Groundwater Development Potential and Conceptual Hydrogeologic Model for Tutuila, American Samoa

On Tutuila, the main island in the Territory of American Samoa, sustainable water
resources management is a high priority. Groundwater provides drinking water to over 90%
of the island’s residents. However the sustainability of this resource is threatened by overuse,
salinization of wells, and reduction of water quality—potentially due to prevalent non-point
pollution sources. Proposed solutions to these and other water issues on the island involve
exploration for new groundwater sources with lower contamination potential and
development of updated tools for management of existing resources. Both of these objectives
benefit from an increased understanding of Tutuila’s subsurface structure and revisions to the
conceptual hydrogeologic model of the island. In this report, currently available hydrological
information was compiled with recently acquired subsurface datasets to inform an updated
conceptual hydrogeological model of Tutuila’s groundwater and surface water resources.
Published reports, recently collected data, and studies from similar basaltic islands were
integrated to explain groundwater behavior in Tutuila’s already developed basal aquifers, and
to inform hypotheses of high-level groundwater occurrence where data limitations exist.
Datasets presented include borehole, geophysical, water level, aquifer test, geomorphologic,
and surface water data.