A civil penalty of not more than $25,000 per day for each day during which the violation continues may be assessed by the Administrator in the case of a violation of the requirements of section
11004 of this title. In the case of a second or subsequent violation the amount of such penalty may be not more than $75,000 for each day during which the violation continues. Any civil penalty under this subsection shall be assessed and collected in the same manner, and subject to the same provisions, as in the case of civil penalties assessed and collected under section
2615 of title
15. In any proceeding for the assessment of a civil penalty under this subsection the Administrator may issue subpoenas for the attendance and testimony of witnesses and the production of relevant papers, books, and documents and may promulgate rules for discovery procedures.