Shelf life of stock-piled topsoil of an opencast coal mine

Abstract

Topsoil is essential to abandoned mines and has to be stock-piled separately for post-mining land reclamation. If the storage period exceeds the 'shelf life' of the topsoil, it cannot be preserved by technical reclamation only. Opencast coal mining production in India is predicted to increase from the present level of 180 million tonnes per year to approximately 256 million tonnes per year by the year 2000. At that time about 60 km2 of land per year would be damaged by direct coal mines and 75 km2 per year would be affected by external overburden dumps and topsoil dumps. A large opencast coal mine was studied to evaluate the effect of stock-piling topsoil. Soil characteristics of soil dumps of six different ages (1, 3, 4, 6, 9 and 10 years old) were compared with those of surrounding unmined sites. Soil profiles were found to change greatly with age. Physico-chemical characteristics of soil dumps were found to deteriorate with respect to unmined soil. It was observed that, as the age of soil dumps increased from one to 10 years, the concentrations of suitable plant growth nutrients in soil gradually decreased and, after six years, the soils were found to be stagnant. This may be considered to be the 'shelf life' of topsoil. Biological reclamation must be adopted to preserve the topsoil if the storage period exceeds the shelf life period. The methodology provides guidelines for assessing the shelf life of topsoil in other areas.