Lanai

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Time domain electromagnetic surveys for assisting in determining the groundwater resources on the Island of Lanai, Hawaii

(Blackhawk Geosciences, Inc., 2001-09-12) Nance, Tom

Time Domain Electromagnetic (TDEM) surveys were performed by Blackhawk GeoSciences for the Lanai Water Company in August 2001. The objective of the TDEM surveys is to add additional detail to previous TDEM interpretations, and to explore for anomalous basal groundwater occurrences. The previous TDEM surveys conducted by Blackhawk are summarized in Blackhawk project report number 9081-000, dated December 15, 1994. In this (present) TDEM survey, seven areas were surveyed. The specific objectives of the present surveys were: • To refine the location of the interpreted groundwater damming structure at selected locations (Areas 1 and 2), and • To explore for anomalous basal groundwater occurrences (Areas 3-7). The TDEM surveys in Area 1 resulted in repositioning of the interpreted groundwater structure approximately 800 to 1,000 feet further west (seaward) than previously interpreted. This new position reduces the available basal groundwater resource in this Area. The TDEM surveys conducted in Area 2 show that the position of the main groundwater damming structure is unchanged; however a geologic structure (interpreted as a rift zone) was interpreted in Maunalei Gulch. Groundwater wells in the vicinity of these structures have historically been poor. The results of the exploration for anomalous basal groundwater occurrences in Areas 3-7 indicate that Areas 4 and 6 may have better than normal basal groundwater resources compared to other basal mode occurrences on Lanai. To date, most wells drilled for basal mode groundwater occurrences on Lanai have been poor. This interpretation is based on the relative depth of the saltwater intrusion over a limited area at the sites. At both sites the depth to saltwater intruded formations is deeper than expected, inferring a thicker brackish/fresh water resource. Other factors, such as a decrease of permeability of the formation, or existence of altered volcanics may contribute to this increase in depth of the saltwater intruded formations. Both of these conditions would result in low production wells. The results from this survey do not indicate that the existence of anomalous basal groundwater resources. The present survey supports the conclusions derived from previous surveys, i.e.: • Basal groundwater is present around the perimeter of the Island, but the fresh/brackish water lens is limited. The thickness of fresh/brackish water above sea level is expected to be a minimal resource. • A geologic/hydrologic discontinuity interpreted as a ground water damming structure is present around the entire Island. The potential for significant high-level ground water is present throughout the central portion of the entire Island. Well data has substantiated this interpretation.

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Time domain electromagnetic surveys for assisting in determining the groundwater resources on the Island of Lanai, Hawaii : preliminary report

(Blackhawk Geosciences, Inc., 2001-08-29) Nance, Tom

"This report contains the results of surface Time Domain Electromagnetic (TDEM) geophysical surveys performed on the Island of Lanai for Lanai Water Company. The surveys were conducted by Blackhawk GeoSciences from August 13 to August 19, 2001. Blackhawk has conducted several previous TDEM surveys on Lanai. The results of these surveys are summarized in Blackhawk project report number 9081-000, dated December 15, 1994. 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. The electrical resistivity of the earth depends on lithology, porosity, and concentration of dissolved solids in the ground water. The general objectives of the measurements on Lanai were to further refine the interpreted location of groundwater damming structures, and explore for possible anomalous basal groundwater occurrences (i.e. springs, relative thick basal layers). TDEM surveys were conducted in seven areas on the Island."

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Time domain electromagnetic surveys for assisting in determining the groundwater resources, Phase II study, Island of Lanai, Hawaii

(Blackhawk Geosciences, Inc., 1994-12-15) Nance, Tom

"Time domain electromagnetic (TDEM) surveys were performed by Coleman Energy & Enviromnental Systems- Blackhawk Geosciences Division (CEES-BGD) under contracts with the Lanai Water Company, to assist in determining the ground water resources of the Island of Lanai, Hawaii. This type of geophysical survey has proven to be a cost effective means to aid in providing an understanding of potential ground water resources on Lanai and other Hawaiian Islands. By comparing TDEM data with known well information and with other surveys in Hawaii, the geophysical data is used to provide knowledge on the geologic/hydrologic regime on the island. A number of wells on Lanai were available for comparison, and they were used to compare interpretations of the ground water resources. Previous TDEM surveys on Lanai and other Hawaiian Islands have reliably mapped the boundary between fresh water in the basal mode and high-level occurrences. Previous surveys were confmed to small segments of islands. This is the first investigation covering an entire island, and therefore, provides an opportunity to address the potential water resources of an entire island. A total of 99 TDEM soundings were collected during three separate periods, February 1993, August 1994, and October-November 1994, and information from twelve wells are available. This report incorporates the findings of all three surveys, and from the twelve wells. TDEM soundings were collected at locations accessible by vehicle, and on the rugged windward side of the island soundings were acquired using helicopter support. The objective in station location selection was to provide adequate data density around the island for delineating areas of basal ground water from areas where ground water damming structures exist, and where high-level water can occur. Additional soundings were placed in areas not previously surveyed so that a map of the entire island in terms of the geologic/hydrologic regime could be constructed. The results of the comprehensive evaluation and interpretation of the TDEM geophysical data indicate that: • Basal ground water is present around the perimeter of the island, but the fresh/brackish water lens is limited. Thicknesses of fresh/brackish water above sea level have been calculated to be a minimal resource. • A geologic/hydrologic discontinuity interpreted as a ground water damming structure is present around the entire island. • The potential for high-level ground water is present throughout the central portion of the entire island. Well data was available for comparison to substantiate these findings in twelve areas near Lanai City and in the Palawai Basin area."

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

(Blackhawk Geosciences, Inc., 1994-09-14) Nance, Tom

"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.

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Geology and ground-water resources of the islands of Lanai and Kahoolawe, Hawaii

(Advertiser Publishing Co., Ltd., 1940) Stearns, Harold T.

Includes illustrations, tables, diagrams frontispiece, plates, and map.

Lanai

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