Administrative Rules of Montana › Department 17 - ENVIRONMENTAL QUALITY › Chapter 17.24 - RECLAMATION › Subchapter 17.24.5 - Strip and Underground Mine Reclamation Act: Backfilling and Grading Requirements › Rule 17.24.520 - THICK OVERBURDEN AND DISPOSAL OF EXCESS SPOIL

Current through Register Vol. 13, July 5, 2024
(1) Thick overburden occurs where the final
				spoil thickness exceeds 1.2 times the sum of the overburden thickness and
				mineral thickness for the entire area to be mined in the permit area. Final
				spoil thickness is the product of the overburden thickness times the swell
				factor, which is also to be determined for the entire area to be mined in the
				permit area.
(2) Where thick
				overburden is encountered, and if the operator wishes to dispose of excess
				spoil outside of the mined area, the operator shall demonstrate that the volume
				of spoil and available waste materials is more than sufficient to restore the
				disturbed area to the approximate original contour. In this case, highwall
				elimination must be achieved by backfilling with spoils and waste materials.
				Any excess spoil material must be disposed of in accordance with the
				requirements of this rule as well as all other rules.
(3) Spoil not required to achieve the
				approximate original contour may be transported to and placed in a controlled
				(engineered) manner in a disposal area other than the mine workings or
				excavations. All of the following conditions, in addition to the other
				requirements of the Act and this subchapter, must be met:
(a) The disposal area must be within the
				permit area, and it must be approved by the department as suitable for
				construction of fills and for reclamation and revegetation compatible with the
				natural surroundings.
(b) The
				disposal area must be located on the most moderately sloping and naturally
				stable areas available as approved by the department. Fill materials suitable
				for disposal must be placed upon or above a natural terrace, bench, or berm if
				such placement provides additional stability and prevents mass
				movement.
(c) The fill must be
				designed using recognized professional standards, certified by a licensed
				professional engineer, experienced in the design of earth and rock fills, to
				ensure stability and meet other applicable requirements of this subchapter, and
				approved by the department.
(d)
				Leachate and surface runoff from the fill must not degrade surface or ground
				waters or exceed the effluent limitations of ARM
				17.24.633.
(e) The disposal area must not contain
				springs, natural water courses, or wet weather seeps unless lateral drains are
				constructed from the wet areas to excess spoil underdrains in such a manner
				that infiltration of the water into the spoil pile will be prevented.
(f) Underdrains must consist of durable rock
				or pipe, be designed and constructed using current, prudent engineering
				practices, and approved by the department. The underdrain system must be
				designed to carry the anticipated seepage of water due to rainfall away from
				the excess spoil fill and from seeps and springs in the foundation of the
				disposal area and must be protected from piping and contamination by an
				adequate filter. Rock underdrains must be constructed of durable, nonacid-,
				nontoxic-forming rock (e.g., natural sand and gravel, sandstone, limestone, or
				other durable rock) that does not slake in water or degrade to soil-like
				material, and which is free of coal, clay or other nondurable material.
				Perforated pipe underdrains must be corrosion resistant and must have
				characteristics consistent with the long-term life of the fill.
(g) All organic material must be removed from
				the disposal area, and the soil must be removed, segregated, and redistributed
				or stockpiled according to the provisions of ARM
				17.24.701 through
				17.24.703, before the excess spoil
				material is placed in the disposal area. However, if approved by the
				department, organic material may be used as mulch or may be included in the
				soil.
(h) Slope protection must be
				provided to minimize surface erosion at the site. Diversion design must conform
				with the requirements of ARM
				17.24.635 through
				17.24.637. All disturbed areas,
				including diversion ditches that are not riprapped, must be vegetated upon
				completion of construction.
(i) The
				spoil must be transported and placed in a controlled manner, in horizontal
				lifts not exceeding four feet in thickness, concurrently compacted as necessary
				to ensure mass stability and prevent mass movement, covered, and graded to
				allow surface and subsurface drainage to be compatible with the natural
				surroundings and to ensure a long-term static safety factor of 1.5. Horizontal
				lifts exceeding four feet in thickness may be allowed if the design ensures
				stability, is certified by a licensed professional engineer, and is approved by
				the department. The final configuration of the fill must be suitable for
				postmining land uses except that no depressions or impoundments may be allowed
				on the completed fill. Terraces must not be constructed unless approved by the
				department to prevent erosion and ensure stability.
