Trace Element and Salt Movement in Retorted Oil Shale Disposal Sites

Abstract

AbstractThe direction and amount of salt and trace element movement within retorted shale disposal piles is a major environmental concern. This study examines the redistribution of soluble salts and trace elements (As, B, Cd, Cu, F, Fe, Mn, Mo, Na, Ni, Pb, Se, and Zn) in retorted shale test plots with different topsoil treatments 6 yr after construction. Topsoil treatments included no topsoil, no topsoil and leached with 76‐cm water, 30‐cm topsoil, 60‐cm topsoil, 90‐cm topsoil, 60‐cm topsoil and capillary barrier, and a disturbed soil control (no retorted shale). Soluble salts (especially Na salts) and F showed considerable movement both upwards and downwards in the profiles. Molybdenum showed some movement in both directions. The remaining elements showed little or no movement out of the shale layer. Increasing topsoil depths resulted in less salt or trace element movement in either direction. Use of a capillary barrier between the topsoil and retorted shale prevented upward migration of salts and trace elements. After 6 yr the exposed shale treatments (both leached and unleached) continued to have considerably higher salt and trace element contents than any other treatment. Because of limited rooting depths, deeper percolation of moisture is occurring on plots containing retorted shale than on the control plot.