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~! Memo - Cathy Begej - 2 - November 3, 1989 Use of Pre-mine Vegetation Data in Determining Revegetation Success Page 816-156a of the presently approved permit application states: "Other than the acreages used to weight the post-mine reference area data, pre-mine vegetation work will be used to establish valid reference areas only and not in the determination of re vegetation success." Page 4.15-13 of the proposed permit application concurs that only reference areas and previously agreed upon standards will be used to determine re vegetation success. In light of these two page references, Kerr Coal needs to explain or adjust the following statement which appears on page 2.05.4-43: "For the Kerr mine area, the reference area standard will be calculated based on data collected from the three (3) reference areas during years nine and ten of the liability period combined with baseline data for the Salt Flat vegetation type." A similar statement also exists on page 2.04.10-21. Statistical Comparisons Page 4.15-18 states that in evaluating re vegetation success, a two tailed t-test will be used. Furthermore, the re vegetation will be considered successful if cover and production mean of the reclaimed area is greater than or equal to the calculated 80% confidence level for the reference area value Page 17 of the Division's Land Use and Vegetation Guidelines and Rule 4.15.7(2)(c) require that tests must pro vi a resu s va i a t e confidence level, using one-sided tests with a 0.10 alpha error probability. Kerr should adjust the text to reflect this requirement. Cover Comparison Rule 4.15.8(3)(b) identifies cover as being ". either canopy or basal cover of living herbaceous and woody vegetation." Kerr Coal is presently committed to a comparison of total plant cover between reference and revegetated mine areas as a part of determining re vegetation success. The herbaceous layer of the Kerr mine site reference areas, often provides only a small amount of cover. Woody plant densities of revegetated areas can be expected to be replaced at levels well below reference area totals. Tables 20, 22, 24, and 26 indicate reference area shrub densities of 23472, 19021, 7689, and 33590 stems per acre for the sagebrush-grass, sagebrush-gravel, treated sagebrush and alkali sagebrush areas respectively. The present standard of 2000 stems per acre does not allow for the replacement of cover on revegetated areas which was provided formerly by shrub species. Furthermore, Grasses and fortis on the sagebrush-gravel and alkali sagebrush reference areas provide absolute covers of only 10.4$ and 10.5 respectively. The Division believes that to comply with Rule 4.15.1(2)(b), which states "The vegetation cover shall be capable of stabilizing the soil surface to achieve erosion control equal to pre-mining levels", the shrub layer of reference areas, which provides an important percentage of cover, should be represented in the revegetated areas. Thus, the Division believes that Kerr should continue to commit to a comparison of total plant cover between reference and revegetated areas.