Current through Register Vol. 6, March 22, 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.