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. Guams
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 Guams 214 sq. miles. The
plateau is also home to the majority of the islands
population and infrastructure, including major military
and civilian airports and the islands 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 islands 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]