If a civil penalty that is assessed under this title is not paid in full within 30 days after the penalty becomes final, the Commissioner or the Central Collection Unit may proceed in the District Court to enforce payment. In a proceeding under this subsection, the Commissioner or the Central Collection Unit is entitled to judgment in the amount of the civil penalty that remains unpaid on a showing that: the penalty was assessed against the defendant; the penalty has become final; no appeal is pending; the penalty is wholly or partly unpaid; and the defendant: was duly served with a copy of the citation in accordance with the applicable regulations of the Commissioner; or contested the citation for which the penalty was assessed.