36.21.801    DEFINITIONS

The following definitions shall apply for monitoring well construction:

(1) "Abandoned well" means a well whose use has been permanently discontinued.

(2) "Annular space" or "annulus" means the space between two concentric tubes or casings, or between the casing and the borehole wall.

(3) "Aquifer" means any geological formation which is capable of yielding water or is capable of recharge.

(4) "Artesian" means a condition in an aquifer wherein groundwater is confined under pressure by an overlying geologic unit of relatively lower permeability.

(5) "Bentonite" means a highly plastic, highly absorbent colloidal clay composed primarily of swelling sodium montmorillonite.

(6) "Board" means the Montana Board of Water Well Contractors.

(7) "Borehole" means an open or cased subsurface hole created by drilling.

(8) "Casing" means tubing which is installed to counteract caving and isolate the zone being monitored of a drilled hole.

(9) "Casing " means tubing which is installed to counteract caving and isolate the zone being monitored of a drilled hole:

(a) "protective" means a section of pipe or tubing that is placed over the well casing at the surface to provide structural protection to the well and restrict unauthorized entrance into the well; and

(b) "surface" means a single section of tubing used to stabilize a borehole near the surface during, and following the drilling of the hole.

(10) "Cement" means Portland cement, usually furnished in 94-pound bags.

(11) "Confined groundwater" means groundwater within a geologic unit(s) that is under pressure significantly greater than atmospheric pressure; the upper limit of the geologic unit being the bottom of a zone of distinctly lower hydraulic conductivity than that of the geologic unit(s) in which the confined water occurs.

(12) "Confining bed" means a layer of geologic materials having very low hydraulic conductivity that hampers the movement of water into and out of an aquifer.

(13) "Contamination" means the degradation of natural water quality as a result of human activities. There is no indication of specific limits, since the degree of permissible contamination depends upon the intended use(s) of the water.

(14) "Cuttings" means fragments or particles of soil or rock, with or without free water, created during the drilling of a borehole.

(15) "Deionized water" means water that contains less than 50 milligrams per liter of dissolved solids.

(16) "Drilling fluid" means a liquid or gas which may be used in the drilling operation to remove cuttings from the borehole, to clean and cool the bit, to reduce friction between the drill stem and the borehole wall, and to seal the borehole to prevent loss of drilling fluids.

(17) "Flowing well" means a well from which water flows from the casing top under natural hydro-dynamic pressure.

(18) "Gravel pack" means the principal filter pack of a well or monitoring device.

(19) "Groundwater" means water encountered below ground surface.

(20) "Hazardous" means a condition where materials or fluids contain sufficient types and amounts of biological, chemical, or physical (including radiological) agents which are likely to cause human illness, disorders, or disability. These include, but are not limited to pathogenic viruses, bacteria, parasites, toxic chemicals, and radioactive isotopes.

(21) "Hydraulic conductivity" means a property of the geological material expressing the relative ease with which water flows through the geological material in response to a differential in total hydraulic head.

(22) "Hydraulic gradient" means the rate of change in total head per unit of distance of flow in a given direction.

(23) "Injection well" means a well utilized for injecting fluids or gases into geologic materials.

(24) "Leachate" means contaminated water resulting from the passage of direct precipitation, surface water, or groundwater through waste.

(25) "Lysimeter" means a device used to obtain soil moisture samples above the water table.

(26) "Monitoring well" means a well that is used for monitoring groundwater quality or flow direction, but is not used for withdrawing groundwater for purposes other than water quality sampling or pump testing.

(27) "Monitoring Well Log Report Form" means DNRC Form No. 603, Well Log Report. The monitor well constructor shall record the well information on the wells constructed and file the report as required by ARM 36.21.639 and 85-2-516 and 85-2-527, MCA.

(28) "Montana Bureau of Mines and Geology (MBMG)" means the Montana Bureau of Mines and Geology located in Butte, Montana.

(29) "Neutron tube" means tubing installed in a borehole for the purpose of measuring soil-water content by neutron moderation techniques. Neutron tubes are constructed of a variety of materials, including plastic, fiberglass, fluorocarbons, or metal.

(30) "Nonbiodegradable fluidizing admixtures" means grout additives that provide temporary reduction of gel strength by dispersing the clay particles. Nonbiodegradable limits the use to only those additives not subject to biological decomposition. Natural polymers are biodegradable and may not be used. Totally synthetic polymers must be used with care, and only after determining that they are chemically acceptable can they be introduced into freshwater systems.

(31) "Nonhydrologic geotechnical" means the purpose of the hole is not to collect hydrologic information. Geotechnical is information on geological, geochemical, and geophysical conditions.

(32) "Observation well" is a well designed to measure the exact depth to the water table. An observation well is often screened or perforated across the water table.

