SACNASP CPD EVENT Natural attenuation of acid mine drainage by various rocks in a typical Karoo coalfield: A case study of the Witbank, Ermelo, and Highveld coalfields, South Africa. In the Karoo coalfields, mining operations that release acid mine drainage (AMD) are threatening groundwater resources. An important parameter controlling the extent and severity of AMD impacts is the natural attenuation of rocks in response to introduced of AMD.