Geophysical survey, ground water evaluation, Haleakala Ranch, Maui, Hawaii

Abstract

At Haleakala Ranch ground water was expected to occur mainly as basal fresh water. The impetus for using geophysics is that the cost of a geophysical station is about one-thousandth the cost of completing a well at elevations above 1,000 ft. Geophysical surveys, combined with other hydrogeologic information, are used to provide optimum locations for well placement and well completion depths. Ground water resources can occur on the Island of Hawaii basically in two modes: • In a basal mode, where a lens-shaped body of fresh water floats on saline water, and • In a high-level mode, where the ground water occurrence is controlled by subsurface damming structures. The surficial volcanic rocks are generally highly permeable and this allows rainwater to infiltrate directly downward through the island mass. Previous TDEM surveys on the Hawaiian Islands have reliably mapped the boundary between fresh water in the basal mode and high-level water occurrences. Geophysical surveys, combined with other hydrogeologic information, are used to provide optimum locations for well placement and completion depths.