When an underground storage tank system is temporarily closed, owners and operators must continue operation and maintenance of corrosion protection and any release detection. However, release detection is not required as long as the underground storage tank system is empty. The underground storage tank system is empty when all materials have been removed using commonly employed practices so that no more than two and five-tenths centimeters [1 inch] of residue, or three-tenths of one percent by weight of the total capacity of the underground storage tank system, remain in the system.
When an underground storage tank system is temporarily closed for three months or more, owners and operators must also comply with the following requirements:
- Leave vent lines open and functioning; and
- Cap and secure all other lines, pumps, manways, and ancillary equipment.
When an underground storage tank system is temporarily closed for more than twelve months, owners and operators must permanently close the underground storage tank system if it does not meet either performance standards in section 33-24-08-10 for new underground storage tank systems or the upgrading requirements in section 33-24-08-11, except that the spill and overfill equipment requirements do not have to be met. Owners and operators must permanently close the substandard underground storage tank systems at the end of this twelve-month period, unless the department provides an extension of the twelve-month temporary closure period. Owners and operators must complete a site assessment before such an extension can be applied for.
- At least thirty days before beginning either permanent closure or a change in service, or within another reasonable time period determined by the department, owners and operators must notify the department of their intent to permanently close or make the change in service, unless such action is in response to corrective action. The required assessment of the excavation zone under section 33-24-08-62 must be performed after notifying the department but before completion of the permanent closure or a change in service.
- To permanently close a tank, owners and operators must empty and clean it by removing all liquids and accumulated sludges. All tanks taken out of service permanently must also be either removed from the ground or filled with an inert solid material.
- Continued use of an underground storage tank system to store a nonregulated substance is considered a change in service. Before a change in service, owners and operators must empty and clean the tank by removing all liquid and accumulated sludge and conduct a site assessment.