PURPOSE: This rule complies with section 444.535.1(3), RSMo by setting forth the requirements for backfilling and grading in order to restore the approximate original contour of the land.

1. (1) General. In order to achieve the approximate original contour, the operator, except as provided in this rule, shall transport, backfill, compact (where advisable to ensure stability or to prevent leaching of toxic materials) and grade all spoil material to eliminate all highwalls, spoil piles and depressions. Cut-andfill terraces may be used only in those situations expressly identified in this rule. The postmining graded slopes must approximate the premining natural slopes in the area as defined in section (2) of this rule.

2. (2) Slope Measurements.

   1. (A) To determine the natural slopes of the area before mining, the approved reclamation plan must show that sufficient slopes to adequately represent the land surface configuration, in accordance with site conditions, have been accurately measured and recorded. Each measurement shall consist of an angle of inclination along the prevailing slope extending one hundred (100) linear feet above and below or beyond the coal outcrop or the area to be disturbed; or, where this is impractical, at locations specified and approved in the reclamation plan. Where the area has been previously mined, the measurements shall extend at least one hundred feet (100') beyond the limits of mining disturbances as determined in the reclamation plan to be representative of the premining configuration of the land. Slope measurements shall take into account natural variations in slope so as to provide accurate representation of the range of natural slopes and shall reflect geomorphic differences of the area to be disturbed. Slope measurements may be made from topographic maps showing contour lines, having sufficient detail and accuracy consistent with the submitted reclamation plan.
   2. (B) After the disturbed area has been graded, the final graded slopes shall be measured at the beginning and end of lines established on the prevailing slope at locations representative of premining slope conditions and approval by the director. These measurements must not be made so as to allow unacceptably steep slopes to be constructed.

3. (3) Final Graded Slopes.

   1. (A) The final graded slopes shall not exceed either the approximate premining slopes as determined according to subsection (2)(A) of this rule or any lesser slope specified in the reclamation plan based on consideration of soil, climate or other characteristics of the surrounding area. Postmining final graded slopes need not be uniform. The requirements of this subsection may be modified in the reclamation plan where the mining is reaffecting previously mined lands that have not been restored to the standards of this section and sufficient spoil is not available to return to the slope determined according to subsection (2)(A) of this rule. Where these modifications are approved, the operator, as a minimum, shall be required to—

      1. 1. Retain all overburden and spoil on the

solid portion of existing or new benches; and

1. 2. Backfill and grade to the most mod-

erate slope possible to eliminate the highwall which does not exceed the angle of repose or lesser slopes as is necessary to assure stability.

1. (B) On approval in the reclamation plan and in order to conserve soil moisture, ensure stability and control erosion on final graded slopes, cut-and-fill terraces may be allowed if the terraces are compatible with the postmining land use approved under 10 CSR 40- 2.030 and are appropriate substitutes for construction of lower grades on the reclaimed lands. The terraces shall meet the following requirements:

   1. 1. The width of the individual terrace

bench shall not exceed twenty feet (20’) unless necessary for stability, erosion control or roads;

1. 2. The vertical distance between terraces

shall be as necessary to prevent excessive erosion and to provide long-term stability;

1. 3. The slope of the terrace outslope shall

not exceed 1v:2h (50%). Outslopes which exceed 1v:2h (50%) may be approved if they have a minimum static safety factor of more than 1.5 and provide adequate control over erosion and closely resemble the surface configuration of the land prior to mining. In no case may highwalls be left as part of terraces; and 10 CSR 40-2

1. 4. Culverts and underground rock drain

outlets shall be used on the terrace only when necessary to prevent erosion and ponding.

1. (C) All operations on steep slopes of twenty degrees (20°) or more shall meet the provisions of 10 CSR 40-2.100.

