Evaluation of Zn in Acid Mine Drainage in the Ohitachi Mining Area, Akita Prefecture, Japan

Abstract

Environmental impact assessment was conducted at the Ohitachi Mine (Cu-Zn-Pb) located in Odate, Akita Prefecture, Japan. Zn concentration in river water exceeded the environmental standard (30 µg/L) even in the downstream of the Mine. Here, treatment facility for acid mine drainage had already constructed, however, the capacity of the facility was not enough to protect the environmental standard of Zn in the downstream. We calculated Zn load (mg/s) and concentration of Zn (µg/L) in individual watershed along the mainstream and branches. Several watersheds which emitted high concentration of Zn were recognized in the mining area. Particularly, discharge of Zn along the mainstream and watershed which includes open adit shows strong effects to concentration and load of Zn in river water. Based on concentration of Zn in river water and flow rate, we calculated mass balance of Zn load between sampling points. In order to protect environmental standard of Zn (30 µg/L) around village in downstream, we have to reduce 4.22 mg/s of Zn load. In that case, we have to reduce discharge of Zn along the mainstream and from open adit in the mining area. Based on the load and concentration of Zn in individual watershed around the mining area, quantitative evaluation is possible to estimate environmental risks of heavy metals in the river water caused by abundant mine.

Keywords

• mine drainage
• heavy metals
• river water
• ohitachi mine
• zn
• environmental standard