104 Wash. 2d 677 (1985).

One-Sentence Takeaway: The operator of a refinery which emitted gases and metal particulates from its smokestack was liable to neighboring landowners under a theory of trespass.

Summary: On certification of the question from the U.S. District Court, the Washington Supreme Court considered whether invasion of plaintiff’s property by airborne particulate matter from defendant’s copper smelter constituted trespass.  The court noted the traditional common law position that invasion by unseen particulate matter and gases did not constitute entry by a “thing” and therefore not a trespass.  Under traditional nuisance law, however, such impositions — if they unreasonably caused substantial interference in the use and enjoyment of plaintiff’s land — would be actionable.

The court concluded that trespass law must adapt to modern science and recognize that even unseen particles are “things.”  Rather than simply extend the concept of physical invasion to the microscopic world, however, the court created a trespass/nuisance hybrid claim.  Airborne particles that dissipate quickly and do not accumulate are to be treated under the law as nuisance.  Particles that do accumulate, however, constitute a trespass; but the “trespass” claim in such circumstances is a modified one that includes elements of nuisance law’s balancing approach.

Under the modified trespass claim, the plaintiff is required to prove: (1) an invasion of plaintiff’s possessory interest; (2) an intentional act that results in the invasion; (3) reasonable foreseeability that defendant’s act would result in such invasion; and (4) substantial damages to plaintiff’s property.

In addition, the court excluded punitive and nominal damages.  The result is a claim that is neither trespass nor nuisance.  Unlike nuisance, it requires proof of invasion of a possessory interest rather than interference with use and enjoyment and does not inquire into the reasonableness of defendant’s conduct.  Unlike trespass, it also requires actual damage to the res and foreseeability of the invasion (as opposed simply the intent to commit the act of releasing the particles that constitute the invasion).  The court’s rationale for this compromise was to allow plaintiffs the opportunity to maintain their claim under a three-year trespass limitations period (as opposed to the two-year nuisance period) without imposing an undue burden on manufacturers who otherwise might be liable to every litigious landowner withing a hundred or more miles of the plant whose property was “invaded” by the particulate matter.

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