Any operator subject to this chapter who, after September 30, 1992, pays increased fees for disposal of waste and substances which have been generated inside of Alabama shall be entitled to a credit of $72 per ton for the amount of such waste generated inside Alabama and disposed of from July 15, 1990, to April 30, 1992. Such credit created under this section shall be credited against any fees which are payable to the General Fund of the State of Alabama and shall be granted at the rate of 1/12 th of such credit per month, beginning October 1, 1993, and until such credit is exhausted. For purposes of this section, no certificate of overpayment must be issued by the state Comptroller.