This exploratory project will investigate field techniques by which natural microbial processes can be stimulated to reverse the conditions of acid-mine drainage. Acid-mine drainage is produced when sulfide minerals excavated during mining operations are exposed to oxidation and hydrolysis at the Earth's surface. However, within the soils and stream deposits of these mine sites there is a community of microorganisms, largely sulfate-reducing and iron-reducing bacteria, that have the capability of reversing the conditions of low pH and elevated heavy metal content typical of affected waters. A field study site will be established at the outflow of Davis Mine, a long-abandoned pyrite mine in western Massachusetts, to monitor the changes in geochemistry that result from the introduction of a reactive fill into the outflow. This reactive fill will consist of a mix of limestone and organic compost that will provide an initial neutralization of the acidic water and a carbon source to stimulate the microbial population. Water samples will be collected at regular intervals upstream and downstream of the experiment site to monitor changes in chemistry resulting from the introduction of the mixture. If persistent positive changes are noted, the microbial communities within the stream sediments both before and after introduction of the reactive fill will be assayed. The results of the investigation will provide important data on the conditions required for successful growth and development of the in situ iron- and sulfate-reducing bacteria that can help in a long-term reversal of acid generation and metal transport.
Acid-mine drainage (AMD) is a global problem that is often associated with extensive coal mining, but it occurs frequently around abandoned base-metal mines in remote areas. Cleaning up these sites often involves elaborate engineering efforts that are both costly and environmentally disruptive. However, if the conditions within the surface waters of an affected mine site can be modified so that the natural community of sulfate- and iron-reducing bacteria can grow and prosper, these microorganisms could establish a self-sustaining method for neutralizing the excess acidity and removing the metals. This project will examine the processes that can optimize the conditions for such a beneficial outcome.
Acid mine-drainage is a problem that affects many places throughout the country and the world, especially areas where there has been extensive coal or gold mining. The oxidation of sulfide minerals in waste piles leads to high levels of acidity (low pH), and very high concentrations of dissolved metals, such as iron (Fe), aluminum (Al), copper (Cu) and lead (Pb). Davis Mine in Rowe, MA is a mine that extracted pyrite (FeS) at the turn of the 19th century and has been abandoned for over 100 years. This small site was used as a test facility for an environmentally friendly treatment of the acid-drainage problem. Specifically, three permeable barriers consisting of mesh bags filled with a reactive material (50% crushed dolomite, 25% shrimp compost, 25% composted cow manure) were installed across the effluent stream for the first 20 meters as it emanated from the mine shaft. The results showed a decrease in many of the dissolved metals in the mine effluentas the water passed tthough the barriers. Prior to the introduction of the reactive barriers, the concentration of many constituents showed an increase from the mine shaft for the first 20 meters. After the barriers were installed, this trend was generally reversed. The changes provide an excellent baseline for further research that will allow calculations of the amount and placement of reactive barriers to more completely reverse the effects of acid-mine drainage. The project provided the data for an independent study and an honors thesis for two undergraduate students, thereby helping in the training of the next generation of environmentally-focused research scientists.
