John A. Cherry, Ph.D. (Northern California)Director of the University Consortium for Field-Focused Groundwater
Contamination Research and Adjunct Professor, University of Guelph
Aquitards… Why They Matter
Dissolution From a Field-Scale Non-Aqueous Phase Liquid and the Implications with Respect to the Evolution and Longevity of Dissolved Phase Plumes
Most sedimentary hydrogeologic systems are comprised of two types of units: aquifers and aquitards. While groundwater is drawn from aquifers for beneficial uses, aquitards typically govern the sustainable yields and land subsidence, and provide some protection from contamination. Aquifers have received nearly all of the research, and they dominate groundwater education. However, aquitards frequently have greater influence on the groundwater system behaviors, both hydrologic and geochemical.
Aquitards composed of clayey sediment typically contain water of geologic age (many thousands of years old or older), especially in settings where fractures do not control groundwater flow. However, where networks of connected fractures dominate, aquitards then become part of the active flow system. Recent studies show that hydraulically active fractures are often much deeper than expected and, for most aquitards, determination of the depth and hydrogeologic nature of the fractures is of critical importance, especially given the worldwide relevance of aquitards for isolation of hazardous and high-level nuclear waste and containment of the impacts of fracking for shale exploitation.
This talk used field examples to illustrate why aquitards are at least as important in hydrogeology as aquifers, and are arguably more interesting. The talk examined the contaminant hydrogeology of some Holocene aquitards in Louisiana and China, Pleistocene aquitards in Ontario and Manitoba, and the nature of some older sedimentary rock aquitards in the United States and Canada.
After obtaining his B.A. degree in Geology at University of California, Santa Barbara, in 1972 and his Ph.D. in Geological Engineering from Colorado School of Mines in 1976, Dave Huntley taught graduate and undergraduate classes in groundwater hydrology for two years at University of Connecticut and 29 years at San Diego State University. Over that same period he has investigated and published on applications of remote sensing to groundwater studies, hydrogeologic controls on geothermal systems, groundwater flow and resources in fractured crystalline rock, geophysical applications to groundwater studies, aquifer testing in granular and fractured rock aquifers, and the effects of geologic heterogeneity on dissolved phase solute transport. His most recent research has focused on assessing the mobility of non-aqueous phase liquids (NAPLs) and field-scale dissolution of multicomponent NAPLs. He is currently Associate Editor of the journals Ground Water and Ground Water Monitoring and Remediation. In addition to his research and journal activities, he is a private consultant for both industry and regulatory agencies throughout the country.