The director may propose to add (or delete from those materials previously added) materials to the definition of hazardous substance.

(1) Additions or deletions to the list shall be made by amendment of this rule pursuant to the Administrative Procedure Act (chapter 34.05 RCW).

(2) The director of ecology shall add or delete materials no more than twice during each calendar year.

(3) For tax purposes, changes in this definition shall take effect on the first day of the next month that is at least thirty days after the effective date of the rule.

(4) For each material proposed for additional listing, the department shall prepare a "basis for listing" which shall include those factors and data which led the director to propose the listing.

(5) The director shall prepare a "basis for deletion" which shall include those factors and data which led the director to propose deletions from materials previously added.