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Mr. Richard Atkinson • May 14, 1981 Page Six shown on Figures 3 and 4 of Exhibit 7, and calculations for the designs contained in Annexures A and B to Exhibit 7. 7. Two permanent diversions along Southern Boundary: The Adequacy Review states that the two permanent diversions a ong the southern boundary should be removed as part of the reclamation and all pre-mining drainage restored. We concur that both of these ditches may be removed as part of final reclamation. However, the removal should be after all of the mine fi II area is fully restored, so as to minimize erosion to the mine fill area. 8. Reestablishment of Surface Drainage: The Adequacy Review raised concerns about the reestab is ment of surface drainage. The proposed post mining drainage pattern consists of drainages along the face of the fills in berm ditches, terrace or contour ditches to the principal drainages which are located approximately as presently located. Drainage along the berms and terraces was selected as a means of minimizing erosion on the slopes. Selection of this method of conveying flow to the principal drainages should also match the pre-mining hydrologic regime closely as the same area is being drained by a complete system of channels. The Adequacy Review also raised concern about several minor valleys draining • to the north boundary of the mine area. In the Section 4 mining area a small area is not being reconnected to its existing drainages, as this is in the final area which will be finished off somewhat lower than the present contour and hence cannot be reconnected to its original drainage pattern. Also the drainage must be directed to a sedimentation pond, and is thus directed into the Taylor Gulch tributary pond. 9. Convex Hillslopes: The Adequacy Review raised concerns over the convexity and and the gradient of the lower hillsides. With the berm, terrace, and contour ditches draining the hillsides to the principal drainages erosion should be well controlled, and there should be no differences between the fills as laid out, and revised fills that would flatten the lower slopes out and add more fill in the center of the area. Additionally, the layout as drawn up, by inspection, appears to approximote the pre-mining condition closer than a revised plan that would add more fill in the center of the mining area. A copy of 29 sheets of computations made in connection with these responses is enclosed. We trust that these responses adequately address the points raised in the Colorado Mined Land Reclamation's Adequacy Review that relate to our engineering work for Colowyo's Permit Applimtion. •