EPA has finalized the guidance and supporting documents recommending Significant Impact levels (SILs) for ozone and fine particle pollution that may be used in the Prevention of Significant Deterioration (PSD) permitting program. SILs have been used in the PSD permitting process for many years to help permit applicants and permitting authorities determine whether proposed construction may be authorized in a Clean Air Act (CAA) permit. These improvements will potentially reduce the cost and time for manufacturers to obtain this type of air pollution permit from states, local permitting authorities and EPA. 

The memo and supporting documents are available below. 

Please note, a detailed Appendix to the Technical Basis for the EPA's Development of the Significant Impact Thresholds for PM2.5 and Ozone is available.  If you would like to receive a copy, please contact Chris Owen.

• Guidance on Significant Impact Levels for Ozone and Fine Particles in the Prevention of Significant Deterioration Permitting Program (PDF)(21 pp, 561 K)
• Legal Memorandum Application of Significant Impact Levels in the Air Quality Demonstration for Prevention of Significant Deterioration Permitting under the Clean Air Act (PDF)(14 pp, 115 K)
• Technical Basis for the EPA's Development of the Significant Impact Thresholds for PM2.5 and Ozone (PDF)(51 pp, 2 MB)
• Peer Review Report for the Technical Basis for the EPA's Development of Significant Impact Thresholds for PM2.5 and Ozone (PDF)(26 pp, 239 K)