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~_ <br />SQecific_Comments and Information <br />1) In order to develop the initial West Pit box cut, the West Pit <br />Excess Spoil Fill area and associated access ramps, a total of <br />313 acres must be stripped of topsoil in 1994. <br />2) During the permitting process for the West Pit Pond (T.R. 25), <br />Colowyo committed to an initial pond design of 11.44 acre-feet <br />of storage. Based upon this initial pond design, if no other <br />containment structure was in place, topsoil stripping would be <br />limited to 124 acres. This acreage calculation is based upon <br />a relationship between theoretical hydrologic modeling <br />assumptions for sediment contribution and runoff occurring <br />from topsoil stripped areas versus available pond capacity. <br />As confirmed by the Division's letter of July 18, 1994, we <br />agree that the ratio used in T.R. 25 was 10.8 acres of topsoil <br />stripping to 1 acre-foot of pond capacity. This ratio was <br />used by Colowyo when addressing internal in-pit hydrologic <br />control structures during West Pit development. <br />3) The as-built configuration of the West Pit Pond was <br />considerably larger than design, with a capacity of 12.4 acre- <br />feet of storage. Therefore, utilizing the 10.8:1 ratio, the <br />topsoil stripping acreage constraint was increased to 134 <br />acres. <br />4) During topsoil stripping operations in the vicinity of the <br />West Pit Fill toe area we encountered a pre-existing slide <br />area. In the process of removing the slide material to insure <br />future stability of the associated area, the pond capacity was <br />increased further to 12.8 acre-feet. Utilizing the 10.8:1 <br />ratio, possible topsoil stripping acreage was increased to 138 <br />acres. <br />5) Initial West Pit topsoil stripping started with the upper pit <br />access ramp areas (internal drainage area #3•of the July 22, <br />1494 certification). The drainage from this area was <br />controlled by drainage structure #3. This 38.9 acre stripping <br />area was excluded from consideration with respect to the "124 <br />acre" issue because Colowyo had constructed the two initial <br />in-pit ponds with 3.86 acre-feet storage capacity. The <br />initial in-pit pond capacity was .26 acre-feet more than <br />necessary to contain any runoff from this area. Although <br />adequate to control runoff from area #3 we later increased one <br />of the ponds to 5.7 acre-feet (or 25°a larger than required) as <br />a natural progression of mine activities. (A copy of the July <br />22, 1994 certification is included for your information.) <br />6) Initial construction of control structure #2 was completed <br />next, providing for an estimated 2 acre-feet of capacity. <br />Based upon the 10.8:1 ratio, this initial box cut structure <br />provided additional capacity to control runoff from an <br />additional 21.6 acres of drainage area. <br />