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May 13, 1983 PSD Increment Consumption Guidance 6.15
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6.15
DATE: May 13, 1983 SUBJECT: PSD Increment Consumption Guidance FROM: Chief, Air Management Branch
TO: Winston Smith Attached is a memo from the Region A&WMD Division Director to Sheldon Meyers relating to a guidance document issued by Sheldon on February 17, 1983, and apparently relating to the manner in which we determine PSD increment consumption. I am not sure I fully understand the comments made by Alexandria Smith, but they do appear to impact on questions which the states have been raising in our region. I would appreciate your scheduling a briefing to bring me up-to-date on this matter. James T. Wilburn Attachment
DATE: MAY 3 1983 SUBJECT: Determination of Air Quality Degradation
FROM: Alexandra B. Smith, Director
TO: Sheldon Meyers, Director In your February 17, 1983 memorandum concerning clarifications of the Emissions Trading Policy, we were pleased to read a firm statement on the policy for determining the amount of degradation of air quality for source specific applications. While you were speaking in the context of the amount of degradation of air quality due to an emissions trade at a source for comparison with significance levels, we noted that this is directly applicable to determining PSD increment consumption. You said that the method of finding maximum changes in air quality impact must be determined on both a spatially and temporally consistent basis. We agree. The maximum amount of PSD Increment consumed must be determined by modeling the net changes in emissions (between the baseline and future cases) sequentially for each time period with at least a full year of meteorological data. The resulting maximum impacts of this type of analysis specify the maximum amount of Increment consumption at each receptor. This is the way we have performed increment analysis in the past and the way we will continue to perform it in the future. We have been told by PSD sources in the past that this is not the proper method of assessing the amount of increment consumed. Instead they suggest that the proper way is to first model the baseline emissions, and determine the maximum baseline impact at each receptor. The maximum increment consumption is then the difference between the maximum baseline and the maximum future impact at a given receptor, disregarding the fact that these maximum impacts may have occurred during different time periods of the modeled year. This approach is spatially consistent, but it is not temporally consistent. Thus, it will not produce a true measure of air quality degradation. Although we have disagreed with applicants on this approach in the past, we have not until now been able to point to clarifying guidance on the issues your memorandum of February 17 provides this guidance and will be very helpful in future discussions on the issue.
cc: Modeling Contacts (Regions 1 - 9) |