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60 to 65 feet above the top of the LDx Seam and only exist in the southern part of the <br />mineable area where the overburden (above LD is at least 60 to 90 ft. thick. Map <br />2.04.6 -3 the LDX Overburden Thickness Map shows the area that has sufficient <br />overburden to contain the clay beds. These clay beds will be mined in the area where the <br />overburden is the thickest. When these two clay lenses are being excavated during <br />mining, they will be thoroughly mixed with coarser textured overburden materials. The <br />mixing and dilution process will be accomplished in the weathered "Bench 1 Surface <br />Spoil or free dig zone" by: 1) the overburden shovel will be digging a full face through <br />the clay beds from top to bottom to load each haul truck for transportation to the backfill <br />area, and 2) the haul trucks with the diluted clay beds which were mixed and diluted <br />during mining, aboard will dump their load along a several hundred foot dump face <br />which will result in significant additional mixing and diluting of the clayey materials. <br />After this process, the concentration of the high clay material will be minimal and <br />compactability of the regraded spoil will be negligible. Where the clay beds may be <br />below the weathered "Bench 1 Surface Spoil or free dig zone" they will be handled as <br />less suitable material along with the rest of the unweathered overburden and be buried in <br />the backfill below the more suitable weathered overburden of Bench 1 Surface Spoil or <br />free dig zone materials. <br />The NHN Mine regraded spoil subsoil will typically have a loamy texture with an <br />approximate particle size distribution of 49 percent sand, 26 percent silt, and 25 percent <br />clay (Section 2.04.6, Geology Description). Surface crusting, which is critical to seedling <br />emergence, is discussed in the Soil Survey (Section 2.04.9), Revegetation Plan (Section <br />2.05.4(2)(e)), and Topsoil Management of this Section. Since clay percentages and <br />shrink -swell potentials are low, stability and trafficability problems are not anticipated. <br />Prior to topsoil replacement, the regraded "Bench 1 Surface Spoil or free dig zone" <br />material will be scarified by deep ripping or chisel plowing on the contour to a depth of <br />12 to 24 inches to: reduce excessive compaction; prevent potential slippage zones; reduce <br />erosion; improve water and air movement; and root growth across the topsoil /subsoil <br />interface. Abandoned roads shall also be ripped and /or chisel plowed prior to topsoil <br />replacement. The erodibility of regraded spoil material is discussed in the Backfilling <br />Section 2.05.4(2)(d) Page 6 January 2012 <br />