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Measurement and Payment Payment for construction of the rolled dip shall be at the unit price bid in Item 2 of the Bid Schedule per rolled dip constructed. Such payment shall be considered full compensation for all labor, materials, equipment and all other items necessary and incidental to the construction of the rolled dips. Payment shall be as this task is completed and approved by the PROJECT MANAGER. Task 3 Sediment Pond Dewatering Device Repair A sediment pond is located at the upper end of the Pit 4 haul road. This pond is known to leak water from the base of the corrugated metal pipe (CMP) dewatering device. The goal of this Task is to seal the base of the CMP through excavation and placement of bentonite and concrete. The pond dewatering device is a forty eight inch (48")CMP riser, which is about ninety two inches (92") tall, as measured from the base of the CMP at the water line. A horizontal CMP spillway is connected to the CMP riser on the embankment side of the riser. The integrity of the spillway (ie: its elevation and slope angle, as well as the integrity of its connection to the riser) must be maintained throughout the duration of the Project. The riser is positioned at the base of the pond embankment so that the bottom of the riser is located just above the base of the pond. The pond embankment rises from the base of the pond at an approximately 2H: 1V slope to its crest. The base of the riser is anchored by a concrete apron of approximately ten inches (10") in width. The thickness of the concrete apron is unknown. Water is observed to pipe around the outside of the concrete apron. In order to remediate problems associated with the CMP riser, CONTRACTOR shall accomplish the following: - The CMP riser shall be cut so that the top surface of the riser is six inches (6")above the elevation of the embankment immediately adjacent to the riser. Because the embankment slopes upward to its crest, the CMP cut will parallel the slope angle. CONTRACTOR shall properly dispose of the remnant CMP material off site. - The embankment shall be excavated a minimum of five feet (5') in all directions (including towards the pond) from the CMP riser. The depth of the excavation shall be no less than one foot six inches (1' 6") below the top of the existing concrete apron. CONTRACTOR shall exercise appropriate care and caution in order to maintain the integrity of the CMP riser and of the horizontal CMP spillway. - Six inches (6") of hydrated bentonite shall be placed on the base and on the sides of the excavation. The bentonite shall be sufficiently hydrated so that it slumps rapidly when placed on a board elevated to forty five degrees (45 ~). Due to the Fluid nature of the bentonite, it will be necessary to construct and place a form within the excavation prior to placing the bentonite slurry. - Concrete, having a minimum compressive strength of 3,500 psi at twenty eight (28) days will be poured into the excavation after placement of the bentonite. Concrete maybe mixed at the site, or may be delivered as'ready mix' at CONTRACTOR'S option. If the concrete is mixed on-site, equipment and mixing procedures shall conform to ACI 301, Chapter 7. If'ready mix' is used, it shall be mixed and transported in accordance with ASTM C 94. Concrete shall be thoroughly compacted by means of a suitable mechanical vibrator. - Upon completion of concrete curing, the dirt excavated from the embankment shall be replaced on top of the new concrete. The material shall be replaced in such a manner so that the slope of the embankment is returned to its original condition, and so that the top of the CMP riser is six inches (6") above the elevation of the embankment slopes. The FlII shall be mechanically compacted during placement. - A hinged steel grate shall be placed over the top of the CMP riser. The grate shall be constructed using 1-1/4" structural rebar welded on eight inch (8") centers in both directions. Two (2) extra heavy duty hinges, having non-removable pins, shall be welded to the CMP riser and to the steel grate cover on the uphill side of the riser. A hasp, constructed of 3/8" steel, and having a circular hole of/z"diameter, shall be welded to the CMP riser and the steel grate on the down hill side of the riser.