Risk mapping of eMalahleni municipal area with focus on coal mining impacts

Abstract

Coal-mining in eMalahleni raises a number of environmental challenges, including coal fires, subsidence, acid mine drainage (AMD) and air pollution. Previous studies by a number of institutions, including the Council for Geoscience, have shown that the impact on the environment and on human health and safety in the Mpumalanga coalfields is threatening the very basic rights entrenched in the South Africa Constitution. Coal fires and their by-products are major contributors to human health and safety problems such as respirational problems in humans, loss of productive land, etc. After the original underground board and pillar mining ceased and the mining operations abandoned the roof material between pillars sagged and collapsed. This resulted in a significant area becoming unsafe. Areas associated with subsidences cannot be used for infrastructural purposes. AMD forms when sulphides are exposed to oxygen and water. AMD can flow into drainage systems and cause heavy metals to become mobilized due to the low pH of the affected water. Air pollution in eMalahleni is generally associated with industrial smelters and coal fly ash. Air pollution can cause respiratory illnesses, cardiovascular illnesses and even death. The focus of this study is the development of a practical method for identifying coal-mining risks. By identifying these risks, hazardous areas can be identified and human access to these areas restricted. By restricting these areas, tragic accidents can be prevented. The results that were obtained from this study can also be used by mining companies for rehabilitation purposes and for environmental risk management. Aerial thermal infrared spectrometry is a technique which can be used to detect coal fires. The technique produces thermal infrared images which can be mosaicked in a GIS program and classified to indicate the localities of coal fires. Subsidence can be detected with Light Detection and Ranging (LIDAR). LIDAR indicates the slope elevation of objects with different colours, thus features such as subsidences can be detected. To identify the subsidences, the LIDAR image has to be analysed in a GIS program. AMD sources such as coal dumps can be located with aerial photos. However, AMD-producing minerals such as goethite have to be detected with hyperspectral satellite data. The AMD pathway can be determined by using an elevation map to identify the flow directions of rivers. Air pollution can be determined by analysing street dust samples. Street dust can be used as a proxy for air quality impacts. Street dust results can be digitised and loaded onto ArcGIS to evaluate the data by means of Kriging estimation. A risk map of eMalahleni can be created to identify all hazardous areas with a risk rating for each potential hazard. The risk map completed for the study, successfully identified high, medium and low potential risk areas.