If your facility emits Hazardous Air Pollutant (HAP), you must determine if you are a major or area source of HAP. Area sources emit less than 10 tons per year (tpy) of any single HAP and less than 25 tpy of combined HAPs. Major sources have facility-wide potential emissions above those thresholds.
For many facilities, maintaining HAP area source status is a key component of their compliance strategy. However, maintaining that status requires a defensible potential-to-emit (PTE) demonstration that accurately reflects facility operations and accounts for all applicable emissions sources.
For some facilities, PTE calculations were originally developed years ago during a permitting project, applicability determination, or compliance review and have changed little since. Meanwhile, operations evolve, production rates increase, new products are introduced, equipment is modified, and wastewater characteristics shift. While these changes may seem incremental, they can significantly impact a facility’s emissions profile over time.
As state agencies and EPA become increasingly sophisticated in their review of area source demonstrations, they are looking beyond emissions totals and examining the calculations, assumptions, methodologies, and supporting documentation behind them. During inspections and permit reviews, facilities may be asked to explain how emissions were calculated, how inventories are maintained, and whether assumptions remain representative of current operations. Facilities that have not revisited their PTE in recent years may be exposed to compliance risks they do not realize exist.
Four Key Areas Receiving Scrutiny
When agencies evaluate area source demonstrations, they are increasingly focused on emissions sources that may have been overlooked, underestimated, or not updated to reflect current operations. While every facility is different, four areas consistently receive attention during regulatory reviews.
Process Vents
Process vents are often among the most visible and well-understood emissions sources at a chemical facility. Because they are routinely evaluated during permitting activities, facilities may assume their process vent emissions are well characterized.
However, agencies are increasingly examining whether calculations accurately reflect current operating conditions. Changes in production rates, product mix, process configurations, operating schedules, or raw materials can all affect emissions estimates. Calculations that were appropriate when originally developed may no longer represent actual operations today.
In addition, regulators are paying closer attention to the methodologies used to estimate emissions and the documentation supporting those calculations. Facilities should be prepared to explain how estimates were developed and demonstrate that assumptions remain current. Furthermore, if applicable regulations dictate how emissions should be calculated for a particular source type, facilities should ensure that those calculations are completed using the EPA’s specified methodology.
Equipment Leaks and Fugitive Emissions
Fugitive emissions continue to be one of the most common vulnerabilities in area source demonstrations. While many facilities immediately think of LDAR programs and leaking components, fugitive emissions can include a much broader range of sources, including equipment leaks, open process vessels, material transfer activities, and other emissions that are not routed through a traditional stack or vent.
Valves, pumps, compressors, connectors, sampling systems, pressure relief devices, agitators, and other equipment components may individually contribute relatively small amounts of emissions. Collectively, however, fugitive emissions can represent a significant portion of a facility’s HAP inventory. Many facilities rely on component inventories that have not been updated as equipment has been added, modified, or removed over time. Agencies are also taking a closer look at whether facilities are using EPA-accepted methodologies and assumptions when estimating fugitive emissions. For PTE evaluations, emissions are generally expected to be calculated assuming continuous operation (8,760 hours per year) unless a lower operating rate can be demonstrated through actual operating constraints or federally enforceable permit limits. As a result, agencies are increasingly evaluating whether fugitive emissions calculations accurately reflect current conditions, use appropriate methodologies, and are supported by complete inventories and documentation.
In some cases, fugitive emissions can represent the difference between maintaining area source status and triggering additional regulatory obligations.
Storage, Loading, and Material Transfer Operations
Storage tanks and loading operations have long been included in air permitting evaluations, but these calculations are not always revisited as facilities evolve. Changes in throughput, material compositions, loading frequencies, operating schedules, and product distribution practices can significantly affect emissions estimates. In addition, facilities sometimes overlook ancillary loading or transfer activities that may contribute emissions to a site’s overall inventory.
