This Administrative Order ( Order ) is issued to Respondents the United States Air Force ( USAF ) and the Arizona Air National Guard ( AANG ) (collectively Respondents ) pursuant to the authority vested in the Administrator of the U.S. Environmental Protection Agency ( EPA ) by Section 1431(a) of the Safe Drinking Water Act ( SDWA ), 42 U.S.C. Section 300i(a). The Administrator of EPA has delegated the authority to take these actions to EPA?s Regional Administrators by Delegation 9-17 (Imminent and Substantial Endangerment) (January 18, 2017), and the Regional Administrator for EPA Region 9 has redelegated the authority to the Director, Deputy Director, and Branch Chiefs of EPA Region 9's Enforcement and Compliance Assurance Division ( ECAD ) pursuant to Regional Directive R9 9-17 (May 9, 2018).