FIELD ASSESSMENT OF ACID MINE DRAINAGE CONTAMINATION IN SURFACE AND GROUND WATERS

Abstract

Both sulphate and conductivity are excellent indicators of AMD contamination. This is due to sulphate being an end product of pyrite oxidation. Unlike pH, they are both extremely sensitive to AMD even where large dilutions have occurred. The advantage of using sulphate to trace AMD is that unlike other ions it is not removed to any great extent by sorption or precipitation processes, being unaffected by fluctuations in pH. These two parameters are also closely associated as would be expected, as conductivity is especially sensitive to sulphate ions. As sulphate is a difficult anion to measure directly in the field then conductivity, for which accurate and robust electrodes and meters are available, is ideal for routine field screening of water samples for AMD contamination. Sulphate analysis is normally carried out by lC which requires sample dilutions. The use of conductivity ensures accurate sulphate analysis by selecting ideal dilutions. There is also potential to use conductivity to predict approximate concentrations of key metals when the pH of the water is within their respective solubility ranges. Conductivity can be used to predict sulphate concentration in both AMD and contaminated surface waters using regression analysis. Most accurate predictions are achieved by using equations given for specific conductivity ranges or AMD sources. However, for general use with AMD (including raw AMD, surface runoff from spoil and workings, and leachate streams or adits) then sulphate (y) can be predicted from the conductivity (μS/cm) (x) using the equation: y=-1974+1.67x For impacted surface waters the general equation below should be used: y=-69.5+0.77x