The director, by rules adopted under chapter 91, may establish state standards which shall supersede interim action levels. As soon as practicable and within two years of the establishment of an interim action level, and every two years thereafter until a federal or state standard is established to supersede an interim action level, the director of health shall review all available scientific information to determine whether there is sufficient basis to establish a state standard to supersede an interim action level. Prior to adopting rules to establish state standards, the director shall conduct at least one public hearing to provide information to the public on the nature of the chemical contaminant under review and to afford the public an opportunity to present information and concerns to the department relating to the chemical contaminant under review.