In what ways can the refinery cause pollution in the land?

The most or all piping systems used in refineries including vessels and towers opearte at extremely high pressures. If it happens that the leak occurs in the pipe, vessel or tower if thats possible, the content falls on the ground. The pumps and valves may leak due to poor mantainance. I doesn't have to be a solid or liquid material that could pollute the lend. The vapours may condense and the condensate fall on the ground.