Geophysical surveys for assisting in determining the ground water resources, Honomalino and Kapua areas, Island of Hawaii

"This report contains the procedures and results of geophysical surveys conducted to assist in determining the ground water resources on properties in the Honomalino and Kapua areas, Island of Hawaii. The surveys were performed by Blackhawk Geometries (Blackhawk) for MacFarms of Hawaii, Inc. (MacFarms) during October 5 to October 9, 1998. The geophysical method employed during this survey was Time Domain Electromagnetic (TDEM) soundings. During these surveys, TDEM soundings were located on Hawaii State Parcel TMK 8-9-1-02 and on property owned by MacFarms as shown on Figure 1-1. TDEM data previously acquired in a 1990 survey for MacFarms has been incorporated into this report. The Honomalino and Kapua areas of Hawaii are in the South Kana District in the southwest portion of the island. The main geologic feature in this area of the Island of Hawaii is the southwest rift zone, which extends away from the summit of Mauna Loa Volcano to the coastline near South Point (Stearns and Macdonald, 1946). The nearest mapped volcanic cone (Puu Ohohia) associated with the southwest rift zone, is located approximately five miles east of the study area. The main objective of the geophysical survey was to assist in characterizing the hydrologic regime in the Honomalino and Kapua areas for a proposed ground water well. Ground water resources can occur on the Island of Hawaii 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 ground water occurrence is controlled by subsurface damming structures. The surficial volcanic rocks are generally highly permeable and this allows rainwater to infiltrate directly downward through the island mass. The basal ground water lens extends from the outer edges of subsurface structures (i.e., dikes) to a discharge area near the shoreline. In the Honomalino and Kapua areas, ground water was expected to occur as a deep 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."Mac Farms of Hawaii, Inc