EPA Finalizes Changes to Storage Tank Emission Calculation Guidance

In November 2019, almost a year and a half after proposing changes to AP-42 Section 7.1 – Organic Liquid Storage Tanks, EPA finalized its revisions. This section, last updated in November 2006, provides guidance for calculating air emissions from fixed and floating-roof storage tanks.

The revisions address several previously noted deficiencies in Section 7.1. EPA also added methodologies for calculating emissions from activities such as roof landings, cleaning operations, and vapor flashing. While these changes likely will not have a major impact on emission estimates for most storage tanks, the most important take-away from this action is that the EPA Tanks 4.09d software no longer follows the current AP-42 calculation methodology.

The idea of moving away from the TANKS 4.09d software is not new. EPA announced in 2012 that it would no longer be supporting the program, but has kept the program available for download. Many deficiencies, such as the program’s inability to accurately calculate monthly emissions, limitations for heated tanks, and lack of functions for calculating flashing, cleaning, and roof landing emissions have been known for years. However, the fact that it is free, easy to use, and generally accepted by state agencies for most tank types, has kept it afloat despite the lack of EPA support.

Now that these changes are final, some agencies are already beginning to act. The Louisiana Department of Environmental Quality (LDEQ) has announced it will no longer accept permit applications containing Tanks 4.09d emission estimates at the end of February 2020. The Alabama Department of Environmental Management (ADEM) has taken the position that Tanks 4.09d may not be accepted in some cases (e.g. cases where Tanks 4.09d estimates calculate emissions just below a regulatory threshold). Other states have indicated they plan to continue accepting Tanks 4.09d, at least for the time being. This could become especially confusing for businesses that operate in multiple states, since Tanks 4.09d is no longer a default program for across-the-board use.

Now that some agencies have ceased accepting TANKS 4.09d, what else is out there? The best option for you depends on your needs.  The most basic solution is to create a spreadsheet to follow the new AP-42 methodology, but this can be a significant undertaking, especially for a site with numerous tanks. Third-party software ranges from simple programs to full support packages where the provider will handle everything from data entry to emissions modelling.  The best solution will depend on your particular facility’s needs and budget.  Regardless of whether you need to estimate emissions from a single diesel storage tank, or a massive tank farm, PPM is ready to help find the solution to best meet your individual needs.


Feel free to give us a call at (251) 990-9000 or email ned.coleman@ppmco.com with any questions or to discuss the various options available now that agencies have begun moving away from Tanks 4.09d.