When directed by the department, owners and operators of the following UST systems must permanently close those systems (decommission and perform site assessments around the systems) in accordance with WAC 173-360A-0810 if the department determines releases from those systems may pose a current or potential threat to human health or the environment or if any additional closure activities are performed:

(1) UST systems permanently closed before December 22, 1988; and

(2) Previously deferred UST systems permanently closed before October 1, 2018.