Humu‘ula Groundwater Research Project

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The primary scientific objective of the Humuʻula Groundwater Research Project (HGRP) is to research and characterize the groundwater resources in the Hawaiʻi Island’s saddle region. The project will develop a complete stratigraphic record of the region to better define the area’s geologic history and document the island’s volcanogenic and environmental history. Previously, very little information was known about this largely unexplored area.

The project will drill two holes on the grounds of the Pōhakuloa Training Area (PTA) about 1 kilometer apart. With depths of 6000’–6500′ from the surface, the holes will reach the theoretical Ghyben-Herzberg freshwater lens, which floats on top of denser seawater in island settings. Each hole will yield a continuous stratigraphic sequence of subaerial shield-stage and post-shield-stage lava rock and ash samples from the Mauna Kea Volcano. Processing, characterization, and logging of the rock core can be used for future scientific work on the samples with reports produced by the methods used for the Hawaiʻi Scientific Drilling Project (HSDP).

To reach the projected depth of 6000′ or more, the planned drilling program involves coring to a depth of 3000′-3500′ using a PQ-sized (3.378” core diameter) bit. Then, the drill pipe can serve as casing for open-hole drilling to the bottom of the hole with an HQ-sized (2.5” core diameter) bit. While the second hole will involve the same drilling plan, the exact PQ-to-HQ transition will depend on the downhole rock stability conditions. During and after coring operations, the groundwater in the boreholes will be monitored and analyzed to determine the viability of a long-term water well or wells that may meet the usage needs of PTA.

The U.S. Army and the National Science Foundation provided funding for the drilling and the initial characterization and logging of the core.

Ghyben-Herzberg diagram:
Ghyben-Herzberg diagram