Geophysical surveys for ground water evaluation, North of Waikoloa Village, Island of Hawaii

"The objective of the geophysical survey was to add additional TDEM information to the existing (1988 and 1990) data set along Kamakoa Gulch, North of Waikoloa Village. The concepts for using geophysical surveys for ground water evaluations can be understood using the generalized hydrogeologic cross section. In the Hawaiian islands, the volcanic rocks are generally highly permeable and rain water rapidly percolates into the ground and migrates downward to the water table. Fresh water in these settings is found in two environments: 1. Dike-confined waters -- Typically, above the rift zone, intrusive dikes originating from a magma source below can form ground water dams, and behind these natural dams significant quantities of ground water can be stored. 2. Basal fresh water -- The high permeability of the volcanic rocks allows sea water to enter freely under the island, and a delicate balance is reached where a lens of fresh water floats on sea water."Waikoloa Development Compan