Lecture Titles and Abstracts
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Cracks in the Clay: The Role of Fractures and Macropores in Critical Zone Hydrology
Fine-grained geologic deposits often contain extensive networks of fractures, root holes and other macropores which can strongly influence groundwater flow and contaminant transport. The extent and depth of these features varies greatly according to the origin and geologic/pedologic history of the material. Rootholes typically persist to depths of only a few meters, although in some clays they can be found at much greater depths. Desiccation fractures, which are common in glaciolacustrine deposits, also tend to rapidly decrease with depth, but fractures caused by sub-glacial stresses may be pervasive throughout thick till seququences. Recent research in weathered clay-rich residuum developed on sedimentary rocks in east Tennessee show evidence of fractures and fracture-induced flow to depths of up to 40 m. Fractures and macropores can also act as pathways for transport of natural and anthropogenic constituents to underlying aquifers. Solutes are transported by advection along the fractures/macropores but can also be strongly attenuated by diffusion into the fine pore structure. In contrast, mineral colloids and microorganisms, are largely size-excluded from the fine-pore structure and hence can travel at much faster rates than solutes. Field tracer experiments in fractured clays in Canada, Denmark and Tennessee showed colloid transport rates of a few m/day to >100 m/day at sites where solute tracers were transported at rates that were 100s of times slower. Immiscible phase liquids, such as industrial solvents or coal tar, can enter some fractures or macropores, even in relatively low hydraulic conductivity materials and can lead to extensive contamination. These immiscible liquids dissolve and diffuse into the fine pore structure, where they can act as long term sources of contamination to adjoining streams or underlying aquifers. Although there has been substantial progress over the past 25 years in developing a better understanding of the role of fractures in controlling flow and transport in clay-rich deposits, considerable work remains to be done. This includes better education of geo-environmental researchers and professionals, as well as development of better conceptual and numerical models of fracture origin, vadose and saturated zone flow, and contaminant transport.
Germs and Geology: Emerging Issues in Waterborne Pathogen Research
This lecture will address how recent hydrological research and development of new analytical methods in molecular microbiology can combine to change how we detect, monitor and predict the exposure of human populations to waterborne pathogens. Much of our understanding of waterborne pathogen occurrence and transport is based on conceptual models and investigative methods that have changed little in the past 30-50 years. Traditional paradigms for waterborne pathogens can be described with terms as simple as coliforms=pathogen-risk, surface-water=bad, groundwater=good, karst=bad, sand=good, true-groundwater=good, and groundwater-under-the-direct-influence-(GWUDI)-of-surface-water=bad. Recent investigations at UT and many other institutions challenge the existing paradigms. For example, a study of community water supply wells in karst aquifers in east Tennessee indicated that enteric viruses are common and can occur even in wells that don’t exhibit other indicators of fecal contamination. Other studies at UT show that very rapid transport of bacteria and viruses can occur in fractured clay-rich sediments and in partially-saturated soils, both of which are settings where slow transport of pathogens is usually expected. There is a great need for additional field-based studies of pathogen occurrence and transport, as well as better collaboration between hydrologists, microbiologists and the public health community. Development of faster or easier to use microbial assays, as well as better sample collection and concentration methods, are providing hydrological researchers with improved tools to help carry out this research. Chief amongst these tools is the development of molecular assays, such as qPCR, which detect pathogens or other fecal microorganisms based on their DNA or RNA signature. Investigators at UT have developed a series of qPCR assays for Bacteroides (a major constituent of feces), which can be used to rapidly and inexpensively determine both the fecal concentration in a water sample and the likely source (human, cattle, horse, etc.). These assays have been used to delineate contaminant sources in watershed studies and have the potential for use in field experiments, allowing bacteria from different fecal sources to be traced throughout a flow system.
Chattanooga Creek: How 30,000 tons of Coal Tar Brought Together Scientists, Social Workers and a Community (this talk is especially suitable for undergraduate institutions or programs)
Chattanooga Creek flows through a mixture of low income urban neighborhoods, commercial developments and old industrial sites. One of the largest contaminant sources in the area is a former manufactured gas/coke plant, which is typical of many of the thousands of such sites found across the U.S. Researchers at the University of Tennessee (UT) investigated distribution and transport coal tar compounds (mostly PAHs) in the soils at the coke plant site and in laboratory experiments. The studies show that immiscible tar and dissolved PAHs can readily penetrate fractures and macropores in the fine-grained soils and are transported through groundwater at substantially higher rates than previously expected. However, contamination is also widespread in the creek, which was the principal concern of local residents. In response to community concerns, we shifted our research to focus on transport and persistence of PAHs in the streambed and floodplain, as well as investigations of the residual contamination that remains after typical excavation-based cleanup measures. In conjunction with the scientific research, we’ve worked with the UT College of Social Work and local community groups to establish an Environmental Health and Justice Collaborative, which is funded by the National Institute for Environmental Health. Activities for the collaborative include environmental education for residents, health and wellness training, mentoring of high schools students and collaboration with environmental health researchers. The point of this story is that successfully dealing with environmental problems often requires collaboration between a variety of different groups, including local residents, community activists, scientific researchers and regulatory agencies.