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,.~- a <br />Revisions to Hvdrolocic Plan - Aoril 1990 <br />As of the spring of 1990, a number of changes were needed in the <br />surface water control system at the mine. These changes by dreg <br />Lewicki and Associates have been incorporated into the original <br />design by Dingery Associates, Inc. <br />A number of ditches and culverts have been removed and other <br />ditches have been ra-designed. The design calculations for all <br />ditches are shown on the following pages. The cross-sections are <br />shown on the revised Plate 1 titled Site Plan. <br />The calculations show that the ditches, as designed, can carry a <br />greater flow than the deign peak flow for the respective drainage <br />areas. This is done to allow flexibility for future sloughage in <br />the ditches. Sunland commits to maintaining the ditches so that <br />the design peak flow can be safely passed. The cross-sections of <br />the ditches shown on Plate 1 era for construction only. Some <br />sloughage can occur in the ditches, yet the design peak flows can <br />still be safely passed. <br />All of the following ditch designs ere based on Meaning's <br />equation for open channel flow. The Meaning's roughness <br />coefficient used for the site ditches (dirt and gravel) is 0.03 or ,035. <br />All design peak flows are shown on pages 154 to 157 of this <br />permit. <br />A Swale has been placed across the County Road to bring drainage <br />to the sediment pond. The design for this Swale is presented on <br />page 162.1. <br />Two small area exemptions for disturbed area draining to the <br />sediment pond are requested. First, nn area of 0.11 acres located <br />Went the Swale in the County Rond contains the office building <br />for the mine. The site is slightly downhill from ditch D-8 and <br />its runoff cannot be channeled to the sediment pond. The area is <br />graveled and produces little runoff. The area downstream shows no <br />signs of erosion problems. <br />Second, a fan portal is located on the hillside above the office <br />building. This area is only 0.05 acres and is overgrown by <br />vegetation. This area has virtually no impact on waters <br />downstream. <br />Ycvm~F P~y~ /SS <br />~3 Y/5/9a <br />-. <br />