82-4-304. Exemption -- works performed prior to promulgation of rules. This part is not applicable to any exploration or mining work performed prior to the date of promulgation of the board's rules pursuant to 82-4-321 relating to exploration and mining. This part is not applicable to the reprocessing of tailings or waste rock that occurred prior to the date of promulgation of the board's rules regarding those activities. If, after the date of promulgation of rules applicable to mills not located at a mine site, work is performed at a mill that does not use cyanide ore-processing reagent and that was constructed and operated before promulgation of those rules, this part applies only to the areas initially disturbed after promulgation of those rules.