Yes, I did the same thing you did.  What is wrong is that you have to put the barrels inside the border.  Put them more in the middle of the dump site.

And there you have it !!! They do say a picture tells a thousand words (or something like that) don't they! As soon as I saw the screenshot with the barrels still visible, I too remembered that my first barrels vanished but later ones didn't straight away and had to be moved a bit within the canyon. Yet initially it makes sense to want to take them outside the border to remove them from the town!

Good suggestion asking for a screenshot Scarlet
Hope the next one doesn't give you so much trouble Norhan