Variations in heavy metal contamination of stream water and groundwater affected by an abandoned lead-zinc mine in Korea

This study evaluated variations in heavy metal contamination of stream waters and groundwaters affected by an abandoned lead-zinc mine, where a rockfill dam for water storage will be built 11 km downstream. For these purposes, a total of 10 rounds of stream and groundwater samplings and subsequent chemical analyses were performed during 2002-2003. Results of an exploratory investigation of stream waters in 2000 indicated substantial contamination with heavy metals including zinc (Zn), iron ( Fe) and arsenic (As) for at least 6 km downstream from the mine. Stream waters near the mine showed metal contamination as high as arsenic (As) 8,923 mu g L-1, copper (Cu) 616 mu g L-1, cadmium (Cd) 223 mu g L-1 and lead (Pb) 10,590 mu g L-1, which greatly exceeded the Korean stream water guidelines. Remediation focused on the mine tailing piles largely improved the stream water qualities. However, there have still been quality problems for the waters containing relatively high concentrations of As (6-174 mu g L-1), Cd (1-46 mu g L-1) and Pb (2-26 mu g L-1). Rainfall infiltration into the mine tailing piles resulted in an increase of heavy metals in the stream waters due to direct discharge of waste effluent, while dilution of the contaminated stream waters improved the water quality due to mixing with metal free rain waters. Levels of As, Cu and chromium (Cr) largely decreased after heavy rain but that of Pb was rather elevated. The stream waters were characterized by high concentrations of calcium (Ca) and sulfate (SO4), which were derived from dissolution and leaching of carbonate and sulfide minerals. It was observed that the proportions of Ca and SO4 increased while those of bicarbonate (HCO3) and sodium and potassium (Na+K) decreased after a light rainfall event. Most interestingly, the reverse was generally detected for the groundwaters. The zinc, being the metal mined, was the most dominant heavy metal in the groundwaters (1758-10,550 mu g L-1) near the mine, which far exceeded the Korean standard of 1000 mu g L-1 for drinking water. The decreases in the heavy metals contents in the groundwaters associated with reduced rainfall were quite different from the increases observed for the stream waters, which is not clearly understood at this time and warrants further investigation.