(a) The final graded slopes shall not exceed in grade either the approximate premining slopes, or any lesser slopes approved by the Commission 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 person who conducts underground mining activities shall, at a minimum:
  (1) retain all overburden and spoil on the solid portion of existing or new benches; and
  (2) backfill and grade to the most moderate slope possible, to eliminate the highwall which does not exceed either the angle of repose or such lesser slope as is necessary to achieve a minimum static safety factor of 1.3. In all cases the highwall shall be eliminated.
(b) On approval by the Commission 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) the width of the individual terrace bench shall not exceed 20 feet unless specifically approved by the Commission as necessary for stability, erosion control, or roads included in the approved postmining land-use plan;
  (2) the vertical distance between terraces shall be as specified by the Commission, to prevent excessive erosion and to provide long-term stability;
  (3) the slope of the terrace outslope shall not exceed 2h:1v (50%). In no case may highwalls be left as part of terraces; and
  (4) culverts and underground rock drains shall be used on the terrace only when approved by the Commission.
(c) Small depressions may be constructed if they:
  (1) are approved by the Commission to minimize erosion, conserve soil moisture or promote vegetation;
  (2) do not restrict normal access; and
  (3) are not inappropriate substitutes for lower grades on the reclaimed lands.
(d) All final grading, preparation of overburden before replacement of topsoil, and placement of topsoil shall be done along the contour to minimize subsequent erosion and instability. If such 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.
(e) Backfilling and grading of previously mined areas shall be subject to the following requirements:
  (1) remining operations on previously mined areas that contain a preexisting highwall shall comply with the requirements of §12.551 of this title (relating to Backfilling and Grading: General Requirements), this section, and §12.553 of this title (relating to Backfilling and Grading: Covering Coal and Acid- and Toxic-Forming Materials), except as provided in this subsection; and
  (2) the requirements of §12.551(b)(1) requiring the elimination of highwalls shall not apply to remining operations where the volume of all reasonably available spoil is demonstrated in writing to the Commission to be insufficient to completely backfill the reaffected or enlarged highwall. The highwall shall be eliminated to the maximum extent technically practical in accordance with the following criteria:
    (A) all spoil generated by the remining operation and any other reasonably available spoil shall be used to backfill the area. Reasonably available spoil in the immediate vicinity of the remining operation shall be included within the permit area;
    (B) the backfill shall be graded to a slope which is compatible with the approved postmining land use and which provides adequate drainage and long-term stability;
    (C) any highwall remnant shall be stable and not pose a hazard to the public health and safety or to the environment. The operator shall demonstrate, to the satisfaction of the Commission, that the highwall remnant is stable; and
    (D) spoil placed on the outslope during previous mining operations shall not be disturbed if such disturbances will cause instability of the remaining spoil or otherwise increase the hazard to the public health and safety or to the environment.

Source Note: The provisions of this §12.552 adopted to be effective April 7, 1997, 22 TexReg 3093; amended to be effective November 4, 1997, 22 TexReg 10640; amended to be effective June 12, 2001, 26 TexReg 4090