; and (7) advisory committees consisting of all interested segments of the public when the establishment of such committees is considered necessary because the issues involved are highly complex or controversial. 70035. Investigatory powers (a) Secretary The Secretary may investigate any incident, accident, or act involving the loss or destruction of, or damage to, any structure subject to this chapter, or that affects or may affect the safety or environmental quality of the ports, harbors, or navigable waters of the United States. (b) Powers In an investigation under this section, the Secretary may issue subpoenas to require the attendance of witnesses and the production of documents or other evidence relating to such incident, accident, or act. If any person refuses to obey a subpoena, the Secretary may request the Attorney General to invoke the aid of the appropriate district court of the United States to compel compliance with the subpoena. Any district court of the United States may, in the case of refusal to obey a subpoena, issue an order requiring compliance with the subpoena, and failure to obey the order may be punished by the court as contempt. Witnesses may be paid fees for travel and attendance at rates not exceeding those allowed in a district court of the United States. 70036. Enforcement (a) Civil penalty (1) In general Any person who is found by the Secretary, after notice and an opportunity for a hearing, to have violated this chapter or a regulation issued under this chapter shall be liable to the United States for a civil penalty, not to exceed $25,000 for each violation. Each day of a continuing violation shall constitute a separate violation. The amount of such civil penalty shall be assessed by the Secretary, or the Secretary’s designee, by written notice. In determining the amount of such penalty, the Secretary shall take into account the nature, circumstances, extent, and gravity of the prohibited acts committed and, with respect to the violator, the degree of culpability, any history of