Understanding the migration of bacterial populations in natural groundwater environments is critical for the successful implementation of bioremediation to contaminated sites. One factor often limiting the effectiveness of bioremediation is the transport of bacteria which are able to degrade chemical contaminants to low permeable regions where contaminants are difficult to remove. Chemotaxis, the directed migration of a bacterial population in response to a chemical concentration gradient, attracts bacteria toward chemically favorable regions to enhance their growth and survival. Many groundwater contaminants also elicit chemotactic responses in bacteria.

A laboratory-scale packed column comprised of a coarse-grained sand core with an embedded chemoattractant source surrounded by a fine-grained annulus was used to simulate a structured heterogeneity in saturated granular media. Chemoattractant diffused outward from the core creating a chemical gradient in the radial direction. A pulse injection of chemotactic bacteria was introduced which responded to the chemoattractant by migrating from the fine-grained annulus toward the coarse-grained core. Bacteria that migrated toward the chemoattractant in the core were retained for a shorter time in the column than bacteria in control experiments without chemotactic effects. Breakthrough curves were monitored to assess chemotaxis on bacterial migration in the packed columns. A range of chemoattractant concentrations, flow rates and columns structures were investigated. Mathematical models were developed to quantify the effect of chemotaxis relative to other transport processes in laboratory column. Results from this study will be used in mathematical models to predict the fate and transport of chemotactic bacteria in contaminated groundwater systems with structured heterogeneity.