A buyer closes on a commercial building, and eleven months later a groundwater sample shows solvent contamination from a dry cleaner that left in 1994. This article explains why the new owner may be liable for the entire cleanup, and what would have prevented it. It covers the federal cleanup statute's four categories of responsible party and why liability is strict, retroactive, and frequently joint and several, so that one solvent party can be made to pay for everyone. It explains the defenses that actually work, the pre-purchase inquiry that is the only reliable protection, and the continuing obligations that a purchaser must satisfy to keep it. It covers the difference between recovering costs and seeking contribution, the deadlines and procedural traps in each, and the parallel state programs where most cleanups actually occur. It closes with what a buyer, a seller, a tenant, and a lender each should do before signing anything.