Step 10: Bury vault with left over dirt.
Put the top on the barrel and secure it tightly. Backfill around the barrel and place a folded (about 3-ft x 3ft) tarp on top. The tarp is there so that removing the dirt later will be easier. Cover the tarp/barrel with the left over dirt to create a mound. It is a good idea to place the grass pieces on the top last to act as natural erosion control (and a little extra insulation).