(a) If the commissioner determines that an undertaking will have an adverse impact on eligible or registered property recommendations shall be formulated which the undertaking agency must consider when exploring all feasible and prudent alternatives. These recommendations shall accompany the notice of adverse impact given by the commissioner pursuant to section 428.7. When appropriate, the commissioner's recommendations shall include methods and standards for the curation and/or disposition of archaeological finds produced as a result of the undertaking.

(b) Unless the agency elects to abandon the project, it shall fully explore and give thorough consideration to the commissioner's recommendations and respond to them in writing within a reasonable time. The agency's response must specify if it agrees or disagrees with the commissioner's recommendations and, if it disagrees, give the factual basis for its position.

(c) If the agency disagrees with one of the commissioner's recommendations. its response under subdivision (b) of this section must also include an alternative proposal which, in the agency's opinion, would avoid or mitigate to the greatest extent possible the adverse impacts identified by the commissioner. Any such proposal must include a statement of the facts which support it.

(d) In formulating recommendations or alternatives, both the commissioner and the undertaking agency must give primary consideration to the State's historic preservation policy as expressed in article 14.00 of the Parks, Recreation and Historic Preservation Law. Other factors such as cost, program needs, safety, efficiency, code requirements or alternate sites may also be considered. However, none of these factors standing alone shall be determinative of whether a particular proposal is feasible or prudent.