A person having to pay a SPDES annual program fee may request that the annual program fee for that calendar year be redetermined based on the actual average daily flow rate during that calendar year. This request must be made under the provisions of section 481.9 of this Title, except that time limits will be extended as stated in section 481.4 of this Title. It is the permittee's burden to prove that actual flow is less than the design flow in the permit. The department may initiate a SPDES permit modification to reduce authorized discharge flow rates when the actual flow is significantly less than the permitted design flow.