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way all of the material in the fills was moved in the past, as well). Colowyo has not <br />documented how this reduction in swell factor was derived. In the initial permitting of <br />the Colowyo Mine and in the permitting of the Streeter Fill as an experimental practice <br />there was a great deal of time was spent analyzing and documenting both the swell factor <br />and the mine achieving AOC in its backfill (since material was being placed in a <br />permanent fill and not being returned to the pit). With the submittal of TR-81 Colowyo <br />has simply changed the 30+ years of historic data associated with the mines swell factor <br />with little more than a statement that the mining method has changed. Please provide the <br />Division with detailed documentation regarding why the swell factor is being changed as <br />well as detailed data to support this change. This documentation and data needs to be <br />included in the permit as an exhibit and a detailed explanation of the swell factor change <br />needs to be included in the permit text. Additionally, Colowyo needs to specify what <br />portions of the mine this change in swell factor applies to. Please provide the Division <br />with detailed documentation and data for the change in swell factor in the South <br />Taylor Pit from 20% to 15%. Please include this documentation in the form of an <br />exhibit. Please include a detailed description of the change in swell factor in the <br />text, beginning on page ST/LW-Rule 4, Page 20. <br />3. Colowyo has proposed to change the swell factor for the South Taylor Pit from 20% to <br />15%. It has been stated (but not documented) that this change in swell is due to the <br />change in mining method from the dragline(s) to the truck/shovel operation. Since the <br />majority of the South Taylor operation is a truck/shovel operation, it would follow that <br />the swell factor for the entire South Taylor Pit would be affected by the change in swell <br />factor, not just the excess spoil fills. Based on this decrease in swell factor, the overall <br />amount of material from the entire pit will experience a decrease in swell. <br />The South Taylor Pit Box-Cut area encompasses approximately 500 acres (Map 23A). <br />Based on Figure 2.04.6-313 - Generalized Stratigraphic Column-South Taylor, Colowyo <br />is planning on Mining to the G8-Seam, which would put the pit floor approximately <br />513.5 feet below the original ground surface. In the currently approved permit, Colowyo <br />will remove approximately 103 million cubic yards from the box-cut (60 million yards in <br />permanent fills and 43 million yards in the temporary overburden stockpiles). This <br />volume is given in loose cubic yards and is based on a swell of 20%. The bank volume, <br />based on this 20% swell, would be approximately 85.8 million yards. If, in fact, the swell <br />factor for the South Taylor Pit box-cu.t area is decreasing to 15% this would lead to a total <br />(swelled) volume of 98.7 million cubic yards of spoil moved out of the pit. This is a <br />decrease in spoil of approximately 4 million cubic yards of spoil material. <br />In TR-81 Colowyo is proposing to increase the size of the permanent fills in the South <br />Taylor Pit area by approximately 10.3 million yards. Colowyo is also proposing to <br />decrease the swell factor from 20% to 15%, leading to a decrease in loose spoil of <br />approximately 4 million yards. The overall result of these two actions would be to <br />decrease the amount of material going back into the South Taylor Pit by approximately <br />14.3 million yards. Based on these observations the Division believes that it would be <br />more appropriate to decrease the size of the South Taylor Fills rather than increase their <br />size. A further increase in the size of these fills would lead to a further decrease in the