DAMS AND EMBANKMENTS: DESIGN AND CONSTRUCTION:

1. A. The design of each dam and embankment constructed of coal processing waste or intended to impound such waste shall comply with the requirements of Subsections B through G of 19.8.20.2017 NMAC modified as follows:

   (1) 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 19.8.20.2017 NMAC;

   (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;

   (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 Paragraph (2) of Subsection A of 19.8.20.2049 NMAC or the publications referred to in 19.8.20.2017 NMAC and for all increments of construction.

2. B. Spillways and outlet works shall be designed to provide adequate protection against erosion and corrosion. Inlets shall be protected against blockage.
3. C. Dams or embankments constructed of, or impounding, coal processing waste shall be designed, constructed and maintained so that at least 90 percent of the water stored during the design precipitation event shall be removed within a 10 day period.
4. D. Each impounding structure constructed of coal processing waste or intended to impound coal processing waste that meets the criteria of 30 CFR 77.216(a) shall have sufficient spillway capacity to safely pass, adequate storage capacity to safely contain, or a combination of storage capacity and spillway capacity to safely control, the probable maximum precipitation of a 6-hour precipitation event, or greater event as specified by the director.

5. E. No impounding structure constructed of coal processing waste or intended to impound coal processing waste shall be retained as a permanent impoundment as part of the approved postmining land use.

   [11-29-97; 19.8.20.2049 NMAC - Rn, 19 NMAC 8.2.20.2049, 9-29-2000; A, 12-31-2007]