PURPOSE: This rule sets forth the requirements for the disposal of underground development waste and excess spoil pursuant to sections 444.810, 444.855.2(15) and 444.860.2(4), RSMo.

1. (1) General Requirements.

   1. (A) Underground development waste and spoil not required to achieve the approximate original contour and which is not used as backfill shall be hauled or conveyed to and placed in designated disposal areas within a permit area, within a time approved by the director in the permit and plan, if the disposal areas are authorized for those purposes in the permit and plan in accordance with sections (1)—(4) of this rule. The material shall be placed in a controlled manner to ensure that—

      1. 1. Leachate and surface runoff from the

fill will not degrade surface or ground waters or exceed the effluent limitations of 10 CSR 40-3.200(2);

1. 2. The fill is stable; and
2. 3. The land mass designated as the dis-

posal area is suitable for reclamation and revegetation compatible with the natural surroundings.

1. (B) The fill and appurtenant structures shall be designed using recognized professional standards, certified by a registered professional engineer experienced in the design of earth and rock fills and approved in the permit and plan. 10 CSR 40-3
2. (C) All vegetative and organic materials shall be removed from the disposal area and the topsoil shall be removed, segregated and stored or replaced in accordance with 10 CSR 40-3.190. If approved in the permit and plan, 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.
3. (D) Slope protection shall be provided to minimize surface erosion at the site. Diversion design shall conform with the requirements of 10 CSR 40-3.040(3). All disturbed areas, including diversion ditches that are not riprapped, shall be vegetated upon completion of construction.
4. (E) The disposal areas shall be located on the most moderately sloping and naturally stable areas available as approved in the permit and plan. If the placement provides additional stability and prevents mass movement, fill materials suitable for disposal shall be placed upon or above a natural terrace, bench or berm.
5. (F) The fill materials shall be hauled or conveyed and placed in horizontal lifts in a controlled manner not exceeding four feet (4') 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 ensure a long-term static safety factor of one and five tenths (1.5). The commission or director may approve a design which incorporates placement of excess spoil in horizontal lifts other than four feet (4') 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.
6. (G) The final configuration of the fill must be suitable for postmining land uses approved in accordance with 10 CSR 40-3.300, except that no depressions or impoundments shall be allowed on the completed fill.
7. (H) Excess spoil that is acidor toxicforming or combustible and shall be adequately covered with nonacid, 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.
8. (I) Terraces may be utilized to control erosion and enhance stability if approved in the permit and plan and consistent with 10 CSR 40-3.260(2)(B).
9. (J) Where the slope in the disposal area exceeds 1v:2.8h (36%), or a lesser slope as may be designated in the permit and plan based on local conditions, keyway cuts (excavations to stable bedrock) or rock toe buttresses shall be constructed to stabilize the fill. Where the toe of the spoil rests on a downslope, stability analyses shall be performed in accordance with 10 CSR 40- 6.120(10) to determine the size of the rock toe buttresses or keyway cuts.

10. (K) The fill shall be inspected for stability by a registered engineer or other qualified professional specialist experienced in the construction of earth and rockfill embankments at least quarterly throughout construction and during the following critical construction periods:

    1. 1. Removal of all organic material and

topsoil;

1. 2. Placement of underdrainage systems;
2. 3. Installation of surface drainage sys-

tems;

1. 4. Placement and compaction of fill

materials; and

1. 5. Revegetation.

2. (L) Certified report. The registered engineer or other qualified professional specialist shall provide to the director a certified report within two (2) weeks after each inspection that the fill has been constructed as specified in the design approved in the permit and plan. The report shall include appearances of instability, structural weakness and other hazardous conditions.

   1. 1. 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.

1. 2. Where excess durable rock spoil is

placed in single or multiple lifts so that the underdrain system is constructed simultaneously with excess spoil placement by the natural segregation of dumped materials, color photographs shall be taken of the underdrain as the underdrain system is being formed.

1. 3. 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.

1. 4. A copy of the report shall be retained

at the mine site.

1. (M) Coal processing waste shall not be disposed of in valley or head-of-hollow fills and only may be disposed of with underground development waste or in other excess spoil fills if that waste is—

   1. 1. Placed in accordance with 10 CSR

40-3.230(4);

1. 2. Demonstrated to be nontoxicand

nonacid-forming; and

1. 3. Demonstrated to be consistent with

the design stability of the fill.

