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Colowyo, C1981-019, PR3 adequacy No. 2 14 April 22, 2011 <br />In order to recognize that most postmining spoil leachate seepage into the downdip pitwall <br />probably will occur in the more permeable beds (the coal seams and cleaner sandstone beds), <br />please use in the pitwall seepage calculation for the Collom Lite Pit a value for K that is within <br />the range of most values for the coal seams and sandstone beds (for example, 0.01 ft/day, rather <br />than the 0.0001 ft/day in the submittal). Also, please use in the calculation of the cross- <br />sectional area of the downdip pitwall only the aggregate net thickness of sandstone and coal <br />beds (that is, exclude the shale and siltstone beds from the measurement of the pitwall height <br />because those beds are not capable of transmitting a significant amount of spoil leachate). The <br />aggregate net thickness can be measured on a geophysical log. <br />Please refer to question 2.04.7(3) above under the heading Alternative Water Supply <br />2. Discussion is also limited with regard to the potential for development of a spoil aquifer and <br />potential long-term discharge of the spoil aquifer to the surface water system. Proposed text <br />narrative provides an analysis indicating that development of a spoil spring, if it occurs, would <br />take 100 years or more to develop to the point where it would discharge to the surface water <br />system. The Division believes a spoil aquifer will develop over time within the confines of the <br />backfilled Collom Lite pit, based on past experience in northwestern Colorado. Long-term <br />discharge of degraded spoil water could therefore impact areas downstream. Alluvial valley <br />floors, as defined by the Coal Rules, are located downstream of the permit area in Collom <br />Gulch. Please expand the permit text narrative regarding the potential for spoil water discharge <br />and impacts to downstream areas. <br />Please revise the prediction of spoil spring discharges to the surface for the Collum Lite Pit to <br />reflect the requested re-calculation of annual pitwall seepage. <br />3. As mentioned previously, the plan for control of surface water drainage through the disturbed <br />area is deficient at this time due to uncertainty of the proposed mine plan and the long-term <br />presence of the temporary spoil pile in the center of the disturbed area. The application does <br />not adequately present how surface water will be handled over the life of the operation (Rule <br />2.05.6(3)(b)(i)). <br />The response is inadequate. The application does not adequately present how surface water <br />will be handled over the life of the operation (Rule 2.05.6(3)(b)(i)). The Division cannot defer <br />sediment control issues to a later date unless CCC is requesting only limited mine plan <br />approval for the Collom Lite and Little Collom X areas. The Division understands the worst <br />case scenario for hydrology and sedimentology and has specific questions related to that review <br />later in this letter. CCC states in response to this question, "Later stages in the mine <br />progression will be reviewed in more detail..." That detail is required for all areas within the <br />Collom proposed permit area in the current revision application (PR-03). Please refer to the <br />original question. <br />4. Please revise the third paragraph on page 132 to reflect the prediction that there will be limited <br />discharge into the pitwalls. <br />5. Please use in the calculations of spoil resaturation time a spoil recharge rate, rather than a <br />bedrock recharge rate. A reasonable spoil recharge rate for the Collom area would be 3.1