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3.3 DRILLING <br /> 3.3.1 Types of Drilling <br /> At Trapper Mine there are three types of drilling: blast hole drilling, explora- <br /> tion drilling and development drilling. Blast hole drilling occurs only within <br /> the permit area and is required for the blasting operation. The holes are needed <br /> for placement of explosives to fragment overburden, interburden and coal. Holes <br /> sizes, depths and spacings vary according to the thickness and nature of the <br /> material to be blasted. Because the holes are drilled just ahead of, or within <br /> an advancing pit, they are removed by stripping or mining within several months <br /> or less. For more detail on blasting, see Section 3.4. <br /> Exploration drilling occurs outside the permit area and is required to determine <br /> the extent of the coal reserves and to provide information on coal depth, thick- <br /> ness and quality. All exploration drilling is conducted in compliance with <br /> applicable U.S. Bureau of Land Management and State of Colorado regulations and <br /> will be handled by separate permits. <br /> Development drilling is required to provide data for planning pit dimensions, <br /> sequencing activities and equipment scheduling. Typically, development drilling <br /> is conducted at or near the projected coal cropline and the economic stripping <br /> limit ahead of advancing pits and where new pits are planned within 'the permit <br /> area. Drilling depths needed to further define the cropline are usually only to <br /> the coal in question. Depending upon the information obtained, drilling may be <br /> conducted defining the cropline to within 25 feet horizontally. The economic <br /> stripping limit is defined in much the same manner except it is not necessarily <br /> located as accurately as the cropline. <br /> Prior to stripping, the overburden is drilled and blasted. Overburden drilling <br /> and blasting precedes stripping by one to five pit widths. Before the overburden <br /> is drilled and blasted, the topsoil is removed. Topsoil removal is conducted <br /> during the fair weather months of May through {October. Therefore, each year's <br /> ` <br /> 3-22 REVISION <br /> APPROVED <br /> DAT 2/g-Sr <br /> REVISED FEB 1 D '88 <br />