Page 1 of 2 December 2, 2011

EPA Docket Center U. S. Environmental Protection Agency

Submitted via E-mail: a-and-r-docket@epa.gov . and via Larry D. Wallace, Ph.D., U.S. EPA, Office of Air Quality Planning and Standards, Air Qual ity Policy Division, e-mail at wallace.larry@epa.gov

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Re: Guidance for 1-Hour SO2 NAAQS SIP Submissions

Attention: Docket ID No. EPA-HQ-OAR-2010-1059.

The Empire District Electric Company (Empir e District) appreciates the opportunity to comment on the Environmental Protection Ag ency’s (EPA) Guidance for 1-Hour SO2 NAAQS SIP Submissions. Empire District is an investor-owned utility serving over 168,000 electric and 44,000 natural gas customer s in the states of Missouri, Kansas,

Oklahoma and Arkansas and is a member of the Edison Electric Institute (EEI).

Modeling Demonstration:

Empire District agrees with the EPA position as stated in the Guidance for 1-Hour SO2 NAAQS SIP Submissions, Appendix A, Modeling Guidance for Non-attainment and Section 110(a)(1) Plans, page A-12.

“Regarding the use of allowable emissions and the modeling of intermittent emissions sources from su ch sources as emergency generators and startup/shutdown emissions, the inclusion of such emissions for the purpose of modeling for SO 2 attainment de monstrations should follow the recommendations in the March 1, 2011 memo “Additional Clarification Regarding Application of Appendix W M odeling Guidance for the 1-hour NO 2 National Ambient Air Quality Standard” (U. S. EPA, 2011a). As stated in this memo, EPA believes the most appropria te data to use for compliance demonstrations for the 1-hour NO 2 NAAQS are those based on emissions scenarios that are continuous enough or frequent enough to contribute significantly to the annual distribution of maximum daily 1-hour concentrations. Although the referenced guidance in this me mo is for NO 2 permit modeling, the common 1 hour averaging time and form of both the NO 2 and SO 2 standards makes this modeling guidance applicable to the 1-hour SO 2 NAAQS and, thus, applicable to SO 2 modeling in su pport of attainment and maintenance

demonstrations”.

A coal base-load power plant is a primary generator of elec tricity in a power company’s fleet and operates continually for the majority of the year with infrequent shut downs, start ups, and malfunctio n trip-offs. Modeling start up, shut down, and malfunction eventsPage 2 of 2 to determine attainment vs. non-attainment c ould prove to be probl ematic for base-load coal combustion units with post combustion co ntrols, such as scrubbers, to control SO2 emissions. Due to the operational constraint s of a scrubber it cannot be operated below certain load levels and thus, cannot cont rol SO2 emissions during start up, shut down, and malfunction trip-off events. Emissions from these infrequent occurrences would have insignificant impact on the overall air quality of an area.

Also, emergency generators operate approxi mately 30 minutes each week for readiness testing and during emergency situation. Emissi ons from the infrequent use of emergency generators would have insignificant impact on the overall air quality of an area and should not be included in determination modeling for the 1-hour SO2 NAAQS.

Monitoring:

AERMOD is an overly conserva tive tool for making air quali ty impact assumptions and is not representative of actual ambient air quality conditions. Empi re District believes that sources should have the opt ion of installing monitors in order to “truth” the model or

that EPA should allow the use of such monitoring in lieu of modeling.

Again, Empire District appreciates the oppor tunity to comment on Guidance for 1-Hour SO2 NAAQS SIP Submissions.

Sincerely,

Jeff Burkett

Environmental Coordinator jburkett@empiredistrict.com (417) 625-4236