2019-07-09_REVISION - M2004044 (32)

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TETRATECH RMC Table 2 shows estimated quantities of fill material required for various parts of the project. The reclaimed 3:1 (H:V)slopes in the west and east cells will probably consist of compacted fines (overburden and mud lens material)from the mining operation. The closer that the high wall can be mined to vertical,the more room there will be for fill. The southwest cell will not have 3:1 (H:V) slopes because current reclamation plans call for it to be filled with fines. The available fill volume in the southwest cell,assuming no shrink or swell,should be similar to the amount of material mined. The quantity shown in Table 2 assumes that all material is removed. Another potential fill area is the paleochannel in the east cell. The quantity shown would fill the deeper parts of the paleochannel and is provided to help you evaluate the economics of additional water storage versus the fines disposal. The fill volume for the overlot grading refers to our memo of April 13,2004 where we did a preliminary design for overlot grading on the west side of the site. Table 2: Estimate of Fill Volumes At Tucson South Site Near Vertical High Walls High Walls at 1:1 Slope West Cell East Cell SW Cell Total Site West Cell East Cell SW Cell Total Site 3:1 Reclaimed Slopes 219,000 630,000 WA 849,000 146,000 420,000 WA 566,000 Fill Below Elevation 4920 c N/A 182,000 N/A 182,000 N/A 173,000 WA 173,000 Backfill of Mined Area N/A N/A 692,000 692,000 N/A N/A 646,000 646,000 Ovedot Grading" 307,000 N/A N/A 307,000 307,000 N/A N/A 307.000 Total: 2,030,000 Total: 1,692,000 ' Assumes all material is removed "Esfirnal�d tvlL'mc,;;uf yaf da�jgned All volumes in place:no shrinkage or swell assumed Figure 1 shows our geologic interpretation of the mud lens extents based on drill logs. The contour lines within the boundary show the estimated thickness of the mud lens. The main mud lens appears to be present in most of the west and southwest cells,but largely absent in the east cell. Figure 2 shows the interpreted top of bedrock contours. It shows that the bedrock in the western part of the site rises to form the blurs at the edge of the South Platte Valley. Also of note is the paleochannel(old stream channel within the bedrock)in the east cell. Plate 1 provides cross-sections developed from the Tucson South geologic model.The cross-sections show the interpreted thickness and extents of the overburden,mud lenses,sand and gravel,bedrock, and water table. The cross-sections also show the potential 1:1 (H:V)mine slopes and 3:1 (H:V) reclaimed slopes. Cross-Section A runs north-south through the western part of the site, showing the flat bedrock surface and western mud lens. Cross-Section B runs north-south through the eastern part of the site, showing the paleochannel,and thin southeastern mud lens. Cross-Section C runs west-east along the northern part of the west and east cells. It shows the rising bedrock surface, western mud lens, and paleochannel. Cross-Section D runs west-east through the southern part of the west and east cells, showing the rising bedrock surface,western mud lens, and the edge of the paleochannel. The quantities and cross-sections described in this memorandum are estimates based on drill logs compiled by Tetra Tech RMC and others. The estimates include geologic interpretation and -2-