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Silver Wing Mine NOI <br /> 4. Sedimentation Pond Cleaning Plan and Sludge Disposal <br /> The Sedimentation Pond was constructed as part of NPS 319 Grant from the Colorado Department of <br /> Public Health and Environment. The pond dimensions are shown on the attached original construction <br /> sketch,and the pond is lined with a 40 mil HDPE liner. <br /> Pond Cleaning Plan <br /> For purposes of cleaning the Sedimentation Pond,the portal discharge water will be routed around the <br /> pond to permit removal of the sludge in a solid/semi solid state by mechanical means (see Exhibit H). <br /> As shown on the attached original construction sketch of the pond,the center section of the pond has a <br /> flat bottom with side slopes of 2H:1V And end slopes of 3H:1V. (Note: the Sedimentation Pond was <br /> constructed in compliance with this plan.) The plan is to utilize an excavator bucket to remove the <br /> sludge from the flat bottom section of the pond. The material on the side slopes and the ends which sits <br /> on the slick HDPE liner will slide by gravity to the center flat bottomed section for removal. It is <br /> expected to remove approximately 80%to 85%of the solids by this method. No attempt to completely <br /> remove all of the sludge will be made—a small layer will be left on the bottom of the pond as a <br /> protection for the liner. The excavator bucket edges will be wrapped with sheet rubber or other <br /> suitable material to protect the liner from accidental damage. <br /> The existing Sedimentation Pond has approximately 1.5 feet of freeboard or is essentially full. When <br /> the pond is empty, allowing for 1 foot of freeboard,the live volume is approximately 6,400 cubic feet or <br /> 48,000 gallons. At 50%full,the live capacity is approximately 3,200 cubic feet or 24,000 gallons. At 50% <br /> full the residence (settling)time at 20 gpm (estimated average portal flow) is 20 hours. The estimated <br /> amount of sediment(primarily limonite) remaining in the bottom of the adit is approximately 3,000 <br /> cubic feet. Any additional sedimentation from the planned investigative programs are expected to <br /> produce minor amounts of solids (less than 500 cubic feet). <br /> In the event,that the liner is damaged,one of two solutions will be employed: <br /> 1. If the damage is small in nature,then the liner will be repaired with a heat fused patch. <br /> 2. If the damage is significant and patching is impractical,then the existing cavity will be cleaned of all <br /> sludge and a new HDPE liner will be installed over the existing liner. The existing liner will serve as <br /> bedding for the new liner. <br /> Sludge Disposal <br /> The Sludge Material will be placed in an on-site trench excavated in an abandoned roadway that is clear <br /> of drainage way and covered with the native material borrowed from the excavated trench. The trench <br /> will be lined and covered with PVC or LDPE liner to prevent any degradation of the background <br /> environment. The Sludge solids have been tested (Exhibit H-2) and pass TCLP requirements for metals. <br /> 1 <br />