Most of what the CAG deals with is the cleanup process under CERCLA. A separate, simultaneous process called Allocation occurs under CERCLA to determine how much each Potentially Responsible Party (PRP) contributed to the contamination in the site. Often times, EPA will enter into settlements with PRPs for an acceptable amount to avoid having to prove exactly how much pollution a particular PRP caused, which can be very costly.
According to a recent Supreme Court Case, CERCLA allows parties who voluntarily pay for cleanup or parties who pay for cleanup under an adminstrative consent order (like Lower Willamette Group) to recover costs of cleanup from other PRPs in a later court proceeding. Knowing that recovery of cleanup costs is possible helps PRPs act quickly to study and then cleanup the contaminated site.