(1) No application for a permit or revision under subchapter 3 or 4 which proposes to use an existing structure which does not conform to the design criteria of this subchapter may be approved unless the department finds, in writing, on the basis of information set forth in the application that:

(a) the structure meets the performance standards of subchapters 5 through 10; and

(b) no significant harm to the environment or public health or safety will result from use of the structure.

(2) If the department finds that an existing structure does not meet the design and performance standards of subchapters 5 through 10 but that:

(a) modification or reconstruction of the structure will bring it into compliance with the design and performance standards of subchapters 5 through 10 within six months of the issuance of the permit;

(b) the risk of harm to the environment or to public health or safety is not significant during the period of modification or reconstruction; and

(c) the applicant will monitor the structure to determine compliance with the performance standards of subchapters 5 through 10; then the applicant shall submit and adhere to an approved compliance plan for modification or reconstruction of the structure to comply with subchapters 5 through 10.

(3) If the department finds that the existing nonconforming structure cannot be reconstructed without causing significant harm to the environment or public health or safety, the applicant shall abandon the existing structure on a schedule approved by the department.