Orijärven kaivoksen rikastushiekka-alueen Orijärveen kohdistuvan ympäristövaikutuksen nykytilan selvitys

Orijärvi mine was the first coppermine in Finland and it's located in Kisko area (Varsinais-Suomi, Salon Seutukunta). Orijärvi mine was operating in years 1757–1956 and during that time sulfide ore (Cu, Pb, Zn) was exploit. Mine was closed without any after treatment done on its operating areas. Studies concerning heavy metal analysis and diatom analysis has been carried out earlier from lake sediments of nearby Lake Orijärvi. Results of these studies reach out up to year 2000. Previous studies testify that acid mine drainage leaching from Orijärvi mine area has affected harmfully to lake Orijärvi during the mining and especially after the closure of the mine. Even though significant environmental impacts of the mine area are demonstrated, there is still no reclamation plan to take care of the mining area. Environmental research of present effect of Orijärvi mine tailing area to lake Orijärvi and to its diatom communities was carried out by diatom analysis from the lake sediment core, by investigating locations of all the mining operations and surveying the loading routes from mine to Lake Orijärvi. Some reclamation options for the tailing area are proposed in this study. In autumn 2014 a lake sediment core was taken from Orijärvi and diatom analysis was carried out to observe diatom taxa representing years 2000–2014. Lake Orijärvi water quality was observed using water quality information from Hertta-database and from previous studies. The functionality of peat covered dam witch partly blocks tailing area was also estimated. Loading routes were detected by using previous studies, stream diatom analysis and watershed modeling. The results reveals that the mining area still affects harmfully lake Orijärvi. Based on the water quality and diatom analysis, biological status of Lake Orijärvi is poor. There are no signs of recovery in diatom communities and heavy metal concentration are high in the lake water. Two loading routes from Orijärvi mine to Lake Orijärvi were identified. One route transports pollution from northern part of the mine and the other route transports pollution from the tailing area to Lake Orijärvi. There was insufficient evidence to properly evaluate functionality of the dams. In situ -cleaning options and passive water treatment options are recommended for reclamation options of the tailing area. Orijärvi mine has a significant environmental effect on nearby areas and Lake Orijärvi and therefore whole mining environment should be restored.