Crews examining the safety of an Indiana sand dune that collapsed on a 6-year-old Illinois boy last month used ground-penetrating radar usually used to find buried barrels of toxic waste or broken underground pipelines.
National Park Service officials hope the device, along with other equipment from the Environmental Protection Agency, will help them figure out whether it's safe to reopen the popular 126-foot high dune at the Indian Dunes National Lakeshore along Lake Michigan, 55 miles east of Chicago.
"We're not going to reopen Mount Baldy until we understand the science of what's going on underneath and determine if we need to mitigate it or route visitors through different areas to make sure they are safe," Park Service Ranger Bruce Rowe said on Monday afternoon.
Emergency workers freed Nathan Woessner after he was swallowed by the dune on July 12. The Sterling, Ill., boy was trapped under 11 feet of sand for more than three hours. He was unresponsive when initially rescued, but began breathing en route to a waiting ambulance. He's since undergone some physical, occupational and speech therapy and is expected to undergo more rehabilitation.
The only sign Monday of where Nathan became trapped was a white pole sticking out from the sand. The large hole created by the heavy equipment used to rescue Nathan was filled in immediately after the rescue, Rowe said. The 42-acre dune has been closed to the public since then.
One theory by Park Service officials is that a decomposed tree trunk under the dune created the void that swallowed Nathan, Rowe said. The theory is based on some old rotted wood or wood fiber found in the area where Nathan was rescued, Rowe said.
A tree stump was visible about 15 feet south of the white pole Monday, and at least three other stumps were visible nearby.
Mount Baldy is unique in that it moves more than most coastal dunes, Rowe said. In the past it usually moved 4 to 5 feet south a year, but in recent years it has moved 10 to 15 feet a year. Park officials believe that's because years of people running up and down Mount Baldy has killed Marram grass that holds the sand in place, Rowe said.
EPA crews using the radar began about 50 feet up the dune from where Nathan was buried. A woman wearing a backpack with a GPS device walked just ahead of the ground-penetrating radar, which looked like a futuristic lawn mower.
The device takes a series of pictures, similar to an ultrasound, as deep as 30 feet below the surface, EPA spokesman Francisco Arcaute said. He said it will create a 3-D underground map of sorts, finding anything abnormal. Crews will remain at the site at least two days, possibly longer, he said.
"We will continue to do samplings until we determine, what, if anything, is here," Arcaute said.