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Required shrub stem densities. The vegetation data also were evaluated to determine whether the <br />shrub revegetation efforts were progressing toward the approved postmining land use of rangeland. <br />For the future Phase III bond release. range sites A and B have a minimum woody plant stem density <br />requirement of 400 stems per acre, including the stems in the shrub clumps. In addition. the woodv <br />stem count must be at least 3763 stems per acre within the shrub clumps. Range si[e C dues not have <br />a woody plant stem density standard. <br />Actual shrub stem densities. Table 2.2-1 of the bond release submital shows the woody plant stem <br />count outside shrub clumps already surpassed the Phase III approved standard in six of the seven <br />blocks that have a woody plant stem density standard. The density of stems per acre ranged from 21=1 <br />to ~ 16 more than the density standard and the averaee density was 369 stems per acre more than the <br />standard. The one block that did not meet the required stem count was block CB39-90, which had <br />only 20~ stems per acre, 19~ stems per acre less than the standard. The vegetation data did not reveal <br />whether this block would have exceeded the Phase III standard if the shrub clumps had been <br />included in the count. The vegetation data also did not show the stem count within any of the shrub <br />clumps. Nonetheless, it would appeaz that the shrub data that is presented in the bond release <br />package supports Trapper's assertion that the reclaimed sites being proposed for Phase II bond <br />release aze progressing towazd the postmining land use of rangeland. <br />Sediment Yield <br />Use of SEDCAD+ rather than water sample data. The most straightforwazd approach to <br />determining if post-mining sediment yields exceed pre-mining yields would be to compare pre- <br />mining and post-mining total suspended solids (TSS) field sample data. Such a comparison would <br />not be valid in Trapper's case, however, because Trapper's post-mining TSS samples have been <br />taken from waters that have passed through sediment control ponds. Consequently, Trapper chose <br />as an alternative acomparison ofpre- and post-mining sediment yields as predicted by the computer <br />program SEDCAD+. <br />Substitution of SEDCAD's settleable solids for regulation's suspended solids. Section <br />3.03.1(3)(b) of the Regulations specifies that "suspended solids" be used in comparing pre- and post- <br />mining sediment yields from lands proposed for Phase II release. SEDCAD+ does not calculate <br />suspended solids, but instead calculates settleable solids; consequently, Trapper used settleable <br />solids for calculating the quantity of sediment yielded by the bond release pazcels. Settleable solids <br />aze the coaser-grained fraction of the sediment load that settles out from a still body of water. <br />Trapper's use of settleable solids, rather than suspended solids, is valid for comparing pre- and post- <br />mining suspended solids because settleable solids and suspended solids comprise the same relative <br />proportion of the source sediment in pre-mining and post-mining conditions. <br />Trapper's 20-acre study areas. Trapper's SEDCAD+computer program runs are in Appendix 2.4 <br />of the bond release submittal and are summarized in Table 2.4-1, on page 2-19 of the submittal. <br />Trapper ran SEDCAD+ for several 20-acre study areas within the bond release parcels. SEDCAD+ <br />calculated the peak settleable solids concentration of runoff flowing to a single discharse point at <br />Trapper Mine Page 8 `12/14/98 <br />Phase II Bond Release <br />