Water quality impact of mining in the Wolmyoung area of Korea, and its short-term changes

The water quality of a stream affected by mining activities was investigated on the basis of a mineralogical study for the related solids, and their subsequent changes were monitored for a year, so as to clarify the impact of the acid mine drainage (AMD) to the stream. The mine-affected stream was classified into Ca-Mg and sulfate type, and the concentrations of its major constituents ranged from tens to hundreds times higher than those of the background stream. This was most likely due to acid-generating reactions involving the oxidation of sulfides in the mineralized zone, and subsequent neutralizations involving calcite and chlorite as possible sources of Ca and Mg, respectively. This interpretation is consistent with the thermodynamic and mass-balance calculations. The concentrations of the dissolved constituents changed seasonally, depending largely on rainfall in the mine-affected stream. However, the dramatic decrease in the ratio of Mg/Ca, independent of rainfall, indicates that some changes did occur in sources, including the heterogeneous distribution of main source materials, the change in chemical conditions, especially in pH, pe(Eh), and P_CO2, in the reacting fluid, and the consequential solubility changes in sources. In spite of the limitations of short-term monitoring, it does provide some meaningful information in order to construct a long-term monitoring program.