This final action addresses the agency's residual risk and technology review (RTR) of the National Emission Standards for Hazardous Air Pollutants (NESHAP) for Municipal Solid Waste (MSW) Landfills. The MSW Landfills NESHAP, subpart AAAA, was promulgated pursuant to section 112(d) of the Clean Air Act (CAA) on January 16, 2003. The NESHAP established emission limitations based on maximum achievable control technology (MACT) for controlling emissions of hazardous air pollutants (HAP) and helped implement the Urban Air Toxics Strategy developed under section 112(k) of the CAA. The HAP emitted by MSW landfills include, but are not limited to, vinyl chloride, ethyl benzene, toluene and benzene. This action implements the residual risk review requirements of CAA section 112(f)(2) and the technology review requirements of CAA section 112(d)(6). The statute directs the EPA to promulgate emission standards under CAA 112(f)(2) if such standards are required to provide an ample margin of safety to protect public health or to prevent, taking relevant factors into account, an adverse environmental effect. Any such standards are to be promulgated within 8 years after promulgation of MACT standards under CAA section 112(d). CAA section 112(d)(6) requires the EPA to review and revise the MACT standards as necessary, taking into account developments in practices, processes and control technologies, no less often than every 8 years. Specifically, the agency proposed that the risks from the MSW Landfills source category were acceptable. The EPA also proposed that no changes were warranted at this time based on the results of the technology review. Finally, the EPA proposed additional revisions to the MSW Landfills NESHAP to promote consistency between the MSW landfills regulations under CAA sections 111 and 112; changes to the wellhead temperature operating standards, and associated monitoring, corrective action, and reporting and recordkeeping requirements for temperature; adjustments to provisions for removal of landfill gas capture and collection systems; and updates to SSM requirements and electronic reporting requirements. Pursuant to a court order, the EPA is obligated to complete the final action by March 13, 2020.