For the purposes of subchapters 13 and 14 and unless otherwise provided, the following terms have the meanings given to them in this rule and must be used in conjunction with the definitions in subchapter 1 of this chapter and those in 75-11-203 and 75-11-503, MCA:

(1) "Day" means a calendar day.

(2) "External leak detection device" means a monitoring system that is located external to and not attached to an underground storage tank system and that is designed and installed to detect a release of the regulated substance stored in the underground storage tank system.  Examples of external leak detection devices include, but are not limited to, soil vapor monitoring wells, observation wells, continuous monitoring equipment, if any, that is installed within the wells to detect a release, and a ground water monitoring well when constructed by a person holding a monitoring well constructor license issued by the board of water well contractors and in accordance with the provisions of ARM Title 36, chapter 21, and ARM 17.56.407(1) (f) .

(3) "Ground water monitoring well" means a monitoring well constructed by a licensed monitoring well contractor and in accordance with the requirements of ARM Title 36, chapter 21, and any associated sensing equipment which is located outside of the tank excavation and is designed and installed to be used to detect releases of regulated substances from underground storage tank systems.

(4) "Installer license" means a license issued to an individual by the department under 75-11-210, MCA, to conduct the installation, closure, or both, of underground storage tank systems.

(5) "Lining" means the addition of a plastic, fiberglass, or other shell of impervious material to the inside of an underground storage tank for the purpose of ensuring that the tank retains its contents. The term includes all steps to be taken in preparation for the addition of the lining and includes re-lining.

(6) "Major installation" means the installation of underground storage tanks, piping, vapor or ground water leak detection monitoring wells, corrosion protection, interstitial tank probes and sensors and corrosion protection system anodes. Repair or modification of the above-listed items, and activities not defined as a "minor installation" are also considered major installations.

(7) "Minor installation" means the installation of replacement spill buckets, offset sleeves on tank risers, boots on piping flex connectors, ball-float vent valves in existing risers, drop-tubes, drop-tube shut-off valves and auto dialers, and the extension or replacement of vent standpipes. Minor installation also includes the decommissioning of ground water and vapor leak detection monitoring wells.

(8) "Modification" means a significant change in the structure or components of an underground storage tank system, and includes, but is not limited to, lining a tank, cutting the walls of a tank, and the addition of internal leak detection devices.

(9) "Observation well" means, for purposes of this subchapter, a device and sensing equipment, if any, which consists of a cased penetration of an underground storage tank's backfill from which ground water and/or soil vapors are monitored to detect whether a release of the regulated substance stored in an underground storage tank system has occurred, and which is located entirely within an underground storage tank system's backfill and does not penetrate beyond the bottom of the tank system's backfill.