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eh <br />ESPEY, HUSTON 8 ASSOCIATES, INC. <br />• <br />The factors of safety obtained by the analyses aze considered adequate <br />for both design and regulatory compliance considerations. <br />13.3.3 Terraces <br />Twenty foot wide terraces aze specified every fifty vertical feet in this <br />disposal pile, (30 CFR 817.102). These terraces will intersect the existing contours <br />at intervals of 50 feet starting with 7075 feet MSL and moving up to elevation <br />7225 feet MSL. The terraces will serve as diversion structures to intercept <br />precipitation sheet flow off the slopes and channel it to the sediment pond <br />collectors which surround the disposal azea. The terraces will be graded to drain to <br />both sides of the disposal pile with the high point equidistant from the two ends of <br />the terrace, Fig. 13.1.2. No terraces aze required in Phase I. <br />• <br />13.3.4 Drainage <br />Two different systems of surface drainage improvements aze proposed <br />for this project. One system is designed for diverting water from the drainage basin <br />above the disposal azea past the disposal facilities and into Curtis Creek. This <br />water will be runoff from undisturbed azeas and therefore will be uncontaminated. <br />The other system collects runoff from the disturbed azeas and drains into the <br />sediment pond. Due to the permeable nature of the soil in the disposal azea, these <br />ditches can be expected to drain any groundwater that is intersected. A secondary <br />benefit of these drainage improvements will be to maintain the potentiometric <br />surface within existing ground and out of the proposed fill. <br />13.3.4.1 The Watershed Diversion Ditch <br />The unnamed tributazy of Curtis Creek influenced by this project drains <br />an azea of 0.32 squaze miles. The 100-yeaz 24-hour discharge from the watershed <br />azea is 200 cubic feet per second (CFS). This peak dischazge was computed utilizing <br />C~ <br />13-10 <br />