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What is a Major Modification for New Source Review Purposes?

Posted on 3/30/2021 by Anthony Cardno, CHMM

When it comes to regulations, words don’t always mean what we think they mean. The Federal government has been known to change or expand the meanings of words. For instance, under the Clean Air Act’s New Source Review (NSR) program, the Environmental Protection Agency (EPA) doesn’t limit the definition of “new” to only brand-new facilities being built from the ground up. They more broadly interpret “new” to mean any facility newly subject to the regulations.

Like many Federal agencies, the EPA doesn’t seem to like the idea of sites being “grandfathered” out of regulations, so this expanded definition of the word “new” enables the agency to pull existing facilities into the New Source Review program.

What is New Source Review?

NSR is a pre-construction review process. Certain new and existing facilities must go through this review if their Potential to Emit any one of the Criteria Pollutants exceeds certain amounts. Brand new facilities are subject to NSR if their PTE causes them to meet the definition of being a new Major Source (the definition of which depends on the designation of the Air Quality Control Region in which the facility is being built). 

But what about existing facilities that already meet the applicable definition of “major source”?

Major Modifications

Existing facilities that meet the applicable definition of “major source” may have existed before the NSR program was introduced or they may have gone through NSR when they were first built. Regardless, they will go through NSR for the first time or again if they intend to make a “major modification” to the facility. If the modification meets the definition of “major modification,” the NSR process must be completed before the modification is made.

Major modifications are defined at 40 CFR 51.166(b)(2) as “any physical change in or change in the method of operation of a major stationary source that would result in:
  • A significant emissions increase of a regulated NSR pollutant; and
  • A significant net emissions increase of that pollutant from the major stationary source.

What are the regulated NSR pollutants?

The NSR program is only concerned about a facility’s potential to emit one or more of the six “criteria pollutants” for which there are National Ambient Air Quality Standards (NAAQS). Those six pollutants are:
  • Carbon monoxide
  • Nitrogen dioxides
  • Sulfur dioxide
  • Particulate Matter (both “fine” particulates” and “course” particulates)
  • Ozone (and its precursors: volatile organic compounds and nitrogen oxides)
  • Lead

What is considered a “significant increase” in PTE?

The answer is different for each of the criteria pollutants:
  • CO: 100 TPY
  • NOx: 40 TPY
  • S02: 40 TPY
  • Ozone: 40 TPY (of VOCs)
  • PM: 25 TPY total
    • 15 TPY PM10
    • 10 TPY PM2.5
  • Lead: 0.6 TPY

How to calculate a “significant increase”

The existing major source must calculate the difference between the source’s actual baseline emissions and the projected increase. The actual baseline emissions are calculated by looking at any consecutive 24-month period within the previous ten years from the planned modification date.

Projected increases are calculated by process engineers based on hourly emissions rates and the projected level of utilization of the source.  If the projected increase itself (not the actual baseline plus the projected increase) meets the definition of “significant” for the criteria pollutant(s) in question, the site must go through NSR before they can make the modification.

What happens next?

The exact requirements of NSR will depend on the AQCR’s designation as “attainment” or “non-attainment.” In either case, the facility will be required to obtain a Permit to Construct (PTC) and during the construction process install appropriate control technologies to limit emissions once the facility is up and running.

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Tags: Clean Air Act, New Source Review, nsr

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