(1) When the status of an active UST system is changed to inactive, owners and operators shall notify the department, in writing, within ten days after the date the UST ceases to be used for dispensing, depositing or storing regulated substances, shall continue operation and maintenance of corrosion protection in accordance with ARM 17.56.302, and shall continue operation and maintenance of any release detection in accordance with subchapter 4. Subchapters 5 and 6 must be complied with if a release is suspected or confirmed. However, release detection is not required as long as the UST system is empty. The UST system is empty when all materials have been removed using commonly employed practices so that no more than 2.5 centimeters (one inch) of residue, or 0.3% by weight of the total capacity of the UST system, remains in the system.

(2) When an UST system is inactive or out of service for three months or more, owners and operators shall also:

(a) empty the UST system;

(b) leave vent lines open and functioning; and

(c) cap and secure all other lines, pumps, manways, and ancillary equipment.

(3) Out of service UST system components that do not meet the corrosion protection requirements of ARM 17.56.201 or 17.56.202 must, within 12 months of being taken out of service or, in the case of a found tank, within 12 months of its discovery, be:

(a) permanently closed in accordance with ARM 17.56.702 through 17.56.706; or

(b) brought into compliance with ARM Title 17, chapter 56, subchapter 2.

(4) In order to return an inactive UST to active status, owners and operators, in addition to complying with all applicable UST requirements under this subchapter, shall:

(a) when an UST has a valid operating permit and is inactive for 12 months or less, provide the department with 30 days advance written notice of the owner or operator's intent to return the UST to active status;

(b) when an UST has a valid operating permit and is inactive for more than 12 months:

(i) provide the department with 30 days advance written notice of the owner or operator's intent to return the UST to active status; and

(ii) perform a precision tank tightness test, line tightness tests and functionality tests of all mechanical and electronic release detection equipment, and submit all test results to the department. The owner and operator may return the UST to active status only upon receipt of notice from the department indicating that the test results are satisfactory. All tests must be conducted in accordance with accepted industry standards and must meet the performance requirements in ARM 17.56.407 and 17.56.408;

(c) when an UST does not have a valid operating permit, but no more than 12 months have passed since the expiration date of the last operating permit issued for the UST:

(i) provide the department with advance written notice as required in (4) (b) (i) ; and

(ii) obtain a conditional operating permit in accordance with ARM 17.56.310 and a compliance inspection in accordance with ARM 17.56.309;

(d) when an UST does not have a valid operating permit, and more than 12 months have passed since the expiration date of the last operating permit issued for the UST:

(i) provide the department with advance written notice as required in (4) (b) (i) ;

(ii) perform a precision tank tightness test, line tightness tests and functionality tests of all mechanical and electronic release detection equipment, and submit test results to the department. The owner and operator may return the UST to active status only upon receipt of notice from the department indicating that the test results are satisfactory. All tests must be conducted in accordance with accepted industry standards and must meet the performance requirements in ARM 17.56.407 and 17.56.408; and

(iii) obtain a conditional operating permit in accordance with ARM 17.56.310 and a compliance inspection in accordance with ARM 17.56.309;

(e) when an UST does not have a valid operating permit, continuous operation and maintenance of corrosion protection in accordance with ARM 17.56.302 cannot be demonstrated, and more than three years have passed since the expiration date of the last operating permit issued for the UST:

(i) meet all the requirements in (4) (d) (i) through (4) (d) (iii) ; and

(ii) show that the UST is structurally sound based upon an internal inspection.