Opinion ID: 621128
Heading Depth: 3
Heading Rank: 8

Heading: Outdated Modeling Methodology

Text: Finally, Montana Sulphur argues that the EPA acted arbitrarily and capriciously because it used outdated modeling in the FIP. In the FIP, the EPA used the Industrial Source Complex (ISC) model, which was the preferred model at the time Montana proposed its SIP. In 2005, the EPA revised its Guideline on Air Quality Models and recommended use of a new dispersion modelAERMOD. 70 Fed. Reg. 68,218 (Nov. 9, 2005). However, the rule grandfathered ISC models for one year (through Nov. 8, 2006), and indicated that during that time AERMOD could, but was not required to, be substituted for ISC for appropriate applications. [13] The EPA proposed the FIP in July 2006, within the one-year transition period. In issuing the final FIP in April 2008, the EPA further defended its choice to stick with the ISC dispersion model: The commenter is correct that a newer model is now available. For new SIPs, we would require states to use EPA's most recent model. However, this is a unique situation. The State developed the Billings/Laurel SO2 SIP using the ISC model, which was current at that time, and we approved various source-specific emission limits in the SIP based on the State's modeling effort. The purpose of this FIP is to fill gaps in the approved SIP. We are not intending or required to re-do the entire SIP. . . . We note that MDEQ tested the performance of the ISC model when the Billings/Laurel SO2 SIP was being developed, and the results showed that the model performance exceeded the performance criteria for models of this type. . . . We also note that ISC remained an accepted EPA model at the time we proposed our FIP, and it is reasonable to finalize the FIP based on the same model. Switching models after our proposal would have required us to re-propose the FIP and would have delayed the FIP further. 73 Fed.Reg. at 21,437-21,438. The EPA's continued use of the ISC model was not arbitrary or capricious. The model was properly employed at both the time of the state SIP and the proposed FIP. The FIP did not replace the entire SIP, but only the limited portions the EPA had disapproved; because use of a different model could have yielded results that did not comport with the remainder of the SIP, it was not arbitrary or capricious for the EPA to continue with the existing model despite some later technological improvements.