In 1959, in Martin v. Reynolds Metals, the Oregon Supreme Court held that the owner of an aluminum factory that cast invisible fluoride ions onto its neighbor's property had trespassed on the neighbor and had to pay damages. The court held that even the invisible could trespass.
The case comes to mind today because after many more years of operations and fluoride emissions (averaging 800 pounds a day at the time of the Martin case) the Reynolds Aluminum (do you remember the "Reynolds Wrap" brand of aluminum foil?) site passed into the hands of Alcoa, a multi-national producer of aluminum. Alcoa closed the plant in 1999, though it still owns the property. The federal government recognized its years of operation, but not in a way that anyone would crow about: it awarded the site a "Superfund" designation in 1994. The cleanup is still going on.
The Port of Portland wants to build an intermodal rail yard (rail-to-truck transfer and vice versa) on the site. Fairview and Troutdale are opposed: those two cities (the two closest to the site) want to see the site redeveloped by and for private industry.
Nobody's talking (at least, not to me) about what Alcoa prefers. Alcoa's going to finish the Superfund cleanup, which is only fair: it and its predecessor made the mess. But the Knower of All Things did mention the story he heard: that if Alcoa sells to the Port, it's going to insist that the Port indemnify Alcoa against the cost of cleaning up any remaining contamination outside the Superfund cleanup.
That's one job the Port shouldn't be taking on.