42 U.S.C. § 8391
Section, Pub. L. 95-620, title V, §501, Nov. 9, 1978, 92 Stat. 3321, mandated that existing electric powerplants owned or operated by an electric utility be considered in compliance with prohibitions under subchapter III of this chapter relating to use of natural gas if there is in effect an approved plan of system compliance for such utility, and set forth requirements for approval of such plan.