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SEHECA II-W PERMIT C-82-057 . Technical Revision 28 Respoase to Division of Minerals and Geology 10/20/97 Adequacy Letter October 28, 1997 1. The cross sections are labeled correctly on Exhibit 20-2. Exhibit 20-4.3, Pre and Post Mining Slopes, was revised to show the proper labeling for Cross-Sections S-5 and S-6. 2. As the Division stated, with the implementation of this revision a change in the characteristics of the subwatershed #4(J1B1SWS4) to disturbed from undisturbed will occur. Sediment Pond 006 will be remodeled taking this change into account. Until the Pond 006 Stipulation is resolved, Seneca proposes the following temporary sediment control measures for the 006 drainage area. This plan will also assist in detaining water from entering the pond until we can adequately remove the existing sediment contained in the pond at the present time. A temporary diversion channel has been constructed from the T- 7 stocktank to the existing bottom portion of the B pit that already contains surface water runoff from the B pit drainage area. This diversion will be a 6 feet wide bottom ditch with 3:1 side slopes and is several feet deep. A SEDCAD+ output for this diversion channel is attached. The 006 Gulch reclaimed channel has a discharge amount of 26.4 cfs from a 100 year - 24 hour storm event. The temporary channel was designed for a conservative discharge of 35 cfs. The temporary diversion flows into a 48 inch diameter culvert that was installed in the pit ramp that is north of the 006 Gulch. A SEDCAD+ output for this culvert is also attached. Seneca will monitor both the temporary diversion and culvert to ensure that they are functioning properly and that their integrity is not compromised. The water will then empty into the bottom of the B pit. A second culvert in the pit ramp is currently utilized to run a hose attached from the pump in the B pit to the entrance of culvert A1. Water will be pumped from the B pit into pond 006 once sediment removal from the pond is completed. Water will also be pumped as necessary from the B pit to maintain a safe water level in the pit as well as in the pond. This plan will be followed until the pond 006 Stipulation has been resolved and the permanent plan can be implemented. 3. The reclaimed 006 gulch will actually begin to be constructed • once spoil material is placed in the drainage as the boxcut pit is stripped. The toe of the boxcut spoil will