The state board shall notify each discharger annually of the fee to be submitted, the basis upon which the fee was calculated, and the date upon which the fee is due. The state board may generate invoices based on the prior year's fee schedule prior to the state board's adoption of the annual fee schedule for the current year as appropriate to maintain an adequate operating balance in the Waste Discharge Permit Fund, in which case the state board shall incorporate any subsequent adjustments to those fees for the current year by issuing credit or debit memoranda for the subsequent year or by issuing refunds or supplemental invoices. The state board may also generate semiannual invoices, with the first semiannual invoice set at an amount equal to one half of the prior year's fee schedule and the second semiannual invoice set at an amount equal to the remainder of the current year's annual fee schedule.