(a) The design of each dam and embankment constructed of coal mine waste or intended to impound such waste shall comply with the requirements of §12.347(a) and (c) of this title (relating to Hydrologic Balance: Permanent and Temporary Impoundments), modified as follows:
  (1) the design freeboard between the lowest point on the embankment crest and the maximum water elevation shall be at least 3 feet. The maximum water elevation shall be that determined by the freeboard hydrograph criteria contained in the U.S. Natural Resources Conservation Service criteria referenced in §12.347 of this title (relating to Hydrologic Balance: Permanent and Temporary Impoundments).
  (2) the dam and embankment shall have a minimum safety factor of 1.5 for the partial pool with steady seepage saturation conditions, and the seismic safety factor shall be at least 1.2; and
  (3) the dam or embankment foundation and abutments shall be designed to be stable under all conditions of construction and operation of the impoundment. Sufficient foundation investigations and laboratory testing shall be performed to determine the safety factors of the dam or embankment for all loading conditions appearing in subsection (a)(2) of this section or the publications referred to in §12.347 of this title (relating to Hydrologic Balance: Permanent and Temporary Impoundments) and for all increments of construction.
(b) Spillways and outlet works shall be designed to provide adequate protection against erosion and corrosion. Inlets shall be protected against blockage.
(c) For an impounding structure constructed of or impounding coal mine waste, at least 90% of the water stored during the design precipitation event shall be removed within the 10-day period following the design precipitation event.

Source Note: The provisions of this §12.378 adopted to be effective April 7, 1997, 22 TexReg 3093; amended to be effective November 4, 1997, 22 TexReg 10640.