GROUNDWATER RESEARCH

Guam relies on groundwater for about 80% of its drinking water production to support 150,000 permanent residents and a rapidly growing tourism industry that serves over 1,000,000 tourists each year. Guam’s principal aquifer, the Northern Guam Lens Aquifer, is tapped by over 100 municipal wells producing over 30 mgd, about half of the current estimated sustainable yield. The aquifer lies beneath the Pleistocene karst plateau formed on the Cenozoic limestone sequence occupying the northern half of Guam’s 214 sq. miles. The plateau is also home to the majority of the island’s population and infrastructure, including major military and civilian airports and the island’s tourist district. Although Guam receives an average of almost 100 inches of rain annually, recharge rates are poorly known, particularly since the surface of the aquifer is being rapidly modified by construction driven by the island’s rapid economic growth.

WERI researchers are mapping the key hydrogeologic features of northern Guam, including plateau and basement topography, faults, fractures, sinks, and coastal seeps and springs. Maps of natural the features are combined with GIS-based maps of precipitation data and human hydrologic modifications of the surface, including storm drainage and ponding basins, urban and suburban housing developments, and large airfields. These data provide the basis for a comprehensive surface hydrologic model, which will enable more accurate estimates of groundwater recharge and the potential effects of surface development. We are coupling the surface model with a numerical groundwater flow/salt water intrusion model. The coupled model will provide means for assisting planners, managers, and regulators with estimates of groundwater discharge into coastal waters as well as aquifer responses to increased extraction and natural or anthropogenic changes in recharge.

For More Information on The Groundwater Modeling Project send e-mail to:
Dr. John Jenson: [email protected]