The Clean Air Act (CAA) calls for the Administrator to add a substance to the CAA section 112(b)(1) list, otherwise known as the HAP list, “upon a showing by the petitioner or on the Administrator’s own determination that the substance is an air pollutant and that emissions, ambient concentrations, bioaccumulation or deposition of the substance are known to cause or may reasonably be anticipated to cause adverse effects to human health or adverse environmental effects.” The Agency has determined that a regulatory infrastructure directly addressing the addition of a HAP is needed to ensure the effective and efficient implementation of requirements triggered by the addition of a new HAP. This action will develop the infrastructure including the opportunity for public comment.