Scientists to Search For Water in Big Island’s Saddle

Residents of the windward side of the Big Island often take plentiful water for granted. After all, some parts of it receive more than 20 feet of rain annually.

But water is much harder to come by in leeward areas, and a proposed project aims to see if that can be remedied.

Don Thomas, of the University of Hawai`i’s Center for the Study of Active Volcanoes, will be in charge of the mother of all divining projects, looking for water in the saddle between Mauna Loa and Mauna Kea.

Much of that area is more than a mile above sea level, where typical sources of fresh water are found.

His dowsing rod will be diamond wireline core drilling derricks.

Saddle Road is sorely in need of a fresh water source. Water for the US Army’s Pohakuloa Training Area, for the astronomical facilities atop Mauna Kea and for recreational use and ranching in the saddle area must be trucked from Hilo.

Thomas oversaw two previous research wells drilled on the Big Island which formed the basis for the new research detailed in a recently released draft environmental assessment.

The first one was drilled in 1993 to a depth of 3,500 feet by the shoreline near Hilo’s breakwater. It literally broke new ground in hydrology theories when it found a source of fresh water more than 1,000 feet below sea level.

The aquifer it discovered was artesian, which means it contained enough pressure to flow up and out of the bore hole.

Scientists believe forcing water that far down likely requires significant water above.

Analysis of the water coming up the well indicated that its source was rain that had fallen at an elevation of more than 6,000 feet on Mauna Kea.

A second, 11,500-foot hole drilled near Hilo’s airport encountered that same water source and additional artesian aquifers, including one nearly 10 times as deep as the first one.

“Nobody expected to find fresh water at 10,000 feet below sea level,” Thomas said.

Armed with that knowledge, scientists realized that additional research was needed to better understand the island’s complex hydrology.

The $6 million project calls for two wells four inches in diameter drilled to about sea level, in this case about 6,400 feet deep.

These small-bore wells are for research purposes, as production water wells are typically a foot or so in diameter.

Three possible locations for the holes were selected based on a variety of criteria. All are located on the US Army’s Pohakuloa Training Area in the vicinity of Mauna Kea State park.

The logistical criteria included access via existing roads, availability of utilities and an area already disturbed to minimize environmental impacts.

The primary scientific criterion was areas where magnetotelluric analysis – a measurement of electrical and magnetic fields and underground resistance – indicated the likely presence of water. Wet rock provides less resistance than dry rock.

“We did a fairly extensive geophysical assessment across the saddle,” Thomas said.

The scientists also wanted to focus on the flanks of Mauna Kea and avoid locations where intrusions of lava from Hualalai volcano might compromise their understanding of the underlying geology.

Usually when a well at higher elevations hits water it is tapping what is known as “perched” water trapped above a layer of ash or bound by intrusive volcanic formations known as dikes.

What Thomas will be looking for is an aquifer – or possibly multiple aquifers – feeding the basal lens of freshwater that is the usual source of groundwater.

He said he’s hoping that could be located as high as 3,500 feet above sea level.

“That would be a significant finding,” Thomas said, adding that could imply high-level aquifers might be found elsewhere on the Big Island’s relatively arid leeward side.