The Use of Groundwater Geochemistry to Prospect for Blind Geothermal Resources in the State of Hawaii

Abstract

The principle goal of this study was centralized on the use of groundwater geochemistry to prospect for blind geothermal resources throughout the State of Hawaii by the collection of water samples, analysis of water geochemistry data, and highlighting of wells that contained chemical signatures indicative of elevated subsurface heat. Water samples were collected in ten locations across the State of Hawaii that were identified as areas of potential geothermal resource in a recent geothermal prospect assessment, and analyzed for temperature, major and minor chemical species, and trace metals. A total of 61 samples were collected: 60 from existing wells and 1 spring was sampled in an area where no wells exist. The aqueous geothermal indicators: silica concentration, chloride/magnesium, sulphate/chloride, and temperature, were chosen because of the relative success as geochemical indicators in Hawaii. Additionally, thresholds were determined, based on compiled historical data and research, as chemical signatures that could signify subsurface heat under Hawaii conditions. As a result, various anomalies were detected on four islands within the State of Hawaii based on the criteria set within the project as potential indications of subsurface heat, and a potential geothermal source was identified on the Island of Lanai. However, positive indications of a subsurface heat anomaly based on this assessment could have an alternative non-thermal explanation. Given that these aqueous geochemical indicators can be affected by both natural and anthropogenic processes, further investigation is necessary. Furthermore, data collected could assist the Hawaiʻi State Legislature to address the state’s growing energy demands through the identification, exploration, and use of available geothermal sources. The subsequent report provides the latest comprehensive water geochemistry data that may be used as a geothermal exploration tool for the State of Hawaiʻi.