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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 Quality Policy Division, e-mail at 

wallace.larry@epa.gov. 

Re: Guidance for 1-Hour SO2 NAAQS SIP Submissions 

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

The Empire District Electric Company (Empire District) appreciates the opportunity to 

comment on the Environmental Protection Agency’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 customers 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 such sources as emergency generators and 

startup/shutdown emissions, the inclusion of such emissions for the purpose of 

modeling for SO 2 attainment demonstrations should follow the 

recommendations in the March 1, 2011 memo “Additional Clarification 

Regarding Application of Appendix W Modeling 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 appropriate 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 memo 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 support of attainment and maintenance 

demonstrations”. 

A coal base-load power plant is a primary generator of electricity in a power company’s 

fleet and operates continually for the majority of the year with infrequent shut downs, 

start ups, and malfunction trip-offs. Modeling start up, shut down, and malfunction events 
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to determine attainment vs. non-attainment could prove to be problematic for base-load 

coal combustion units with post combustion controls, such as scrubbers, to control SO2 

emissions. Due to the operational constraints of a scrubber it cannot be operated below 

certain load levels and thus, cannot control 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 approximately 30 minutes each week for readiness 

testing and during emergency situation. Emissions 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 conservative tool for making air quality impact assumptions and 

is not representative of actual ambient air quality conditions. Empire District believes 

that sources should have the option 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 opportunity to comment on Guidance for 1-Hour 

SO2 NAAQS SIP Submissions. 

Sincerely, 

Jeff Burkett 

Environmental Coordinator 

jburkett@empiredistrict.com 

(417) 625-4236