br />tions of the control monuments Mere determined by running a closed <br />transverse from the mine benchmark. Snowmass Coal Company's survey sys- <br />tan of coordinates is used for ell monitoring Mork. <br />Monument Construction <br />Two general types of subsidence monitoring monuments have been lnstall- <br />ed: subsidence/strain points and leveling points. <br />• TMO general types of subsidence/strain points Mere installed. Figures <br />4.6.1.5.4-1 and 4.6.1.5.4-2 illustrate construction details for soil/ <br />weathered bedrock points and bedrock points. <br />The subsidence/strain points are designed to accept aself-centering <br />trivet assemble attached to the surveying target. This system 1s de- <br />signed to permit rapid set-up on a point with minimum centering error. <br />These monuments are designed to provide detailed data on both vertical <br />and horizontal ground motion. <br />The leveling points consist of 3/4-1n rebar driven to refusal. ; A <br />center-punched cap 1s installed on each rebar leveling point to provide <br />• a constant measuring point. These points are designed to provide <br />vertical ground motion data. <br />29 <br />