Response to EPA’s Comments of May 29, 2008 

1. Comment: WRAP needs to justify using 0.5 deciviews as a threshold for determining 

whether sources are subject to BART. 

Response: EPA’s BART guidelines state that “As a general matter, any threshold that 

you use for determining whether a source ‘contributes’ to visibility impairment should 

not be higher than 0.5 deciviews.” The guidelines give states the discretion to establish a 

lower threshold “if they conclude that the location of a large number of BART-eligible 

sources within the State and in proximity to a Class I area justify this approach. When 

developing the modeling protocols for the visibility analysis, the four participating states 

established the threshold at 0.5 deciviews because it is consistent with EPA guidelines, 

and is consistent with long-standing visibility modeling practices. Significant BARTeligible sources that are in proximity to Class I areas in the west have been addressed 

through the reasonably attributable visibility impairment process, and there is not a large 

concentration of BART-eligible sources that are in proximity to a Class I area. In 

addition, the backstop trading program will include all sources with emissions over 100 

tons/year and will therefore still include sources that may not be subject to BART. The 

guidelines do not require states to establish a lower threshold, and the four participating 

states do not believe that a lower threshold is needed or justified. 

Language has been added to the Better Than BART demonstration to explain that the 0.5 

deciview threshold is consistent with EPA’s BART guidelines. 

2. Comment: When estimating BART emission reductions WRAP excluded some nonutility sources that it characterizes as potentially subject to BART and this not consistent 

with regulatory requirements. 

Response: The analysis excluded a small number of non-utility sources that in aggregate 

represent 1% of the regional milestone. EPA has not established a presumptive control 

level for these sources and there is little benefit to doing a case-by-case analysis because 

the results would have a negligible impact on the regional milestone. These sources will 

still be included in the backstop trading program. 

3. Comment: When establishing milestones, WRAP used presumptive levels in some 

cases and source specific information in others. A consistent approach is needed. 

Response: The WRAP addressed this issue in the Better Than BART demonstration in 

response to earlier comments from EPA (see the end of Section D, page 7). An alternate 

analysis was conducted that assumed that all EGUs that were subject to BART (including 

units that are smaller than 750 MWs or are already operating at greater than 50% control) 

would be operating at the presumptive SO2 emission rate of 0.15 lb/MMBtu. The 

estimated SO2 emission reductions using this simpler approach were 91,872 tons. This is 

comparable to the estimated reduction of 91,760 that was calculated using the more 

detailed method. The participating states chose to use the more detailed method because 

it was based on the best information that was available rather than relying on the 
Response to EPA’s Comments of May 29, 2008 

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presumptive level for all sources. However, the alternate analysis is useful to show that a 

simpler consistent approach achieves the same result. 

4. Comment: The alternative program must include all BART-eligible sources not just 

sources that are subject to BART. 

Response: As recognized in EPA’s comments, the alternative program applies to all 

sources with actual emissions greater than 100 tons/year SO2 and is likely to include all 

BART-eligible sources. However, to address the possibility that there may be an unusual 

source that would not be included based on actual emissions, each of the participating 

states will either include language in their backstop trading rule to ensure that all BARTeligible sources that are BART-eligible due to SO2 emissions are subject to the backstop 

trading program, or will include an analysis in their SIP that demonstrates that all BARTeligible sources meet the 100-ton SO2 threshold. 

5. Comment: The alternative program does not directly address the distribution of 

emissions. At a minimum the SIP should include a determination, supported by a clear 

weight of evidence that Section 309 achieves greater reasonable progress than would be 

achieved through the installation and operation of BART. 

Response: The WRAP conducted modeling that compared command and control BART 

to a trading program during the development of the Annex. A new Section H has been 

added to the end of the Better Than BART demonstration to reference the results of that 

analysis that was submitted to EPA in 2000.