Baseline actual emissions are the adjusted average annual emissions that occurred during any consecutive 24-month period during the past 10 years (five years for an electric utility steam generating unit (EsUSGU)).
Facilities other than EUSGUs may use any consecutive 24-month period in the past 10 years to determine baseline actual emissions. EUSGUs may use any consecutive 24-month period in the past five years. In either case, emissions must be adjusted downward to reflect removal of any equipment and any legally enforceable emission limitations that became effective after the selected 24 months, or adjusted upward to reflect new emission units that began operating after the selected 24 months.
- Q: I had to install control equipment two years ago, but did not have controls during the baseline period. I have done stack testing and know that I am achieving better than the required efficiency (for example, 95% vs. 90%). How do I adjust the baseline emissions for the operation of these?
A: For a baseline period prior to operation of the controls, you use the permit/rule requirement only, or 90%. However, if you choose to use the two most recent years for your baseline, you use the efficiency where it actually operated, or 95%. You can’t raise the baseline to reflect a required efficiency that was lower than that actually achieved.
- Q: What about voluntary controls that were in place during the baseline? Can you adjust those actual emissions UP since the controls were not required?
A: You do not adjust the baseline UP to account for voluntary controls. For example: if a source has been operating voluntary controls for the entire 10 years, the baseline reflects the operation of those controls. If a source that installed voluntary controls in 2000 chose 1997 and 1998 for the baseline, then the baseline does not include the voluntary controls. If they are now required controls, the 1997-1998 baseline would be adjusted down to reflect their operation.
- Q: I installed control equipment a couple of years ago. My current air permit does not actually contain a specific control efficiency for the control equipment, just a requirement to operate and maintain the controls. How should I adjust my baseline emissions for operation of the control equipment without a specific efficiency?
A: There is a legal obligation to adjust the baseline down to reflect the operation of the controls. The percentage should be practical, based on what the device should achieve based on whatever data is available (for example, site-specific testing, vendor data, Minn. R. 7011.0070, Air Permit Application Form GI-05A, etc.).
- Q: What are the baseline actual emissions for a new unit that has not yet begun normal operation?
A: The baseline actual emissions for a new unit that is under construction/startup (still in the shakedown period) is "zero." The baseline once it begins operation, but has operated less than 24-months, is the PTE or allowable emissions.
- Q: What are the baseline actual emissions for an existing unit that was constructed during the baseline line period but that did not operate during that 24-month period?
A: For all emissions units constructed prior to or during the baseline period, the baseline actual emissions are the average actual emissions during the baseline period -- so for this unit, the baseline actual emissions would be zero.
(The baseline period chosen is at the discretion of the applicant. The applicant can choose another baseline period, but the trade-off would be losing older emission units in order to capture newer emission units.)