1. (N) If the disposal area contains springs, natural or man-made water courses or wet weather seeps, an underdrain system consisting of durable rock shall be constructed from the wet areas in a manner that prevents infiltration of the water into the spoil material. The underdrain system shall be protected by an adequate filter and shall be designed and constructed using standard geotechnical engineering methods.
2. (O) The foundation and abutments of the fill shall be stable under all conditions of construction and operation. Sufficient foundation investigations and laboratory testing of foundation materials shall be performed in order to determine the design requirements for stability of the foundation. Analyses of foundation conditions shall include the effect of underground mine workings, if any, upon the stability of the structure.
3. (P) Underground development waste and excess spoil may be returned to underground workings only in accordance with the disposal plans submitted under 10 CSR 40- 6.120(16) and approved in the permit and plan and by the Mine Safety and Health Administration (MSHA).

1. (2) Disposal of Underground Development Waste and Excess Spoil in Valley Fills. Valley fills shall meet all of the requirements of section (1) of this rule and the additional requirements of this section.

   1. (A) The fill shall be designed to attain a long-term static factor of safety of one and five-tenths (1.5.), based upon data obtained from subsurface exploration, geotechnical testing, foundation design and accepted engineering analyses.

   2. (B) A subdrainage system for the fill shall be constructed in accordance with the following:

      1. 1. A system of underdrains constructed

of durable rock shall—

1. A. Meet the requirements of para-

graph (2)(B)4.;

1. B. Be installed along the natural

drainage system;

1. C. Extend from the toe to the head of

the fill; and

1. D. Contain lateral drains to each area

of potential drainage or seepage;

1. 2. A filter system to ensure the proper

functioning of the rock underdrain system shall be designed and constructed using standard geotechnical engineering methods;

1. 3. 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. Rock used in underdrains shall meet the requirements of paragraph (2)(B)4. of this rule. The minimum size of the main underdrain shall be—

Minimum Size

Predominant of Drain in

Total Amount of Type of Fill Feet Fill Material Material Width Height Less than 1,000,000 yd3 Sandstone 10 4 Do Shale 16 8 More than 1,000,000 yd3 Sandstone 16 8 Do Shale 16 16

and

1. 4. Underdrains shall consist of non-

degradable, nonacidor nontoxic-forming rock, such as natural sand and gravel, sandstone, limestone or other durable rock, that will not slake in water and will be free of coal, clay or shale.

1. (C) Underground development waste and excess spoil shall be hauled or conveyed and placed in a controlled manner and concurrently compacted as specified in the permit and plan in lifts no greater than four feet (4') or less if required in the permit and plan to—

   1. 1. Achieve the densities designed to

ensure mass stability;

1. 2. Prevent mass movement;
2. 3. Avoid contamination of the rock

underdrain or rock core; and

1. 4. Prevent formation of voids.
2. (D) Surface water runoff from the area above the fill shall be diverted away from the fill and into stabilized diversion channels designed to pass safely the runoff from the one hundred (100)-year, twenty-four (24)- hour precipitation event or larger event specified in the permit and plan. Surface runoff from the fill surface shall be diverted to stabilized channels off the fill which will safely pass runoff from a one hundred (100)-year, twenty-four (24)-hour precipitation event. Diversion design shall comply with the requirements of 10 CSR 40-3.200(3)(F).
3. (E) The tops of the fill and any terrace constructed to stabilize the face shall be graded no steeper than 1v:20h, (5%). The vertical distance between terraces shall not exceed fifty feet (50').
4. (F) Drainage shall not be directed over the outslope of the fill.
5. (G) The outslope of the fill shall not exceed 1v:2h, (50%). The permit and plan may require a flatter slope.

1. (3) Disposal of Underground Development Waste and Excess Spoil: Head-of-Hollow Surface Coal Mining and Related Activities

Fills. Disposal of underground development waste and excess spoil in the head-of-hollow fill shall meet all standards set forth in sections (1) and (2) of this rule and the additional requirements of this section.

1. (A) The fill shall be designed to completely fill the disposal site to the approximate elevation of the ridgeline. A rock core chimney drain may be utilized instead of the subdrain and surface diversion system required for valley fills. If the crest of the fill is not approximately at the same elevation as the low point of the adjacent ridgeline, the fill must be designed as specified in section (2) of this rule, with diversion of runoff around the fill.

2. (B) The alternative rock core chimney drain system shall be designed and incorporated into the construction of head-of-hollow fills as follows:

   1. 1. The fill shall have along the vertical

projection of the main buried stream channel or rill a vertical core of durable rock at least sixteen feet (16') thick which shall extend from the toe of the fill to the head of the fill and from the base of the fill to the surface of the fill. A system of lateral rock underdrains shall connect this rock core to each area of potential drainage or seepage in the disposal area. Rocks used in the rock core and underdrains shall meet the requirements of subsection (2)(B) of this rule;

1. 2. A filter system to ensure the proper

functioning of the rock core shall be designed and constructed using standard geotechnical engineering methods; and

1. 3. The grading may drain surface water

away from the outslope of the fill and toward the rock core. The maximum slope of the top of the fill shall be 1v:33h, (3%). Instead of the requirements of subsection (1)(G) of this rule, a drainage pocket may be maintained at the head of the fill during and after construction to intercept surface runoff and discharge the runoff through or over the rock drain if stability of the fill is not impaired. In no case shall this pocket or sump have a potential for impounding more than ten thousand (10,000) cubic feet of water. Terraces on the fill shall be graded with a three percent to five percent (3%–5%) grade toward the fill and a one percent (1%) slope toward the rock core.

