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1 <br />~l <br /> 2. Provide an outfall for the impounded water either by open ditch or <br /> pipe. <br />' 3. Allow the impoundment to eliminate itself naturally by siltation from <br />upstream. <br /> A significant problem in the first two solutions is getting any type of <br />' equipment from the haul road down to the blockage area to perform the <br /> necessary work. It is suggested that either an access road be cut aloni;the <br /> slope for this purpose or equipment be lowered by cable and winch from the <br /> haul road directly down the slope. An access road along the slope would <br /> likely be difficult to construct and would require obliteration and reveget«tion <br /> after work is complete. Lowering equipment directly down the slope would <br /> have little impact environmentally, but may be difficult depending on the <br />' equipment required to do the corrective work. <br /> The greatest unknown element in selecting a solution is the stability of <br /> the slide and the affect of disrupting the toe of the slide during the remedial <br /> activity. It is recommended that a qualified geotechnical consultant, <br /> experienced in dealing with natural slope stability problems be contacted for <br /> an opinion regarding disruptive activity at the toe oP the slope. <br /> It is recommended that a combination of filling the impoundment area and <br /> cutting an open trench beyond the toe of the slide material be considered as <br />' the most practical and efficient solution. The degree to which each is clone <br /> depends largely on the geotechnical recommendations. <br />' The vegetation in the impoundment area is all dead and there is virtually <br />no vegetation on the slide material. The slide has created a relatively level <br />terrace area at the toe. This terrace is 40'-50' wide and is 5'-6' above the <br />' contact between the slide material and the natural ground. It is suggested <br />that using the slide material for a depth of 3'-4' off oP the terrace to fill the <br />impoundment area be considered. In addition, a trench could be excavated all <br />in the natural ground material just beyond the toe of the slide to a depth of <br />' 4'-6' to effectively lower the outlet ditch and water surface. This trench <br />length would need to be 30'-40' depending on depth to daylight. A <br />combination of filling and lowering the outlet should result in reducing the <br />' impoundment and hopefully eliminating it completely. Eventually, natural <br />siltation would complete the filling. <br />A schematic cross-section is included to illustrate this combinatlon of <br />filling and outlet trench construction. The unknown element, as indicated, is <br />the impact of this activity on the stability of the slide, but given the <br />relatively level nature of the terrace at the toe and the concept that it would <br />' be lowered together with the trench construction in undisturbed material, .it is <br />felt that this activity would not weaken the existing condition significantly. <br />The geotechnical recommendations will hopefully substantiate this observation. <br />1 <br />3 <br /> <br />