The USEPA has posted the draft guidance on Significant Impact levels (SILs) for ozone and fine particle pollution on August 1 and is requesting public comments.  USEPA will be accepting public comment on the draft guidance and supporting documents through September 30, 2016.  SILs are used in Prevention of Significant Deterioration (PSD) permitting program and are like a de minimis threshold which helps determine whether proposed construction may cause or contribute to a violation of PSD increment or the National Ambient Air Quality Standards (NAAQS).

The USEPA has developed a new analytical approach in the proposed guidance to identify SILs for ozone and PM2.5.  The detailed discussion of the technical analysis used by the USEPA to develop these SILs are provided in supporting technical document also available with the guidance document.  With this effort, the USEPA is providing a non-binding guidance where permitting authorities can use their discretion to apply and justify the application of the SIL values on a case-by-case basis for individual permitting decisions.

Eventually, the USEPA will use the information gathered to assess and further refine these SIL values and its application for potentially binding rule making.  Until the USEPA conducts a rulemaking, permitting authorities can use their discretion to use or not to use the proposed SILs in particular PSD permitting actions.

For more information regarding guidance document and supporting technical document, please click here.