Using GIS to predict, quantify and visualise water quality and long term stream ecology effects/changes caused by acid mining drainage

Acid mine drainage (AMD) has been a detrimental by-product of coal mining for many years. At present, acid mine drainage continues to pose a potential problem in some areas, despite improved prediction and prevention techniques. The formation of AMD, caused by exposing iron disulfide minerals (mainly pyrite) to an oxidizing environment, is a complex geochemical and microbiology mediated process. This work describes the development of MAPLE, a computer model that predicts future AMD quality to assess the environmental impact on the stream ecology. MAPLE (Mine Acid Production Long-term Estimation - Tool), developed as a extension for the ESRI ArcGIS® Desktop, combines the results of free draining leach tests and the amount of overburden to calculate the acid loads for the different streams, which drain the waste rock dumps. MAPLE also calculates the acid generation of overburden under different treatment conditions. Hence, MAPLE assists environmental managers in their decision-making, to minimize the environmental impact caused by AMD. MAPLE has been tested, using the Stockton Coal Mine, which is situated near Westport South Island of New Zealand and managed by Solid Energy New Zealand Ltd. Stockton overburden dumps are drained by two main streams (Mangatini and St. Patrick) and Solid Energy New Zealand Ltd has installed an intensive monitoring program to observe water quality in these streams. MAPLE successfully simulated AMD from the Stockton Mine and based on these results it was possible to calculate future Total Acidity and Al+ concentrations in the streams for specific years, like end of mine life 2014, and post-closure periods to 2040