EAGER -- Field tests of low-impact treatment for acid mine drainage

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

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.