Geophysical surveys for ground water evaluation, central aquifer and west beach areas, Oahu, Hawaii

Abstract

In the Central Aquifer area the TDEM soundings taken near wells at the 400-ft elevation show good agreement with borehole data in depth to the unconformity between the Koolau and Wainae flows and in the depth to fresh-brackish water. TDEM soundings taken at other locations failed to detect the unconformity. However, data density across much of the Central Aquifer area was inadequate to properly define the existence of the unconformity. The low data density was mainly due to property access restrictions imposed during the field survey. TDEM soundings taken at the West Beach area show excellent agreement with water well data in the area, and indicate that a hydrologic barrier (possibly a dike) exists in the vicinity of soundings WB2W and WB4W. In the Central Aquifer area additional TDEM soundings would be helpful to better define the orientation of the unconformity between the Koolau and Waianae flows detected on Line lN. Additional data between Lines lN and 2N and east of Kunia Road would also help to define the position of the fresh water head in this area.