The Board may adopt regulations or orders closing any river, stream, lake or other body of water in this Commonwealth to fishing, boating, swimming or any other usage if the Board finds, and states the reasons and precise factual basis for finding, that a toxic substance as defined in § 32.1-239 is present in such river, stream, lake or other body of water in such manner as to constitute a present threat to public health and welfare. Such regulation or order may be temporary or permanent and may be issued initially on an emergency basis. Thereafter it may be promulgated as a final regulation or order upon the completion by the Board of the procedural requirements set forth in the Administrative Process Act (§ 2.2-4000 et seq.). If the Commissioner determines that the threat to public health and welfare has abated in whole or in part, the State Health Commissioner may modify or revoke any such regulation or order in a manner that lessens the restrictions placed upon fishing, boating, swimming, or other usage. Such modification or revocation by the Commissioner shall not be subject to the requirements of the Administrative Process Act but shall be filed with the Registrar of Regulations in accordance with § 2.2-4103. The Board shall review such modification or revocation at its next regularly scheduled meeting after such action by the Commissioner and shall affirm, reverse, or modify the Commissioner’s action. Review by the Board shall also be exempt from the provisions of the Administrative Process Act.