The Administrator of General Services, with respect to standards issued under section 4152 of this title, and the Secretary of Housing and Urban Development, with respect to standards issued under section 4153 of this title, and the Secretary of Defense with respect to standards issued under section 4154 of this title, and the United States Postal Service with respect to standards issued under section 4154a of this title—

(1) is authorized to modify or waive any such standard, on a case-by-case basis, upon application made by the head of the department, agency, or instrumentality of the United States concerned, and upon a determination by the Administrator or Secretary, as the case may be, that such modification or waiver is clearly necessary, and

(2) shall establish a system of continuing surveys and investigations to insure compliance with such standards.