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<br />After ten years of growth, the Test Plots on the Roadside Mine RDA were evaluated in <br />' 1993 to determine whether revegetation success could be achieved (based on the <br />parameters of vegetation cover, herbaceous production, woody plant density, and <br />' species diversity) with less than the statutory mandated four feet of non-toxic non- <br />combustible material. Based on three sampling events in 1986, 1988, and 1993, the <br />answer to the question is in the affirmative. <br />' Vegetation cover in this growing season (1993) on Test Plots with six inches of <br />material or more were equivalent or greater than the vegetation revegetation success <br />' standard derived from the cover of the Shadscale Shrubland Reference Area. The only <br />areas which did not meet the cover success standard were those treatment plots located <br />on the flat surface of the RDA in Test Plot 1. In these treatments, cover increased to a <br />' maximum on the 24" depth treatments. The additional two feet of soil afforded on the <br />48" treatment did not yield increased vegetation cover. <br />' Herbaceous production in 1993 met or exceeded the revegetation success standard on <br />Test Plots with twelve inches of cover with one exception. The flat Test Plot 1 yielded <br />lower herbaceous production than the standard in all treatments except the 24" <br />' treatment. <br />' Woody Plant Densities on the RDA appear to be largely affected by the moisture <br />regime determined by aspect. All soil depths on Test Plot 2 met or exceeded the <br /> woody plant density re-establishment success standard of the regulatory agency. <br />' Treatments on the other Test Plots did not. <br /> With respect to species composition and diversity, Test Plots were consistently more <br />' diverse than the Reference Area. Test Plots revealed greater representation by <br /> desirable perennial grasses and woody plants than was found on the Reference Area. <br /> Shrub growth was found to be acceptable at all soil depths, as evidenced by measured <br />' heights and diameters. <br />Concern regarding migration of soil cations from the refuse into the plant rooting zone <br />prompted analysis of the soil column on the Test Plots. Salt migration has occurred <br />within the soil column, with downward leaching occumng at depths between 0 and <br />12". SAR and EC levels above recommended revegetation guidelines have developed <br />predominantly in depths greater than 18". Soil replacement depths greater than this <br />should be avoided based on data from the Test Plots. <br />' With all parameters considered, successful vegetation can be established on the <br />Roadside RDA with between twelve and twenty four inches of soil material placed over <br />' the refuse, based on results of the 1986, 1988, and 1993 sampling of Test Plots and the <br />Shadscale Shrubland Reference Area. <br />79 <br />