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backfilling the basin area with spoils, grading to blend with surrounding areas, topsoil replacement, and <br />revegetation. <br />Water Handling and Quality Considerations <br />Given that the Thickener Sump is designed and utilized in overflow, emergency, or unplanned maintenance <br />situations, to contain the partial or full contents of the Thickener Tank, the water and other materials in the sump <br />would not normally be suitable for direct discharge, due to high suspended solids concentrations. The current <br />float pump installation on the Thickener Sump is designed to route any discharge from the sump back to either <br />the Thickener Tank or the Coal Preparation Plant make-up water inlet, avoiding the need for discharge to either <br />sedimentation ponds or surface drainages. It is anticipated that some coal solids will settle-out and accumulate <br />in the sump. The sump is designed so that small mobile equipment can access the sump basin to clean-out any <br />significant accumulations of solids. Sump clean-out will be conducted on an as-needed basis, following <br />removal of any water and slurred coal (pumped back to the Thickener Tank), and the sediments will be loaded <br />into trucks and hauled to the existing coal refuse disposal facility. <br />Incident Precipitation and Run-On -The surface area of the Thickener Sump is only approximately 0.086 acres, <br />so water contributions from normal incident precipitation are negligible (0.013 ac-ft fora 10-year, 24-hr event or <br />2.9 percent of pond capacity). A drainage collection ditch (Ditch D-2) intercepts any surface runoff from the <br />south and routes it around the Thickener Sump to Pond D and other surrounding areas are graded to drain away <br />from the sump, so water contributions from run-on are similarly negligible. For design dewatering purposes, the <br />contribution from incident precipitation for the Probable Maximum Precipitation (PMP) event (13.2 inches over <br />24-hours) is 0.09 acre-feet, or approximately 21.5 percent of pond capacity and slightly over 1-Foot of depth <br />with the pond near its maximum design water level. With a capacity of 250 gpm, the Thickener Sump float <br />pump installation can discharge the accumulated precipitation from the PMP over a period of about 2.0 hours. <br />Water Ri¢Itts -Because any water, other than the negligible incident precipitation, discharged to the sump is process <br />water that will be recycled back into the Preparation Plant system, all such water is covered by existing water rights <br />associated with the process water supply. <br /> <br />TR 05-48 Ex8W-2 Revised - Mazch 2005 <br />