All4 Inc.

PSD and the Dreaded Major Modification

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Courtesy of All4 Inc.

The implementation at the state level of the major New Source Review (NSR) rules that include both prevention of significant deterioration (PSD) and nonattainment new source review (NNSR) have evolved over  a long period of time.   During the last decade that evolution has been substantially impacted by the “NSR Reform” revisions of 2002; the regulation of particulate matter less than 10 microns (PM10) and particulate matter less than 2.5 microns (PM2.5); and the seemingly routine changes in form and reductions of national ambient air quality standards (NAAQS) following required reviews. Historically “process” changes in the NSR program were documented via guidance memoranda, policy statements, and precedence made publicly available on the U.S. EPA NSR guidance database.  However, formal U.S. EPA guidance related to NSR virtually disappeared since the promulgation of the NSR Reforms of 2002 and has really only appeared again in rare instances as a result of specific permit reviews and/or court decisions.  This 4 The Record article is the first in a series of articles related to the NSR regulations that have been promulgated under Section 110 of the Clean Air Act (CAA) and addresses the dreaded PSD major modification.

For almost 30 years now, the term “major modification” has struck fear into the hearts of environmental managers associated with facilities that are classified as “major stationary sources” under the NSR regulations.  In many instances, such fear is valid because the air permitting path associated with major modifications can be sufficiently complicated and fraught with uncertainty that the very viability of a given project could be threatened.   In this article, ALL4 provides a brief overview of the NSR regulations and describes what a major modification actually is under the PSD regulations. 

The NSR regulations include both the PSD regulations and the NNSR regulations.  PSD applies to new major sources and to major modifications at existing major stationary sources for pollutants where the area the source is located is in attainment or unclassifiable with the NAAQS.  NNSR applies to new major sources and to major modifications at existing major stationary sources for a pollutant where the area the source is located is classified as non-attainment with the NAAQS.  Health-based NAAQS currently exist for nitrogen dioxide (NO2), sulfur dioxide (SO2), PM10, PM2.5, carbon monoxide (CO), ozone (O3), and lead (Pb).  The NAAQS serve as the “backbone” to the NSR regulations and to state implementation plans (SIPs).  The NSR regulations were established to ensure that the NAAQS are attained and maintained even as emissions sources change and facility expansion projects are implemented.  

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