Geophysical log data from Basalt Aquifers near Waipahu on the Island of Oahu and Pahoa on the Island of Hawaii, Hawaii
Two relatively new geophysical logging techniques, the digitally enhanced borehole acoustic televiewer and the heat-pulse flowmeter, were tested from 1987 to 1991 at two sites in Hawaii: Waipahu on the island of Oahu, and Pahoa on the island of Hawaii. Although these data were obtained in an effort to test and improve these two logging techniques, the measurements are of interest to hydrologists studying the aquifers in Hawaii. This report presents a review of the measurements conducted during this effort and summarizes the data obtained in a form designed to make that data available to hydrologists studying the movement of ground water in Hawaiian aquifers. Caliper logs obtained at the Waipahu site indicate the distribution of openings in interbed clinker zones between relatively dense and impermeable basalt flows. The flowmeter data indicate the pattern of flow induced along seven observation boreholes that provide conduits between interbed zones in the vicinity of the Mahoe Pumping Station at the Waipahu site. The televiewer image logs obtained in some of the Waipahu Mahoe boreholes do not show any significant vertical or steeply dipping fractures that might allow communication across the dense interior of basalt flows. Acoustic televiewer logs obtained at the Pahoa site show that a number of steeply dipping fractures and dikes cut across basalt flows. Although flow under ambient hydraulic-head conditions in the Waipahu Mahoe Observation boreholes is attributed to hydraulic gradients associated with pumping from a nearby pumping station, flow in the Waipio Deep Observation borehole on Oahu and flow in the Scientific Observation borehole on Hawaii are attributed to the effects of natural recharge and downward decreasing hydraulic heads associated with that recharge.