Geophysical survey : ground water evaluation, Mauna Kea Properties

Date
1990-08-22
Authors
Nance, Tom
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Blackhawk Geosciences, Inc.
Tom Nance Water Resource Engineering
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"This report contains the results of a geophysical survey for ground water resource evaluation on the Mauna Kea Properties area on the Island of Hawaii. The work was performed for Mauna Kea Properties (MKP) by Blackhawk Geosciences, Inc. (BGI) from July 27 through July 30, 1990. The general objective of the geophysical survey at the MKP area was to assist in characterizing the hydrologic regime in the study area. The volcanic rocks are generally highly permeable and this allows rainwater to percolate with little impedance directly downward through the island mass. The fresh water in these island settings is generally 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. In cases of hydrostatic equilibrium, the Ghyben-Herzberg relation states that for every foot of fresh water head above sea level there will be about 40 ft of fresh water below sea level. At MKP, ground water was expected to occur mainly as basal fresh water. The impetus for using geophysics is that the cost of a geophysical sounding is about one-thousandth the cost of completing a well at elevations above 1,000 ft. Geophysical surveys, combined with other hydrogeologic information, are used to provide optimum locations for well placement and well completion depths. The geophysical method employed was time domain electromagnetic (TDEM) soundings. This method was selected because it has proven effective in prior surveys in similar settings in Hawaii."
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groundwater, TDEM, Mauna Kea, Big Island, Hawaii, Geology--Hawaii, Groundwater--Hawaii, Water-supply--Hawaii, Geology, Groundwater, Water-supply
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39 pages
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