75-2-424. Adjustment of fee. (1) The department shall adjust from time to time the amount of the penalty assessment calculated or the payment schedule proposed by such owner or operator under 75-2-425(2)(a) if the department finds after notice and opportunity for a hearing on the record that the penalty or schedule does not meet the requirements of 75-2-421 through 75-2-429.

(2) Upon making a determination that a source with respect to which a penalty has been paid under 75-2-421 through 75-2-429 is in compliance and is maintaining compliance with the applicable requirement, the department shall review the actual expenditures made by the owner or operator of such source for the purpose of attaining and maintaining compliance and shall make a final adjustment within 180 days after such source comes into compliance and:

(a) provide reimbursement with interest to be paid by the state at appropriate prevailing rates for overpayment by such person; or

(b) assess and collect an additional payment with interest at appropriate prevailing rates for any underpayment by such person.