Oahu

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Geophysical test surveys with FDEM methods, Ewa Marina, Oahu, Hawaii

(Blackhawk Geosciences, Inc., 1990-05-30) Nance, Tom

This report contains the results of a geophysical test survey conducted on May 22, 1990, for Haseko (Hawaii) Inc. near Ewa Marina on the Island of Oahu, Hawaii. The test data were acquired on two lines. The objective of the survey was to determine the lateral boundary between saline saturated and fresh/brackish water saturated limestones. Due to the large change in electrical resistivity between saline saturated and fresh/brackish water saturated limestones, a method which is sensitive to the ground resistivity (or its inverse, conductivity) was chosen for the test. The geophysical method utilized was frequency domain electromagnetic (FDEM) measurements with the Geonics EM-34. The EM-34 is a rapid and inexpensive method which is highly sensitive to lateral changes in resistivity. Data coverage in the study area was somewhat limited to existing roads, due to the thick vegetation, and time constraints.

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Time domain electromagnetic surveys for assisting in determining the groundwater resources at the Pearl Harbor Well Field, Island of Oahu

(Blackhawk Geosciences, Inc., 2011-08) Nance, Tom

"This report contains the procedures and results of surface Time Domain Electromagnetic (TDEM) geophysical surveys performed for groundwater resource evaluation in Central Oahu near Kunia and Waipio Acres, Oahu. The property included land owned by the State of Hawaii Department of Land and Natural Resources (DLNR), Waikele Farms, Inc. (WFI) and Honbushin International Center (HIC). Zapata Incorporated (ZAPATA) performed the surveys for Belt Collins Hawaii Ltd. (BCH) and Tom Nance Water Resource Engineering (TNWRE) from July 13 through July 16, 2011. The main objective of the TDEM surveys was to identify basal or high-level groundwater at the sounding sites to refine the boundary between the two. The surveys were conducted at five TDEM sounding sites to help determine the location for future groundwater wells. 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, degree of saturation, and concentration of dissolved solids in the groundwater. Geophysical surveys, combined with other hydrogeologic information, are used to provide optimum locations for water well placement and well completion depths."

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Time domain electromagnetic surveys at the Lihi Lani project site, Pupukea, Koolauloa District, Oahu, Hawaii

(Blackhawk Geosciences, Inc., 1992-07-15) Nance, Tom

This report contains the resUlts of time domain electromagnetic (IDEM) surveys conducted at the Lihi Lani Project Site, Pupukea, Koolauloa District, on the Island of Oahu, Hawaii. The survey was performed by Blackhawk Geosciences, Inc. (BGI) for Kuilima Development Company during June 1992. The overall objective of the survey was to assist in defining potential fresh water resources at the project site. The two major factors which influence the location and availability of fresh ground water in this geologic setting are (i) the elevation of the fresh water - salt walter interface for basal ground water occurrences, and (ii) the location and attitude of potential ground water damming structures (e.g., dikes) and aquitards. Thus, the specific objectives of this survey were to • map the fresh water - salt water interface underlying the survey area, and • identify and map geologic structures or lithologic units which may affect ground water distribution. In TDEM surveys, the electrical resistivity of the subsurface is measured. Previous TDEM surveys on the Hawaiian Islands have shown large resistivity contrasts to occur between volcanics saturated with fresh water and saline water. In most cases, also significant resistivity contrasts exist between geologic structures and between weathered and unweathered volcanics.

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Geophysical surveys for ground water evaluation, central aquifer and west beach areas, Oahu, Hawaii

(Blackhawk Geosciences, Inc., 1990-04-10) Nance, Tom

In the Central Aquifer area the TDEM soundings taken near wells at the 400-ft elevation show good agreement with borehole data in depth to the unconformity between the Koolau and Wainae flows and in the depth to fresh-brackish water. TDEM soundings taken at other locations failed to detect the unconformity. However, data density across much of the Central Aquifer area was inadequate to properly define the existence of the unconformity. The low data density was mainly due to property access restrictions imposed during the field survey. TDEM soundings taken at the West Beach area show excellent agreement with water well data in the area, and indicate that a hydrologic barrier (possibly a dike) exists in the vicinity of soundings WB2W and WB4W. In the Central Aquifer area additional TDEM soundings would be helpful to better define the orientation of the unconformity between the Koolau and Waianae flows detected on Line lN. Additional data between Lines lN and 2N and east of Kunia Road would also help to define the position of the fresh water head in this area.

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Geophysical surveys for ground water investigations, Central Oahu, Hawaii

(Blackhawk Geosciences, Inc., 1990-09-11) Nance, Tom

Time domain electromagnetic (TDEM) soundings were used to assist in the ground water evaluation of the Central Oahu area on the island of Oahu, Hawaii. The results of the TDEM survey show: (1) The unconformity between the Waianae and Koolau lava flows was detected and mapped on four TDEM survey lines from line 3N toward the south and not detected north of line 3N. Good agreement was observed about the presence, depth of occurrence, and thickness of the unconformity mapped in a borehole and interpreted from TDEM soundings. From TDEM measurements along lines on both sides of the unconformity no consistent influence of the unconformity on fresh water head could be observed. (2) The elevation of the fresh-salt water interface was mapped throughout the survey area. Over most of the survey area the elevation of the salt water interface ranges from -600 ft to -900 ft below msl. This range is consistent with observations of fresh water head in wells, although locally some differences between TDEM interpretations and heads observed in wells occur. An important conclusion from the TDEM survey is that large fresh water resources exist uniformly throughout the survey area with heads above 15 ft.

