Financial responsibility required by this subsection may be established in accordance with regulations promulgated by the Administrator by any one, or any combination, of the following: insurance, guarantee, surety bond, letter of credit, qualification as a self-insurer or any other method satisfactory to the Administrator. In promulgating requirements under this subsection, the Administrator is authorized to specify policy or other contractual terms including the amount of coverage required for various classes and categories of underground storage tanks pursuant to
section 6991b(d)(5) of this title, conditions, or defenses which are necessary or are unacceptable in establishing such evidence of financial responsibility in order to effectuate the purposes of this subchapter.