Field-scale study to evaluate the role of bacterial chemotaxis in natural attenuation of groundwater contaminants

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0408454FordThe remediation of polluted groundwater is often limited because chemical contaminants trapped within interstices of the soil matrix are not accessible to groundwater flow paths. One mechanism by which pollutant-degrading bacteria may penetrate these less conductive regions is chemotaxis, the ability of bacteria to sense chemical concentration gradients and swim toward higher concentrations of contaminants. Chemotactic bacteria able to migrate from highly conductive regions of the aquifer toward the contaminant source would increase the microbial population in the vicinity of the contaminant and thereby enhance the overall rate of degradation and removal. Objective and Approach: The objective of this project is to determine the degree to which chemotactic bacteria may enhance the degradation of chemical pollutants near a source zone in natural groundwater systems. A series of field-scale investigations will be conducted at the USGS Cape Cod Toxic-Substances Hydrology Research Site. To aid in the design of the field-scale study, preliminary studies will be conducted in well-controlled two-dimensional sand box systems. The sand box design provides the added benefit of being able to visualize the flow patterns and analyze the spatial distributions of contaminant and bacteria along the flow path without all the complexities of a large field study.Intellectual Merit: Although number of laboratory-scale experiments have implicated bacterial chemotaxis as an important mechanism for transport of bacteria through saturated porous media, its ramifications at the field-scale have not been evaluated. A culminating experiment at the field-scale will address the question of whether chemotactic responses observed over length scales of centimeters in the lab give rise to larger scale effects that are observable in the field.Broad Impact: A new partnership between researchers at the University of Virginia and the US Geological Survey brings together expertise in bacterial chemotaxis and extensive field experience involving motile microorganisms. Investigators with a proven commitment to recruiting underrepresented groups in engineering will broadly educate one graduate and two undergraduate students through the University of Virginia's Program for Interdisciplinary Research in Contaminant Hydrology. Outreach to two local high schools will introduce students and their teachers to molecular biology techniques and the use of engineered organisms in laboratory and field-scale investigations. Results from this study will be used to assess the feasibility of monitored natural attenuation as a treatment option at contaminated sites where biological degradation has been documented