2007-01-31_REVISION - M1986015 (2)

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MINING PLAN Wash water for the processing of gravels is taken from the lake near the river. This lake is part of the sediment control circuit. Therefore, when the plan[ is operating the draw down of the lake helps reduce the volume discharged [o the river, but the discharge is still far more than could possibly be used for [he plant. The wash water is pumped to the plant in a separate, closed line. During some periods, [he wash water may be derived directly from the mining pit by altering the piping path. The following diagram (Figure 1) shows [he current dewatering and process water circuit. This diagram is taken from the Amendment 1 plan. It is expected this method will continue to be used as it is quite successful. The only problem that might occur is if [he amount of water [hat needs [o be pumped out, especially in the spring of the year when the river is running high, exceeds the capability to pump it out. That has no[ occurred, but [he limit is being approached. On the plus side, when water tends to build up in [he pit due to input exceeding output it dilutes sediment in the water resulting in very clear and clean water except in [he immediate vicinity of the mining. The size of the pit also provides many locations for establishing temporary sumps for pre-settling and clarification of the water prior [o pumping into the sediment control system. One action that would improve matters considerably is to establish more sediment basins against the wall of [he pi[. This would reduce the input of water greatly. PHASE 2: Requirement: All dewatering of [he Phase 2 area shall be done via the initial pit in the northeastern corner of Phase 2. Discharge from [he initial pi[ may be into Phase 1 or into the adjacent existing channel (see next requirement). DISCUSSION: The problems in Phase 2 are much simpler to deal with because the groundwater barrier wall will likely be installed before or soon after the excavation is begun. Dewatering will be into the initial pit in the northeast corner of the site or directly into Phase L (see Exhibit C-4B). Most likely it will be the former with the initial pi[ becoming the dewatering settling basin. Water from there can be pumped to Phase I, if the volume is not so great that i[ overloads the capacity of the Phase I system. Requirement: If discharge is into [he adjacent channel then a series of step dams must be installed in the channel to reduce water velocity and remove sediment prior to its discharge into the river in accordance with the standards se[ forth in the NPDES permit. DISCUSSION: Alternatively, the water from the initial pit could be discharged to the river via [he adjacent existing drainage channel. However, that route may not provide sufficient control of Pueblo East Pit Amendment 3 (2007) Exhibit D Page 20 of 34