Many subsurface vadose sites around the nation are severely contaminated with heavy metals that are migrating into the groundwater. Suitable treatment methods to remove these metals are not available. Current methods of immobilization, including adsorption, ion exchange, or precipitation, are not effective for some metals and allow slow release and continued migration of other metals. This project will investigate a unique biological method to stabilize metals by forming a limestone monolith from microbially enhanced precipitates in situ. This technique, employed successfully for sealing channels in petroleum reservoirs, would immobilize all metals present, and the process could be readily reversed for future metals removal, as suitable technologies become developed. This process requires only the dispersion of bacteria and substrates in solution in the soil and could be readily applied to many soil types. The technique could also prove very useful for rapid stabilization of zones around a toxic spill. Phase I of this project will identify the best microorganisms and substrate concentrations to carry out the reactions to biologically produce limestone in situ. Experiments will be conducted in reactors simulating in-situ conditions to measure the permeability and metal migration within the biological limestone. The cost of this method of solubilization will be projected. Phase II will optimize the process and examine the parameters on a larger scale. Studies will be performed to determine methods to effectively and quickly disperse nutrients and bacteria within contaminated zones for various soil heterogeneities. A field demonstration at a selected site will also be conducted in Phase II. Anticipated Results /Potential Commercial Applications as described by the awardee:Successful completion of Phase I and Phase II of this project will provide an inexpensive and effective method for stabilizing existing contaminated regions, as well as future spill areas. The method should apply to all metal or organic contaminants and to most vadose zone soils. The U.S. has several thousand waste sites where this technology can be applied once successfully demonstrated.
