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• ATTACHb1ENT 6 in CR 220. Other overburden layers with intermediate clay contents were dis- cussed in section 3.23. The settling volume was very high for three overburden layers with clay contents above 40% i.e. 64' - 109' and 161' - 172' in Cr 220, and 114' - 145' in CR 223. It was high for two other samples which contained an estimated 35X clay (150' - 184' in CR 222) and 40% clay (96' - 111' in CR 223). These five samples with clay contents of 35% or more were the only samples with ESP values greater than 15. These same five samples had the lowest values for hydraulic conductivity. The settling volume for all the weathered samples was plotted against percent water at 0.33 bar in figure 4.21 and against percent weight less than 270 mesh in 'figure 4.22. These curves show a sharp break at 25% water at 0.33 bar and at 40% weight less than 270 mesh. This big change in settling volume coincides with estimated clay contents above 35%. These data indicate that this method or test of settling volume will be useful as a field guide and method to locate overburden layers that have high values of ESP and high clay contents. In figure 4.23, the relationship is shown between Y, of water at 0.33 bar and Y, weight less than 270 mesh. A high correlation erists between these two measurements on these weathered materials. These two measurements are use- • ful in characterizing textural differences in the overburden materials. /~ ~ ~ The very low values for hydraulic conductivity in some of the overburden samples weathered from shale indicates serious problems could arise from erosion and poor water inflitration if these materials occur at Che surface intended for revegetation. Mixing of these layers with other layers containing less clay will decrease erosion hazards. Other practices may be chosen such as a topsoil cover, graded terraces and mulches of straw, wood fiber, excelsior, stone or gravel, and wood chips which will be beneficial in reducing erosion in these areas where the overburden contains over 35% clay. 4.3 Chemical properties These data for the weathered samples appear in table 6. Data for the corresponding unweathered samples appears in tables 3A, 3B, and 3C. The pH in water decreased from weathering in 18 of the 21 samples and in 12 of the 21 samples for pH in 0.01 M CaC12 solution. ;cost of the changes in pH appears to be due to the reaction of C02 with soluble carbonates. An increase in soluble salts was observed in every sample. This change would also reduce the pH. Weathering released soluble salts because it changed the larger particles into smallec particles. The ESP values did not change significantly due Co weathering. Available K increased in every sample as a result of weathering and available P increased in 15 of the 21 samples. ._, Water soluble boron appears to be somewhat high in three samples where iC exceeds 1.5 ppm. This level of concentration is marginal for sensitive crops; more tolerant crops can withstand higher concentrations. 17