The owner and operator of a hazardous waste disposal site shall, without limitation, be responsible for the site for a period of 20 years after closure of the site, or such longer period of time as required by the federal Resource Conservation and Recovery Act of 1976, P.L. 94-580, or regulations issued thereunder, or by Board regulation adopted pursuant to subsection 22(a) or (f) of this Act. The owner and operator shall monitor such site for gas migration, drainage problems, erosion, settling, ground and surface water pollution and other environmental and safety problems which occur, and shall take whatever remedial action is necessary to solve any such problems which occur at the site during the period of responsibility. Notwithstanding the provisions of this Section, nothing contained herein shall be construed to limit any duties or liabilities imposed on an owner or operator of a solid waste disposal site pursuant to this Act or regulations thereunder or arising by operation of law.