2008-12-16_REVISION - C1981022 (3)

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Elk Creek Mine TR-60 2nd Adequacy Review 16 Dec 2008 Page 5 of 9 11. Map 2.05-E1-BCA2 does not show how the lay down area will be accessed. Please explain if a road will be needed and whether this road will require a road culvert in the small drainage just north of the lay down area. The Division has no further concerns. A light use road/access ramp for the laydown area is being proposed in the'November 26, 2008 submittal. Oxbow proposes to make drainage channel BCCD-1 into a swale where the ditch crosses the light use road. 12. In comparing the existing topography shown on Map 2.05-El-BCAI with the proposed post mining topography shown on Map 2.05-M6, it appears that there is an area just to the north of the lay down area that will be disturbed. However, this area does not appear to be designated as disturbed on Map 2.05-El-BCA2. Please explain. In their November 26, 2008 submittal, Oxbow responded that the post mine topography area in question covers the laydown area. The Division still has a question about this issue, so will approach it in a different way. Comparison of the contour lines on Drawing 2.05-E1-BCA1, "Existing Conditions", with those on Drawing 2:05-El-BCA2, "Facilities Layout", shows that no grading of the laydown area is proposed. However, referring to the contour lines shown on Drawing 2.05-M6, Sheet 7 of 7, "Facility Post Mine Topography", it appears that there will be regrading of the laydown area and the area just east and north of the laydown area after operations cease and the area is reclaimed. Please explain why the post mine topography map shows regrading of the laydown area and the area east and north of the laydown area when the other two maps show that no grading will occur in those areas? 13. In the TR-60 Sedcad designs for the ditches and for the Bear Creek culvert, the horizontal distances used in deriving the time of concentration values for each subwatershed appear to be considerably longer than the hydrologic flow path length of their corresponding subwatersheds. For instance, in the Sedcad runs for ditch BCCD-2 and the side postmine channel, the total horizontal distance used for subwatershed area 1 amounts to 24, 770 feet, even though the drainage area amounts to only 53.1. acres and, referring to Map 2.05-El-BCA2, the longest hydrologic flow path appears to be no more than 3, 500 feet. In another example, for the Bear Creek culvert, the horizontal distances given for subwatershed area 1. add up to 41, 383 feet. However, referring to Map 2.05-E1-BCA2 again, the longest hydrologic flow path for the drainage area appears to be less than 30,000 feet in length. Please explain.