WATER-RETENTION BY SOILS CONTAINING COAL

Soil water retention and transport functions are needed to model infil tration and redistribution of water in reclaimed mineland profiles. Be sides primary particles of sand, silt, clay, and rock fragments, some mineland soil profiles in west-central North Dakota also contain ligni te coal fragments ranging in sizes from <1 to about 300 mm or more. Th e objective of this study was to evaluate the water retention properti es of soil mixed with coal fragments. For preliminary investigations i n the laboratory, disturbed soil and coal samples of sizes <2.0 mm wer e used. Two types of coal samples, one commercial lignite with high wa ter repellency and the other a degraded lignite with low water repelle ncy, were mixed with three types of soils. The soil samples collected from subsoil and minespoil materials of reclaimed minelands included a sandy loam, a loam, and a sodic silty clay loam (equivalent to premin e B and C horizons of Straw loam, a nne-loamy, mixed Cumulic Haploboro ll). Air-dry samples of soil and coal were thoroughly mixed and bulk m ixtures with coal contents of 5, 10, 15, 25, and 50% by oven-dry weigh t were produced. The subsamples of the components and the mixtures wer e wetted with water and desorbed at air pressures ranging from 5 to 15 00 kPa. Water contents of the mixtures, in general, were linearly prop ortional to the coal contents. From the soil water content vs. pressur e head relationships of ingredient soil and coal samples, volumetric w ater contents of soil-coal mixtures were predicted by using mass and v olume balance interpolation equations. At all pressures heads, the pre dicted volumetric water contents approximated the measured values with a high degree of accuracy.