Most equipment that is soaked in oil because of operations within the area needs to be cleaned off after it returns back from operations. You just don't leave equipment a mess because it has to go out the next day. Most equip isnt designed to be operated continuously in a bath of oil.
Also, as far as I know port operations haven't been halted so many of the cargo ships moving further up the mississippi need to be cleaned off before they move up river.
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