2007-01-31_REVISION - M1986015 (2)

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bottom of the topsoil layer and the gravel layer is considered overburden, even though i[ may also be considered subsoil. On [his site overburden does no[ appear to have much value as a growth medium in the same sense as topsoil. It is often saline and/or alkaline, or it contains other properties that does not make it suitable for use as a dryland growth medium. However, disposing of [his material as backfill on land where groundwater is near the surface and wetlands will be created is a suitable use of the overburden. The leaching effect in a wetland situation will remove much of the undesirable chemistry and the constant exposure [o hydric conditions makes i[ useful in wetland situations. Many wetland plants are also adapted to such conditions. Other stripped overburden will either be temporarily stockpiled near locations where it will be used as backfill, or it will be disposed of immediately into an area that needs to be backfilled. Thus, overburden storage should not become a serious problem. To reduce the amount of land that might require augmentation where groundwater is exposed, use of the overburden to backfill mined areas is highly beneficial. Requirement: The arrangement of berms and sediment basins in Phase 1 will be done such that all basins have at least one side connected to adjacent undisturbed land, and groundwater can continue to flow through Phase 1 [o lands to the east of [he operation. The actual arrangement shall be at the discretion of the operator so long as the connection and flow-through requirements are met. The arrangement shown on Exhibit C-4A is a possible arrangement [hat would meet the requirements. Other configurations are possible that would meet the requirements. DISCUSSION: Backfilling Phase 1 will not be done by simply dumping the overburden in the pit. Instead, overburden will be used primarily in constructing the individual sediment basin cells where fines from the processing of gravels at the processing plant can be contained. It has been found [hat [he bermed boundaries of these cells need to be well compacted to be stable and not subject to breakage. In / the past, where such structures have been built, high compaction results in a very stable and practically ~/ seep-free edge for sediment basins. Initially this is important because these cells are primarily containing wash water from [he plant discharge. But as the sediment accumulates in the cells, [he water is displaced by the sediment which results in an even stronger structure. Thus, much of the overburden removed from Phase 1 and from Phase 2 will be used to construct the berms that define the cells. The cells, of course, are put in locations where [he gravel has been removed. Bu[ the pattern of constructing the cells is initially biased toward cell construction along the southern side of [he pit. Only later will cells be constructed toward the middle of the pit. There are three reasons for preferring the outer edges of the pit for initial cell construction. First, it greatly strengthens the outer wall of the open pit. This reduces the possibility of breaching the pit by Pueblo East Pit Amendment 3 (2007) Exhibit D Page 28 of 34