How can oil refineries create underground holding tanks that are environmentally safe, and not landfills?

Question

Ok i mean look at at all the landfills, wasteing land, couseing pulution to underground water supplies, Ect. Why cant they say bury in it in underground cavern, tanks as you will, Far beneeth the ocean floor, like they do oil reserves, gases, Ect. At the same time maybe build barear islands witch it could be buryed but buryed in a manner like a holding tank, concrete, steele, even filtered for fumes Ect. witch the top of the islands could act as a nesting areas, Ect. for wildlife. Louisiana, and the southern states need such for debri removal, and huracain protection, and wetland restorations, all made enviromentaly safe. Plus alot more can be done im sure.

Answer 1

Because oil is a liquid, easily pumped through a small pipe to a large, possibly odd shaped, underground cavern. By comparison, trash is solid and cannot simply be pumped down a pipe and expected to fill a cavern without people down there to shovel it into all the corners.