Patterson et al. 2018 - Effects of stockpiling on selected properties of opencast coal mine soils

ABSTRACT: Soil stockpiling is a necessary component of opencast coal mining and, because most of the soils involved have arable potential, this involves the possibility of serious soil degradation. A study at four mines on the Highveld of South Africa involved sampling a number of stockpiles of various ages and origins. Samples were also collected from unmined adjacent soils, as well as rehabilitated areas. Results of stockpiling showed a deterioration in all physical and chemical parameters studied. The soil profile texture gradient was disturbed, due to mixing of surface and subsurface materials. Stockpile bulk density rose by 4% from unmined soils and by a further 6% in rehabilitated areas, indicating continuing compaction problems. Cation exchange capacity values did not entirely correspond with the textural changes, suggesting increased leaching, whereas pH values decreased for many stockpiles, requiring post-mining liming to re-establish suitable environments. Organic carbon levels on stockpiles fell by 5%,

and by a further 35% to rehabilitated areas. Increasing age of stockpile did not seem to equate to a correspond- ing increase in degradation, except possibly for pH, which showed a weak correlation. Recommendations from

the study include the use of ‘cut and cover’ rehabilitation techniques; continuous soil specialist consultation, and limitations on stockpile height and duration.