AFOs are facilities where animals are raised for eggs, dairy, or slaughter. AFOs emit a number of pollutants regulated by the Clean Air Act (CAA), 42 U.S.C. § 7401 et seq., the Comprehensive Environmental Response, Compensation, and Liability Act, 42 U.S.C. § 9601 et seq. (CERCLA), and the Emergency Planning and Community Right-to-Know Act, 42 U.S.C. § 11001 et seq. (EPCRA) (collectively, the Acts). Pollutants include ammonia, hydrogen sulfide, particulate matter, and volatile organic compounds. An AFO emitting these pollutants in quantities below the statutory thresholds has no obligation under the Acts to obtain permits or report its emissions. Ps claim that their members suffer effects ranging from reduced enjoyment of the outdoor portion of their property to adverse health effects such as respiratory and heart problems. D cannot enforce the statutory and regulatory requirements without determining an AFO's emissions. There is no existing methodology to measure reliably an AFO's emissions. D’s solution was to offer AFOs a consent agreement under which the AFOs will assist in developing an emission estimating methodology. D agreed it will not pursue administrative actions and lawsuits against the AFOs for a defined period of time. D published the final draft of the Agreement, invited interested AFOs to sign up, and sought public comment. D concluded that the 'vast majority' of the comments received 'were ones that had been previously expressed to D, and they had already been considered in the development of the Agreement.' Several thousand AFOs have signed Agreements. Each AFO, although not admitting any violation of the Acts, agrees to pay a civil penalty for potential violations based on the size and number of its farms. It agrees to help fund a nationwide study that will monitor, over a two-year period, emissions from animal housing structures and manure storage and treatment areas. It also agrees to permit its facility to be monitored in the study upon request. Each agreement was approved by the Environmental Appeals Board (EAB). Ps appealed. Ps argue that EPA lacks authority to achieve compliance in this manner. Ps believe that the procedures are rulemaking and no meaningful opportunity for comment as required by the Administrative Procedure Act was afforded and that the agreements were subject to judicial review. D counters that this is a valid exercise of the agency's enforcement discretion. D also argues that even if the Agreement constitutes a rulemaking, D did not violate the notice and comment requirements of the APA.