Not later than 12 months after October 22, 1994, the Director shall conduct a study and inventory of open dumps on Indian lands and Alaska Native lands. The inventory shall list the geographic location of all open dumps, an evaluation of the contents of each dump, and an assessment of the relative severity of the threat to public health and the environment posed by each dump. Such assessment shall be carried out cooperatively with the Administrator of the Environmental Protection Agency. The Director shall obtain the concurrence of the Administrator in the determination of relative severity made by any such assessment.