Upon adoption by the Service of a 5-year plan providing for solid waste disposal and energy and heat generating projects and approval of such plan by the affected municipalities a service district shall be established in the manner and following the schedule set forth in the 5-year plan providing for a solid waste disposal and energy and heat generating project. The Service is responsible for the disposal of solid wastes, including any wastewater treatment residue, as set forth in the 5-year plan providing for solid waste disposal projects. Within the service district, no subdivision or person may dispose of solid wastes except through projects of the Service or of a subdivision or person designated by the 5-year plan or under reasonable conditions the Service stipulates; however, it is not intended by this Section that the Service, in the absence of an agreement to do so, be required to assume responsibility over any wastewater treatment activity or project or over any solid waste activity or project of any person or subdivision that exist on the effective date of this Act. Nothing contained in this Act shall affect the power of the Environmental Protection Agency to undertake any of the actions authorized in the Environmental Protection Act.