As used throughout the initial regulatory program the following terms have the specified meanings unless otherwise indicated:

Acid drainage means water with a pH of less than 6.0 discharged from active or abandoned mines and from areas affected by coal mining operations.

Acid-forming materials means earth materials that contain sulfide mineral or other materials which, if exposed to air, water, or weathering processes, will cause acids that may create acid drainage.

Alluvial valley floors means unconsolidated stream-laid deposits holding streams where water availability is sufficient for subirrigation or flood irrigation agricultural activities but does not include upland areas which are generally overlain by a thin veneer of colluvial deposits composed chiefly of debris from sheet erosion, deposits by unconcentrated runoff or slope wash, together with talus, other mass movement accumulation and windblown deposits.

Approximate original contour means that surface configuration achieved by backfilling and grading of the mined area so that the reclaimed area, including any terracing or access roads, closely resembles the general surface configuration of the land prior to mining and blends into and complements the drainage pattern of the surrounding terrain, with all highwalls and spoil piles eliminated; water impoundments may be permitted where the regulatory authority determines that they are in compliance with §715.17.

Aquifer means a zone, stratum, or group of strata that can store and transmit water in sufficient quantities for a specific use.

Combustible material means organic material that is capable of burning either by fire or through a chemical process (oxidation) accompanied by the evolution of heat and a significant temperature rise.

Compaction means the reduction of pore spaces among the particles of soil or rock, generally done by running heavy equipment over the earth materials.

Disturbed area means those lands that have been affected by surface coal mining and reclamation operations.

Diversion means a channel, embankment, or other manmade structure constructed for the purpose of diverting water from one area to another.

Downslope means the land surface between a valley floor and the projected outcrop of the lowest coalbed being mined along each highwall.

Embankment means an artificial deposit of material that is raised above the natural surface of the land and used to contain, divert, or store water, support roads or railways, or other similar purposes.

Essential hydrologic functions means, with respect to alluvial valley floors, the role of the valley floor in collecting, storing, and regulating the natural flow of surface water and ground water, and in providing a place for irrigated and subirrigated farming, by reason of its position in the landscape and the characteristics of its underlying material.

Flood irrigation means irrigation through natural overflow or the temporary diversion of high flows in which the entire surface of the soil is covered by a sheet of water.

Ground water means subsurface water that fills available openings in rock or soil materials such that they may be considered water-saturated.

Head-of-hollow fill means a fill structure consisting of any material, other than coal processing waste and organic material, placed in the uppermost reaches of a hollow where side slopes of the fill measured at the steepest point are greater that 20° or the profile of the hollow from the toe of the fill to the top of the fill is greater than 10°. In fills with less than 250.00 cubic yards of material, associated with contour mining, the top surface of the fill will be at the elevation of the coal seam. In all other head-of-hollow fills, the top surface of the fill, when completed, is at approximately the same elevation as the adjacent ridge line, and no significant area of natural drainage occurs above the fill draining into the fill area.

Highwall means the face of exposed overburden and coal in an open cut of a surface or for entry to an underground coal mine.

Hydrologic balance means the relationship between the quality and quantity of inflow to, outflow from, and storage in a hydrologic unit such as a drainage basin, aquifer, soil zone, lake, or reservoir. It encompasses the quantity and quality relationships between precipitation, runoff, evaporation, and the change in ground and surface water storage.

Hydrologic regime means the entire state of water movement in a given area. It is a function of the climate, and includes the phenomena by which water first occurs as atmospheric water vapor, passes into a liquid or solid form and falls as precipitation, moves thence along or into the ground surface, and returns to the atmosphere a vapor by means of evaporation and transpiration.

Impoundment means a closed basin formed naturally or artificially built, which is dammed or excavated for the retention of water, sediment, or waste.

Intermittent or perennial stream means a stream or part of a stream that flows continuously during all (perennial) or for at least one month (intermittent) of the calendar year as a result of ground-water discharge or surface runoff. The term does not include an ephemeral stream which is one that flows for less than one month of a calendar year and only in direct response to precipitation in the immediate watershed and whose channel bottom is always above the local water table.

Leachate means a liquid that has percolated through soil, rock, or waste and has extracted dissolved or suspended materials.

