SECTION 460:20-43-24. Disposal of excess spoil: general requirements

(a)   General. Excess spoil shall be placed in designated disposal areas the permit area, in a controlled manner to:

(1)   Minimize the adverse effects of leachate and surface water runoff from the fill on surface and ground waters;

(2)   Ensure mass stability and prevent mass movement during and after construction; and

(3)   Ensure that the final fill is suitable for reclamation and revegetation compatible with the natural surroundings and the approved postmining land use.

(b)   Design certification.

(1)   The fill and appurtenant structures shall be designed using current, prudent engineering practices and shall meet any design criteria established by the Department. A qualified registered professional engineer experienced in the design of earth and rock fills shall certify the design of the fill and appurtenant structures.

(2)   The fill shall be designed to attain a minimum long-term static safety factor of 1.5. The foundation and abutments of the fill must be stable under all conditions of construction.

(c)   Location. The disposal area shall be located on the most moderately sloping and naturally stable areas available, as approved by the Department, and shall be placed, where possible, upon or above a natural terrace, bench, or berm, if such placement provides additional stability and prevents mass movement.

(d)   Foundation.

(1)   Sufficient foundation investigations, as well as any necessary laboratory testing of foundation material, shall be performed in order to determine the design requirements for foundation stability. The analyses of foundation conditions shall take into consideration the effect of underground mine workings, if any, upon the stability of the fill and appurtenant structures.

(2)   Where the slope in the disposal area is in excess of 2.8h:1v (36 percent), or such lesser slope as may be designated by the Department based on local conditions, keyway cuts (excavations to stable bedrock) or rock toe buttresses shall be constructed to ensure stability of the fill. Where the toe of the spoil rests on a downslope, stability analyses shall be performed in accordance with Section 460:20-27-19(c) of this Chapter to determine the size of rock toe buttresses and keyway cuts.

(e)   Placement of excess spoil.

(1)   All vegetative and organic materials shall be removed from the disposal area prior to placement of the excess spoil. Topsoil shall be removed, segregated and stored or redistributed in accordance with Section 460:20-43-7. If approved by the Department, organic material may be used as mulch or may be included in the topsoil to control erosion, promote growth of vegetation or increase the moisture retention of the soil.

(2)   Excess spoil shall be transported and placed in a controlled manner in horizontal lifts not exceeding 4 feet in thickness; concurrently compacted as necessary to ensure mass stability and to prevent mass movement during and after construction; graded so that surface and subsurface drainage is compatible with the natural surroundings; and covered with topsoil or substitute material in accordance with Section 460:20-43-7 of this Chapter. The Department may approve a design which incorporates placement of excess spoil in horizontal lifts other than 4 feet in thickness when it is demonstrated by the operator and certified by a qualified registered professional engineer that the design will ensure the stability of the fill and will meet all other applicable requirements.

(3)   The final configuration of the fill shall be suitable for the approved postmining land use. Terraces may be constructed on the out slope of the fill if required for stability, control of erosion, to conserve soil moisture, or to facilitate the approved postmining land use. The grade of the outslope between terrace benches shall not be steeper than 2h: Iv (50 percent)

(4)   No permanent impoundments are allowed on the completed fill. Small depressions may be allowed by the Department if they are needed to retain moisture, minimize erosion, create and enhance wildlife habitat, or assist revegetation; and if they are not incompatible with the stability of the fill.

(5)   Excess spoil that is acid- or toxic-forming or combustible shall be adequately covered with nonacid, nontoxic and noncombustible material, or treated, to control the impact on surface and ground water in accordance with Section 460:20-43-8, to prevent sustained combustion, and to minimize adverse effects on plant growth and the approved postmining land use.

(f)   Drainage control.

(1)   If the disposal area contains springs, natural or manmade water courses, or wet weather seeps, the fill design shall include diversions and underdrains as necessary to control erosion, prevent water infiltration into the fill, and ensure stability.

(2)   Diversions shall comply with the requirements of Section 460:20-43-10.

(3)   Underdrains shall consist of durable rock or pipe, be designed and constructed using current, prudent engineering practices and meet any design criteria established by the Department. The underdrain system shall 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 shall be protected from piping and contamination by an adequate filter. Rock underdrains shall 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 material, and which is free of coal, clay or other nondurable material. Perforated pipe underdrains shall be corrosion resistant and shall have characteristics consistent with the long-term life of the fill.

(g)   Surface area stabilization. Slope protection shall be provided to minimize surface erosion at the site. All disturbed areas, including diversion channels that are not riprapped or otherwise protected, shall be revegetated upon completion of construction.

(h)   Inspections. A qualified registered professional engineer, or other qualified professional specialist under the direction of the professional engineer, shall periodically inspect the fill during construction. The professional engineer or specialist shall be experienced in the construction of earth and rock fills.

(1)   Such inspections shall be made at least quarterly throughout construction and during critical construction periods. Critical construction periods shall include at a minimum:

(A)   Foundation preparation, including the removal of all organic material and topsoil;

(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 shall also be conducted during placement and compaction of fill materials.

(2)   The qualified registered professional engineer shall provide a certified report to the Department promptly after each inspection that the fill has been constructed and maintained as designed and in accordance with the approved plan and this Chapter. The report shall include appearances of instability, structural weakness, and other hazardous conditions.

(3)   Drainage systems.

(A)   The certified report on the drainage system and protective filters shall 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 shall be certified separately.

(B)   Where 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 Section 460:20-43-26, color photographs shall be taken of the underdrain as the underdrain system is being formed.

(C)   The photographs accompanying each certified report shall 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.

(4)   A copy of each inspection report shall be retained at or near the mine site.

(i)   Coal mine waste. Coal mine waste may be disposed of in excess spoil fills if approved by the Department and, if such waste is:

(1)   Placed in accordance with Section 460:20-43-30;

(2)   Nontoxic and nonacid forming; and

(3)   Of the proper characteristics to be consistent with the design stability of the fill.

(j)   Underground disposal. Excess spoil may be disposed of in underground mine workings, but only in accordance with a plan approved by the Department and MSHA under Section 460:20-31-18 of this Chapter.

[Source: Amended at 12 Ok Reg 3592, eff 10-12-95]