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1 <br />water conditions and analytical methods which form the basis for <br />this conclusion were developed as part of an extensive drilling <br />program undertaken in the pit area for determining pit wall <br />stability. <br />The south wall of the west pit will experience some seepage <br />towards and into the pit from the Rito Seco through the surface <br />alluvium, if exposed during mining operations, and to a lesser <br />extent the Santa Fe Conglomerate. The extent of the surface <br />' alluvium along the south wall can not be determined until mining <br />exposes this area. The seepage may have some effect on the <br />stability of the south wall. During mining operations the seepage <br />into the pit through the surface alluvium and the Santa Fe <br />Conglomerate will be actively collected or intercepted and <br />managed if necessary to prevent slope deterioration. Following <br />cessation of mining operations, the seepage management operations <br />are expected to cease and additional measures may be necessary <br />to ensure long term stability of the south wall of the Hest Pit. <br />To resolve any concerns about the long term stability of the <br />south wall of the West Pit, BMR will implement engineering <br />solutions to stabilize the wall. Pit wall stability will be <br />' maintained through construction of a rock buttress composed of <br />interburden waste rock materials. The preliminary buttress design <br />is shown on Figure E.3.1-2 and discussed in revised Section <br />E.3.1. Final design for the buttress will be determined when the <br />exact characteristics of the south wall and seepage through the <br />south wall are known. The design will be finalized in the first <br />two years of mining along the south wall or when the weak <br />constituents of the wall have been fully exposed and submitted <br />to the Division for approval. <br />If seepage management operations indicate that there is a <br />1 potential for large volumes of seepage which may affect the long <br />term stability of, the rock buttress, a low permeability barrier <br />such as a slurry wall or cutoff trench will be installed through <br />' the alluvium and keyed into the underlying Santa Fe Conglomerate <br />to cut-off seepage through the alluvium. The preliminary design <br />is shown on Figure E.3.1-2. BMR will evaluate the need for the <br />low permeability barrier during the first two years of mining in <br />the south wall area. if the barrier is determined necessary, BMR <br />kill submit final designs to the Division for approval. <br />' The stratigraphy, material characteristics, ground water <br />conditions and analytical methods which form the basis for the <br />preliminary design of the buttress and low permeability barrier <br />were determined from the initial drilling program and a drilling <br />program conducted in the fall of 1988. <br />By implementing the placement of a rock buttress and committing <br />to evaluating the need for a low permeability element BMR <br />believes that long term stability of the proposed post mining <br />configuration can be ensured. <br />_' <br /> <br />