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52,05 APPLICATION FOR PERMIT FOR SDRFACE OR UNDERGROUND MINING ACTIVITIES -- <br />MINIMUM REQUIREMENTS FOR OPERATION AND RECLAMATION PLANS. <br />2.05.6 Mitigation of Surface Coal Mining Operation Impacts. (Cont'd.) <br />(3) (b) Ci) (Cont'd.) <br />1Determined from configuration show in in <br />Plate I. <br />zRecommended lower limit design storm <br />(USDI, MESA, "Engineering and Design Manual <br />-- Coal Refuse Facilities," 1976). <br />3Flows computed assuming control of i)pper <br />Basin run-off from PMTS. <br />4q = 25 c.f.s. CCN 80) at Node 10 is be- <br />- plieved to be sufficiently conservative for <br />design. <br />SProbable Maximum Thunderstorm. <br />Map 8-1 shows all culverts, ditches and drains <br />constructed to control runoff from mine facil- <br />ities. <br />• The third element of the drainage plan is a <br />series of four (4) sedimentation ponds. These <br />are existing structures. See 2. 05. 3(3)(b) - <br />Operations Plan and maps 8A-1 and 8A-4 for <br />specifications on these dams. Any runoff gen- <br />erated from disturbed areas is routed through <br />these sedimentation ponds. The ponds retain <br />surface runoff from disturbed areas, thereby <br />dissipating energy and reducing flow rate <br />which allows sediment to be deposited within <br />the reservoir. Source-area sediment yields <br />from the mine site are 1o w. ~:hannel erosion <br />rates also appear to be low. Under natural <br />conditions, much of this type of activity re- <br />sults from short duration thunderstorms. The <br />water balance analysis previously discussed <br />supports this conclusion. Of course, exten- <br />sive disturbance of the vegetation and land <br />surface has increased the runoff potential <br />from snowm elt; the near-surface flow compo- <br />nent, which is of most significance to on site <br />and channel processes, will now account for <br />. Revised OS/O1/84 <br />Revised 10/01/87 <br />173 <br />