Bulletin 040

Bulletin 040

BUL 040

The Effects of Surface Mining of Coal on Water Chemistry near Grande Cache, Alberta

Author(s) Hackbarth, D.A. Date 1980-01-01

Streams and springs in and near surface coal mines located on the eastern slopes of the Canadian Rocky Mountains were sampled between 1972 and 1978. Dominant ions in streams unaffected by mining activity characteristically are calcium, magnesium, and bicarbonate. Total dissolved solids concentrations usually range between 125 and 231 g/L. Sulfate is usually about 20 percent of the anions and has a concentration less than 75 mg/L. Relative amounts of sodium, potassium, chloride, and nitrate are less than 6 percent of the ions. pH ranges between 7.6 and 8.2.

The effects of mining activity on water quality vary in intensity, but follow a consistent pattern. The relative proportions of the various cations do not change, although their concentrations may rise to 4 times those of background values. The concentration of anions lso increases, with a shift in the relative proportions from bicarbonate to sulfate and, at the more strongly affected sites, to nitrate. pH is not significantly different from unaffected sites.

Enhanced oxidation of sulfide minerals, which account for less than about 0.07 percent of the loose, unsaturated spoil piles, is probably responsible for the increase in sulfate ions. The hydrogen ion produced during the oxidation of the sulfide minerals is consumed in the dissolution of the abundant carbonate minerals thus releasing calcium and magnesium. Concentrations of nitrate increase from the use of ammonium nitrate for blasting.

The estimated rate of chemical denudation at sites unaffected by mining activity ranges from 4 to 18 mg/sec-ha. The rate at affected sites varies from 4 to 55 mg/sec-ha.

Concentrations of iron, manganese, lead, and copper occasionally exceed drinking water standards regardless of the influence of mining and do not appear to be increased by that activity. Zinc, strontium, and mercury concentrations may increase as a result of mining ctivity, but the evidence is not conclusive and concentrations are well below drinking water standards.

Hackbarth, D.A. (1981): The effects of surface mining of coal on water chemistry near Grande Cache, Alberta; Alberta Research Council, ARC/AGS Bulletin 40, 72 p.