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selected, thereby compromising the integrity of the wall if the cut goes very deep into the slurry wall I <br />corridor. [f a steel wall is installed destroying [he wall with headward erosion is no[ such a risk, but <br />•~- t <br />headward erosion could expose the wall which could cause a portion to collapse. Repair of suc~i a <br />collapse, after replacing the slope, would be easier and likely more effective than would occur if a slurry <br />wall was installed. <br />Furthermore, volume analysis has shown that if the pi[ slopes in Phase 2 are constructed of <br />backfill, primarily overburden, there will be insufficient material left to complete the backfilling of <br />Phase 1 even if other sources of fill from this site are acquired. Although this means a loss of gravel <br />reserves in the unmined slopes, mining than gravel would likely make the reclamation plan for this <br />operation unable to b comp t ~ y, p ~ ~~ <br />If a steel wall is installed rather than a slurry wall [hen it might be feasible to construct slopes of <br />backfill material. But, as noted above, it is not expected that volume of material will be available. If <br />sufficient fill is available and if a steel wall is installed, then constructing all or a part of the slope with <br />backfill will be acceptable. <br />Requirement: In the initial mining area of Phase 2 (northeast corner) the south slope adjacent to <br />the groundwater barrier wall will be mined to a grade not steeper than 3:1. The other three slopes <br />can be steeper. <br />DISCUSSION: The first mining in Phase 2 will occur in [he far northeastern corner of the site. <br />This small area is located outside the groundwater barrier wall and will therefore need to be dewatered <br />during the extraction. All of the edges of the pit in this area, except for the south edge, will be similar to <br />those created in the mining of Phase 1, that is, they will be fairly steep. The south edge of this pi[ will be <br />mined at a 3:1 slope because that slope is adjacent to [he groundwater barrier wall. Once the area is <br />mined, the water will be allowed to fill the pit with backfilling occurring over time and into the small <br />lake. This area will also be used during the dewatering of the remainder of Phase 2 for both [he initial <br />dewatering and any maintenance dewatering. <br />Requirement: Gradual backfilling of [he initial mining area in Phase 2 will use a mixture of <br />solidified waste concrete and overburden. <br />DISCUSSION: The purpose of this area is to no[ only provide a settling basin during the <br />mining, but a smooth connection from [he 25'" Lane residential areas to the river so groundwater flowing <br />through [he 25`" Lane area has an outlet that avoids the creation of closed groundwater pockets. This will <br />allow water containing waste from septic systems to flush out of the area so water quality does not decline <br />as would occur if there were groundwater pockets created where contaminated water would accumulate. <br />Pueblo East Pit Amendment 3 (2007) Exhibit D Page 32 of 34 <br />