Water in the Aquifers
The potential for an aquifer to provide a reliable source of good-quality water depends on the amount of recharge that occurs from rainfall, the physical properties of the aquifer, and how the water is pumped or removed from the ground. Because of Saipan's relatively small size and oceanic setting, groundwater resources are vulnerable to overpumping and saltwater intrusion.
Freshwater and Saltwater in Saipan’s Limestone Aquifer and Volcanic Rock
Only a small portion of rainwater reaches Saipan’s aquifers; most runs off into streams, evaporates, or moves into the air through plants. Water that infiltrates the soil and passes the roots of plants continues downward to recharge groundwater in the aquifers. The groundwater system is dynamic: fresh groundwater flows through the aquifers from areas of recharge to areas of natural groundwater discharge, such as springs, streams, and coastal seepage, and some groundwater is pumped from wells.
Saltwater also enters the aquifer from the ocean. In the high-permeability limestone aquifer, fresh groundwater forms a thin lens-shaped body that overlies denser saltwater that has permeated the aquifer from the ocean. Between the freshwater lens and the underlying saltwater is a transition zone of brackish groundwater. Groundwater also occurs in the volcanic-rock basement of Saipan, but this water is not easy to pump because the rock has such low permeability.
