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Chapter II <br /> Obstructions to emergency and/or principal spillways; <br /> Properly cleaned, maintained dewatering devices; <br /> Sediment storage volume; <br /> Sloughing, tension cracks , piping, etc. <br /> The sediment ponds have been designed to be dewatered after each <br /> major runoff event. The ponds will be dewatered by natural seepage <br /> and infiltration, or through the use of an automatic or manual <br /> dewatering device. The automatic dewatering device is designed to <br /> be non-clogging and to have a discharge rate that will achieve and <br /> maintain the required detention time. The devices have been <br /> located at the lower elevation of the 10-year storm capacity <br /> volume, although not below the maximum elevation of the sediment <br /> storage volume. <br /> Sediment pond maintenance includes removal of sediment when <br /> sediment storage exceeds 60% of the designed sediment volume. <br /> The ponds at Outfalls 001 , 020 and 016 are cleaned as necessary, <br /> throughout the year. Cleaning of the other sediment ponds is done <br /> when ground conditions are dry enough to allow access by the <br /> necessary equipment. This is generally in the summer, and cleaning <br /> usually progresses from ponds at the lower elevations to ponds at <br /> the upper elevations (according to the pattern of snowmelt) . <br /> The muck removed in cleaning of the sediment ponds is placed on the <br /> Sutey coal refuse pile (MR. July 11, 1985) . In addition, approval <br /> has been given for placement of sediment pond cleanings on the rock <br /> tunnel disposal area. (MR-8 . March 15, 1988) . Placement of pond <br /> cleanings on the rock tunnel disposal area is done so as to <br /> maintain surface slopes and adequate drainage of the pile. (MR-18 . <br /> July 1, 1989) . Approval has been given for placement of pond <br /> cleanings from the four ponds at Portals No. 1 and No. 2 on Pad #4 , <br /> which is a former storage area situated near the ponds (MR-28. <br /> July 28, 1990) . Approval has been given for continued placement of <br /> pond cleanings on the old refuse pile prior to topsoil placement <br /> (MR-29 . August 16 , 1990) . <br /> In addition, ditches and culverts are inspected periodically and <br /> cleaned as necessary to keep them open and free of debris. The <br /> timing for clean-up at the end of winter also depends upon when the <br /> ground dries enough to allow access for the necessary equipment. <br /> 5. Topsoil. <br /> a. Existing Topsoil Stockpiles. <br /> In the previous permit term (1983-1988) surface disturbance <br /> resulted from expansion of the coal refuse disposal areas, the <br /> Adit/Rock Tunnel spoil disposal area, and upgrading of the <br /> hydrologic diversion and sediment control systems. Topsoil and <br /> soil horizons, as required by MLRD, were salvaged and stored. <br /> 33 <br />