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

Abstract

The general objective of the geophysical survey at the Ulupalakua Ranch property was to assist in characterizing the hydrologic regime in the study area. The volcanic rocks are generally highly permeable and this allows rainwater to percolate with little impedance directly downward through the island mass. 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.