For the purposes of this subchapter the following are defined:

(1) "Area of review" means the area surrounding an injection well to a radius calculated according to the criteria set forth in ARM 36.22.1425 or a fixed radius of one quarter mile, or for an area project, plus the project area plus a radius calculated according to the criteria set forth in ARM 36.22.1425, or the project area plus a circumscribing area the width of which is one quarter mile.

(2) "Confining zone" means the geological formation or formations, or the portion of a formation that is capable of limiting fluid movement out of the injection zone.

(3) "Corrective action" means the reworking, repair, replugging, or other activity taken for the purposes of preventing migration of injected fluids into underground sources of drinking water through any existing wellbore that penetrates the injection zone within the area of review.

(4) "Class II injection well" means a well that:

(a) injects fluids brought to the surface in conjunction with conventional oil and gas production and may be commingled with waste waters from gas plants which are an integral part of production operations, unless those waters are classified as a hazardous waste at the time of injection;

(b) is used to inject brines or other fluids brought to the surface in connection with oil or gas production or gas storage operations;

(c) is used to inject brines or other fluids described in (4)(b) which, prior to injection, have been:

(i) used onsite for purposes integrally associated with oil and gas production or storage;

(ii) chemically treated or altered to the extent necessary to make them useable for purposes integrally related to oil and gas production or storage; or

(iii) commingled with fluid wastes resulting from the treatment described in (4)(c)(ii), so long as they do not constitute a hazardous waste;

(d) is used to inject freshwater (i.e., water containing less than 10,000 mg/L total dissolved solids) from groundwater or surface water sources, added to or substituted for the brine may also be injected, as long as the only use of the water is for purposes integrally associated with oil and gas production or storage;

(e) is used to inject fluids for the enhanced recovery of oil or gas;

(f) is used to inject fluids for storage of hydrocarbons that are liquid under standard conditions of temperature and pressure; or

(g) is used to inject exempt waste fluids associated with oil or natural gas exploration and production as long as their physical state allows it, including produced fluid, drilling fluids, drill cuttings, rigwash, well completion fluids, workover wastes, gas plant dehydration wastes, gas plant sweetening wastes, spent filters and backwash, packing fluids, produced sand, production tank bottoms, gathering line pigging wastes, hydrocarbon-bearing soil, and waste crude oil from primary field sites.

(5) "Class III well" means a well that injects for the extraction of minerals other than oil or gas including:

(a) mining of sulfur;

(b) in situ production of uranium or other metals other than by solution mining of conventional mines;

(c) solution mining of salts or potash.

(6) "EPA" means the United States Environmental Protection Agency.

(7) "Injection well, new" means a Class II well that began injecting after the effective date of the UIC program delegation by the EPA.

(8) "Injection well, existing" means an injection well other than a new injection well.

(9) "Injection zone" means the geological formation, group of formations, or portion of a formation that receives the injection fluids through a well.

(10) "Injected fluids" means any material or substance which flows or moves and is emplaced in an injection zone through a Class II injection well.

(11) "Mechanical integrity" means that:

(a) there is no significant leak in the casing, tubing, or packer of the injection well; and

(b) there is no significant fluid movement into an underground source of drinking water (USDW) from the injection zone or from a non-USDW geologic stratum or zone of rock overlying the injection zone, or flow between adjacent USDWs through channels adjacent to the injection wellbore.

(12) "Program director" means that employee of the Montana Board of Oil and Gas Conservation (board) designated by the board as the principal administrator or the Montana Underground Injection Control Program delegated by EPA.

(13) "UIC" means underground injection control.

(14) "Underground source of drinking water (USDW)" means an aquifer or portion thereof which supplies drinking water for human consumption, or an aquifer which contains fewer than 10,000 mg/L total dissolved solids and is not an exempt aquifer under ARM 36.22.1418.

(15) "Well" means a bored, drilled or driven shaft, or a dug hole, whose depth is greater than the largest surface dimension.

(16) "Well injection" means the subsurface emplacement of fluids through a bored, drilled, or driven well; or through a dug well, where the depth of the dug well is greater than the largest surface dimension.

(17) "Well plug" means a watertight and gastight seal installed in a borehole or well to prevent movement of fluids.

(18) "Well stimulation" means several processes used to clean the wellbore, enlarge channels, and increase pore space in the interval to be injected thus making it possible for wastewater to move more readily into the formation, and includes surging, jetting, blasting, acidizing, and hydraulic fracturing.

(19) "Well monitoring" means the measurement, by onsite instruments or laboratory methods, of the quality of water of a well.