Evaluating Best-Practice Capacities for a Carbonate Island Karst Aquifer: Northern Guam Lens Aquifer, Guam, USA

Monday, December 4, 2017: 2:50 p.m.
Nathan Habana, PhD , Water & Environmental Research Institute of the Western Pacific, University of Guam, Mangilao, Guam
John Jenson, PhD , Water & Environmental Research Institute of the Western Pacific, University of Guam, Mangilao, Guam
Stephen Gingerich, Ph.D. , Oregon Water Science Center, U.S. Geological Survey, Portland, OR

The Northern Guam Lens Aquifer (NGLA) provides 90% of Guam’s drinking water. Recent modeling results provided insights into how the existing water-production system might respond to new development and natural changes in recharge, but local policy makers and water managers have also asked “What is the ultimate volume of water that could be sustainably withdrawn from the aquifer if we had the best possible production system?” Answering this question requires, first, specifying a best-practice production system—which we define as one that is constructed and operated to deliver maximum production attainable for a given quality standard, constrained, of course, by the available technology and capital. Second, it requires reliable knowledge of the natural limits imposed by recharge and aquifer properties.

We present results from an ongoing modeling study directed at estimating aggregate production that could be achieved by a system of about the same number of vertical wells as in the present system but in which well locations and well-field production are chosen to maximize production for specified standards of salinity. Natural limits are imposed by specifying the same recharge and aquifer properties employed in the recent successful modeling study of the existing system.

Although an ideal production system as defined above may not be feasible in the near term, if ever, an estimate of the total production that could be obtained by such a system for specified salinities provides helpful insights for long-term planning and future decisions regarding sustainable management of the NGLA.

Nathan Habana, PhD, Water & Environmental Research Institute of the Western Pacific, University of Guam, Mangilao, Guam
Dr Habana is Assistant Professor of Groundwater Hydrology at the University of Guam's Water & Environmental Research Institute of the Western Pacific (WERI). His duties at WERI include serving as Coordinator for the Guam Hydrologic Survey Program, which compiles and analyzes basic data on Guam’s freshwater resources. His current research interests include modeling of vadose and phreatic transport, and the management of salinity and nitrate contamination in island aquifers.


John Jenson, PhD, Water & Environmental Research Institute of the Western Pacific, University of Guam, Mangilao, Guam
Dr Jenson is Professor of Groundwater Hydrology, and Director of the University of Guam's Water & Environmental Research Institute of the Western Pacific (WERI). His current research interests include development of the Carbonate Island Karst Model and its application to numerical modeling and sustainable management of island karst aquifers.


Stephen Gingerich, Ph.D., Oregon Water Science Center, U.S. Geological Survey, Portland, OR
Dr. Stephen Gingerich has been a research hydrologist for the U.S. Geological Survey since 1995, and is now located in Portland, Oregon. Dr. Gingerich has extensive experience in the hydrology and water resources of oceanic islands - he has worked on groundwater resources issues on islands all over the world, with a focus on Hawaii. He performed field studies to characterize island coastal aquifers, recharge, and hydrogeology, and he is an expert on numerical modeling of seawater intrusion in coastal aquifers.


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