30 Tex. Admin. Code § 117.4125
Where a person can demonstrate that an affected unit cannot attain the requirements of § 117.4105 of this title (relating to Emission Specifications), as applicable, the executive director, on a case-by-case basis after considering the technological and economic circumstances of the individual unit, may approve emission specifications different from § 117.4105 of this title for that unit based on the determination that such specifications are the result of the lowest emission limitation the unit is capable of meeting after the application of controls to meet the nitrogen oxides emission specifications of § 117.4105 of this title. Any owner or operator affected by the decision of the executive director may file a motion to overturn the executive director's decision. The requirements of § 50.139 of this title (relating to Motion to Overturn Executive Director's Decision) apply. Executive director approval does not necessarily constitute satisfaction of all federal requirements nor eliminate the need for approval by the United States Environmental Protection Agency in cases where specified criteria for determining equivalency have not been clearly identified in applicable sections of this division (relating to Nitric Acid Manufacturing--Ozone Nonattainment Areas).
30 Tex. Admin. Code § 117.4125