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• 3. Soil erodibility characteristics. <br />4. Drainage basin length and slope characteristics. <br />5. Drainage basin slope and channel cross-section characteristics. <br />6. Rainfall storm intensity and duration characteristics and total flow <br />calculations for the study area were evaluated for pre-existing and <br />pot-mine topographic characteristics. <br />The ponds are designed pursuant to CMLRD 4.05.6 and located at the outlets <br />of watershed areas A and B and will contain runoff from areas A, B, C, and D, as <br />shown on Map 9 (designed) and Map 10 (as-built). Conceptual impoundment designs <br />are presented on Maps 11, 12, 13, and 14. Flow calculations are presented in <br />Appendix 2.05.3-6, and sediment analyses are discussed in Appendix 2.05.3-7. <br />Area capacity curves were calculated using a trapezoidal method, with the <br />area contained within the impoundment calculated by digitizing the area con- <br />• tained within each two-foot contour interval. <br />Rough grading and excavation of the diversion and impoundments was con- <br />current with overburden grading at the mine site. As overburden placement and <br />rough grading were completed, the completed post-mine topography was surveyed <br />and final grading performed. After final grading, an on-site inspection was <br />performed to identify any changes necessary to the conceptual surface impound- <br />ment designs to stake out excavation into competent material for the surface <br />impoundments and to perform sufficient materials tests to identify best compac- <br />tion methods and moisture levels for building compacted embankments. <br />During impoundment construction, impoundment materials were placed in <br />12-inch lifts and compacted to 90 percent relative compaction in accordance with <br />ASTM procedure D1557. (Appendix 2.05.3-8 presents impoundment certification <br />• report and "as-built" flow calculations.) <br />- 190 - (Rev. 5/86) <br />