Page 1 of 3 Attachment 3 Request for Comments on the Dra ft Guidance Documents on the Implementation of the Ex ceptional Events Rule

1. The EPA has developed draft exceptional even t implementation guidance with the goal of establishing clear expectations to enable aff ected agencies to better manage resources as they prepare the documentation required unde r the EER. These draf t guidance documents identify mechanisms (e.g., demonstration prioritization, review time lines, High Wind Action Plans) to streamline the demonstration development, submittal, and review process. The EPA seeks comment regarding other sp ecific, broadly app licable, streamlining mechanisms that the EPA could incorporat e into the exceptional event implementation

process.

2. The EPA has modified the exceptional events website at http://www.epa.gov/ttn/analysis/exevents.htm to include additional links to tools, such as the DataFed website, that submitting agencies may use in the development of their demonstration submittals. The EPA has also pos ted exceptional event demonstrations that have already been reviewed and acted upon by the EPA. The EPA solicits feedback regarding other web-based information, links, to ols, or methodologies that we can similarly post on our website.

3. In the draft exceptional events guidance documents, the EPA defines the high wind

threshold as the minimum threshold wind speed capable of overwhelming reasonable controls on anthropogenic sources (i.e., capable of causing significant dust emissions from controlled sources) or causing emissions from natural undisturbed areas. The EPA further notes that this area-specific threshold, along with the submitter’s analysis of implemented

reasonable controls and other f actors, helps inform the analysis of the “not reasonably controllable or preventable” criterion. The EP A intends to allow air agencies to use wind

data from a multitude of sources in the deve lopment of high wind thresholds. The EPA has identified several sources of local wind speed data including the National Weather Service, the National Climate Center, and local air mon itoring stations. In addi tion, states may use models such as MM5, WRF, and NAM, to deve lop local wind speed data. The EPA solicits

feedback on additional available sources of wi nd data and their applicability in informing local high wind analyses.

4. As mentioned in Question 3, demonstrations for high wind dust events necessarily include wind speed analyses. Generally, the EPA will accep t that high winds could be the cause of a high 24-hour average PM10 or PM2.5 concentrati on if there was at le ast one full hour in which the hourly average wind speed was a bove the area-specific high wind threshold. Potential issues arise when determining the hourly average wind speed if wind speeds are not recorded at spec ified intervals throughout each hour. While some sources of wind speed data use hourly averages, other data sources employ 1 - 5 minute (“short-period”) averages. When the available wind speed data consist of only the wind speed during a fixed short period of each hour (e.g., the first or last five minutes of each hour) or the wind speedPage 2 of 3 during the variable short period when wind sp eed was at its maximum during the hour, the EPA will generally accept that the hourly average wind speed was above the threshold if the reported short-period wind speed was above the threshold. Where wind speed is recorded at specified intervals throughout each hour, agencies should use all recorded data to calculate the hourly average wind speed. AERMINUTE, a preprocessor to AERMOD that takes short-period wind speed observa tions and calculates an hourly average wind, can assist in this calculation. AERMINUTE data, or other sub-hourly data with a resolution equal or greater than five-minutes, can be fed into AERMET, the AERMOD meteorological

processor to get a use r-friendly output. The EPA solicits additional feedback and tools to convert 1 - 5 minute wind speed data to hourly averages.

5. Within the EPA’s Air Quality System (AQS), monitoring agencies can use two types of data validation, or data qualifier, codes: the Request Exclusion flags (“R”) and the Informational Only flags (“I”). Agencies should use the “I” series flags when identifying informational data and the “R” series flags to identify data points for which the agency intends to request an exceptional event exclus ion and the EPA’s concurrence. Given that the EPA can act/concur only on “R” flags, some agencies have questioned the utility of “I” flags. Do AQS users find “I” flags in AQS us eful? If so, how do users employ these flags?

6. In response to comments received and in an effort to streamline the development of high wind demonstrations, the EPA has added an optional “Prospective Controls Analysis” process by which states, local agencies, and tr ibes can voluntarily provide information on attainment status, identify natural an d anthropogenic windblown dust sources and emissions, provide the status of SIP submittals (if applicable), and identify the wind speed up to which the collective windblown dust contro ls are expected to be effective. This optional analysis can facilitate agreement betw een states/local agenci es/tribes and the EPA

as to what constitutes “reasonable” controls in advance of an actual event. The EPA has also added an optional “High Wind Action Plan” th at states/local agencies/tribes can use to document current in-place contro ls, document controls on new s ources that need reasonable controls for future events, and/or document current and/or planned mitigation measures. Both of these approaches are described in more detail in the revised draft High Winds Guidance document. The EPA anticipates that air agencies would submit the prospective controls analysis in advance of or with a de monstration package and similarly expects that air agencies would submit the High Wind Action Plan following th e EPA’s initial review of a demonstration package. The EPA recognize s that the information contained in the prospective controls analysis and the High Wind Action Plan is likely to overlap. The EPA solicits feedback on the anticipated use and f unctionality of these plans. Specifically, the EPA requests that commenters identify: (1) spec ific elements in the prospective controls analysis and High Wind Action Plan that are us eful, (2) whether these concepts should be combined or kept separate, and (3) whethe r the flexibility to implement needed dust controls provided by the High Wind Action Plan as a voluntary alternative to the traditional regulatory nonattainment design ation process is helpful.Page 3 of 3 7. In Table 3 of the revised draft High Winds Gu idance document, the EPA identifies example technical analyses that air agencies should consider when preparing their high wind dust event controls analysis to demonstrate the not reasonably controllable or preventable

criterion. The EPA solicits comment on the identi fied analyses and any additional technical analyses that air agencies could use to dem onstrate that the wind exceeded an identified high wind threshold and that the exceedan ce was caused by emissions that were not reasonably controllable.

8. The EPA acknowledges that certain extreme exceptional event cases may require more limited demonstration packages. Whether a part icular event should be considered “extreme” for this purpose depends on the type and seve rity of the event, po llutant concentration, spatial extent, temporal extent, and proximity of the event to the viol ating monitor. Several meteorological phenomena that could be cons idered extreme events include hurricanes, tornadoes, haboobs, and catastrophic volcanic eruptions. The EPA addresses “extreme” high wind dust events in the draft Q&A docum ent, but solicits comment on whether and how specific events of various types s hould be considered to be “extreme.”