Application of Deep Electrical Soundings for Groundwater Exploration in Hawaii

Abstract

Forty‐five resistivity soundings, using Schlumberger and equatorial dipole electrode configurations, were made on the islands of Oahu and Hawaii to determine the applicability of direct current resistivity methods for locating freshwater aquifers in the State of Hawaii. The soundings were made on the northwestern part of the island of Oahu near the town of Waialua and on the island of Hawaii on the “saddle” area near Pohakuloa and Humuula. Interpretation of 32 sounding curves obtained on the island of Oahu indicates that it is possible to correlate five stratigraphic units underlain by a vesicular basalt basement and that the determination of the approximate depth to the fresh‐water‐saline‐water interface within the basalt is feasible. Two of these Schlumberger soundings with electrode spacings [Formula: see text] reaching 6000 ft yielded sounding curves of the maximum and minimum types whose terminal branches asymptotically approach a resistivity of about 30 ohm‐m, which is believed to be the true resistivity of basalt saturated with sea water. Near the town of Waialua the aquifer is a coral zone as well as parts of the weathered vesicular basalt basement. On the island of Hawaii, near Pohakuloa, an exploratory well drilled in basalt to a depth of 1001 ft (prior to the resistivity survey) proved to be dry. Interpretation of thirteen deep soundings made with Schlumberger and equatorial arrays suggests that the minimum depth to a conductive layer, which may represent basalt saturated with fresh water, is about 2700 ft below land surface. The groundwater appears to be dike impounded.

Hydrologic and Isotopic Modeling of Alpine Lake Waiau, Mauna Kea, Hawai'i

“…Research on Mauna Kea hydrogeology establishes that the near-summit hydrologic system is dominated by ephemeral stream flow in response to storm-induced precipitation and rapid snowmelt (Stearns andMacdonald 1946, Woodcock andGroves 1969). Electrical resistivity studies show that the main water table on Mauna Kea is many thousands of meters below the summit of the mountain (Zohdy and Jackson 1969). Shallow subsurface flow is guided downhill by the presence of impermeable substrates (Woodcock 1980).…”

Preliminary Geothermal Evaluation of the Mokapu Peninsula on the Island of Oahu, Hawaii.

“…If this is the case, the low resistivities observed below sea level could be explained without the need for higher-than-normal temperatures. Zhody and Jackson (1969) give a value of 3 ohm-m for clay saturated with brackish-to-saline water that they observed close to the coast in the Waialua area, about 30 kilometers west of Mokapu Peninsula. The presence of clay to a depth of more than 100 meters below sea level in this area does not have any direct confirmation from other data.…”

Interpretation of time-domain electromagnetic soundings in the East Rift geothermal area of Kilauea Volcano, Hawaii

“…Conductivities do increase with depth in the logs of well HGP-A (Rudman, 1978), substantiating this hypothesis. Utilizing the test well HGP-A as a control point and assum- saturated basalt (Zohdy and Jackson, 1969). Below 1,200 m, this resistivity decreases to about 5 ohm-m.…”