A waste management worker collected the trash Monday from Normandy Village in Michigan City.
As he drove to a facility in nearby Kingsbury, an explosive device went off.
When the trash was unloaded, two more devices went off.
The Bureau of Alcohol, Tobacco and Firearms was contacted, and 11 additional devices were discovered.
No one was hurt, but ATF agents collected the other dumpsters from the apartment complex to be inspected.
No intact devices were recovered and the ATF believes this to be an isolated incident, said Special Agent Kim Riddell.