Groundwater Quality: Remediation and Protection (Proceedings of the GQ'98 Conference held at <-MO Tubingen, Germany, September 1998). IAHS Publ. no. 250, f998. z4y In situ treatment of groundwater at Burgas Copper Mines, Bulgaria, by enhancing microbial sulphate reduction STOYAN GROUDEV Department of Engineering Geoecology, University of Mining and Geology, Studentski grad— Durvenitza, Sofia 1100, Bulgaria ANTONY KONTOPOULOS Laboratory of Metallurgy, National Technical University of Athens, Zografos 15780, Greece IRENA SPASOVA Department of Engineering Geoecology, University of Mining and Geology, Studentski grad— Durvenitza, Sofia 1100, Bulgaria KOSTAS KOMNITSAS Laboratory of Metallurgy, National Technical University of Athens, Zografos 15780, Greece ANATOLI ANGELOV, PLAMEN GEORGIEV Department of Engineering Geoecology, University of Mining and Geology, Studentski grad— Durvenitza, Sofia 1100, Bulgaria Abstract The groundwater in the area near the tailings ponds at the Burgas Copper Mines, Bulgaria, is contaminated with radionuclides, sulphates and toxic heavy metals (mainly copper, lead, molybdenum and manganese) by drainage waters from the pond. The groundwater level and the quality of groundwater were monitored regularly by a system of piezometers. It was found that natural cleanup processes took place during groundwater flow. The main cleanup process is the microbial dissimilatory sulphate reduction carried out by the indigenous sulphate-reducing bacteria. The hydrogen sulphide, produced as a result of this process, reduced the hexavalent uranium to the insoluble tetravalent state and precipitated the heavy metal ions as the relevant insoluble sulphides. The in situ activity of the sulphate- reducing bacteria was enhanced by adding nutrients (soluble organic matter, ammonium and phosphate ions) to the groundwater through injection boreholes. The concentration of pollutants decreased below the permissible levels after such treatment. INTRODUCTION The area around the Vromos Bay, which is located on the west coast of the Black Sea, is heavily polluted as a result of the intensive mining and mineral processing activities carried out at the Burgas Copper Mines during the last 45 years. The groundwater in the area contains radioactive elements, sulphates and toxic heavy metals (mainly copper, lead, molybdenum and manganese) in concentrations much higher than the relevant permissible levels for waters intended for use in agriculture and/or industry. The main source of these pollutants are the flotation tailings