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northern abutement of Streeter Canyon and the additional load <br />imposed by the dump will be small. <br />l Some collapse of the old mine to the west due to the <br />dump surcharge is possible. However the chances of sink- <br />holes appearing at the surface of the dump must be regarded <br />as low due to the bridging nature of the dump material it- <br />self. Should these features develop they should occur con- <br />~~ currently or shortly after placement of the waste dump. <br />6.0 COiiCi.i1SI0NS AND RECO\71+4E_":DATIONS <br />In general, the proposed waste dump slope design is <br />rather conservative and could be increased provided that ground <br />water is adequately controlled. Specifically, our conclusicns <br />and recommendations include: <br />1. Present design of 4:1 slopes is adequate if not <br />somewhat conservative. <br />2. It appears feasible to increase the slopes to 2:1 <br />provided ground cvater does not build up •.vithin the <br />fill. Significant ground water buildup will pro- <br />babl}% not occur for several reasons. The area has <br />~+ low rainfall. The natural sorting of the end dump <br />fill procedure will tend to produce a coarser <br />gradation at the bottom of each lift which may <br />act as a drainage blanket. Als~.~, the waste dump <br />fill will probably have a high permeability once <br />your excavation works well into the bedrock and away <br />from the poorer shallow materials. Thus, ~.ve recom- <br />mend that filling can begin based on a final design <br />~ slope of 2:1. <br />i <br />F`l <br />