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Geophysical survey with FDEM methods, Ewa Marina, Campbell Industrial Park and Barbers Point Harbor, Oahu, Hawaii

(Blackhawk Geosciences, Inc., 1990-08-08) Nance, Tom

A geophysical survey was conducted in three areas in the vicinity of the Barbers Point Naval Air Station on Oahu, Hawaii. The areas are designated as Ewa Marina, Campbell Industrial Park, and Barbers Point Harbor. The objective of the survey was to infer from the geophysical data information about the thickness of a brackish water lens floating on saline water in the limestone aquifer of this region. A geophysical method was employed that allows relatively quick areal coverage for determining lateral variation in the thickness of the brackish water lens. To also derive from the survey information about the thickness of the brackish water lens, the geophysical data was correlated to salinity observations in boreholes placed in the three survey areas. The results of the survey are given as profiles of the thickness of the brackish water lens along lines generally perpendicular to the shore. The profiles are mainly characterized by a rapid increase in the thickness of the brackish water lens in the first 150 ft from the shore. The thickness of the brackish water lens varies from about 100 ft in the Ewa Marina area to less than 50 ft in the Barbers Point Harbor area.

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Geophysical survey for ground water evaluation, West Beach Estates area, Oahu, Hawaii

(Blackhawk Geosciences, Inc., 1990-09-10) Nance, Tom

TDEM soundings were conducted in the West Beach Area along four lines during March and July 1990, to attempt to map a postulated hydrologic barrier inferred from prior drilling results. Heads calculated from the TDEM data, using the Ghyben Herzberg relation along line lN, show good agreement with measured heads in nearby boreholes. The likely location of the hydrologic barrier has been delineated on three of the survey lines (lS, lN, 2N) and the position of the barrier. On line .2S the barrier was not detected, mainly because measurements could not be made far enough to the east to intercept the expected position of the barrier. The location of the hydrologic barrier is inferred from (i) an increase in the resistivity of the lower layer (possibly due to dolomitization or other lithologic change), and (ii) a rapid change in depth to the salt water saturated zone east of the barrier. This rapid change in depth to salt water was detected on three lines. Accuracy in determining depth to the salt water saturated zone is expected to be about ± 5% of the total depth. If it is important to determine the course of the hydrologic barrier further to the south then additional soundings on the east side of line 2S would be necessary, and an additional line parallel and south of line 2S would further assist in locating its position.

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Records of the drilled wells on the Island of Oahu, Hawaii

(Advertiser Publishing Co., Ltd., 1938) Stearns, Harold T. ; Vaksvik, Knute N.

Includes tables and diagram.

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Geologic map and guide of the island of Oahu, Hawaii, with a chapter on mineral resources

(Advertiser Publishing Co., Ltd., 1939-08) Stearns, Harold T.

"This road guide has been prepared to meet the constant demand for more knowledge about the geology of Oahu and should greatly increase the usefulness of the geologic map. Many kinds of geologic phenomena are found on the island: dissected as well as recent volcanic craters and fissures from which lava and ash were erupted, landslides and fossiliferous volcanic mud flows, spectacular features of marine, stream, and wind erosion, conspicuous evidences of great submergence and emergence, coral reefs, stream and marine terraces, deltas, fans, tropical rain belts and deserts with their associated contrasting types of weathering and erosion. This concentration of so many diverse geologic features in such a small area makes Oahu outstanding among the islands of the world. This verdurecovered island surrounded by a blue sea is an ideal place to become acquainted with earth processes and products. Moreover, many of these geologic features are readily reached by automobile. The logs given on the following pages have been made for an autoist travelling the main highways around the island starting at the Kamehameha statue on King Street, Honolulu (pl. 1). It is assumed that the traveler will have available the street map of Honolulu issued free by the Hawaii Tourist Bureau. The mileage reads up if driving clockwise around the island and down if going counterclockwise. The route from Haleiwa to Wahiawa is over the new highway not shown on plate 2. Likewise, the route to Waianae is over the new Waipahu cut-off, although this road is not shown on plate 2. The mileage varies slightly with different odometers due to many factors, but a sufficient number of landmarks are given so that frequent checks can be made. A few of the main side roads having interesting geologic exposures are also included (pl. 1)."

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Geology and ground-water resources of the island of Oahu, Hawaii

(Maui Publishing Co., Ltd., 1935) Stearns, Harold T. ; Vaksvik, Knute N.

Prepared in cooperation with the U.S. Geological survey.

Oahu

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