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<br /> <br /> <br />t <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />co~~s~~~Er- <br />4. Rule 4.05.6(3)(c) requires a non-clogging dewatering device at the 1008 <br />sediment storage level to remove water storage resulting from inflow. <br />The opening should provide for at least 24 hours detention time. <br />Designs do not indicate a dewatering device for existing or proposed <br />sediment ponds. <br />RESPONSE <br />A small hole will be cut into the riser pipe providing gradual release of <br />stored water. The hole will be 5" in diameter with a centerline elevation <br />of 7514. Calculations supporting these dimensions are attached. <br />COt4MFNT <br />5. The pond at Pit 4 and the pond at Pit <br />2 acre-feet. To be in compliance <br />Engineer, the applicant must obtain <br />charge of water stored in excess of 2 <br />s 5 and 6 store water in excess of <br />with requirements of the State <br />water rights or provide for dis- <br />acre-feet within 36 hours. <br />RESPONSE <br />The dead storage of the pond is nominally 2 acre-feet or less. The water <br />which is occassionally retained by the pond is released within 24 hours. <br />For this reason, no water rights are required. <br />COMMENT <br />Diversion and Collection Ditches <br />1. A number of ditch sections have 10 year-24 hour storm velocities which <br />are erosive. Erosive velocity would not be a concern where ditches are <br />in bedrock sandstone, but ditch sections which have erosive velocities <br />and are in unconsolidated material should be lined with rock riprap. <br />Numerous channel sections have slopes in excess of the listed slopes on <br />page III-18 and as a result have higher than indicated velocities. The <br />ditch section near the northeast corner of Pit 4 has a slope of over <br />15~ and an estimated velocity of 9 fps. Potentially erosive ditch sec- <br />tions and channel types should be identified by the applicant and an <br />acceptable plan should be submitted for minimizing channel erosion in <br />segments of concern. <br />RESPONSE <br />As ditches are excavated during development of the pit, steep sections will <br />be identified. These sections will be inspected periodically by mine <br />personnel. If erosion is substantially altering the dimensions and/or flow <br />conditions in the ditch, the ditch will be enlarged and rock riprap will be <br />added to prevent further erosion. <br />