(j) The fill must be inspected for stability
				at least quarterly by the licensed engineer or other qualified professional
				specialist under the direction of a licensed engineer. The engineer or
				specialist must be experienced in the construction of similar earth and water
				structures. The above-described inspections must be made during critical
				construction periods to assure removal of all organic material and soil,
				placement of underdrainage and surface drainage systems, and proper placement
				and compaction of fill materials, and revegetation. The permittee shall provide
				a report by the licensed engineer or other qualified professional specialist
				within two weeks after each inspection. The report must certify that the fill
				has been constructed as specified in the design approved by the department. A
				copy of the report must be retained at the mine site.
(i) "Critical construction periods" include,
				at a minimum:
(A) foundation preparation,
				including the removal of all organic material and soil;
(B) placement of underdrains and protective
				filter systems;
(C) installation of
				final surface drainage systems; and
(D) the final graded and revegetated fill.
				Regular inspections by the engineer or specialist must also be conducted during
				placement and compaction of fill materials.
(ii) The qualified licensed professional
				engineer shall promptly provide to the department a certified report discussing
				whether the fill has been constructed and maintained as designed and in
				accordance with the approved plan and this subchapter. The report must address
				indications of instability, structural weakness, and other hazardous
				conditions.
(iii)
(A) The certified report on the drainage
				system and protective filters must include color photographs taken during and
				after construction, but before underdrains are covered with excess spoil. If
				the underdrain system is constructed in phases, each phase must be certified
				separately.
(B) Whenever excess
				durable rock spoil is placed in single or multiple lifts such that the
				underdrain system is constructed simultaneously with excess spoil placement by
				the natural segregation of dumped materials, in accordance with (3) (j) (iv),
				color photographs of the underdrain must be taken as the underdrain system is
				being formed.
(C) The photographs
				accompanying each certified report must be taken in adequate size and number
				with enough terrain or other physical features of the site shown to provide a
				relative scale to the photographs and to specifically and clearly identify the
				site.
(iv) The department
				may approve the alternative method of disposal of excess durable rock spoil by
				gravity placement in single or multiple lifts, whenever the following
				additional conditions are met:
(A) the excess
				spoil must consist of at least 80% nontoxic-forming rock that does not slake in
				water and will not degrade to unconsolidated soil-like material. Whenever used,
				noncemented clay shale, clay spoil, unconsolidated or other nondurable excess
				spoil materials must be mixed with excess durable rock spoil in a controlled
				manner so that no more than 20% of the fill volume, as determined by tests
				performed by a licensed engineer and approved by the department, is not durable
				rock;
(B) an earthquake safety
				factor of at least 1.1 must be used; and
(C) surface water runoff from areas adjacent
				to and above the fill must not be allowed to flow onto the fill and must be
				diverted into stabilized diversion channels designed to meet the requirements
				of ARM 17.24.635 and
				17.24.637 and to safely pass the
				runoff from a 100-year, 24-hour precipitation
				event.
(k) Coal
				mine wastes and coal processing wastes may not be disposed of in excess spoil
				fills and may be disposed of in the mine excavations only upon the prior
				approval of the department. See ARM
				17.24.505 and
				17.24.510.
(l) The foundation and abutments of the fill
				must be stable under all conditions of construction and operation. Sufficient
				foundation investigation and laboratory testing of foundation materials must
				include the effect of underground mine workings, if any, upon the stability of
				the structure.
(m) Excess spoil,
				coal mine wastes and coal processing wastes may be returned to underground mine
				workings, but only in accordance with a disposal program approved by the
				department and the mine safety and health administration upon the basis of a
				plan submitted under ARM
				17.24.901(1) (b),
				17.24.920,
				17.24.924(1),
				17.24.930, and
				17.24.932(1).
(n) Excess spoil must not be disposed of in
				valley fills or head-of-hollow fills.
(o) To achieve approximate original contour,
				the department may require that a spoil pile, or part thereof, be retained in
				an unreclaimed condition to be returned to the mine workings at a later
				date.