(1) The department may impute the value when the coal is sold or used under the following circumstances:

(a) the operator of a coal mine is using the produced coal in an energy conversion or other manufacturing process; or

(b) a person sells coal under a contract which is not an arm's length agreement and the transaction price is less than market value.

(3) The department will maintain the confidentiality of all comparable contract data and will use contract data provided by the producer in question whenever possible.