40 CFR 307.41 - Subrogation of claimants' rights to the Fund.
(a) The United States acquires by subrogation all rights of the claimant to recover the amount of the claim paid by the Fund from the person or persons liable under section 107 of CERCLA for the release giving rise to the response action.
(b) Claimants shall assist in any cost recovery action that may be initiated by the United States. The claimant and the claimant's contractors shall furnish the personnel, services, documents, and materials needed to assist EPA in the collection of evidence to document work performed and costs expended by the claimant or the claimant's contractors at the particular site in order to aid in cost recovery efforts. The claimant and the claimant's contractors shall also provide all requested assistance in the interpretation of documents detailing work and costs that may be needed as evidence, and shall testify on behalf of the United States in any judicial or administrative cost recovery proceeding regarding the response costs claimed. All of the claimant's contracts for implementing the PDD shall expressly require their contractors to provide this cost recovery assistance.