EPA Proposes Changes to Storage Tank Emission Calculation Guidance

On July 25, 2018, EPA proposed revisions to AP-42 Section 7.1 – Organic Liquid Storage Tanks. This section, lasted updated in November 2006, provides guidance for calculating air emissions from fixed and floating-roof storage tanks. Along with EPA’s TANK 4.09d software, this section has formed the backbone for most industrial facilities’ tank emissions estimates for many years. Is it possible that these changes mark the final nail in the coffin for the free software and the shift towards alternate solutions?

The proposed revisions address several previously noted deficiencies in Section 7.1 EPA is proposing to add methodologies for calculating emissions from activities such as roof landings, cleaning operations, and vapor flashing. EPA is also slightly modifying some of the existing calculation methodologies, and adding emission calculation methodologies for tanks containing unstable liquids, agitated tanks, and pressure tanks. EPA is accepting comments on the proposed revisions until September 24, 2018.

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.

Once EPA finalizes the updates to AP-42 Section 7.1, TANKS 4.09d will go from a slightly outdated program that can still accurately calculate emissions from the majority of storage tanks, to a program that no longer follows AP-42 guidance for most tanks. While the overall emissions impact of the new methodology is likely to be minor for most tanks, many state agencies will likely favor the current methodology and cease accepting TANK 4.09d results in new air permit applications and annual emission inventories.

If agencies cease 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 enter and run emissions for you. The best solution will depend on a 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 email ned.coleman@ppmco.com with any questions to discuss the various options available to move forward after the obsolescence of Tanks 4.09d.


Contributed by Ned Coleman, P.E. Senior Environmental Engineer