Laboratory leaching tests including 10:1 and 40:1 water to sediment ratios and saturated-paste extracts , have been used to determine the salt yielding properties of overburden materials as well as coal ash. This salt yield data, expressed as soluble salt in the appropriate water to sol ids ratio for field conditions, can be used to predict the salinity and composition of spoil groundwater, and the effects of coal ash disposal on spoil groundwater chemistry. The concentration of ionic species at varying sediment to water ratios is computed using the aqueous geochemical model PHREEQE, which allows consideration of mineral solubility constraints (particularly calcite, dolomite and gypsum) , various partial pressures of carbon dioxide, and ion exchange.
The predictive model has been tested at three mine sites in central Alberta, with ash disposal considered at two sites. There is good agreement between the predicted and observed spoil groundwater chemistry at Diplomat Mine (mainly glacial drift overburden) , Vesta Mine (mixed Horseshoe Canyon Formation bedrock and drift overburden) and Highvale Mine (mixed Paskapoo Formation bedrock and drift overburden). Disposal of coal ash in mine pits at Diplomat and Vesta Mines is predicted to increase the total dissolved sol ids in the spoil groundwater to 10,300 mg/L above a background of 5000 mg/L at Diplomat Mine and to 10,500 mg/L above a background of 6,500 mg/L at Vesta Mine. The predicted groundwater composition and salinity for ash in spoil at Vesta Mine is in excellent agreement with the composition and TDS of 10,383 mg/L observed in a well installed in an ash site at Vesta Mine .