Harford County and Aberdeen Proving Ground work closely together to ensure public safety from the time suspected ordnance is found through its handling and disposal. Unexploded ordnance is the small percentage of munitions that did not detonate at the time they were fired or were disposed of by burial. They may lie on the ground surface or may have penetrated the surface either by land or in the water. Aberdeen Proving Ground's has identified some disposal sites and impact areas though field investigations and record searches. In addition to sites already known, others may exist on the proving ground.
Unexploded ordnance is categorized by the type of fill inside the munitions.
Types are conventional high explosive or chemical. Chemical fills include chemical warfare material, smoke and tear gas. Chemical warfare materiel was designed for use in military operations to cause varying degrees of injury to enemy troops. Chemical warfare materiel may be found in munitions and in other types of containers, such as laboratory vials. The majority of the munitions tested over the years at the proving ground did not contain chemical warfare materiel.