The CERCLA rule requires trustees to develop a demand specifying the damages sought from the potentially responsible party. If the potentially responsible party refuses to comply with the demand, the trustees file a claim for damages. The OPA rule requires that the responsible party be given the option of implementing the restoration action itself instead of paying damages.
43 CFR 11.91(a)
At the conclusion of the assessment, the authorized official must present to the potentially responsible party a demand in writing for the damages determined in accordance with this part and the reasonable cost of the assessment. . . The authorized official must deliver the demand in a manner that establishes the date of receipt. The demand shall adequately identify the Federal or State agency or Indian tribe asserting the claim, the general location and description of the injuries, and the damages sought from that party.