Basic Requirements: Citizenship. Citizenship of the United States. (Non-citizens may be appointed when it is not possible to recruit qualified citizens in accordance with chapter 3, section A, paragraph 3g, this part.) Education. There are no specific educational requirements for this occupation. Education may be substituted for experience only at the GS-4 and GS-5 levels. See the grade requirements part of this standard for information regarding educational substitutions. Licensure or Certification. Licensure or Certification is not required for this occupation; however, it is strongly desirable at GS-6 or above as evidence of possession of the essential knowledge, skills, and abilities. For certain functional areas at the higher levels or supervisory assignments, specific certifications