Modelling the Hyclrogeochemistry of Decommissioned Opencast Coal Mines

摘要

Water quality improvement in underground mines after the initial flush can render these mines as potential water supplies. However, in certain settings, opencast mining is often preferred. With the prospect of an initial flush in backfilled opencast mines, it is essential to study the initial flush in this setting as these mines may also show water supply potential.Previous work focused on idealised curve fitting to existing mine water chemistry data, analytical calculations, simplified geochemical modelling and numerical transport models. The study presented here combines components of each to predict the initial flush from backfilled opencast mines. An additional component is the calibration of geochemical- and numerical flow and transport modelling data, with existing groundwater monitoring- and laboratory analysis data. A statistically defined mineral assemblage, based on analysis data, is used as input to geochemical models and calibrated using leaching test data. Leaching test data is further compared to speciation calculations and mine water analysis data to ensure representative laboratory data. Long term geochemical modelling results are then used as input to transport models, which are calibrated against groundwater monitoring data.The study presents a calibrated modelling approach which shows that calibration can provide realistic estimates which is supported by existing work, showing the duration of the initial flush in underground mines to be a few decades. The calculated duration of the initial flush in this study ranged between 20 and 100 years. Results obtained are considered to be more representative than static estimates and can aid in the improvement of rehabilitation techniques and the management of post-mining groundwater quality, with calculated concentrations calibrated up to a 1% error range.