Memorandum reaffirms EPA's commitment to having potentially responsible parties (PRPs) conduct the remedial investigation/feasibility study (RI/FS) at Superfund sites wherever appropriate. Regions should continue to carefully review each case to ensure that the EPA is effectively using its enforcement authorities to maximize PRP performance of the RI/FS, thus preserving Hazardous Substances Trust Fund resources for sites where there are no viable responsible parties capable of performing the RI/FS. Issued 3/20/2012.