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On approval by the department, 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 must meet the following requirements:

(1) The width of the individual terrace bench may not exceed 20 feet, unless specifically approved by the department as necessary for stability, erosion control, or roads included in the approved postmining land use plan.

(2) The vertical distance between terraces must be as specified by the department to prevent excessive erosion and to provide long-term stability.

(3) The slope of the terrace outslopes may not exceed 1v:5h (20%) .   Outslopes that exceed 1v:5h may be approved, if they have a minimum safety factor of more than 1.3 for any condition of load likely to be encountered, provide adequate control over erosion, and closely resemble the surface configuration of the land prior to mining.   In no case may highwalls be left as part of terraces.

(4) Culverts and underground rock drains must be used in the terrace only when approved by the department.

(5) Terraces must be installed in such a way so as not to prohibit vehicular access or revegetation procedures.

(6) Additional surface manipulation procedures must be installed as required by the department.

History: 82-4-204, MCA; IMP, 82-4-232, MCA; NEW, 1980 MAR p. 725, Eff. 4/1/80; AMD, 1989 MAR p. 30, Eff. 1/13/89; TRANS, from DSL, 1996 MAR p. 3042.

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