Time domain electromagnetic surveys near Kukaiau, Hamakua Coast, Island of Hawaii

Abstract

"This report contains the results of time domain electromagnetic (TDEM) surveys conducted near Kukaiau, on the Hamakua Coast, Island of Hawaii. The survey was performed by Blackhawk Geosciences, Inc. (BGI) for Frank S. Hahn during June 1992. The overall objective of the survey was to assist in defining the potential fresh water resources at a study site which lies about 12,000 ft south of Kukaiau at an elevation of 2,200 ft. To gain an understanding of the geohydrologic regime at the study area, measurements were taken on a south to north transect which extends from the study area towards the ocean across land owned by Hamakua Sugar. The two major factors which influence the location and availability of fresh ground water in this geologic setting are (i) the elevation of the fresh water - salt walter interface for basal ground water occurrences, and (ii) the location and attitude of potential ground water damming structures (e.g., dikes) and aquitards. Thus, the specific objectives of this survey were to • map the fresh water - salt water interface underlying the survey area, and • identify and map geologic structures or lithologic units which may affect ground water distribution. In IDEM surveys the electrical resistivity of the subsurface is measured. Previous IDEM surveys on the Hawaiian Islands have shown large resistivity contrasts to occur between volcanics saturated with fresh water and saline water. In most cases, also significant resistivity contrasts exist between geologic structures and unweathered volcanics."