Modelling the evolution of minewater pollution at Polkemmet Colliery, Almond catchment, Scotland

Polluted discharges from abandoned mines are a major cause of freshwater po llution in central Scotland, often contributing high Fe, SO42- and acidity to receiving streams. The Central coalfield has been extensively mined for over a century and Polkemmet was the last colliery to close in 1985. Recent monitoring indicates that the rate of groundwater recovery is approximatel y 0.15 to 0.2 m per week. Without intervention, this trend would result in complete recovery by 2000 and probable discharge into the River Almond. Geo chemical modelling indicates that pyrite oxidation, calcite dissolution and goethite precipitation are primarily responsible for the evolution of grou ndwater chemistry currently observed at Polkemmet. Predictive modelling usi ng PHREEQE suggests that unregulated minewater discharges will have marked effects in the River Almond, with goethite being initially precipitated at a rate of up to 36 kg/day, dissolved sulphate concentrations ranging betwee n 170 and 800 mg/l and pH bring depressed to 6.5. Combined active lime floc culation and passive aerobic wetlands may be the most effective means of tr eating the predicted minewater discharges.