(a) In lieu of the requirements of §§12.364 and 12.365 of this title (relating to Disposal of Excess Spoil: Valley Fills, and to Disposal of Excess Spoil: Head-of-Hollow Fills), the Commission may approve alternate methods for disposal of hard rock spoil, including fill placement of dumping in a single lift, on a site specific basis, provided the services of a qualified professional engineer experienced in the design and construction of earth and rockfill embankments are utilized and provided the requirements of this section and §12.363 of this title (relating to Disposal of Excess Spoil: General Requirements) are met. For this section, "hard rock spoil" shall be defined as rockfill consisting of at least 80% by volume of sandstone, limestone, or other rocks that do not slake in water. Resistance of the hard rock 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.
(b) Spoil is to be transported and placed in a specified and controlled manner which will ensure stability of the fill.
  (1) The method of spoil placement shall be designed to ensure mass stability and prevent mass movement in accordance with the additional requirements of this section.
  (2) Loads of noncemented clay shale and/or clay spoil in the fill shall be mixed with hard rock spoil in a controlled manner to limit on a unit basis concentrations of noncemented clay shale and clay in the fill. Such materials shall comprise no more than 20% of the fill volume as determined by tests performed by a qualified professional engineer and approved by the Commission.
(c) Requirements for design of earth and rockfill embankments shall include the following:
  (1) stability analyses shall be made by the qualified professional engineer. Parameters used in the stability analyses shall be based on adequate field reconnaissance, subsurface investigations, including borings, and laboratory tests; and
  (2) the embankment which constitutes the valley fill or head-of-hollow fill shall be designed with the following factors of safety:
Attached Graphic
(d) 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) Anticipated discharge from springs and seeps and due to precipitation shall be based on records and/or field investigations to determine seasonal variation. The design of the internal drainage system shall be based on the maximum anticipated discharge.
  (2) All granular material used for the drainage system shall be free of clay and consist of durable particles such as natural sands and gravels, sandstone, limestone or other durable rock which will not slake in water.
  (3) The internal drain shall be protected by a properly designed filter system.
(e) 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 pass safely the runoff from a 100-year, 24-hour precipitation event. Diversion design shall comply with the requirements of §12.341(6) of this title (relating to Hydrologic Balance: Diversions).
(f) The top surface of the completed fill shall be graded such that the final slope after settlement will be no steeper than 20h:1v (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.
(g) Surface runoff from the outslope of the fill shall be diverted off the fill to properly designed channels which will pass safely a 100-year, 24-hour precipitation event. Diversion design shall comply with the requirements of §12.341(6) of this title (relating to Hydrologic Balance: Diversions).
(h) 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) the slope of the outslope between terrace benches shall not exceed 2h:1v (50%);
  (2) to control surface runoff, each terrace bench shall be graded to a slope of 20h:1v (5.0%) toward the embankment. Runoff shall be collected by a ditch along the intersection of each terrace bench and the outslope; and
  (3) terrace ditches shall have a 5.0% slope toward the channels specified in subsection (g) of this section, unless steeper slopes are necessary in conjunction with approved roads.

Source Note: The provisions of this §12.366 adopted to be effective April 7, 1997, 22 TexReg 3093; amended to be effective November 4, 1997, 22 TexReg 10640; amended to be effective December 28, 2020, 45 TexReg 9503