A Fairfax County, Virginia, worker inspecting a drain made an unusual discovery in a residential neighborhood Tuesday morning -- a round of bazooka ammunition possibly dating back to the Korean War era.

The bazooka shell was found in a drain on the 9300 block of Glenbrook Road in the Mantua neighborhood, Fairfax County Police said. Officers responded about 10:45 a.m. and kept neighbors away as they investigated.

The device was determined to be an inert, "blank" round likely used in training, police said. It wasn't immediately clear how long the shell had been there.

Police and fire officials stayed on the scene near the Mantua Hills Swim Club for almost four hours, leaving about 2:30 p.m.