When directed to do so by the Department, owners and operators of an UST system which was permanently closed before December 22, 1988, shall assess the excavation zone and close the UST system in accordance with R18-12-271, R18-12-272, and R18-12-274 if known, suspected, or potential releases from the UST system, in the judgment of the Department, may pose a current or potential threat to human health or the environment.
Ariz. Admin. Code § R18-12-273