Advanced Monitoring Approaches for Contaminant Behavior
Natural Systems
Remediation of contaminant plumes, such as technetium and uranium, in the vadose zone has been challenging with respect to site characterization prior to and following remedial activities, design for treatability, and monitoring of treatment efficacy, to name a few. Characterization of physical and geochemical properties is achieved through advances in sensor technologies, modeling, and well placement. However, the biotic composition within the subsurface is also an important component that adds an additional biochemical contribution not currently being assessed. Remedial agent(s) and the long-chain surfactants used to provide the foam-delivery media will come into contact with, not only the targeted contaminant plume, but indigenous microorganisms as well.
Microorganisms almost never exist as single species in nature, but as integrated communities that process available nutrient resources which impact their environment. There is little information for understanding the community dynamics that maintain stable metabolic outputs or produce changes in the environment. Microorganisms adhere directly to surfaces and are the initial contact surface between solid and fluid phase environments Changes in the environment have impacts to the composition of microbial communities at this solid/fluid phase interface. .
The introduction of the remedial amendments may provide an abundant food source for microorganisms in the vadose zone and alter community dynamics. Such changes to the microbial community composition may have dramatic effects on bulk community biochemistry, which in turn may affect the quality of the remedial treatment in terms of effectiveness and transport through the altered environment. Data are needed to enable quantitative field-scale measurement and modeling capabilities of subsurface microbial communities in the vadose zone for baseline characterization, monitoring of treatment impacts, and long-term monitoring of environmental stability. Moreover, baseline assessment of microbial community structure with depth across the remedial area will be compared with relative geochemistry to determine profiling of community composition with available environmental resources. Introduction of remedial and delivery agents will likely cause short-term community changes that can be monitored and assessed concomitant with contaminant fate and transport. Continued monitoring of community shift and stabilization will also be compared with contaminant tracking to assess effectiveness of remedial treatment and reaction of community dynamics. This profiling can be performed rapidly at the point source, and at downstream gradients where microbial community changes may occur in advance of measurable geochemical metrics, thereby, providing an highly sensitive "warning" of possible changes in contaminant plume behavior or the need for additional in situ remediation.