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"E" Seam Adequacy - 2 - April 10, 1986 <br />2. There is no aquifer analysis based on the concept of multiple <br />completions even though this would be the case during development of <br />the No. 6 Mine. A leaky aquifer model may be a useful analogy in this <br />instance. <br />3. Technical revision narrative, page III-73, paragraph 1, sentence 2: <br />How can the assumption that the cone of influence being 10,000 feet be <br />used for the case of the proposed Mine No. 6 access and development <br />when the conditions are probably different. Anew cone of influence <br />should be calculated. The size of the mine proposed, configuration of <br />the strata being mined, and the configuration of mining, are not the <br />same as those used in Mine No. 5. <br />4. Technical revision narrative, page III-73, paragraph 3, sentence 2: <br />Again an assumed cone of depression (cone of influence) was given, this <br />time however, at 1,000 ft. beyond the mine. What is this assumption <br />based on? <br />5. Technical revision narrative, page III-73a, paragraph 1, sentence 2: <br />From what are the 10 ft. drawdowns derived, calculations or estimations? <br />6. Technical revision narrative, page III-78, paragraph 3: The statement <br />• made that indicates no impact will occur by development in the "E" seam <br />access on surface streams is not supported by enough evidence. <br />Furthermore, this statement is in disagreement with the statement on <br />page III-71, paragraph 2 that implies the "E" seam access is located <br />near the subcrop exposure in the stream valley, and that the seam is <br />partially saturated at this point which could mean a possible direct <br />hydrological connection to the recharge area by virtue of its partial <br />saturation. <br />7. The operator purposes to utilize a culvert to pass flow under the <br />permanent rock waste disposal area. Due to the minimal size of the pile, a <br />culvert may be acceptable verses the more commonly used rock drain. However, <br />the following need to be specified in the design of the culvert. <br />a. Compaction standards to be followed around the culvert. <br />b. The wall thickness of the culvert. <br />For future reference, if the pile height is to be increased, the load may <br />exceed the culvert's strength, thus requiring removal and installation of a <br />rock drain or other suitable drain prior to increase in the height of the pile. <br />8. The NPDES permit CO-0034142 describes outfalls 002 and 003 as <br />consisting of underground mine drainage from Mines No. 9 and 5. The operator <br />must contact the Health Department to include Mine No. 6 in this description. <br />• 9. The peak flow determination in Appendix IV-4 is uncorrected for inches <br />of rainfall. Multiplying by 1.7 inches of rainfall gives 29 cfs for the 10 <br />year peak. The culvert is capable of passing this flow with six feet of <br />headwater. With this depth of headwater, sedimentation may occur at the inlet <br />and diligent maintenance will be required. <br />