1. (C) The drainage control system shall be capable of safely passing the runoff from a one hundred (100)-year, twenty-four (24)- hour precipitation event or larger event specified in the permit and plan.

1. (4) Durable Rock Fills. In lieu of the requirements of sections (2) and (3) of this rule, the permit and plan may contain alternate methods for disposal of hard rock spoil, including fill placement by dumping in a single lift, on a site specific basis, provided the services of a registered professional engineer experienced in the design and construction of earth and rock fill embankments are utilized and provided the requirements of this section and section (1) of this rule are met. For this section, hard rock spoil shall be defined as rockfill consisting of at least eighty percent (80%) by volume of sandstone, limestone or other rocks that do not slake in water. Resistance of the hard rock waste or spoil to slaking shall be determined by using the slake index and slake durability tests in accordance with guidelines and criteria established by the commission or director.

   1. (A) Waste or spoil is to be transported and placed in a specified and controlled manner which will ensure stability of the fill.

      1. 1. The method of waste spoil placement

shall be designed to ensure mass stability and prevent mass movement in accordance with the additional requirements of this section.

1. 2. Loads of noncemented clay shale,

clay spoil, or both, in the fill shall be mixed with hard rock waste spoil in a controlled manner to limit on a unit basis concentrations of noncemented clay shale and clay in the fill. These materials will comprise no more than twenty percent (20%) of the fill volume as determined by tests performed by a registered engineer and approved in the permit and plan.

1. (B) Stability Analyses.

   1. 1. Stability analyses shall be made by

the registered professional engineer. Parameters used in the stability analyses shall be based on adequate field reconnaissance, subsurface investigations, including borings and laboratory tests.

1. 2. The embankment which constitutes

the valley fill or head-of-hollow fill shall be designed with the following factors of safety:

Minimum Factor of

Case Design Condition Safety I End of Construction 1.5 II Earthquake 1.1

1. (C) The design of a head-of-hollow fill shall include an internal drainage system which will ensure continued free drainage of anticipated seepage from precipitation and from springs or wet weather seeps.

   1. 1. Anticipated discharge from springs

and seeps and due to precipitation shall be based on records, field investigations, or both, to determine seasonal variation. The design of the internal drainage system shall be based on the maximum anticipated discharge.

1. 2. All granular material used for the

drainage system shall be free of clay and con- 10 CSR 40-3

sist of durable particles, such as natural sands and gravels, sandstone, limestone or other durable rock, which will not slake in water.

1. 3. The internal drain shall be protected

by a properly designed filter system.

1. (D) Surface water runoff from the areas adjacent to and above the fill shall not be allowed to flow onto the fill and shall be diverted into stabilized channels which are designed to safely pass the runoff from a one hundred (100)-year, twenty-four (24)-hour precipitation event. Diversion design shall comply with the requirements of 10 CSR 40- 3.200(3)(F).
2. (E) The top surface of the completed fill shall be graded so that the final slope, after settlement, will be no steeper than 1v:20h, (5%) toward properly designed drainage channels in natural ground along the periphery of the fill. Surface runoff from the top surface of the fill shall not be allowed to flow over the outslope of the fill.
3. (F) Surface runoff from the outslope of the fill shall be diverted off the fill to properly designed channels which will safely pass a one hundred (100)-year, twenty-four (24)- hour precipitation event. Diversion design shall comply with the requirements of 10 CSR 40-3.200(3)(F).

4. (G) Terraces shall be constructed on the outslope, if required, for control of erosion or for roads included in the approved postmining land use plan. Terraces shall meet the following requirements:

   1. 1. The slope of the outslope between ter-

race benches shall not exceed 1v:2h, (50%);

1. 2. To control surface runoff, each ter-

race bench shall be graded to a slope of 1v:20h, (5%) toward the embankment. Runoff shall be collected by a ditch along the intersection of each terrace bench and the outslope; and

1. 3. Terrace ditches shall have a five per-

cent (5%) slope toward the channels specified in subsection (4)(F) of this rule, unless steeper slopes are necessary in conjunction with approved roads.

AUTHORITY: section 444.810, RSMo 1994.* Original rule filed Aug. 8, 1980, effective Dec. 11, 1980. Amended: Filed Sept. 15, 1988, effective Jan. 15, 1989. Amended: Filed July 3, 1990, effective Nov. 30, 1990. *Original authority 1979, amended 1983, 1993.