For the purposes of an impact analysis in support of provisions of Subparts 231-7 and 231-8 of this Part, the significant impact levels defined in section 231-12.6 of this Subpart will serve to determine whether a new or modified source will have a significant air quality impact or a contribution to potential standards violation or PSD increment exceedances in both the attainment area of the proposed project and in any adjacent nonattainment areas. The levels in section 231-12.6 of this Subpart apply in all attainment areas in the State for the specific NSR contaminant and serve as the required modeling demonstration to show insignificant impacts for that contaminant. A showing that the maximum impacts from the proposed new or modified facility for any regulated NSR contaminant are below the lesser of these significant impact levels or the difference between the NAAQS and the background concentration for that regulated NSR contaminant will be deemed adequate as the required impact analysis to demonstrate that the source will not contribute to a standards violation or PSD increment exceedance for that regulated NSR contaminant. However, such a demonstration will not exclude the performance of any other required impact analysis to satisfy other applicable provisions of Subparts 231-5 to 231-8 of this Part, including the modeling for air quality related values in Federal class I areas.