Ground-water resources of selected high volcanic islands of Truk with emphasis on small village supplies

Existing water supply sources in the Truk State were assessed. The first part of the assessment includes the high islands in the Truk Lagoon and the second part includes the principal inhabited outer islands of the Truk State. The high islands in the lagoons are remnant peaks of a partly sunken volcano. Coral atolls form the periphery of the lagoon. The islands are composed of tight, massive lavas and cemented rock fragments. Although saturated, the rocks yield little water to springs or wells. Weathering causes some increase in permeability, and where the weathering is the deepest as in valleys, these materials make up the main reservoirs of groundwater. Rainfall averages about 140 inches/yr and is sufficiently persistent to provide water for drinking and cooking from small rain catchments, springs and seeps with little or no storage. This situation is not desirable because rainless periods, even short ones, cause springs, seeps, and rain barrels to go dry quickly. (USGS)