MIGRATION OF HEAVY METALS FROM MINE WASTE ROCK DUMP END ENVIRONMENTAL IMPACT ON GROUNDWATERS AND SEDIMENTS

The environmental impact of mine waste rock dump, located in the region of Srednogorie, Bulgaria on groundwaters and sediments was studied. The acid mine drainage with low pH (2.43 - 3.53), high electrical conductivity (1500 - 4400 μS cm-1), content of Fe, Mn, Cu, Zn, Al, As and high concentration of sulfates (540 - 6905 mg L-1) are formed after heavy rainfall. The content of heavy metals, except manganese, in groundwater was significantly lower than that in the acid mine drainage, and the pH was in the range of 5.43 to 6.62. Sediments in the non-consequential vicinity of the mine waste rock dump had a pH in the range of 2.86 - 4.53 and contained heavy metals and As at concentrations higher than those in the mineral waste due to precipitation, co-precipitation and sorption reactions. An increase in the copper and zinc content in the exchangeable and organic matter fractions was found in the sediment sample. A relationship was found between arsenic and iron concentration in the sediments, which was mainly due to the retention of arsenic in the Fe and Mn oxides fraction. The concentration of total Mn in the sediments was lower than that in the mining waste due to the high mobility of manganese.