Metal mobility and transport from an oil-shale mine, Lake Nõmmejärv, Estonia

Abstract: Mining activities have a large impact on the environment, for example by the release of heavy metals from acid mine drainage and erosion of mine waste. North-eastern Estonia has the largest commercially exploited oil-shale deposit in the world. Waste from the mining processes have led to contamination of groundwater and streams polluted by phenols, oil products, sulphates and heavy metals. This thesis concerns the metal mobility from oil-shale mines in north-eastern Estonia, through water flow in the drainage system directed into Lake Nõmmejärv, which acts as a sedimentation basin for the mining water. A sediment core along with lake bottom surface samples were retrieved and analysed for heavy metals associated with mining. Water samples were collected and analysed for TOC. The sedimentary records show distinctively the change with the high inflow of water. The analysis of heavy metal content does not suggest a high impact on the environment, possibly because of a buffering effect by the limestone bedrock. The contents of heavy metals are somewhat elevated compared to background contents in Swedish lake sediments, but only cadmium and nickel levels are in the range that can be hazardous for the survival of organisms.