Atlantic Research Corporation (Atlantic) (plaintiff) leased property at a naval ammunition depot operated by the U.S. Department of Defense (defendant) where it retrofitted rocket motors. Using a high-pressure water spray, Atlantic removed pieces of propellant from the motors and then burned the pieces. The runoff generated by the burning contaminated the soil and groundwater at the site. Atlantic cleaned the site at its own expense and then filed suit against the United States to recover a portion of the cleanup costs under §§ 107(a) and 113(f) of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). The district court granted the government’s motion to dismiss, citing the U.S. Supreme Court’s holding in Cooper Industries, Inc. v. Aviall Services, Inc., 543 U.S. 157 (2004). In Cooper Industries, the Court held that a private potentially responsible party (PRP) could not recoup CERCLA-related costs from other PRPs, like the federal government. Atlantic appealed. The court of appeals reversed and held that § 107(a)(4)(B) provided Atlantic with a cause of action. The U.S. Supreme Court granted certiorari to clarify its holding in Cooper Industries.