The interface is in the form of a transition zone from freshwater to saltwater and slopes downward and landward from the coastline. Freshwater from the aquifer moves up this interface to discharge at the sea floor. The chemical quality of water in the Kingshill aquifer is marginal for human consumption and most other uses. Dissolved-solids concentrations generally exceed 1,000 milligrams per liter, which is the definition of saline water used in this report. These values are for the part of the aquifer that contains the least mineralized water.
Water quality deteriorates with depth and is highly saline in some areas.
The island environment of the Kingshill aquifer has an influence on ground-water quality. The source of ions in the water is not only from partial dissolution of aquifer minerals, but includes ions from seawater that is transported to the land surface by precipitation, waves, and sea spray and percolates downward to recharge the aquifer. Chloride in the ground water is largely from sea spray or residual salts in the aquifer matrix. Other ions are probably derived from dissolution of aquifer minerals, which include carbonate minerals as well as siliceous volcaniclastic material incorporated in the aquifer. Water in the Kingshill aquifer becomes highly mineralized with depth.