40 C.F.R. § 51.1204
At any time prior to January 13, 2017, the air agency may submit to the EPA federally enforceable SO2 emissions limits (effective no later than January 13, 2017) for one or more applicable sources that provide for attainment of the 2010 SO2 NAAQS in the area affected by such emissions. The submittal shall include associated air quality modeling and other analyses that demonstrate that all modeling receptors in the area will not violate the 2010 SO2 NAAQS, taking into account the updated allowable emission limits on applicable sources as well as emissions limits that may apply to any other sources in the area. The air agency shall not be subject to the ongoing data requirements of § 51.1205 for such area if the air quality modeling and other analyses demonstrate that the area will not violate the 2010 SO2 NAAQS.
40 C.F.R. §51.1204