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The location of the interceptor trench was selected to reach as deeply into the landslide mass as <br />possible and the intercept groundwater flow higher on the landslide before it can reach the area <br />around the left dam abutment. To achieve these objectives, it was decided to install this trench at the <br />slope break at the back (south side) of the flat portion of the borrow area located south of the access <br />road. Because the borrow area would excavate into the landslide mass, the trench could be excavated <br />deeper into the landslide colluvium, thus further reducing porewater pressures. The interceptor trench <br />will be excavated nearly east-west through the back of the borrow area and extend across the access <br />road to exit into the channel that comprises the lower portion of the spillway. It will be backfilled <br />with free-draining, granular material. <br />The upper pond ditch will drain the year-round water that collects at the base of the landslide scarp. <br />This ponding water accumulates about 650 feet southeast of the access road and acts as a source of <br />water infiltration into the landslide mass. The ditch, which will be approximately 150 feet long, will <br />drain this wetland area and carry the water into the natural drainage that is located near the camping <br />area on the south side of the access road. The ditch will not be backfilled with freely draining <br />material, but will consist of an open channel. <br />P:\Mpls\06 CO\26\0626067\WorkFiles\DesignReport\FINAL\DesignReportFINAL.doc 45 <br />