With diffusion being a foundational aspect of solutes mixing in solutions, the water should have an even distribution of the contaminants. However, the tidal force of water associated with a storm surge probably throws a wrench in the plan here. But generally, it's evenly spread throughout and will be found in relatively even amounts everywhere the water settles.

It'll be in the air too. Anything in the soil will become dust in the air for years. It'll get kicked into the air every time a lawn is mowed, a hole gets dug, a dry season occurs, etc