On the date of TNRCC assumption of the administration of the Texas Pollutant Discharge Elimination System (TPDES) permit program, after the Environmental Protection Agency (EPA) approves the TPDES permit program, and the issuance of national pollutant discharge elimination system (NPDES) permits is delegated from the EPA to the state, the state adopts all EPA permits and pretreatment programs, except that EPA shall retain jurisdiction over certain EPA-issued or proposed permits until their expiration which it has issued as may be specified in a state/federal Memorandum of Agreement. This provision does not affect the right of the EPA to issue NPDES permits for facilities which expired in the 12 months preceding the date of program assumption or to modify NPDES permits under Clean Water Act, §304(l). If the requirements of a state permit and an EPA permit issued to the same permittee or for the same facility are not of equal stringency, any requirements of the state-issued permit that are more stringent shall apply above and beyond those requirements contained in the corresponding EPA permit.