HOW CAN WE SUSTAIN GROUNDWATER QUALITY IN KARST AND FRACTURED-CARBONATE AQUIFERS?

Fractured-carbonate and karstic aquifers provide important, but vulnerable, sources of drinking water. The dual-porosity nature of these aquifers-- high-permeability fractures or conduits transmit the majority of the water while the lower-permeability matrix blocks provide the storage capacity -- make them exceedingly susceptible to contamination, challenging to characterize, and difficult to model. These aquifers typically exhibit high spatial variability, rapid transport times, and variable water quality. Characterization of these aquifers is often limited by budget constraints and thus precludes the detailed characterization of high-permeability pathways. Yet many potentially-polluting land-use activities – such as farming or waste disposal – are located atop these vulnerable aquifers. As hydrogeologists, what insight can we provide that will help sustain these aquifers as future sources of water supply? This talk will use case studies from Wisconsin to illustrate the state of both our knowledge and our regulation of these aquifers.

Wisconsin is an agriculturally intensive state. Existing water-quality samples from counties that lie above the fractured Silurian-dolomite aquifer in eastern Wisconsin suggest that elevated levels of nitrate and bacteria are pervasive. Previous monitoring attempts were unable to document an improvement in water quality with the implementation of agricultural Best Management Practices (BMPs). So what advice can we give resource planners? Can we apply BMPs developed for porous-medium aquifers? Do we need to develop and enforce a new set of BMPs?

In a second example, a proposed landfill expansion, also sited atop the Silurian-dolomite aquifer, will provide the context for exploring the current regulations that govern the design and operation of monitoring systems in these settings. Are current rules adequate? How can hydrogeologists characterize existing site conditions and design monitoring systems that are cost-effective yet are capable of capturing the complexity of these systems?

These questions cannot be answered in this presentation. Yet if we hope to be able to continue to use these productive aquifers as a source of future water supplies, hydrogeologists must begin to address these issues.