Time domain electromagnetic survey for assisting in determining the groundwater resources at the Palawai Basin, Windward Coast and Northwest Rift Project areas, Hawaii

Nance, Tom
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Blackhawk Geosciences, Inc.
Tom Nance Water Resource Engineering
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"This report contains the results of time domain electromagnetic (TDEM) surveys conducted to assist in determining the ground water resources at three project areas (Palawai Basin, Windward Coast and Northwest Rift) on Lanai Company properties on the Island of Lanai, Hawaii. The surveys were performed by Blackhawk Geosciences Division of Coleman Energy & Environmental Systems (CEES-BGD) for Lanai Water Company, Inc. (LWCI), an affiliate of Dole Food Company, Inc. from August 5 to August 19, 1994. Previous TDEM survey data taken during 1993 near the Manele Bay Hotel have been incorporated into this report. Ground water resources occur on the Hawaiian Islands basically in two modes: • in a basal mode where a lens of fresh water floats on saline water, and • in a high-level mode where the ground water occurrence is controlled by damming structures. These two modes of ground water occurrences are illustrated in Figure 1-2. Previous IDEM surveys on Lanai and other Hawaiian Islands have reliably mapped the boundary between fresh water in the basal mode and high-level occurrences. Normally, this main ground water boundary generally parallels the coastline in a volcanic setting. Water well production data from the Palawai Basin on Lanai has shown that other secondary damming structures exist above the main damming structure. A major ring fracture developed from a caldera which is shown near parallel to the shoreline. Also shown are radial fractures which are shown to form near perpendicular to the major caldera ring fracture. Not shown are subsequent minor ring fractures which are postulated to occur within the major ring fracture. It is also postulated that the fracture areas are zones of weakness where intrusive dikes may preferentially form and these dikes can be impermeable. These radial fractures could be numerous and they could divide the high-level water into different compartments behind the major ring fractures. The resultant water production from a single compartment will be determined by several important factors which include permeability, porosity, size of and recharge to the compartment. Based on the hydrologic information described above, the objectives for each of the three project areas are given in the following: • determine if potential high-level ground water occurs throughout the Palawai Basin Project Area at locations above the approximate 1,000 ft (305m) elevation level, • determine the approximate inland position of the basal to high-level ground water boundary at the Windward Coast Project Area, and • attempt to determine the boundary width of the expected rift zone at the Northwest Rift Project Area.
groundwater, TDEM, Palawai Basin, Lanai, Hawaii
195 pages
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