(a) The provisions of § 12-301(10) notwithstanding, an action by or on behalf of the Mayor to recover the cost of a response action under this section must be commenced within 6 years after the initiation of physical onsite response work.
(b) An action to compel the Mayor or another person to perform a duty brought under this section shall be commenced within 2 years after the date that the duty became nondiscretionary.