# COMAR Title 26 — Department of the Environment

## Subtitle 20 — Surface Coal Mining and Reclamation Under Federally Approved Program

### Chapter 27 — Waste Handling

#### Regulation .11 Design and Construction Requirements for Coal Mine Waste Impounding Structures.

*COMAR 26.20.27.11*

A. The design of each dam and embankment constructed of coal mine waste, or intended to impound this waste, shall comply with the permanent and temporary impoundment requirements of the Regulatory Program, 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. Soil Conservation Service criteria referenced in COMAR 26.20.21.08A(5).

  (2) The dam and embankment shall have a minimum safety factor of 1.5 for the partial pool with steady seepage saturation conditions, and a seismic safety factor of at least 1.5.

  (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 shown in §A(1) and (2) of this regulation, 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. The combination of principal and emergency spillways shall be able to safely pass the 100-year, 6-hour design precipitation event.

C. Dams or embankments constructed of or impounding waste materials shall be designed so that at least 90 percent of the water stored during the design precipitation event shall be removed within a 10-day period.