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• Slope Protection: We recommend that all of the cut and fill slopes be protected from erosion by revegetating <br />the finished slopes. Pond inlet and outlet discharge areas should be protected from erosion by placement of rip <br />rap aprons or some other means. The erasion protection required should be based on the actual flow velocities. <br />Overbuild: The embankment foundation soils will undergo a negligible amount of settlement. The <br />embank®ent materials will consohda[e with time, and based on our experience, we estimate [ha[ the settlement <br />will be on the order of 2 to 4 inches. We recommend that the embankment section be overconstructed with <br />approximately 6 inches of additional material in the central portion of the dam. <br />Slone Stability: No formal stability analyses were performed to evaluate the slopes recommended above. <br />Published literature and our experience with similar cuts and fdls indicate the proposed slopes should have <br />adequate factors of safety if properly constructed. If a detailed stability analysis is required, a qualified <br />geotechnical engineer should be consulted. <br />SPILLWAYS <br />It is our understanding that the primary spillways for the proposed ponds will consist of an 8-inch I.D. HDPE <br />pipe. The invert elevation for the primary spillway pipes will be set approximately 2 feet below the crest of the <br />dams at an elevation of 6329.0'. Based on our calculations, the spillway conduit will have a discharge capacity of <br />approximately 1400 gallons per minute when flowing 3/4 full. <br />The emergency spillways will consist of 6-inch HDPE pipes placed in each of the cells. The invert elevation for <br />• the emergency spillway pipes will be se[ approximately 1 foot below [he crest of [he dams at an elevation of <br />6330.0'. Based on our calculations, each of the spillway conduits will have a discharge capacity of approximately <br />705 gallons per minute when flowing 3/4 full. <br />The inflow Gom the dewatering borehole will be approximately 350 gallons per minute received on an <br />intermittent basis. The 10-year, 24hour precipitation event will add an additional 1.7 inches of water [o each of <br />the cells. Based on the surface area of the ponds, this results in an additional inflow 15,081 gallons of water per <br />cell during [he 10-year, 24hour event. The storage capacity of each cell with a freeboard of 2 feet will be <br />966,003 gallons. This results in a detention time of 45.3 hours per cell. I[ is our understanding that only 2 hours <br />of detention time is required for the settling agent. Design calculations showing the volumes associated with the <br />inflow from the 10-year, 24hour even[ and the capacity of [he spillways are shown in Appendix A. <br />If you have any q~stions regarding [his report or if we may be of further service, please do not hesitate to <br />contact [his office <br />Sincerely, <br />Brian D. <br />u <br />Job No. 96-25Tt Nonhrest Coloratlo Consullanis, Inc. Page 3 <br />