The 1990 Clean Air Act Amendments included Section 234, inserted by then-Wyoming Senator Alan Simpson, requiring EPA to "analyze the accuracy" of modeling analyses designed to predict impacts to short-term particulate NAAQS from surface coal mine fugitive emissions. The section also requires EPA to "make revisions as may be necessary to eliminate any significant over-prediction of air quality effect of fugitive particulate emissions from such sources." It provides that, until EPA complies, "the State may use alternative empirical based modeling approaches pursuant to guidelines issued by the Administrator." In May 2011, McVehil-Monnett Associates released this draft white paper assessing EPA's compliance with the requirement (which included a 3-year deadline) and the current state of fugitive particulate modeling.
This statement in a 1996 memo from EPA to Senator Simpson appears to be the final word on the matter:
"Since the model still appears to overpredict the impacts of surface coal mines, the Agency does not plan to use it for regulatory applications involving these sources. As a consequence, the regulatory procedures currently in place will remain in effect. These procedures are contained in the January 24, 1994 Memorandum of Agreement (MOA) between EPA Region VIII and the State (copy enclosed) and were summarized in the Federal Register on September 12, 1995 (60 FR 47290). The MOA allows the State to conduct monitoring in lieu of short term modeling for assessing coal mining-related impacts in the Powder River Basin. We believe that these procedures provide adequate protection for the environment and are also acceptable to the stakeholders. At this time, we and the various stakeholders believe that the interim procedures work well, and therefore we do not currently plan any further analyses. If in the future EPA is able to correct the model’s tendency to overpredict as described above, it may, of course, review these regulatory procedures."
The author also points out that the Wyoming Supreme Court issued a ruling in March of this year stating, in part, that EPA still has not remedied the situation addressed by the Simpson amendment.
Wyoming has a specific Memorandum of Agreement with EPA regarding modeling (or not) of surface coal mine fugitive PM. Their agreement relies heavily on an approved monitoring network and valid data and on requiring Best Available Work Practices (BAWPs). They also had to work through PSD increment issues, although it appears that the rather creative fixes no longer apply and any further work to address the issue is at a standstill.
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