Molokai

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Time domain electromagnetic surveys for assisting in determining the groundwater resources on Kawela Plantation property, Island of Molokai

(Blackhawk Geosciences, Inc., 2006-01) Nance, Tom

"This report contains the results of surface Time Domain Electromagnetic (TDEM) geophysical surveys performed for groundwater resource evaluation at the Kawela Plantation Property located approximately two miles east of the town of Kaunakakai on the Island of Molokai. Blackhawk a Division of ZAPATA ENGINEERING (Blackhawk) conducted the surveys from January 13 through 16, 2006 for Kawela Plantation Homeowners Association (Kawela) of Kaunakakai, Hawaii and Tom Nance Water Resources Engineering (TNWRE) of Honolulu, Hawaii. TDEM is a geophysical method that determines from the surface the geoelectric section (resistivity layering) of the subsurface. From the geoelectric section, information about geology and water quality can be inferred. This is possible because the electrical resistivity of the earth depends on lithology, porosity, the degree of saturation, and concentration of dissolved solids in the groundwater. The main objective of the TDEM surveys on Molokai was to explore for possible basal groundwater occurrences at the survey areas. The TDEM surveys were conducted along the approximate 525 ft (160 m) elevation level on Kawela Plantation Properties I, II and III located above the town of Kawela, Hawaii. Geophysical surveys, combined with other hydrogeologic information, are used to provide optimum locations for well placement and well completion depths."

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Geophysical surveys for assisting in determining the groundwater resources, Puu O Hoku Ranch site, Island of Molokai, Hawaii

(Blackhawk Geosciences, Inc., 1999-01-12) Nance, Tom

This report contains the procedures and results of surface geophysical surveys conducted to assist in determining the groundwater resources on property owned by Puu o Hoku Ranch, Ltd., Island of Molokai, Hawaii. The geophysical method employed during this survey was Time-Domain Electromagnetic (TDEM) soundings. The surveys were performed by Blackhawk Geometries (Blackhawk) for Puu o Hoku Ranch, Ltd. during December 5 to December 8, 1998. Survey oversite was provided by Tom Nance of Tom Nance Water Resource Engineering (TNWRE). The TDEM soundings for this survey were positioned on the ranch property above and below the main water tank, and on pasture land located below the ranch buildings. The Puu o Hoku Ranch of Molokai is located on the eastern portion of the island. The ranch property lies on the eastern dipping flank of the East Molokai Volcano. The main geologic feature on this portion of the Island of Molokai is the eastward trending rift zone, which is suggested by Fiske and Jackson (1972) to extend away from the caldera complex of the East Molokai Volcano toward the coastline to the mouth of Halawa Valley. A mapped volcanic cone near Koalii (Stearns and Macdonald, 1947) is also located in the study area. The main objective of the geophysical survey was to assist in characterizing the hydrologic regime at the Puu o Hoku Ranch site for a proposed groundwater well. Groundwater resources can occur on the Island of Molokai basically in two modes: • In a basal mode, where a lens-shaped body of fresh water floats on saline water, and • In a high-level mode, where the groundwater occurrence is controlled by subsurface damming structures. The surficial volcanic rocks in an island setting are generally highly permeable, and this allows rainwater to infiltrate directly downward through the island mass. The basal groundwater lens extends from the outer edges of subsurface structures (i.e., impervious dikes) to a discharge area near the shoreline. The subsurface structures can impede the flow of groundwater from the interior of the island toward the sea and result in fresh water-filled compartments that can extend above and below sea level. These types of occurrences are referred to as high-level ground water on the Hawaiian Islands. At the Puu o Hoku Ranch study area, groundwater was expected to occur mainly as a basal fresh-brackish water lens. Previous TDEM surveys on the Hawaiian Islands have reliably mapped the boundary between fresh water in the basal mode and high-level water occurrences. Geophysical surveys, combined with other hydrogeologic information, are used to provide optimum locations for well placement and completion depths.

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Geophysical surveys performed on the Island of Molokai, Hawaii : final report

(Blackhawk Geosciences, Inc., 1995-12-18) Nance, Tom

The TDEM geophysical technique was effective at mapping the fresh/saline groundwater interface in the Kawela Plantation area of Molokai. Soundings were made along two survey lines which extended from an elevation of approximately 1,300 ft (400 m) ASL to 2,700 ft (820 m) ASL. Below approximately 2,100 ft (640 m) ASL, the fresh/saline water interface was mapped in both lines. In Line 2, a significant thickening of the basal groundwater lens occurs between soundings made at elevations of 1,470 ft (450 m) ASL and 2,100 ft (650 m) ASL. It is likely that a change in horizontal hydrologic permeability, possibly caused by a leaky volcanic dike, is present in the area between the lines. Above approximately 2,100 ft (640 m) ASL, the TDEM soundings do not map the saline/fresh groundwater interface. The- depth of exploration for these soundings indicates that the interface has to be below an elevation of approximately 750 ft below sea level. Although it is probable that volcanic dike damming structures occur either at the higher elevation soundings or immediately down slope from them, it is unknown if high-level groundwater is present at these sites.

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Time domain electromagnetic survey -- western portion of the Island of Molokai, State of Hawaii

(Blackhawk Geosciences, Inc., 1990-01-12) Nance, Tom

This report covers the results of the time domain electromagnetic (TDEM) survey performed by Blackhawk Geosciences, Inc. (BGI) for Alpha U.S.A. Inc., (Alpha) on the Island of Molokai, Hawaii. The field work was done between November 29, 1989 and December 13, 1989. The objectives of the survey were to: 1. Map the thickness of the brackish water basal lens underlying the western portion of the island. Identify areas of potential high level dike impounded ground water. 2. To accomplish these objectives a total of 42 TDEM soundings were performed. These soundings were located on Alpha's property on Molokai and on Molokai Ranch property in areas that are of interest to Alpha.

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Geophysical surveys -- Island of Molokai, Hawaii

(Blackhawk Geosciences, Inc., 1990-03-29) Nance, Tom

This report covers the results of geophysical surveys conducted by-Blackhawk Geosciences, Inc. (BGI) for Alpha U.S.A., Inc. (Alpha) on the island of Molokai, Hawaii. The field work was performed between February 15 and March 4, 1990. Three separate geophysical surveys were used by BGI. The geophysical surveys conducted and their individual objectives are as follows: 1. Seismic refraction surveys were utilized to map the depth to volcanic rocks and the seismic velocity distribution of the rock units in the area of Kamkaipo located in the southwest corner of the island. The seismic velocity distribution was subsequently correlated to mode and ease of excavation. 2. Gravity surveys were performed to outline intrusive (dense) bodies which may form a base to dike-impounded ground water and may be a source of vertical impounding dikes. 3. Time domain electromagnetic CTDEM) surveys were conducted to map the thickness of the fresh to brackish water lens and the location of dike-impounded ground water to better outline the geohydrologic system of Molokai's central aquifer area. In addition, work was performed to further delineate areas of relatively thick brackish water lenses identified in the previous TDEM survey in the western portion of Molokai. The report is written in two parts. The first part consists of the TDEM and gravity surveys which address the mapping of ground water resources on Molokai, and the results of the seismic survey are contained in the second portion.

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Geology and ground-water resources of the Island of Molokai, Hawaii

(U.S. Geological Survey, 1947) Stearns, Harold T. ; MacDonald, Gordon A.

Includes illustrations, plates, two maps, and bibliographical footnotes.

Molokai

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