Technical experts will start sampling and inspecting soil on Thursday in a Colorado Wildlife Refuge outside of Denver.
In October, Army contractors found a chemical agent from World War I at the Rocky Mountain Arsenal. The plan has been approved by federal, state and local public health and environment officials. The contractors detected Lewisite while excavating a trench in a restricted area of the arsenal.
Lewisite, like mustard gas, is a blistering agent. The Rocky Mountain Arsenal National Wildlife Refuge has been closed as a precaution. The Army manufactured chemical weapons at the 27 square mile site.