Dist. Ct. did not err in granting plaintiff-govt.'s motion for preliminary injunction in CERCLA action to compel defendant to complete environmental cleanup of PCBs that had been discharged into Fox River. While defendant asserted that it was no longer required to comply with prior remedial order because it had already performed more of cleanup than its proportional share of pollution, Dist. Ct. did not err in finding that harm to Fox River was not reasonably capable of apportionment where defendant's pollution by itself would require approximately same amount of remedial cleanup measures as measures needed to clean up PCB pollution from all sources. Moreover, preliminary injunction was proper where any delay in Fox River's cleanup would inflict irreparable harm to public, and where defendant's concern regarding its ability to eventually recoup cleanup costs from other polluters was insufficient to overcome equities in granting instant injunction.