Contract workers use a ground penetrating radar device on the upper portion of the concrete slab spillway at Gavins Point Dam in South Dakota on May 9, 2012. The radar will assist engineers with the Omaha District of the U.S. Army Corps of Engineers in conducting a damage assessment to the spillway to see if any repairs may be needed to the frost blanket beneath the concrete. Preliminary tests indicated that at least some of the granular material in the blanket may have been removed by the action of floodwaters during last year's high releases.