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Shrub stem densities. The vegetation data also were evaluated to determine whether the shrub <br />revegetation efforts were progressing toward supporting the approved pos[mining land use of <br />rangeland. For the future Phase III bond release, range sites A and B have a minimum woody plant <br />stem density requirement of 400 stems per acre. (Range site C, which is not in this bond release. does <br />not have a woody plant stem density standard.) <br />Actual shrub stem densities. Table 3, below, shows the woody plant stem count already surpassed <br />the Phase III (Final bond release) approved standard in all three blocks. The density of stems per acre <br />ranged from 458 to 1009. <br />Table 3 <br /> Comparison of s hrub density <br /> Bond release block Bond release <br />Bond 1999 sample standard in <br />release density permit <br />block (stems/acre) (stems/acre) <br />A Pit 1009 400 <br />RSA&B <br />D P[t 458 400 <br />RSA&B <br />H Pit RSB 509 400 <br /> <br />Division's finding that shrub stem density is sufficient foe Phase II bond release. Based on <br />the comparison in Table 3, above, and recognizing that that the shrub density standazd is based on <br />what is sufficient to support the post-mining land use of rangeland, the shrub data indicate the <br />reclaimed sites being proposed for Phase II bond release are progressing towazd supporting the <br />postmining land use. <br />Sediment Yield <br />Use of sediment yield calculations, rather than water sample data. The most direct approach to <br />determining if post-mining sediment yields exceed pre-mining yields would be to compare total <br />suspended solids (TSS) field sample data for pre-mining and post-mining conditions. Such a <br />comparison would not be valid in Trapper's case, however, because Trapper's post-mining TSS <br />samples have been taken from waters that have passed through sediment control ponds. <br />Consequently, Trapper chose in its bond release application to compare pre- and post-mining <br />sediment yields by calculating the expected sediment yields for both conditions. Trapper used two <br />different calculation methods, the Universal Soil Loss Equation (USLE) and the computer program <br />Trapper Mine <br />Phase II Bond Release Page 9 12/21/99 <br />