Reida Johnson, a technician with Tetra Tech, uses a metal detector to scan for buried munitions in the area aboard Marine Corps Base Quantico known as UXO 21 May 12. Before the new middle/high school can be built here, the site must cleared of potential unexploded ordnance. - Reida Johnson, a technician with Tetra Tech, uses a metal detector to scan for buried munitions in the area aboard Marine Corps Base Quantico known as UXO 21 May 12. Before the new middle/high school can be built here, the site must cleared of potential unexploded ordnance.