You could call Nuclear Waste Dump an inverted Columns. In Columns, your goal is to align three blocks of the same type in a column, row, or diagonal. In Nuclear Waste Dump, you have to strictly avoid placing two blocks af the same type above or beside each other. As soon as that happens, the game is over.
The barrels hover only for a short while before they drop, so you have to be quick. There are some helpers: freezers will neutralize the barrels left and right, but most important TNT will blow up all the barrels next to it as soon as something is dropped upon it. This is vital, for when the piles get too high, the game is over as well.
The gameplay concept goes back to an old 8-bit Atari game called Uncle Henry's Nuclear Waste Dump which is, incidentally, older not only than Columns, but than Tetris itself.
Nuclear Waste Dump, like Penta a production of the demo crew Paradize, is an international cooperation. The coder (Matthias Arndt) is from Germany, the graphic artist from France, the musician from Sweden. I have listed it as a German game, since I tend to give the programmer more weight in such a case.