The Board shall review the comments of the Administrative Officer, Director and Engineer and make its own study to assure compliance with these regulations and substantial conformity to the approved preliminary plat or conditionally approved plat subject to modifications requested. Pursuant to Iowa Code § 354.8, the Board shall not issue final approval of a subdivision plat unless it conforms to Iowa Code §§ 354.6 and 354.11. The Board shall approve or disapprove the final plat within 30 days after submission of final plat materials by the subdivider to the Administrative Officer; failure of the Board to act within 30 days shall be deemed to be approval, unless, however, the subdivider and the Board have mutually agreed to an extension of time. The Board shall make known immediately to the Clerk and the Council its action upon the final plat.