2002-03-04_REVISION - M1986015 (8)

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RECLAMATION PLAN Final slopes into the reservoir and inside the slurry wall location will be graded to a slope not steeper than 3:1 and generally to 4:1. This provides the best protection for wave cut action on the reservoir shore so wave action does not cut back into the location of the slurry wall and thereby disrupt its integrity. Backfilling outside of the slurry wall location will be to a slightly lower elevation than the zone where the slurry wall will be installed. The depth of backfill here will be reduced to provide for the revegetation plan in those areas. Materials Handling -Slurry Wall Construction In many slurry wall applications the slurry wall is installed prior to mining the area. This greatly reduces the amount of dewatering required to create a dry pit operation. At this site, the slurry wall will not be installed until after the mining is completed. Therefore, rather than the slurry wall construction description being in the mining plan, it is in the reclamation plan because the slurry wall is a reclamation action. As shown on Exhibit F-1, most of the slurry wall installation will occur in backfilled material. Only portions of the slurry wall will be installed in native material. The slurry wall on the west and part of the north side of the reservoir containment will be placed in native material. Everywhere else it will be installed in backfilled overburden. There are some advantages to installing the slurry wall into backfilled overburden rather than native material. The overburden on this site ranges from a sandy to clayey material whereas most of the native material is a porous sand and gravel. By installing the slurry wall into sandy to clayey material it is less likely that leaking will occur. The sand and clay itself will help to seal the reservoir basin with the slurry wall providing the final seal. If installed in native material, the only seal would be the slurry wall itself. Another advantage to installing in overburden is protection of the slurry wall structure itself. This is particularly true in the southwest and southeast corners of this phase. On the maps it can be seen that each of these corners could potentially be affected by the river if the cutting bank of the nearby meanders were to extend northward into the mined area. This is particularly true of the southwestern corner of the site. Although this bank has been well armored with concrete patties and `5etties" as well as the continuing establishment of woody growth along the bank (previously completed under a Nationwide 404 permit), further protection of the slurry wall is advantageous for long term use of the site for water storage. If the slurry wall was installed only 100 to 150 feet from the river in native material, severe river flooding might cut away the armored bank and rather easily cut through the gravel and into the slurry wall. But if the mining Pueblo East Pit Amendment Exhibit E Page 4