If you imported three times and didn't mix or otherwise mess with the three folders (iPhoto Library, iPhoto Library (1) and iPhoto Library (2) ) You can just delete the second two folders (1) and (2).
That should get rid of the dups. If you did move things around you will need to go third party, Aperture does not have any built in duplicate identification.
Duplicate Annihilator is mentioned here often.
Thank you for this suggestion. IF I simply drag the iPhoto Library (1) and (2) into Aperture's Trash folder will Aperture:
1.) Somehow show me if any active iPhoto Books or Projects are affected (when I open them up), and
2.) If I want to drag the iPhoto Libray back out of Trash can I just simply do that as well without affecting anything?
My thinking is that if I drag the libraries into Trash and nothing is affected then I can simply empty trash and remove the duplicates that way.
Duplicate Annihilator does work for Aperture - at least it shows me which files are duplicated - but it doesn't show if any projects are using the duplicates. So, I am hesitant to go ahead and "annihilate" them.
If you place things in the Aperture trash you can always recover them as long as you haven't emptied the trash. There is a command, put back, that does this in addition to dragging items out of the trash.
If you place iPhoto Library (1) and (2) in the trash and Aperture continues to behave as expected then it should be safe to empty the Aperture trash.
Another way to approach this is to select iPhoto Library in Aperture and then exporting that as a new library. Then open this new library in Aperture and see how it behaves. If all is OK you could delete the other Aperture library.
Finally if you haven't done any work in Aperture since you imported you iPhoto libraries and you still have the iPhoto library then you could just make a new Aperture library and do the import from iPhoto again making sure you do it only once. Then once you check out this new library you could delete the original one.