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Test site 2. Witbank - Conceptual site model

This section shows a conceptual site model (CSM) for the Witbank coalfield, South Africa and for Bank Colliery, South Africa which has been selected to demonstrate the automated time-lapse electrical resistivity monitoring (ALERT) system of a leachate plume. The full report including detailed description of parameters can be retrieved here.

It presents the available information regarding known apparent environmental impacts. This information is derived from a literature review and from the findings of surveys conducted as part of work package WP1. Additionally the principal socio-economic impacts defined by WP1 have been presented. It goes on to consider the environmental factors that influence the transport of contaminants from the source to the exposed individuals or environmental receptors, through identified potential exposure pathways, describing the source- pathway-receptor interactions through two conceptual site models (CSMs), one for the Witbank Coal Mining region and the other for Bank Colliery. A CSM for the socio-economic impacts has also been attempted.

Examining the CSM results in the identification of data gaps and information needed for a full environmental assessment of mining in Witbank and provides the rational for EO selection.

Present and past coal mining in Witbank is associated with a number of environmental problems, including: acid mine drainage (AMD) derived from the oxidation of pyrite in the coal, specific contaminants including potentially harmful metals and arsenic (which occur in the mining environment and in dust associated with both the operation of the mines and the transport of the coal) and ground gases that are both naturally occurring and a consequence of self-combustion of the coal and waste dumps. A wide range of ecological and socio-economic impacts result from these impacts, including the impacts on land value and agriculture. Additional problems include ground subsidence due to pillar collapse, which has further consequences on the migration of AMD and self-combustion.

The CSMs have been used to idenfity the key direct or indirect indicators of mining impacts and an assessment of the potential to monitor these using Earth Observatory (EO) assessments has been made. The majority of the indicators lend themselves to EO assessment in one form or another.

Three models have been generated: site-specific environmental, regional environmental and regional socio-economic, following the source – pathway – receptor paradigm (see following figures, respectively). These models represent a range of scale of mining impacts and it is intended that they should form the basis for establishing the key indicators of mining impacts, which can be assessed in terms of their suitability for Earth Observation.