((a)) ** Equitable relief** Except as provided in subsection (b) of this section, any person may commence a civil action for equitable relief on that person’s behalf in the United States District Court for the District of Columbia—

((1)) against any person who is alleged to be in violation of any provision of this chapter or any condition of a license or permit issued under this subchapter; or

((2)) against the Administrator when there is alleged a failure of the Administrator to perform any act or duty under this chapter which is not discretionary,

((b)) ** Notice** No civil action may be commenced—

((1)) under subsection (a)(1) of this section—

((A)) prior to 60 days after the plaintiff has given notice of the alleged violation to the Administrator and to any alleged violator; or

((B)) if the Administrator or the Attorney General has commenced and is diligently prosecuting a civil or criminal action with respect to the alleged violation in a court of the United States; except that in any such civil action, any person having a valid legal interest which is or may be adversely affected by the alleged violation may intervene; or

((2)) under subsection (a)(2) of this section, prior to 60 days after the plaintiff has given notice of such action to the Administrator.

((c)) ** Costs and fees** The court, in issuing any final order in any action brought under subsection (a) of this section, may award costs of litigation, including reasonable attorney and expert witness fees, to any party whenever the court determines that such an award is appropriate.

((d)) ** Relationship to other law** Nothing in this section shall restrict the rights which any person or class of persons may have under other law to seek enforcement or to seek any other relief. All vessel safety and environmental requirements of or under this chapter shall be in addition to other requirements of law.