PURPOSE: This rule sets forth the requirements for backfilling and grading pursuant to sections 444.810, 444.855.2(3), and 444.860.2(4), RSMo.

1. (1) General Requirements.

   1. (A) Surface areas disturbed incident to underground mining activities shall be backfilled and graded in accordance with the time schedule approved in the permit and plan as a condition of the permit.

   2. (B) Backfilling and Grading.

      1. 1. All areas affected by surface opera-

tions shall be returned to approximate original contour. All spoil shall be transported, backfilled and compacted (where advisable to ensure stability or to prevent leaching) and graded to eliminate all highwalls, spoil piles and depressions.

1. 2. Backfilled material shall be placed to

minimize adverse effects on groundwater, minimize off-site effects and support the approved postmining land use.

1. 3. The postmining graded slopes need

not be uniform.

1. 4. Cut-and-fill terraces may be used

only in those situations expressly identified in section (2) of this rule.

1. (2) General Grading Requirements.

   1. (A) The final graded slopes shall not exceed in grade either the approximate premining slopes or any lesser slopes approved in the permit and plan based on consideration of soil, climate or other characteristics of the surrounding area. Postmining final graded slopes need not be uniform but shall approximate the general nature of the premining topography. The requirements of this section may be modified in the permit and plan where the underground mining activities are reaffecting previously mined lands that have not been restored to the standards of this chapter and sufficient spoil is not available to otherwise comply with this section. The person who conducts underground mining activities, at a minimum, shall—

      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 either the angle of repose or lesser slope as is necessary to achieve a minimum static safety factor of one and three-tenths (1.3). In all cases the highwall shall be eliminated.

1. (B) On approval in the permit and 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 approved postmining land use 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 specifically approved in the permit and plan as necessary for stability, erosion control or roads included in the approved postmining land use plan;

1. 2. The vertical distance between terraces

shall be as specified in the permit and plan 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 one and three-tenths (1.3), 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

1. 4. Culverts and underground rock drains

shall be used on the terrace only when approved in the permit and plan.

1. (C) Small depressions may be constructed if they—

   1. 1. Are approved in the permit and plan

to minimize erosion, conserve soil moisture or promote vegetation;

1. 2. Do not restrict normal access; and
2. 3. Are not inappropriate substitutes for

lower grades on the reclaimed lands.

1. (D) All underground mining activities on slopes above twenty degrees (20ş) or on lesser slopes that the commission or director defines as steep slope shall meet the provisions of 10 CSR 40-4.040.
2. (E) All final grading, preparation of overburden before replacement of topsoil and replacement of topsoil shall be done along the contour to minimize subsequent erosion and 10 CSR 40-3

instability. If this grading, preparation or placement along the contour is hazardous to 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.

1. (3) Covering Coal and Acidand Toxic- Forming Materials.

   1. (A) Cover.

      1. 1. Exposed coal seams, acidand toxic-

forming materials and combustible materials exposed, used or produced during mining shall be adequately covered with nontoxic and noncombustible material or treated, to control the impact on surface and ground water in accordance with 10 CSR 40-3.200, to prevent sustained combustion and to minimize adverse effects on plant growth and the approved postmining land use.

1. 2. 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 permit and plan shall specify thicker amounts of cover using nontoxic material.

1. 3. 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.

1. (B) Stabilization. Backfilled materials shall be selectively hauled or conveyed and compacted, wherever necessary to prevent leaching of acidand toxic-forming materials into surface or ground waters and wherever necessary to ensure the stability of backfilled materials. The method and design specifications of compacting material shall be approved in the permit and plan before acidand toxic-forming materials are covered.

1. (4) Regrading or Stabilizing Rills and Gullies. When rills or gullies deeper than nine inches (9") form in areas that have been regraded and topsoiled, the rills and gullies shall be filled, graded or otherwise stabilized and the area reseeded or replanted according to 10 CSR 40-3.270. The permit and plan shall specify that rills or gullies of lesser size be stabilized and the area reseeded or replanted if the rills or gullies are disruptive to the approved postmining land use or may result in additional erosion and sedimentation.

AUTHORITY: sections 444.530 and 444.810, RSMo 1994.* Original rule filed Aug. 8, 1980, effective Dec. 11, 1980. Amended: Filed Dec. 10, 1980, effective April 11, 1981. Amended: Filed July 3, 1990, effective Nov. 30, 1990. Amended: Filed May 15, 1992, effective Jan. 15, 1993. *Original authority 1979, amended 1983, 1993.