In this month’s column in The Legal Intelligencer / Pennsylvania Law Weekly, I address a problem that comes up from time to time:  the industrial or commercial tenant who vacates, leaving environmentally regulated materials behind in a building.  Should the landlord sue the vacating tenant (or its officers or owners) for an injunction requiring them to come back and clean up?  Should the landlord clean up and then sue to get its money back?  Should the landlord call the regulators immediately or delay until the landlord knows what it wants to do?  The situation is more of a puzzle than you would think.  The Tenant Who Leaves Trash Behind, 55 PLW 933 (Sept. 28, 2010).