Janet Herman, Ph.D. - US grants

Fundamental and applied problems associated with the contamination of the subsurface environment are receiving attention at local, national, and international levels. Groundwater contamination is clearly an urgent technical issue in our society. The University of Virginia has taken an interdisciplinary approach to the study of quantitative contaminant hydrogeology that places it in a unique position of national prominence in the field. With additional support for graduate students, the ongoing research and teaching program should allow them to craft a cohesive program that will provide the basis for understanding the fundamental technical issues of groundwater contamination and produce competent professionals who can address the details of this complex interdisciplinary problem from a variety of perspectives. Collaboration across departments is generating new research funds, additional faculty members, and new space; the University of Virginia is primed to expand its role in the training of critically needed technical professionals. This interdisciplinary academic program, encompassing hydrogeology, geochemistry, microbial ecology, chemical engineering, and civil engineering, shall evolve into a national resource by producing outstanding graduates to fill positions at other universities, national research facilities, federal agencies, and industry, and to train them to contribute to solving our Nation's problems in contaminant hydrogeology.

9410120 Herman This award will support a workshop involving academic scientists and federal agency liaisons to plan a new initiative in environmental geochemistry. The initiative will provide earth scientists with a mechanism by which new ideas and new approaches to environmental studies are fostered. The research conducted under the proposal initiative is expected to increase our knowledge and understanding of basic mechanisms and processes, at many different scales of space and time, that comprise the broad topical field of environmental geochemistry. Such research is essential for the well-being of the global environment and to mitigate the environmental consequences of human activities.

Ford
0083839

The release of chemical pollutants into groundwater disturbs the resident microbial community and triggers a complex network of feedback loops affecting the groundwater geochemistry, soil structure and microbial diversity of the system. Human intervention in the form of engineered remediation to restore the site introduces yet another disturbance to which the microbial community and abiotic components of the systems must respond. An emergent property typically associated with microbial communities is homeostasis. The objective of this research is to test the homeostasis hypothesis for a subsurface microbial community under the stress of a chemical pollutant release and the remedial actions which may follow.

To accomplish this objective will require effective collaboration among a team of scientists and engineers with expertise in microbiology, hydrology, biogeochemistry, engineering, ecological modeling, adaptive control theory, and data visualization. Incubator activities are designed to foster communications between experimentalists with an understanding of the physical system and mathematical modelers with quantitative tools for characterizing and predicting properties of the system. A relatively simple laboratory experiment [two bacterial species within a fixed-film flow-through column with a reactive mineral surface (iron) that serves as an alternative election acceptor in the absence of oxygen] is defined in order to explore three modeling approaches: (1) system of nonlinear partial differential equations for each species, (2) metabolic modeling, and (3) adaptive control theory. This prototype system will be used to focus the interdisciplinary discussions on a concrete problem and facilitate productive interactions. Additional modeling approaches will be explored through a brainstorming session, computer systems and a follow-up videoconference. A written summary from the workshop will be published in technical news journals to benefit the scientific community at large.

9909491
Herman

Colloids, mobilized within the vadose zone during rainfall events, scavenge and carry contaminants to underlying groundwater. Despite the importance of colloids as agents of vadose-zone contaminant transport, the factors influencing colloid movement through partially saturated porous media have not been rigorously explored nor formalized into a quantitative model. In particular, the role of flow transients on colloid interactions at solid-water interfaces, at air-water interfaces, and within thin films of water has not been adequately investigated to date. This research, carried out jointly by investigators at Yale and at UVA, will integrate laboratory-scale and field-scale experiments with mathematical modeling. We will measure colloid transport in laboratory experiments conducted with ideal media and with intact cores, and we will use these data to guide the development of a numerical model for the coupled advective-dispersive transport and mass transfer of colloids in unsaturated soils. The structure of the numerical model identified from analysis of the laboratory-scale experiments will form the foundation for a stochastic streamtube model, a model capable of accounting for the effects of spatial variability in soil properties on colloid fate and transport. The streamtube model will be tested against data from a field experiment in which colloid mobilization and transport is measured in response to transient flow events induced by controlled sprinkling over an instrumented field plot. Our work represents the first systematic approach to identifying the controls on colloid movement in water-unsaturated media under transient-flow conditions and provides a means to evaluate the contribution of the colloid track to contaminant fluxes within vadose-zone environments.

0208386
Mills
In field studies of groundwater in a range of hydrogeological settings, the rates of microbially mediated geochemical reactions have been shown to be far faster than hydrological transport rates. These relative rates lead to large changes in concentration of a variety of redox-sensitive chemical species over short distances within aquifers. In some systems, however, transient hydrological events (e.g., heavy precipitation on dry soil or floods in streams) can rapidly alter the geochemical environment in which the microbes exist. In that circumstance, the time constants associated with the physical events approach those of the microbially mediated processes. The proposed research addresses the question: How do hydrological processes and biogeochemical processes interact in the riparian-hyporheic zone of streams where time scales of the various processes are on the same order - hours to weeks? The proposed research will examine the effect of bank-storage events on reductive microbiological processes occurring in the riparian-hyporheic zone of a low-relief coastal plain stream. In particular, the concentration of nitrate-N in the groundwater feeding the stream is about 15 mg/liter, but the stream-water concentrations average only 1.6 mg/liter, suggesting high denitrification activity in the riparian- hyporheic zone. We envision the disruption of anaerobic processes during rain events in which rapid infiltration raises the water table and "flushes" chemicals (viz., nitrate) in the pore water out into the stream and perfuses the area with oxygenated water. We expect a similar disruption without flushing during storms in which a rapid rise in stream level pushes oxygenated water into the stream banks, thereby transiently extending the hyporheic zone. We will also examine the effect of flushing or bank-storage events on the denitrification and will document the rate of return of the functional abilities of the microbial communities to the pre-disturbance levels. Because these transient events have the potential to affect release of chemicals like nitrate from the groundwater into the surrounding surface waters, we will investigate how transient conditions in riparian soils affect the overall budget of biologically active chemicals. The proposed work includes detailed field observations, field manipulation experiments, laboratory batch and "mesocosm" experiments and mathematical modeling. We anticipate that we will learn how microbially mediated geochemical reactions and transient hydrological processes with time scales on the same order are linked. We will develop quantitative descriptions of these processes and investigate how frequently biogeochemical processes are "reset" by different hydrological events the synoptic data that we will examine how the transient effects of local processes influence regional nutrient fluxes.