Regulation 39-29-106. Coal.
1) In addition to all other taxes, there is levied a tax upon the severance of coal from the earth within this state. The tax on coal is subject to an exemption of the first 300,000 tons per calendar quarter, which need not be prorated for taxable periods of less than a calendar quarter. This exemption is allowed for each person, which shall be considered to be any combined unitary economic interest consisting of one or more related operations that are supportive of, or dependent upon, each other for the production of coal. Such person shall be liable for the payment of the tax imposed. 

2) Exemptions.
a) There is allowed a credit equal to fifty percent of the severance tax on production of lignitic coal. 
b) There is allowed a credit equal to fifty percent of the severance tax on production of underground coal.