(a) If you pay a fee based on a percentage of the value of coal, you must include documentation supporting the claimed coal value with your fee payment and production report. We may review this information and any additional documentation we may require, including examination of your books and records. We may accept the valuation you claim, or we may determine another value of the coal.

(b) If we determine that a higher fee must be paid, you must pay the additional fee together with interest computed under § 870.21.