Water in Saddle Higher, More Plentiful Than Expected

A project involving drilling for high-elevation water in the Big Island’s saddle has found that and more, the scientist in charge said.

Don Thomas said the well drilled at about the 6,400-foot-elevation at the Pohakuloa Training Area, in the vicinity of Mauna Kea State Park, found water more than a mile above sea level.

Before the federally funded project began, scientists had hoped to find water as high as 3,500 feet above sea level.

Groundwater is usually located near sea level, forming a basal lens sitting on top of sea water.

Water has occasionally been found at higher elevations. That so-called perched water was believed to be accumulating above intrusive volcanic formations known as dikes.

But the latest findings showed that an interaction between lava and soil plays a much more prominent role than previously thought in the hydrology of the Big Island.

Researchers examine cores taken from the research well.

Thomas said drillers encountered areas of “glassy contact,” where hot lava covered wet soil which was then baked into an impermeable layer.

In one case, perched water 500 feet in depth was standing on a layer just a few inches thick.

“This tells us that these perching formations, even though they can be quite thin, can play a much larger role in groundwater movement and storage than we’ve generally assumed,” said Thomas, a geochemist at the University of Hawaii’s Center for the Study of Active Volcanoes.

And the baked soil layer apparently works to contain rain water on both sides.

Pockets of fresh water found nearly 10,000 feet below sea level in a previous research project had been thought to have been forced there by huge amounts of water above.

Thomas said the baked soil layer is believed to play a major role in that process by trapping water underneath it and forcing it to flow well below sea level.

“Even though these impermeable layers make up less than a few percent of the material in the stratigraphic column, they have very strong influence over how water is moving inside the island,” he said.

And the water found recently was not only much higher than expected, it was also much thicker.

The drill rig used in the research project, which uses a technology called wireline coring.

The coring drill encountered a second, lower aquifer that began at an elevation of about 4,600 feet and continued to the bottom of the hole 4,000 feet further down.

That prompted researchers to change locations for the project’s second hole. Based on research that suggests that deep aquifer may involve a series of dikes extending some seven miles west, they proposed drilling the next one in the Keamuku area mauka of Waikii Ranch.

According to a supplemental environmental assessment for the project, the findings are helping scientists develop a better understanding of groundwater within Mauna Kea which in turn will allow for better management of the crucial resource.

The EA noted that water is critically needed in the saddle region for use by the Army, by ranchers on Hawaiian Home Lands and for use in recreational activities.

Although perched water has been found near Waikii Ranch, most of the water used in the saddle area has to be trucked up at significant expense.