2016-06-08_PERMIT FILE - C1982056A (4)

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Soil Stabilization Plan •Proper site preparation and soil handling strategies will be utilized to control wind and water erosion. The movement and manipulation of topsoil materials in a moist condition minimizes wind and water erosion. As explained by Bauer et al. (1976), a protective surface seal develops as silt and clay fractions bond together after reapplication of topsoil. This phenomenon is attributable to the rapid evaporation of surface moisture from redistributed soil materials. Disturbed areas will be subjected to final grading, but will remain in a rough condition to assist stability and resist slippage of topsoil after reapplication. Leaving the graded surface in a roughened configuration also improves moisture permeability between the spoil/topsoil interface (Bauer et at. 1976). Scrapers will reapply topsoil along the contour whenever possible. The tracks made by scrapers create a "terracing" effect that helps to reduce overland surface flow and the potential loss of topsoil. Following topsoil reapplication, but before seeding, the topsoil will be graded to insure a uniform and stable thickness which will be consistent with the reclamation and revegetation requirements. Prior to seeding, which will be initiated as soon as practical after final grading, topsoiled sites will be chisel -plowed in order to alleviate compaction and promote water infiltration. Chisel -plowing has been a highly effective means of temporary stabilization prior to vegetation establishment. Dollhopf et al. (1977) reported that chisel -plowed topsoil at the Savage, Beulah and Colstrip Surface Mines were only surpassed by the radical treatment of dozer basins in reducing overland water flow from reclaimed mine sites. The water detention capacity of chisel -plowed topsoil is reported by Dollhopf et al. (1977) as 176,400 liters per hectare, or 2,521.3 cubic feet per acre. Another stabilization technique which serves to minimize erosion is contour furrowing. Disturbed land within the proposed permit area will be contour furrowed following seeding. A typical cross section of a contour furrow is depicted in Figure 12, Design of Typical Contour Furrow. According to data derived from studies at the Energy •Mine No. 1, the water detention capacity of these furrows, when spaced thirty feet apart, is 2,599.7 cubic feet per acre. A brief evaluation of the total projected impact from a 10 -year, 24-hour rainfall event is illustrative of the effectiveness of chisel plowing and contour furrowing techniques. The projected precipitation from a 10 -year, 24- hour rainfall event is 1.8 inches, or 6,534 cubic feet per acre. The water detention capacity of reclaimed sites prepared with both chisel -plowing and contour furrowing techniques amounts to 5,121 cubic feet per acre, or 78% (1.41 inches) of the projected 10 -year, 24-hour rainfall event. Therefore, the total amount of water capable of becoming surface runoff from a rainfall event of this magnitude is only .39 inches. Research recently conducted at Energy Mine No. 1 and at the Edna Mine demonstrates that a reasonable estimate for infiltration of water on reclaimed land is 85% of detention capacity (McWhorter 1979; John Gilley, USDA -SEA unpublished data). Hence, the infiltration potential of reclaimed lands within the proposed permit area is 1.19 inches or approximately three times greater than total potential surface water runoff (.39 inches) from a 10 -year, 24- hour rainfall event. Consequently, the detention capacity and infiltration potential of reclaimed lands taken together, will allow all rainfall to be potentially available for plant growth, and will minimize runoff from reclaimed lands. The aforementioned surface treatments are designed to reduce overland flow of water and shall be supplemented by techniques suggested by Clyde, et al., (1978) if the need arises. The techniques recommended by these researchers include the use of barriers, check dams, erosion stops, matting and roughened surfaces. These treatments can be implemented with various kinds of straw bales, nettings and mattings to effectively reduce overland flow. If results of the annual rill and gully survey indicate excessive erosion has occurred, Twentymile Coal Company will initiate remedial measures. Gullies may be blocked with one of the above-mentioned treatments to provide the opportunity for natural stabilization through the growth of vegetation. Corrective actions, where needed, will be completed by October 31 of the year following the survey. RN08-05 2.05-107 03/12/10