Noxious plants means species that have been included on official State lists of noxious plants for the State in which the operation occurs.

Overburden means material of any nature, consolidated or unconsolidated, that overlies a coal deposit, excluding topsoil.

Outslope means the exposed area sloping away from a bench or terrace being constructed as a part of a surface coal mining and reclamation operation.

Productivity means the vegetative yield produced by a unit area for a unit of time.

Recharge capacity means the ability of the soils and underlying materials to allow precipitation and runoff to infiltrate and reach the zone of saturation.

Roads means access and haul roads constructed, used, reconstructed, improved, or maintained for use in surface coal mining and reclamation operations, including use by coal-hauling vehicles leading to transfer, processing, or storage areas. The term includes any such road used and not graded to approximate original contour within 45 days of construction other than temporary roads used for topsoil removal and coal haulage roads within the pit area. Roads maintained with public funds such as all Federal, State, county, or local roads are excluded.

Recurrence interval means the precipitation event expected to occur, on the average, once in a specified interval. For example, the 10-year 24-hour precipitation event would be that 24-hour precipitation event expected to be exceeded on the average once in 10 years. Magnitude of such events are as defined by the National Weather Service Technical Paper No. 40, “Rainfall Frequency Atlas of the U.S.,” May 1961, and subsequent amendments or equivalent regional or rainfall probability information developed therefrom.

Runoff means precipitation that flows overland before entering a defined stream channel and becoming streamflow.

Safety factor means the ratio of the available shear strength to the developed shear stress on a potential surface of sliding determined by accepted engineering practice.

Sediment means undissolved organic and inorganic material transported or deposited by water.

Sedimentation pond means any natural or artifical structure or depression used to remove sediment from water and store sediment or other debris.

Slope means average inclination of a surface, measured from the horizontal. Normally expressed as a unit of vertical distance to a given number of units of horizontal distance (e.g., 1v to 5h = 20 percent = 11.3 degrees).

Soil horizons means contrasting layers of soil lying one below the other, parallel or nearly parallel to the land surface. Soil horizons are differentiated on the basis of field characteristics and laboratory data. The three major soil horizons are—

(a) A horizon. The uppermost layer in the soil profile often called the surface soil. It is the part of the soil in which organic matter is most abundant, and where leaching of soluble or suspended particles is the greatest.

(b) B horizon. The layer immediately beneath the A horizon and often called the subsoil. This middle layer commonly contains more clay, iron, or aluminum than the A or C horizons.

(c) C horizon. The deepest layer of the soil profile. It consists of loose material or weathered rock that is relatively unaffected by biologic activity.

Spoil means overburden that has been removed during surface mining.

Stabilize means any method used to control movement of soil, spoil piles, or areas of disturbed earth and includes increasing bearing capacity, increasing shear strength, draining, compacting, or revegetating.

Subirrigation means irrigation of plants with water delivered to the roots from underneath.

Surface water means water, either flowing or standing, on the surface of the earth.

Suspended solids means organic or inorganic materials carried or held in suspension in water that will remain on a 0.45 micron filter.

Toxic-forming materials means earth materials or wastes which, if acted upon by air, water, weathering, or microbiological processes, are likely to produce chemical or physical conditions in soils or water that are detrimental to biota or uses of water.

Toxic-mine drainage means water that is discharged from active or abandoned mines and other areas affected by coal mining operations and which contains a substance which through chemical action or physical effects is likely to kill, injure, or impair biota commonly present in the area that might be exposed to it.

Valley fill means a fill structure consisting of any material other than coal waste and organic material that is placed in a valley where side slopes of the fill measured at the steepest point are greater than 20° or the profile of the hollow from the toe of the fill to the top of the fill is greater than 10°.

Waste means earth materials, which are combustible, physically unstable, or acid-forming or toxic-forming, wasted or otherwise separated from product coal and are slurried or otherwise transported from coal processing facilities or preparation plants after physical or chemical processing, cleaning, or concentrating of coal.

Water table means upper surface of a zone of saturation, where the body of ground water is not confined by an overlying impermeable zone.

[42 FR 62677, Dec. 13, 1977, as amended at 44 FR 30628, May 25, 1979]