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10 <br />changes in the Ash Pit portion of the Johnson Gulch watershed pre- and post-mining. Figure 7 of the <br />accompanying Mattern report (Attachment 2) shows the pre- and post-mining drainage patterns for the <br />Ash Pit and surrounding areas. <br />Table 6 Johnson Gulch Drainage Characteristics within the Ash Pit Pre- and Post-Mining <br />Condition Acreage <br />Drainage Density <br />(mi/mi2) Gradient (%) <br />Sediment Yield <br />Per Acre (tons) <br />Pre-Mining 1,432 3.1 9.3 1.03 <br />Post-Mining 1,435 3.2 7.8 0.56 <br /> <br />Based on the Mattern evaluation, the Johnson Gulch watershed would be slightly larger. The watershed <br />characteristics would be very similar with similar drainage densities and less steep drainage gradients <br />and about half of the sediment yield based on the SEDCAD evaluation. <br />Drainage patterns would be designed to blend with surrounding drainage patterns and would not <br />represent a change from the surrounding drainage patterns. Figure 6 shows the proposed drainage <br />patterns for the AOC variance post-mining topography for the Ash Pit area and the drainage patterns <br />within the surrounding areas. As shown on the figure the proposed post-mining drainage pattern blends <br />with the surrounding drainage patterns. <br />There would not be any significant changes in the post-mining watershed areas that would impact <br />seasonal or flood flows from the post-mining reclaimed areas or adversely affect surrounding ecology or <br />any existing or planned use of surface water or groundwater. <br />5.0 Landowner Agreements <br />Attachment 3 contains a letter of concurrence with the AOC variance from Trapper Mining Inc, the <br />owner of the land associated with the L Pit. Attachment 3 also contains a letter of variance for <br />concurrence of the AOC variance from the Colorado State Land Board owner of the land associated with <br />the Ash Pit. <br />6.0 Conclusions <br />As discussed in the text above and accompanying attachments, a variance from AOC for the final cut of <br />the L Pit and for the Ash Pit would result in a more stable long-term post-mining configuration and in <br />improvements in the overall watershed for the two pit areas. The variance would not impact approved <br />methods for backfilling, grading, topsoil replacement or revegetation. <br />The L Pit shows overall pre-mining topography with slopes of 16° or steeper and steeper slopes that <br />exceeded 20° in the southern portion of the L Pit area. Post-mining the slopes would range from 4 to 14° <br />and would blend with the surrounding topography. <br />The post-mining backfill configuration for the L Pit would decrease the depth of spoil placed at the head <br />of the slope and increase the depth of spoil placed at the toe of the slope to act as a buttress to any <br />movement. Shallower overall surface topography also would increase the stability of the backfilled spoil. <br />The stability analysis showed that the post-mining stability for the AOC variance has improved Safety <br />Factors when compared to restoring the L Pit to AOC.