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Frequently Asked Questions and Answers

What are the major measures and factors that make up the Weight of Evidence argument?

The May 30, 2007 DFW 8-hour ozone SIP included a chapter on the Weight of Evidence (WOE) programs that help to corroborate that attainment will be achieved by June 2010.  The details of the WOE and corroborative evidence are found in chapter 3 of the SIP.  This evidence included local pilot programs, TERP, trend analyses, and new initiatives in the area which are identified on pages 4-15 to 4-22 of the SIP. 

Portions of the WOE analysis are quantifiable, and have been modeled -- principally, TERP and compression engines.  Since the submission of the SIP, higher funding levels were adopted by the legislature, and joint collaboration occurred between EPA and TCEQ resulting in anticipated emission reductions from TERP quantified to achieve 14.2 tpd of reductions.  In addition, the TCEQ completed a quantification of emissions from compressor engines.  This was based on a request of the TCEQ Commissioners to research the issue.  The TCEQ survey results indicated approximately 1,170 gas fired IC engines in the DFW inventory with an additional 200 engine installations by 2009.  With controls required on these compressor engines, a 47 tpd NOx reduction is expected in the future case.  The overall net effect after control, due to the more accurate survey information, is a 3 tpd increase in emissions.  These emissions will be expected in the Johnson, Parker and Tarrant Counties.  Details of the survey and maps of the sources in the area are included in the TCEQ letter to EPA dated April 23, 2008.  Therefore, the net quantifiable reductions in the Weight of Evidence evaluation is 14.2 tpd -3 tpd = 11.2 tpd reduction.

EPA believes that the modeled attainment demonstration, as strengthened by the additional analyses in the WOE section, support our conclusion that all monitors in the DFW area will show attainment by the end of the 2009 ozone season.

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1. Why is EPA proposing a conditional approval of the DFW SIP?
2. What are accumulated pollution credits?
3. What measures are included in the DFW SIP?
4. Will the measures in the DFW SIP bring the area into attainment? How soon?
5. When will EPA consider final approval for the DFW SIP?
6. How does the new 8-hour ozone standard (0.075 ppm) impact this plan?
7. Will the state have to draft a new SIP once the new 8-hour standard goes into effect?
8. Why didn’t the DFW area just request a ‘bump up’ like Houston?
9. How long did it take the TCEQ to develop the DFW SIP?
10. How long did it take EPA to review the DFW SIP?
11. What is the significance of Texas being first in the nation to have its SIP approved?
12. Why is EPA taking public comments on the proposed approval?
13. When are the public comments due?
14. What will EPA do with the public comments?
15. What are the major controls in the DFW 8-hour SIP passed by TCEQ on May 23, 2007?
16. Isn't it true that the modeling that has been conducted does NOT predict attainment of the 8 hour standard at all DFW monitors?
17. What has been done to improve the Dallas Fort Worth 8-hour Ozone SIP since it was submitted to EPA Region 6?
18. What are the major measures and factors that make up the Weight of Evidence argument?
19. What would be the consequences if EPA did not approve the DFW 8-hour SIP?
20. What are our options if we approve the SIP and the area does not reach attainment by the June 15, 2010 attainment date?

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