1. (4) Small Depressions. The requirement of this rule to achieve approximate original contour does not prohibit construction of small depressions if approved in the reclamation plan to minimize erosion, conserve soil moisture or promote revegetation. These depressions shall be compatible with the approved postmining land use and shall not be inappropriate substitutes for construction of lower grades on the reclaimed lands. Depressions approved under this section shall have a holding capacity of less than one (1) cubic yard of water or, if it is necessary that they be larger, shall not restrict normal access throughout the area or constitute a hazard. Large, permanent impoundments shall be governed by section (5) of this rule and by 10 CSR 40- 2.060(11).
2. (5) Permanent Impoundments. Permanent impoundments may be retained in mined and reclaimed areas; provided, all highwalls are eliminated by grading to appropriate contour and the provisions for postmining land use (10 CSR 40-2.030) and protection of the hydrologic balance (10 CSR 40-2.060) are met. No impoundments shall be constructed on top of areas in which excess materials are deposited pursuant to sections (12) and (13) of this rule. Impoundments shall not be used to meet the requirements of section (10) of this rule.
3. (6) Definition of Thin and Thick Restored Overburden. The thin overburden provisions of section (7) of this rule may apply only where the final thickness is less than 0.8 of the initial thickness. The thick overburden provisions of section (8) of this rule may apply only where the final thickness is greater than 1.2 of the initial thickness. Initial thickness is the sum of the overburden thickness and coal thickness. Final thickness is the product of the overburden thickness times the bulking factor to be determined for each mine area. The provisions of sections (7) and (8) of this rule apply only when operations cannot be carried out to comply with the requirements of section (2) of this rule to achieve the approximate original contour.

4. (7) Thin Overburden. In coal strip mining operations carried out continuously in the same limited pit area for more than one (1) year from the day coal removal operations begin and where the volume of all available spoil and suitable waste materials is demonstrated to be insufficient to achieve approximate original contour, coal strip mining operations shall be conducted to meet, at a minimum, the following standards:

   1. (A) Transport, backfill and grade, using all available spoil and suitable waste materials from the entire mine area, to attain the lowest practicable stable grade, which may not exceed the angle of repose, and to provide adequate drainage and long-term stability of the regraded areas;
   2. (B) Eliminate highwalls by grading or backfilling to stable slopes not exceeding 1v:2h (50%);
   3. (C) Transport, backfill, grade and revegetate to achieve an ecologically sound land use compatible with the prevailing land use in unmined areas surrounding the permit area; and
   4. (D) Transport, backfill and grade to ensure the impoundments are constructed only where it has been demonstrated that all requirements of 10 CSR 40-2.060 have been met and that the impoundments meet the requirements of this rule and all other applicable federal and state regulations.

5. (8) Thick Overburden. In surface coal mining operations where the volume of spoil is demonstrated to be more than sufficient to achieve the approximate original contour, coal strip mining operations shall be conducted to meet, at a minimum, the following standards:

   1. (A) Transport, backfill and grade all spoil and wastes not required to achieve approximate original contour in the strip mining area to the lowest practicable grade;
   2. (B) Deposit, backfill and grade excess spoil and wastes only within the permit area and dispose of those materials in conformance with this section;
   3. (C) Transport, backfill and grade excess spoil and wastes to maintain the hydrologic balance in accordance with this section and to provide long-term stability;
   4. (D) Transport, backfill, grade and revegetate wastes and excess spoil to achieve an ecologically sound land use compatible with the prevailing land uses in unmined areas surrounding the permit area; and
   5. (E) Eliminate all highwalls and depressions except as stated in section (5) of this rule by backfilling with spoil and suitable waste materials.
6. (9) Regrading or Stabilizing Rills and Gullies. When rills or gullies deeper than nine inches (9") form in areas that have been regraded and the topsoil replaced, whether vegetation has been established or not, the operator shall fill, grade or otherwise stabilize the rills and gullies and reseed or replant the areas according to 10 CSR 40-2.090. Rills or gullies of lesser size shall be stabilized if the rills or gullies will be disruptive to the approved postmining land use or may result in additional erosion and sedimentation.

7. (10) Covering Coal and Acid-Forming, Toxic- Forming, Combustible and Other Waste Materials; Stabilizing Backfilled Materials; and Using Waste Material for Fill.

