In any settlement agreement regarding alleged violations of environmental law in which a defendant agrees to perform a diesel emissions reduction Supplemental Environmental Project, the Administrator of the Environmental Protection Agency shall require the defendant to include in the settlement documents a certification under penalty of law that the defendant would have agreed to perform a comparably valued, alternative project other than a diesel emissions reduction Supplemental Environmental Project if the Administrator were precluded by law from accepting a diesel emission reduction Supplemental Environmental Project. A failure by the Administrator to include this language in such a settlement agreement shall not create a cause of action against the United States under the Clean Air Act [42 U.S.C. 7401 et seq.] or any other law or create a basis for overturning a settlement agreement entered into by the United States.