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<br />ATTACHM1tENT 6 <br />3.23 Exchangeable sodium percentage (ESP) <br />This value is calculated from the fraction of the cation exchange <br />capacity occupied by Na. When ESP is LS or more the overburden material (and <br />soil) exhibits a poor structural stability, i.e. it [ends [o swell and disperse <br />in contact with water; it has a low hydraulic conductivity for water, and a <br />low infiltration rate of water. These properties enhance erosional problems, <br />high runoff and usually lead to a Lower supply of avai1a61e water for plants. <br />In the West Panel high ESP values were found only in hole CR 218. Three <br />layers showed a high ESP but only the lower layer (246' - 263') would be likely <br />to cause problems. This profile contains thick layers of sandstone associated <br />with the three bottom layers of coal. The mining operation will likely mix these <br />layers and dilute the effect of the high ESP layer. <br />In the East Panel high ESP values can be expected to cause problems in <br />the weathered overburden From holes CR 220, 222, and 223. ESP values were low <br />in the overburden from holes CR 219 and 221. The high ESP values are associated <br />with high clay contents as indicated by data in tables 4 and 5 on the weathered <br />samples. Estimates of clay content from water percentage at 0.33 bar (from a <br />regression curve) showed a range from 25 [0 64 percent clay in five samples. <br />In CR 220 the overburden layer (64' - 109') is estimated to contain 64% <br />clay but this layer will likely be buried since two coal seams lie below it. <br />•~ The overburden layer in CR 220 (161' - 172') contains an estimated 44% clay and <br />` ~ a high ESP. It is above the lowest coal seam but also adjacent to a layer of <br />`~ ~ sandstone plus siltstone (133' - 161') which contains an estimated 10Y. clay and <br />a low ESP. These two layers will likely became mixed and the mixed layer should <br />produce near normal plant growth. <br />In CR 222 the overburden layer (150' - 184') lies between the two lower <br />coal seams. This layer contains an estimated 35% clay and a high ESP. These <br />properties of this layer will likely reduce plant growth below normal. If same <br />mixing can be attained with an adjacent layer (124' - 145') with only an esti- <br />mated 47. clay and a low ESP, Che mixed layer should yield normal plant growth. <br />In CR 223 the overburden layer (96' - 111') contains an estimated 40% <br />clay and a high ESP. The overburden layer (114' - 145' except for coal seams) <br />that lies adjacent contains an estimated 55% clay and a high ESP. The nearest <br />overburden layer (47' - 80') with sandstone is not convenient for mixing. There- <br />fore, the unmixed layers (96' - 145') of overburden in CR 223 will likely pro- <br />duce below normal plant growth. <br />A high ESP in the weathered overburden if it occurs at [he surface enhances <br />erosional problems. Sandstone and siltstone fragments in the unweathered over- <br />burden will counteract tendencies to erode because these fragments create surface <br />roughness, slow down surface water movement, and break the impact of raindrops. <br />Hole CR 218 contains ample sandstone to offset erosional hazards due to a high <br />ESP layer. <br />In the East Panel thinner sandstone layers will not provide as many bene- <br />fits in controlling erosion. In hole CR 220, sandstone was found in 31 feet, in <br />contrast with 100 feet in CR 218, of the overburden. Holes CR 222 and CR 223 <br />contained about 60 feet of sandstone in the overburden. All of these holes had <br />13 <br />