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• Section 780.21(b) Continued. <br />"Ground Water Quantity protection," and as demonstrated by Lusky and <br />Toy (1976), can result in a decrease in the infiltration rate, and <br />thus, an increase in the runoff volume. <br />Modification of small ephemeral drainages may change the pattern of <br />surface water runoff and may change the rate of runoff slightly, but <br />will not change the amount of water available downstream. Based on <br />field observations, the ephemeral drainages located within the area <br />to be mined, particularly in the eastern half of Section 22, do not <br />have distinctive or defined stream channels. <br />Methods of Protection and Mitigation. <br />Kerr Coal intends to utilize numerous methods to minimize the <br />potential reduction in downstream water availability and to mitigate <br />any adverse effects, if necessary. Sedimentation ponds are the <br />. single most important contributor to the potential reduction; but as <br />discussed in detail below, the ratio of water permanently impounded <br />to the total discharge of the subject watershed will be very low. <br />Sedimentation ponds will be constructed and maintained so that most <br />of the detained water can be released after it meets all applicable <br />effluent limitations. The average volume of water detained is <br />determined by the design sediment storage volume. Since all ponds <br />will be cleaned out when the sediment volume reaches 60% of its <br />design volume, the average volume of sediment will be 30% of the <br />design volume. Therefore, the average volume of water remaining in <br />the ponds, or "dead storage", will be 70% of the design sediment <br />j storage volume. <br />Designs of all sedimentation ponds are discussed under Sections <br />1 780.25, 816,46, and 816.49, and in Exhibit 42, Drainage and Sediment <br />Control Plan: The total volume of dead storage capacity in all <br />~~ sedimen- <br />I <br />780-100 aaR Revised - January, 1991 <br />