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Ground-Water Availability from the Hawi Aquifer in the Kohala Area, Hawaii

Water-Resources Investigations Report 95-4113

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Abstract

A ground-water study consisting of test-well drilling, aquifer tests, and numerical simulation was done to investigate ground-water availability in the basal part of the Hawi aquifer between the western drainage divide of Pololu Valley and Upolu Point in Kohala, Hawaii. The test-well drilling provided information on geology, water levels, water quality, vertical extent of the freshwater, and the thickness of the freshwater-saltwater transition zone in that aquifer. A total of 12 test wells were drilled at eight locations. Aquifer tests were done at five locations to estimate the hydraulic conductivity of the aquifer. Using information on the distribution of recharge, vertical extent of freshwater, hydraulic conductivity, and geometry of the basal aquifer, a numerical model was used to simulate the movement of water into, through, and out of the basal aquifer, and the effect of additional pumping on the water levels in the aquifer. Results of the modeling indicate that ground-water withdrawal of 20 million gallons per day above the existing withdrawal of 0.6 million gallons per day from the basal aquifer is hydrologically feasible, but that spacing, depth, and pumping rates of individual wells are important. If pumping is concentrated, the likelihood of saltwater intrusion is increased. The additional withdrawal of 20 million gallons per day would result in a reduction of ground-water discharge to the ocean by an amount equal to pumpage. Although model-calculated declines in water-level outside the area of pumping are small, pumping could cause some reduction of streamflow near the mouth of Pololu Stream.

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Ground-Water Availability from the Hawi Aquifer in the Kohala Area, Hawaii
Series title:
Water-Resources Investigations Report
Series number:
95-4113
Edition:
-
Year Published:
1995
Language:
ENGLISH
Publisher:
Geological Survey (U.S.)
Contributing office(s):
Pacific Islands Water Science Center
Description:
vi, 57 p.