(33) "Packer" means a transient or dedicated device placed in a well, which plugs or seals a portion of the well or well annulus at a specific level.

(34) "Permeability" means a measure of relative ease with which a porous medium can transmit a liquid under a potential gradient. It is a property of the medium that is dependent upon the shape, size, and degree of interconnection of the pores.

(35) "Piezometer" is a well device or instrument designed to measure the hydraulic potential (water level elevation) at a specific point in the subsurface.

(36) "Radius of influence" means the radial distance from the center of a pumped well to the point where there is no lowering of the water table or potentiometric surface (the edge of the cone of depression).

(37) "Recovery well" means a well installed to recover contaminates that have been introduced into the groundwater table, but is not used for monitoring groundwater quality or flow direction.

(38) "Saline seep" means an artificially created groundwater system of poor quality, created by a change in the land use, which generally occurs in materials of very low transmissivity.

(a) "Saline seep well" means a well used for recharge area identification and for monitoring water table levels.

(39) "Sealing" means the operation by which seal material is placed in the borehole.

(40) "Sealing material" means an impervious or low permeable inorganic material used for the purpose of preventing interaquifer contamination and/or surface water infiltration. Types of sealing material include:

(a) asphaltic concrete, which is a mixture of dense graded sand or sand and gravel and asphalt cement with less than eight percent air voids;

(b) bentonite clay grout, which is a mixture of at least 1.5 pounds of bentonite clay per gallon of potable water;

(c) bentonite pellets and chips, which are particles of bentonite passing a 0.75-inch sieve and retained on a #4 sieve;

(d) compacted clay cuttings, which are uncontaminated cuttings, a sample of which can be rolled into a thread of 0.125 inch in diameter or smaller, and compacted to a density of at least equal to the formation from which they were cut. Bentonite powder passing a #200 sieve may be mixed with the cuttings. When attempting to roll the thread, particles of sand and gravel larger than a #40 sieve may be removed.

(e) cuttings slurry grout, which is a mixture of uncontaminated water and a minimum of 15 percent solids by weight consisting of uncontaminated clay or shale cuttings, and a minimum of ten percent bentonite by weight. The mixture shall have a unit weight of at least 9.00 pounds per gallon;

(f) granular bentonite, which is bentonite sand size particles, most of which passes a #4 sieve, and most of which are retained on a #200 sieve;

(g) neat cement grout, which is a mixture of not more than six gallons of potable water per 94-pound sack of Portland cement. Up to five pounds of bentonite clay per sack of cement may be added. When bentonite is added, the quantity of water may be increased 0.1 gallon for each pound of bentonite per sack of cement. Commercial fly ash may be substituted on a weight basis for up to half of the Portland cement; and

(h) Portland cement concrete, which is a mixture of sand, Portland cement, potable water, and four to eight percent air. The mixture may contain gravel, and fly ash may be substituted for up to 25 percent of the Portland cement. It shall contain at least six sacks of cement per cubic yard and have a 28-day compressive strength of at least 4000 psi.

(41) "Static water level" means the elevation of the top of a column of water in a well, which is no longer influenced by effects of installation, pumping, or other temporary conditions. Static water levels are transitory and therefore will change due to temporal and seasonal effects. 

(42) "Surfactants" mean synthetic detergents.

(43) "Transmissivity" means the rate at which water of prevailing kinematic viscosity is transmitted through a unit width of an aquifer under a unit hydraulic gradient.

(44) "Tremie pipe" means a pipe or tube that is used to transport grout or other material from above ground surface into a borehole annulus of a monitoring well or other groundwater monitoring device.

(45) "Unconfined aquifer" means an aquifer in which hydrostatic pressures at the water table are equal to atmospheric pressure. In unconfined aquifers, the water table is exposed to the atmosphere through openings in the overlying materials.

(46) "Vapor detection well" means a well or borehole used to obtain soil-gas samples above the water table.

(47) "Water cement ratio" means the proportion of the weight of mixing water to the weight of cement.

(48) "Water table" means the surface in an unconfined aquifer at which the pressure is atmospheric. This level is determined at a location by the static water level in a monitoring well or piezometer screened across the top of the zone of saturation.

(49) "Well screen" means pipe or cylindrical tubing with slots of a uniform width, orientation, and spacing.

(50) "Zone of saturation" means a hydrologic zone below the water table in which the interstices are filled with groundwater.

History: 37-43-202, MCA; IMP, 37-43-202, MCA; NEW, 1988 MAR p. 2503, Eff. 11/24/88; AMD, 1991 MAR p. 913, Eff. 6/14/91; AMD, 1997 MAR p. 65, Eff. 1/17/97; AMD, 2010 MAR p. 1614, Eff. 7/16/10.