The Administrator of General Services, with respect to standards issued under , and the Secretary of Housing and Urban Development, with respect to standards issued under , and the Secretary of Defense with respect to standards issued under , and the United States Postal Service with respect to standards issued under —

((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.