THE CHARACTERISTICS OF GROUNDWATER CONTAMINATION BY HEAVY METALS AT AN ABANDONED IRON MINE IN KOREA

The study area is famous for an old iron ore deposits developed about 1,500 years ago. The mine called the Ulsan Mine was recently reactivated in 1960s, and was abandoned in 1993 because of the decreased ore body and increased cost. After abandonment, the mine area was in a state of total neglect. Geology in the study area consists of crystalline limestone and sandy shale of sedimentary rocks, granite intruding sedimentary rocks, hornfels metamorphosed by granite intrusion, and ultrabasic serpentinite. The geology belongs to the Cretaceous Period of the Mesozoic Era and early Tertiary Period of the Cenozoic Era. Serpentinite was formed with an elliptical shape around crystalline limestone, and contains olivine, serpentine, hornblende, diopside, and orthopyroxine. Some limestone was changed to marble by mineralization. Iron ore deposits were formed into the scarn type of limestone affected by hydrothermal solution. Magnetite, arsenopyrite and sheelite had been produced in the Ulsan Mine. Ore body was formed with an elliptical type of 100m in the long axis and 50m in the short axis. It was developed to the depth of 360m. Since the abandonment of the mine, toxic water has been effluent, and contaminated soil and groundwater around the mine area.

pH of groundwater is ranged from 5.71 to 8.69, and EC is from 60 to 2,850µS/cm. Acidic mine drainage was controlled by limestone in the site. As is from 0.335 to 0.815 mg/L in alluvial aquifer, and from 0.133 to 0.377 mg/L in bedrock aquifer. Zn is from 1.7 to 19.6 mg/L in alluvial aquifer, and from 1.1 to 8.8 mg/L in bedrock aquifer. Ni is from 0.14 to 0.34 mg/L in alluvial aquifer, and from 0.05 to 0.22 mg/L in bedrock aquifer. XRD and XRF analyses indicated that As came mainly from arsenopyrite (FeAsS), and Zn and Ni from serpentinite. According to Piper Diagram, river water belongs to CaSO₄ type, and most of groundwater samples in alluvial deposits also to CaSO₄ type. Some of alluvial groundwater samples belong to CaHCO₃ type. However, about the half of groundwater samples in bedrocks are affiliated to CaSO₄ type and the rest to CaHCO₃ type. Groundwater samples in serpentinite are mostly affiliated to CaSO₄ type, but groundwater samples in limestone are mostly to CaHCO₃. Groundwater samples in shale, hornfels and granite are fallen to CaHCO₃.