2014-08-19_PERMIT FILE - C1980007 (10)

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• Segregation of materials during placement is minimized Based on the permeability for this blend and an assumption that there is one 7.5 gpm seep every 50 feet along the length of the slide area, and assuming that bedrock benches have only a gentle slope to the north, a thickness of 4.8 feet was computed for the drainage blanket. This was rounded to a nominal thickness of 5 feet for construction purposes to give a small factor of safety and to allow for variability in the bedrock surface. The recommendation for the thickness of the drainage blanket against nearly vertical rock faces was that it could be thinned to 3 feet, which was a reasonable minimum constructible dimension. A toe drain consisting of an aggregate filter around a slotted high-density polyethylene pipe was constructed adjacent to the northern limit of the drainage blanket to collect seepage water and convey it into the main sediment ditch as shown in Figure 4. The toe drain is shown on Figure 5. In the West Slide area, a similar construction methodology was employed. The main difference was that a much shorter chimney drain was installed. The soils to the north of the bedrock bench were found to be dry when excavated, so these soils were backfilled to approximately pre -slide slopes and compacted. Since the soils to the north of (lower than) the bedrock bench were dry, drain construction in this area was limited to the chimney drain only; a drainage blanket was not placed on the bedrock bench. The chimney drain was near vertical and placed directly against bedrock (extended about 2 feet above the top of the bedrock face to ensure that all bedrock strata are intercepted). Furthermore, a 16" HDPE pipe (slotted in the seepage area) was installed in a shallow trench along the upslope (south) edge of the drainage blanket adjacent to the bedrock face. This pipe was sloped downward to the east until it reached the 12" HDPE (solid wall) coming down from the upper interceptor trench further east. These pipes then were extended parallel to each other down the hillside to discharge the clear water past the sediment ditch, ultimately draining into to the North Fork of the Gunnison River. 2.3 Construction Observation Representatives from Barr and a subconsultant (Rock Logic Consulting) were present on a part-time basis to observe the removal of material and the construction of the design elements described above as the work progressed. Nuclear moisture -density testing was performed by Lambert & Associates periodically during construction activities. Construction moisture -density test results and particle size gradations are provided in Appendix A. P:\Mpls\06 CO\26\06261003 Haul Road Slide Repair\WorkFiles\Report\MCC_Slump_Repair-Instrumentation-Drain Rev 2012-12-12.docx 7