BIG ISLAND (HawaiiNewsNow) - Not that long ago, a drilling rig bore a hole into the Big Island's Pohakuloa Training Area. Scientists were looking for groundwater. And they found it! "It looks as though the islands really act like huge containers," University of Hawaii Geochemist Donald Thomas said. Thomas and his colleagues worked with the U.S. Geological Survey on the project. The search focused on the saddle region between Mauna Kea and Mauna Loa. It's dry on the surface with only 5 to 15 inches of rain a year. Hidden underground, Thomas and his team found a high-elevation pocket of groundwater. "The stable water table within the saddle is not 500 feet above sea level, it's more like 4,500 feet above sea level," he said. The Army spends about $2 million a year to truck water to the training area. Thomas believes the underground reserve could be a water source for PTA and the Department of Hawaiian Homelands, which controls 56,000 acres of land in the area. "The conventional model that we've worked with for years and years is that we have a relatively thin basal freshwater lens, a layer of freshwater saturated rock that rises very slowly as we move inland," he said. Another discovery was that the water at the deeper levels was hotter than the water near the surface. Thomas said that raises the possibility of it being used as a geothermal source to generate electricity. "We are able to develop scientific information that I think is of fundamental importance to Hawaii," he said. Thomas said the chemistry of the groundwater at Pohakuloa is about the same as drinking water on Oahu. He plans to expand the search to another high-elevation site on Mauna Kea. He wants to use the lessons from the Big Island to explore groundwater resources statewide.