The Clean Air Act requires EPA to review maximum achievable control technology (MACT) standards and to revise them "as necessary (taking into account developments in practices, processes and control technologies)" no less frequently than every 8 years. Under the "residual risk" provision of the Clean Air Act, EPA must evaluate the MACT standards within 8 years after promulgation and promulgate standards if required to provide an ample margin of safety to protect public health or prevent an adverse environmental effect. The MACT for phosphoric acid and phosphate fertilizer were promulgated in June 1999. Facilities subject to these rules were required to be in compliance by June 2002. This action will address both the residual risk and technology reviews for the phosphoric acid and phosphate fertilizer source categories, as well as address other regulatory actions for the source category as deemed appropriate. The production processes for these two source categories typically are located at the same facilities.