While individual sources may appear minor when viewed independently, their combined impact can become significant when evaluated as part of a facility-wide PTE demonstration. As regulators take a more comprehensive view of sitewide emissions, storage and loading operations are receiving increased attention.
Wastewater Collection and Treatment Systems
Wastewater systems remain one of the most frequently underestimated emission sources at chemical facilities. Collection systems, junction boxes, trenches, sumps, equalization tanks, treatment units, aeration systems, and sludge handling activities can all contribute HAP emissions. Yet wastewater calculations are often based on historical assumptions, limited sampling data, or operating conditions that no longer exist.
As facilities change products, production rates, or process chemistry, wastewater characteristics can change as well. Without periodic reevaluation and supporting data, facilities may be relying on emissions estimates that no longer reflect actual operations.
A Few Questions Worth Asking
As agencies continue to increase their focus on area source demonstrations, facilities may benefit from taking a fresh look at the foundation of their PTE calculations.
Consider the following:
- When was the facility’s sitewide PTE last comprehensively updated?
- Do current calculations reflect actual production rates and operating conditions?
- Have process vent calculations been reviewed since operational changes occurred?
- Are equipment leak inventories current and complete?
- Have storage and loading emissions been reevaluated using current throughput information?
- Are wastewater emissions based on representative and up-to-date data?
- Could the assumptions used in the demonstration withstand detailed agency review?
- Does the facility need an enforceable synthetic minor limitation in its operating permit to maintain and demonstrate that actual emissions are below major source thresholds?
If these questions are difficult to answer, it may be a good indication that a more comprehensive review is warranted.
Why It Matters
An accurate PTE affects much more than a facility’s source classification. Area source determinations can influence permitting requirements, regulatory applicability, compliance obligations, monitoring requirements, and long-term operational flexibility.
For facilities operating close to regulatory thresholds, the margin for error can be surprisingly small. A few underestimated storage tanks, an outdated wastewater model, incomplete equipment counts or overlooked trace HAP emissions may not seem significant individually. However, when evaluated collectively, these omissions can materially affect a facility’s source classification and potentially create the need for federally enforceable permit limits to maintain area source status.
In many cases, the issue is not that calculations were originally incorrect, but that operational changes have gradually created a disconnect between documented emissions estimates and actual facility conditions. Periodic reviews of emissions calculations, supporting documentation, equipment inventories, wastewater data, and permitting assumptions can help identify vulnerabilities before they become compliance concerns.
Looking Ahead
Facilities that have not recently evaluated their PTE may want to consider whether existing calculations, assumptions, and documentation would withstand a detailed agency review.
In our recent webinar, “Will Your Area Source Status Survive Agency Review? Part 1 – What’s in a Chemical Plant PTE,” we discussed common vulnerabilities in area source demonstrations and explored calculation approaches for key emissions categories, including process vents, equipment leaks, storage and loading operations, and wastewater treatment systems.
The conversation continues on November 17th with our complimentary webinar:
Will Your Area Source Status Survive Agency Review? Part 2 – Obtaining Effective Federally Enforceable Permit Limits
Maintaining area source status often requires more than accurate emissions calculations. Facilities must also ensure that any permit limitations used to cap emissions are federally enforceable, appropriately monitored, and structured to support operational flexibility.
Part 2 will explore:
- What makes a permit limit federally enforceable
- Monitoring and recordkeeping strategies that support permit conditions
- Approaches for developing effective permit language
- Strategies for working with state agencies to establish limits that provide complete coverage while minimizing compliance burden
Sign up for Part 2 of our Area Source Webinar Series here: https://shop.trinityconsultants.com/training/160617/Will-Your-Area-Source-Status-Survive-an-Agency-Review?-Part-2—Obtaining-Effective-Federally-Enforceable-Permit-Limits
Need help assessing your facility’s area source status or evaluating potential gaps in your current demonstration? Trinity’s Chemical Sector Services team can help review PTE calculations, identify risks, assess permit strategies, and develop practical solutions tailored to your operation. Contact us to learn more.
