A low-flying helicopter is circling above the community of Lost Hills, checking for water below the ground. The flights are being done by U.S. Geological Survey researchers on behalf of state water officials, and the work will continue next near Buttonwillow. Officials say they’re developing 3D maps of where there’s fresh and salty groundwater in certain oil field areas in the state. The first phase of that big project is the work underway in Kern County. “We will be trying to find places where it’s likely that fresh water exists,” USGS research geophysicist Lyndsay Ball told Eyewitness News on Thursday.