Biodegradation and Movement of Organic Pollutants in Soil
An understanding of the factors that affect the movement of pollutants through the unsaturated zone is critical to the preservation of groundwater. Since chemical contamination often reaches the water table by way of vertical movement through surface and subsurface layers, transport and fate processes in these regions above the saturated zone are of utmost importance to groundwater quality. In previous work, I have examined the effects of several environmental factors on biodegradation (a major mechanism by which pollutants can be detoxified before they reach groundwater) in unsaturated soil columns. The results of those studies indicate that, in general, any physical factor that reduces the contact time between soil microorganisms and a pollutant that is flowing through the unsaturated zone will increase groundwater contamination. However, an exception to this trend was observed when preferential flow channels were inserted through soil columns. Under some conditions, the total amount of a test compound that leached from columns (i.e., into groundwater) containing open vertical channels was reduced relative to the amount that leached from columns that did not contain channels. The reason for this phenomenon is not clear.
I am continuing to explore the problem by studying the distribution of bacteria, oxygen, pollutant, and bacterial metabolites during the transport of a pollutant through soil columns that contain open channels. These studies will further our understanding of the factors that affect groundwater pollution and would aid in the development of realistic transport and fate models.