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SCB backfill will be a composite of selected excavated material from the trench, borrow clay, bentonite slurry, dry powdered bentonite, and Portland cement. SCB backfiti is typically mixed in mixing boxes or alongside the trench with a dozer and has the consistency of wet concrete when placed. The SCB backfill is placed from one end of the trench and advances across the trench at aself-seeking slope typically inclined at 5:1 (horizontal :vertical). This method of backfilling is known as the continuous trench method. The Backfill Mix Design Report presents performance results for backfill and slurry from a demonstration backfill mix design for this project. 3.06 Slurry Wall Working Platform and Construction Limits Slurry wall construction requires a stable and flat working platform from which excavation, backfill mixing, and backfill placement can occur. The perimeter dirt roads provide a basis for a suitable working platform within the City's property boundary. Some earthwork may be required by the contractor to achieve a minimum working platform width necessary for construction in areas where the current roadway is not wide enough of flat. Drawing 104 shows working platform configurations extending from the slurry wall centerline to achieve additional width. The working platform shall not exceed a grade of one percent and an elevation lower than 4,663 ft (NGVD 1929 datum). This elevation represents the lowest existing ground surface elevation encountered along the alignment. As shown on Drawing 104, the portion of the ' working platform in the immediate vicinity of the slurry wall centerline will require compaction when fill is placed to enhance near surface trench stability. The construction limits are shown on Drawings 102 and 103. An area designated to serve as amain staging and support area is located at the southeast comer of the Site. Construction activities will not be allowed within the banks of the Cache la Poudre River. Site access is from 25th Avenue as shown in Drawings 101 and 102. 3.07 Clay Borrow Area The clay borrow areas will provide clay and silt to be used in the backfill mix as needed. The clay borrow areas include the natural overburden in the embankment located between the two gravel pit ponds and overburden material stockpiled on the southeast comer of the site. The locations of the borrow areas are shown in Drawing 102. The Geotechnical Data Report presents a description of subsurface conditions at the clay borrow areas. 3.08 Construction Water Water for construction activities including slurry and backfill mixing is available from the two ponds located within the site. The Backfill Mix Design Report presents water quality information for [his water.