4 The record articles

A Fundamental Major NSR Applicability Question

Posted: April 20th, 2012

Author: All4 Staff 

Here’s a question that we hear all the time related to changes at existing major stationary sources…Why do I have to do a New Source Review (NSR) applicability evaluation when my modification project will result in emissions that are less than my current permit limits?  This is a good question and many plant managers as well as environmental professionals may find the answer a bit confusing.  The answer resides in how U.S. EPA defines the procedure for calculating whether a significant emissions increase will occur as a result of the project.  For a modification of an existing emission unit an “Actual-to-projected-actual” or “Actual-to-potential” applicability test is required.  The critical parameter is not the emissions that the unit is allowed to produce, but the emissions that the unit has actually historically produced.  So, if you have historically run the unit to be modified well below its permitted limit and you want to run that unit, after the modification, close to the permit limit, the change could result in a significant emission increase thereby triggering major NSR even though the unit, after the change, would be operating under the existing limits established in your permit.  The takeaway is that any physical change or change in the method of operation at an existing major source can be a modification and is a “trigger” for the NSR applicability test.  The NSR applicability test will determine if the change results in a significant emissions increase based on a comparison of the historic “baseline” emissions to the projected future actual or the potential emissions.  Failure to recognize the NSR applicability test trigger can have serious air permitting and compliance implications.  This example illustrates how inflated permit limits (well above what you can actually reach) are meaningless when evaluating NSR applicability.


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