Backfill,

Backfill, when used as a noun, means the spoil and waste materials used to fill the void resulting from an excavation created for the purpose of extracting coal from the earth. When used as a verb, the term refers to the process of filling that void. The term also includes all spoil and waste materials used to restore the approximate original contour.

Source

30 CFR § 701.5

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Scoping language

As used in this chapter, the following terms have the specified meanings, except where otherwise indicated:

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