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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 /> Sediment pond maintenance Includes removal of sediment when sediment storage exceeds 60%of the <br /> designed sediment volume. The sediment is removed by using either a small dragline or a backhoe. <br /> The sediment ponds have been designed to be dewatered after each minor runoff event. The ponds will <br /> be dewatered by natural seepage and infiltration, or through the use of an automatic or manual dewatering <br /> device. The automatic dewatering device Is designed to be non-clogging and to have a discharge rate <br /> that will achiev and maintain the required detention time. The devices have been located at the lower <br /> elevation to the 10-year storm capacity volume, although not below the maximum elevatton of the <br /> sediment storage volume. <br /> The ponds are cleaned, if necessary, at the end of winter,when the ground around them becomes dry <br /> enough to allow access by the necessary equipment. This is in the late spring to early summer, and <br /> usually progresses from ponds at the lower elevations to ponds at the upper elevations (according to the <br /> pattern of snowmelt). <br /> MLRD approved a minor revision July 11, 1985, allowing Mid-Continent to place the muck from cleaning of <br /> the sediment ponds on the Sutey coal refuse pile. The muck is truck-hauled to the refuse pile and placed <br /> at random intervals across the pile. The refuse pile is south-facing and dries out relatively fast. The coal <br /> refuse Is spread out in a fan shape one to two feet thick and sediment from the ponds is spread out in <br /> layers six inches or less in sections of up to approximately 200'width across the top of the pile so that it's <br /> not concentrated In any one area. <br /> Approval has been given for placement of sediment pond cleanings on the rock tunnel disposal area <br /> (MR•8. March, 1986). Approval has been given for placement of pond cleanings from the four ponds at <br /> Portals No. 1 and No.2 on Pad#4;which is a former storage area situated near the ponds. (MR-28. July, <br /> 1990). <br /> Ditches and culverts are inspected periodically and cleaned as necessary to keep them open and free;of <br /> debris, The timing for clean-up at the end of winter also depends upon when the ground dries enough to <br /> allow access for the necessary equipment. <br /> 5. Topsoil <br /> a. Existing Topsoil Stockpiles. <br /> In the previous permlt term (1983.1988) surface disturbance resulted from expansion of the coal refuse <br /> disposal areas,the Adit/Rock Tunnel spoil disposal area, and upgrading of the hydrologic diversion and <br /> sediment control systems. Topsoil and soil horizons, as required by the MLRD,were salavaged and stored. <br /> 33 <br />