Dikewater relationships to potential geothermal resources on Leeward West Maui, State of Hawaii

Abstract

The West Maui Volcano has not been active in historic times. Thus, the discovery of thermal waters in the 1930s, a product of volcanic activity, was not anticipated in West Maui wells. However, distinctly warm waters were found on the leeward side of West Maui in three groundwater developments: (1) drilled wells at the Pioneer Mill in Lahaina (30°C); (2) a Maui-type well in Ukumehame (35°C); and (3) a high-level horizontal water development tunnel in Olowalu (24°C). West Maui volcano differs from most Hawaiian volcanoes by having steeper dips, more large intrusive bodies, thicker dikes with a more radial distribution and a more nearly circular form. The massive dike complex and radial dike form provide abundant water storage in the West Maui Mountains. The vast amount of water in the dike swarms is due to the high rainfall in the mountains, the exceptionally high permeability of the intervening Wailuku flows, low permeability of the dikes and their radial divergence from the area of high recharge t which disperses water in all directions, and enough dike intersections to create semi-isolated dike compartments with high heads and considerable storage. The investigation, where results are reported here, relates to the warm groundwaters of the Olowalu-Ukumehame are of West Maui (designated Sub-Area C, Lahaina District, by the U. S. Geological Survey). It was undertaken to determine, so far as possible, the relationship of the occurrence of these warm waters to the geologic structure and groundwater hydrology of the area, the source of their heat, and the potential for development of energy from them. In this investigation spring and well waters were sampled and analyzed for the major ions and for the tritium isotope. These methods, combined with standard hydrologic methods, provide the data on which this study is based.