WRRCTMR No.13 Geophysical Evidences for Ground Water Conditions in the Vicinity of Anaehoomalu and Lalamilo

Because rainfall in this area of the island of Hawaii is so low; and because the porosity and vertical permeability of the ground in the region are so high, it appears that the dominant flux of water through this sector occurs as slow, subterranean flow at about sea level. Consequently, it appeared that reconnaissance work should be concentrated in that area where the ground-water flow can most easily be studied. This is at a shallow depth that may occur near a shoreline. Therefore, two reconnaissance surveys were made in the vicinity of the coastline from near Puako Bay to Anaehoomalu Bay. An offshore reconnaissance consisting of continuous surveillance of conductivity from a boat piloted as close as possible to the shoreline did not detect distinctly fresh water. However, eleven areas of discharge of brackish water, all with probable chloride concentrations greater than 1000 parts per million, were detected. Although it is extremely difficult to determine the exact volume of discharge, a reasonable estimate of the volume of flow of brackish water discharges ranges from a few tens of thousands of gallons per day at nine discharge points to perhaps one million gallon per day from the two largest zones of shoreline discharge. It appeared that the desired quantity of (potable) ground water might conceivably be discharged into the ocean in such a diffuse manner as not to he discernible by conductivity measurements at sea. Therefore, an electrical resistivity profile was also planned for one kilometer inland from the shorelin