2010-05-25_REVISION - C1981008 (8)

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file at the mine site and will be reported within the topsoil balance /spoil quality report to be submitted annually on April 15th of each year. 6.0 New Horizon 2 Spoil Compatibility and Erodibility Determining the compaction potential of disturbed overburden is important to assess postmine spoil conditions including: hydraulic conductivity, revegetation success, landscape stability, and equipment traffic. Generally, stability and /or compaction problems are related to soils high in shrink/swell clays, soils with large proportions of sand and clay (sandy clay texture), and soils with approximately equal proportions of the sand, silt, and clay -size particle fractions. These three conditions are not highly desirable since a high shrink/swell clay content in postmine landscapes causes poor stability and low permeability conditions, a sandy clay textured soil develops surface crusting problems, and an equal particle -size distribution causes excessive compaction which results in restricted water movement and root growth. The first two considerations listed above were among those used for establishing the grading system for texture. Unsuitable clay textures were identified within two thin lenses of the upper overburden in the western half of the study area (Section 2.04.6). These clay lenses occur only near overburden Drill Site 870E (see Map 2.04.6 -1, Geologic Cross Section and Sample Locations for New Horizon 2 Study Area). These clay lenses are in the projected mining disturbance area and when they are being excavated, they will be thoroughly mixed with non clay type overburden. The mixing and dilution process will be accomplished by: 1) blasting, which will start the mixing of clay lenses with non clay formations above and below the clay seam 2) the overburden shovel will be digging a full face through the clay lense from top to bottom to load each truck for transportation to the backfill, 3) and finally, the trucks with the diluted clay lenses on board will dump their load along a several hundred foot dump face. After this process, the concentration in any one spot of clay like material will be minimal and compatibility of the backfill will be negligible. The New Horizon 2 postmine spoil textures will typically be loamy with an approximate particle size distribution of 65 percent sand, 25 percent silt, and 10 percent clay (Section 2.04.6, Geology Description). Surface crusting, which is critical to seedling emergence, is discussed in (Revised October 2009) 2.05.4(2)(d) -11