Effect of mining and geology on the chemistry of stream water and sediment in a small watershed

Chemical characteristics of the stream water and sediment in the small watershed with two distinctive mineralization zones (Cu and Pb-Zn), 7 abandoned mines and an active quarry were investigated to examine the effects of mining activity and regional geology on the chemistry. The stream water affected by the abandoned mines had Ca-SO₄ type but the other had Ca-HCO₃ type. The mine affected stream water and sediment showed relatively high concentrations of metals (Cu, Pb, Zn, Cd, Co, Ni, Mn, Al and Fe). The concentrations of Al, Mn, Fe and Cu of the stream water collected near an abandoned mine (Guryong) exceeded the EPA surface water quality standards (Al: 5.52 mg L^-1, Mn: 1.58 mg L^-1, Fe: 1.49 mg L^-1, Cu: 0.63 mg L^-1). The effect of mining activity on the stream water chemistry was attenuated in a relatively short distance from the source (< 200 m) along the watercourse but the signature in the sediment showed a longer lasting effect (about 2 km) than that in the stream water. The residual and reducible forms were the dominant fractions of the heavy metals in the stream sediment. The particulate transportation was the major cause of the dispersion of heavy metals in the watershed. There was a contrasting spatial distribution of background metal concentration in the stream sediment: a relatively higher concentration of Cu in the Cu mineralization zone and a relatively higher concentration of Pb, Zn and Mn in the Pb-Zn mineralization zone.