   1. (A) Cover. All exposed coal seams remaining after mining and any acid-forming, toxicforming, combustible materials, gob or any other hazardous waste materials identified by the commission that are exposed, used or produced during mining shall be covered with a minimum of four feet (4') of nontoxic and noncombustible material; or, if necessary, treated to neutralize toxicity in order to prevent water pollution and sustained combustion, and to minimize adverse effects on plant growth and land uses. In the reclamation plan where necessary to protect against upward migration of salts, exposure by erosion, to provide an adequate depth for plant growth or to otherwise meet local conditions, the commission may specify thicker amounts of cover using nontoxic material. Acidor toxic-forming material shall not be buried or stored in proximity to a drainage course so as to cause or pose a threat of water pollution or otherwise violate the provisions of 10 CSR 40- 2.060.
   2. (B) Stabilization. Backfilled materials shall be selectively placed and compacted wherever necessary to prevent leaching of toxicforming materials into surface or subsurface waters in accordance with 10 CSR 40-2.060 and wherever necessary to ensure the stability of the backfilled materials. The method of compacting material and the design specifications shall be approved by the director before the toxic materials are covered.
   3. (C) Use of Waste Materials as Fill. Before waste materials from a coal preparation or conversion facility or from other activities conducted outside the permit area such as municipal wastes are used for fill material, it must be demonstrated by hydrogeological means, and chemical and physical analyses that use of these materials will not adversely affect water quality, water flow and vegetation; will not present hazards to public health and safety; and will not cause instability in the backfilled area.
8. (11) Grading Along the Contour. All final grading, preparation or overburden before replacement of topsoil, and placement of topsoil, in accordance with 10 CSR 40-2.050, shall be done along the contour to minimize subsequent erosion and instability. If grading, preparation or placement along the contour would be hazardous for equipment operators, then grading, preparation or placement in a direction other than generally parallel to the contour may be used. In all cases, grading, preparation or placement shall be conducted in a manner which minimizes erosion and provides a surface for replacement of topsoil which will minimize slippage.

9. (12) Disposal of Spoil in Other Than Valley or Head-of-Hollow Fills. Spoil not required to achieve the approximate original contour shall be transported to and placed in a controlled (engineered) manner in disposal areas other than the mine workings or excavations only if approved in the reclamation plan and all the following conditions, in addition to the other requirements of this rules, are met:

   1. (A) The disposal areas shall be within the permit area, if suitable for construction of fills in accordance with the requirements of this section;
   2. (B) The disposal areas shall be located on the most moderate sloping and naturally stable areas available. Where possible, fill materials suitable for disposal shall be placed upon or above a natural terrace, bench or berm if that placement provides additional stability and prevents mass movement;
   3. (C) The fill shall be designed using recognized professional standards certified by a registered professional engineer;
   4. (D) Where the slope in the disposal area exceeds 1v:2.8h (36%), measures such as keyway cuts (excavations to stable bedrock) or rock toe buttresses shall be constructed to stabilize the fill;
   5. (E) The disposal area does not contain springs, natural water courses or wet weather seeps unless lateral drains are constructed from the wet areas to the underdrains in a manner that infiltration of the water into the spoil pile will be prevented;
   6. (F) All organic material shall be removed from the disposal area and the topsoil must be removed and segregated pursuant to 10 CSR 40-2.050 before the material is placed in the disposal area. However, if approved in the reclamation plan, organic material may be used as mulch or may be included in the topsoil;
   7. (G) The spoil shall be transported and placed in a controlled manner, 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 long-term stability. The final configuration of the fill must be suitable for postmining land uses approved in accordance with 10 CSR 40-2.030. Terraces shall not be constructed unless approved in the reclamation plan in accordance with subsection (3)(B) of this rule;
   8. (H) If any portion of the fill interrupts, obstructs or encroaches upon any natural drainage channel, the entire fill is classified as a valley or head-of-hollow fill and must be designed and constructed in accordance with the requirements of section (3) of this rule; and
   9. (I) The fill shall be inspected for stability by a registered engineer or other qualified professional specialist during critical construction periods to assure removal of all organic material and topsoil, placement of under-drainage systems and proper construction of terraces according to the approved reclamation plan. The registered engineer or other qualified professional specialist shall provide a certified report after each inspection that the fill has been constructed according to the reclamation plan.

