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<br />-14- <br />filled or stabilized and the area reseeded or replanted if the the <br />rills or gullies prohibit successful re vegetation, and are <br />disruptive to the approved post-mining land use, or may result in <br />excessive erosion or sedimentation. <br />Rule 4.14.6 was rewritten to reflect the nature of semi-arid areas as <br />found in the State of Colorado. Rilling and gullying are part of the <br />natural erosional process in ephemeral watersheds. The elimination of <br />all large rills and gullies, as required by the Federal Regulations, is <br />technically unfeasible. However, it is possible through the proper <br />geomorphic design of reclaimed surfaces and proper revegetation to <br />minimize rilling and gullying (i.e., prevent excessive rilling and <br />gullying). <br />Rills and gullies greater than nine inches have been noted as a <br />continuing problem at the mine and this section of the permit needs to be <br />reevaluated. Since the Colorado program does allow rills and gullies <br />yreater than nine inches if they are not excessive and they are <br />consistent with the approved post-mining land use, CYCC can provide the <br />required demonstration. The demonstration should evaluate the extent of <br />rilling and gullying in adjacent undisturbed areas, the environmental <br />factors causing the rills and gullies in undisturbed areas and the <br />relationship of the reclaimed land to similar undisturbed areas where <br />rills and gullies have formed. A list of possible references is attached <br />to this review which may assist you in the demonstration. <br />The rills and gullies stabilization plan approved in the application is <br />intended to prevent rills and gullies from forming. These include <br />mulching, contour furrows to lessen overland flow, barriers, check dams, <br />erosion stops, matting and roughened surfaces. <br />It is the Division's opinion that the use of contour furrows may be <br />aggravating the rilling and gullying problem rather than preventing its. <br />in some cases. The contour furrows work well to reduce sheet flow during <br />small storm events. However, during large rainfall or snowmelt <br />conditions, the furrows have a tendency to breach in sequence and cause a <br />concentrated flow that results in rills or small gullies. The source of <br />many rills and gullies, as observed in field inspections is where water <br />has breached the furrow. <br />Therefore, the effectiveness of contour furrows to prevent rills and <br />gull,~ies should be evaluated. The evaluation could include an experiment <br />using different treatment practices for gullies, designing furrows with <br />shorter lengths or eliminating furrows on some slopes and comparing the <br />rills and gullies on the furrowed slopes to the unfurrowed slopes. <br />In order to resolve this problem the Division finds that CYCC must <br />evaluate the effectiveness of the currently approved rill and gully <br />stabilization plan, especially the use of contour furrows. In those <br />cases where CYCC determines the rills and gullies are not excessive and <br />they are consistent with the approved post-mining land use, the <br />demonstration required by Rule 4.14(2) must be made. <br />