WATER-RETENTION BY SOILS CONTAINING COAL

Soil water retention and transport functions are needed to model infiltration and redistribution of water in reclaimed mineland profiles. Besides primary particles of sand, silt, clay, and rock fragments, some mineland soil profiles in west-central North Dakota also contain lignite coal fragments ranging in sizes from <1 to about 300 mm or more. The objective of this study was to evaluate the water retention properties of soil mixed with coal fragments. For preliminary investigations in the laboratory, disturbed soil and coal samples of sizes <2.0 mm were used. Two types of coal samples, one commercial lignite with high water repellency and the other a degraded lignite with low water repellency, 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 premine B and C horizons of Straw loam, a nne-loamy, mixed Cumulic Haploboroll). Air-dry samples of soil and coal were thoroughly mixed and bulk mixtures with coal contents of 5, 10, 15, 25, and 50% by oven-dry weight were produced. The subsamples of the components and the mixtures were wetted with water and desorbed at air pressures ranging from 5 to 1500 kPa. Water contents of the mixtures, in general, were linearly proportional to the coal contents. From the soil water content vs. pressure head relationships of ingredient soil and coal samples, volumetric water contents of soil-coal mixtures were predicted by using mass and volume balance interpolation equations. At all pressures heads, the predicted volumetric water contents approximated the measured values with a high degree of accuracy.