10. (13) Disposal of Spoil in Valley or Head-of- Hollow Fills. Waste material must not be disposed of in valley or head-of-hollow fills. Spoil to be disposed of in natural valleys must be placed in accordance with the following requirements:

    1. (A) The disposal areas shall be within the permit area and be approved in the reclamation plan as suitable for construction of fills in accordance with the requirements of this section;
    2. (B) The disposal site shall be near the ridge top of a valley selected to increase the stability of the fill and to reduce the drainage area above the fill. Where possible, spoil shall be placed above a natural terrace, bench or berm, if that placement provides additional stability and prevents mass movement;
    3. (C) The fill shall be designed using recognized professional standards certified by a registered professional engineer;
    4. (D) All organic material shall be removed from the disposal area and the topsoil must be removed and segregated pursuant to 10 CSR 40-2.050 before the material is placed in the disposal area. However, if approved in the reclamation plan, organic material may be used as mulch or may be included in the topsoil;
    5. (E) Where the slope in the disposal area exceeds 1v:2.8h (36%), measures such as keyway cuts (excavations to stable bedrock) or rock toe buttresses shall be constructed to stabilize the fill;
    6. (F) A system of underdrains constructed of durable rock shall be installed along the natural drainage system, shall extend the toe to the head of the fill and contain lateral drains to each area of potential drainage or seepage. In constructing the underdrains, no more than ten percent (10%) of the rock may be less than twelve inches (12") in size and no single rock may be larger than twenty-five percent (25%) of the width of the drain. No rock shall be used in the underdrains if it tends to easily disintegrate and then clog the drain or if it is acidor toxic-forming. The minimum size of the main underdrain shall be—

Total Amount Predominant Minimum Size of Fill Material Type of Fill of Drain in Feet Material Width Height Less than 1 Sandstone 10 4 million yd3

Less than 1 Shale 16 8 million yd3

More than 1 Sandstone 16 8 million yd3 More than 1 Shale 16 8 million yd3

1. (G) Spoil shall be transported and placed in a controlled manner and concurrently compacted in lifts that are less than four feet (4') thick in order to achieve the densities designed to ensure mass stability, to prevent mass movement, to avoid contamination of the rock underdrain and to prevent formation of voids. The final configuration of the fill must be suitable for postmining land uses approved in accordance with 10 CSR 40- 2.030;
2. (H) Terraces shall be constructed to stabilize the face of the fill. The outslope of each terrace shall not exceed fifty feet (50') in height and the width of the terrace shall not be less than twenty feet (20');
3. (I) The tops of the fill and each terrace shall be graded no steeper than 1v:20h (5%) and shall be constructed to drain surface water to the sides of the fill where stabilized surface channels shall be established off the fill to carry drainage away from the fill. Drainage shall not be directed over the outslope of the fill unless approved in the reclamation plan;
4. (J) All surface drainage from the undisturbed area above the fill shall be directed away from the fill by approved structures leading into water courses;
5. (K) The outslope of the fill shall not exceed 1v:2h (50%); and
6. (L) The fill shall be inspected for stability by a registered engineer or other qualified 10 CSR 40-2

professional specialist during critical construction periods and at least quarterly throughout construction to assure removal of all organic material and topsoil, placement of underdrainage systems and proper construction of terraces according to the approved reclamation plan. The registered engineer or other qualified professional specialist shall provide a certified report after each inspection that the fill has been constructed as specified in the reclamation plan.

AUTHORITY: section 444.535.1(3), RSMo 1986.* Original rule filed July 13, 1978, effective Jan. 13, 1979. *Original authority: 444.535, RSMo 1978, amended 1988.