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• area. The herbaceous cover component for each type will be multiplied by the acreages relative to each type in the premining surface area. The products for each type will be added and then div ld ed by the acreage total for [he reference area types occurring Sn the premining surface area. The resulting weighted herbaceous cover value will be multiplied by a factor of three in order to determine the actual value to be used as the cover comparison standard. The cover standard will then be compared to the average vegetation cover determined from the revegetatlon areas sub]ec[ to bond release. For vegetative cover, the revegetated area shall be considered acceptable Sf It is not less than 90 percent of the cover standard with 90 percent statistical confidence. The weighting formula to be used Sn determining successful revegetatlon for cover Sn the reclaimed mine area is as follows: xREV ~ •90 (3x (Aa) 17CA) + IMBa) (7CMB1 + ISea) (7CSB) ) Ta with 90 percent statistical confidence where: SfREV Average vegetation cover for revegetated area Aa = Aspen type acreage, premining surface area • MBa =Mixed brush t e acrea e reminin surface area yp g , p g SBa =Sagebrush type acreage, premining surface area zA = Average reference area herbaceous cover - aspen type xMB =Average reference area herbaceous cover - mixed brush type zSB =Average reference area herbaceous cover - sagebrush type Ta = Total of relative community type acreages, premining surface area. Average vegetation cover las opposed to only herbaceous cover) is to be used for the revegetatlon areas because monitoring data at the Seneca II Mine shows that vegetation cover in reclaimed areas is, for all practical purposes, comprised of herbaceous species. This Ss true even in reclaimed areas with the highest shrub densities. The above method allows for the effects of climatic variability to enter into comparisons. An example of a projected cover comps rlson value Ss presented here. Using the vegetation covet data collected in 1990 baseline studies for the Yoast Mine (Appendix A to Attachment 10-1, Tab 10, Vegetation), a weighted herbaceous cover value was estimated. This value multiplied by three resulted in an example cover comparison value of approximately 63 percent. This • example illustrates that when the standard Ss met, a sufficient level of cover will be pressor to control erosion and stabilize the surface, particularly when one considers that 39 Revised 12/12/95