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ATTACHMENT 6 5. Conclusions and recommendations An analysis of the chemical and physical properties of the artificially weathered overburden in the lease area indicates [hat serious problems could be expected in management and reclamation of some of these materials if they occur at [he surface intended for revegetation. [lost of the coal layers have shale of shale plus siltstone deposited immediately above them. This condition occurs in 35 of 48 coal layers. These problems stem from high exchangeable sodium percentages (ESP) and high clay contents of shaly layers, which cause a low hydraulic conductivity, poor structural stability, and a strong tendency to erode. These difficulties are mostly evident in the East Panel and in the northern portion of this section. The unweathered overburden appears to be resis- tant to erosion, so the degree of weathering that occurs before grading and re- vegetation will strongly influence [he erosion potential. Good conditions exist in most cases, however, for mixing overburden layers having poor chemical and physical properties with adjacent or nearby overburden layers that have good chemical and physical properties. The degree of mixing of these overburden layers during mining operations may be quite important. A well- mixed layer will likely produce near normal plant growth with proper fertiliza- tion provided conditions are good for seed germination and moisture supply. The distribution of particle sizes has a significant effect on the • erosional hazards of the overburden. The unweathered overburden contains a very low percentage (average of 3.3%) of silt and clay size particles which ~~ erode more readily than the sand fraction., Thus, the initial overburden should resist erosion, but as weathering proceeds the erosion potential will ' increase. Therefore, significant predictions about erosion hazards of the un- weathered overburden depend on the degree of weathering. Artificial weathering was induced by freeze-thaw cycles of water^ saturated overburden. Possibly, the 40 cvcles simulate were=ing that might occur naturally over 2 to 5 years. If grading, topsoil cover, and revegetation procedures fo ow wl in one year after mining, the erosional hazards of the overburden should be small. Initial erosional problems with the overburden, before grading and revegetation is completed, will be alleviated by sandstone (and siltstone) fragments in the overburden. These fragments create surface roughness, reduce surface water movement, and break the impact of raindrops. Before the over- burden is compacted by grading and weathering, its low bulk density and high porosity will likely impart a higher rate of water infiltration than the same material after grading and weathering. This property of the initial overburden will reduce erosional hazards, especially [he conditions that could lead to gully erosion between ridges. If the initial overburden in Che East Panel proves to be unstable and erosive, grading to form terraces will be advisable. This alternative seems unlikely if grading and revegetation follows within one year after mining. The topsoil in most of the lease area has excellent physical and chemical • properties especially if N and P will be added as needed to increase the avail- able supply of these nutrients. Most of the topsoil in [he lease area has been weathered from loess or windblown material carried into the area from other regions. This deposition of loess has created much deeper soils in much of the area in comparison with areas where residual soils develop from underlying materials. 18