North Dakota’s Approach to a Periodic Review to Determine the Status of Consumption of PSD Class I Sulfur Dioxide Increments WESTAR Fall Technical Conference, September 13-17, 2003

This power point presentation follows the handout prepared for this conference. Slides are numbered and labeled as in the handout.

1. Brief History Late in 2000: EPA presents draft SIP call – Triggered by flawed draft modeling showing exceedances of Class I SO 2 24-hr increment Late 1977: PSD minor source baseline date Late 1970s, 1980s and 1990s: NSR modeling and several FLM certifications of no adverse impact

2. Response Actions Legal and technical research completed Emission inventories updated Meteorological drivers updated Modeling protocol updated and executed Two public hearings held First known periodic review completed

5. Modeling Protocol Issues Status of EPA adoption of Calpuff Calculation of “actual emissions” Calculation of “baseline concentration” and deterioration or improvement in air quality Choice of meteorological drivers Local input & settings for Calmet and Calpuff Calmet/Calpuff performance

6. Baseline Concentration The baseline concentration is a single value (i.e., second highest) for the year for the averaging period – which respects law, rule and poor paired-in-time model performance. -- It is the reference point for calculating changing air quality conditions; i.e., deterioration or improvement of worst-case concentrations. -- It is not a value for each averaging period throughout the year for each model receptor.

7. Sulfur Dioxide Source Scenario Source types in North Dakota and adjacent areas – coal-fired electricity generating plants – a synthetic natural gas production plant – natural gas processing plants – oil refineries – a charcoal briquette production plant – oil & gas production wells, and gas treaters

7. continued Sources are geographically dispersed Some sources constructed before the PSD trigger date – some still operating, emissions of some decreased or increased – some retired after the minor-source baseline date Some sources constructed after the PSD minor-source baseline date (19 Dec 1977)

8. Application of emission inventories Two sulfur dioxide emission inventories updated – One for the baseline period – One for the current period Each inventory of emitted sulfur dioxide modeled, which provides a model output data set of predicted concentrations for each inventory consistent with EPA’s 1980 precepts

8. continued Number of point sources throughout the years for each source type – 18,coal-fired electricity generating plants – 4,a synthetic natural gas production plant – 4,natural gas processing plants – 8,oil refineries – 2,charcoal briquette production plant – 872 (1977), oil & gas production wells, treaters – 557 (2000), oil & gas production wells, treaters

8. continued Benefits of modeling each inventory were: Current-period inventory –Predicted concentrations were compared to real concentrations from monitoring provided cumulative or total concentrations Baseline-period inventory –Predicted concentrations were used to establish the baseline concentration, since no real concentration data collected during the baseline period.

9. Actual Emission Rate Actual emissions are existing rates in tons during the year, modified by operating hours – which respects the rule definition, the 1980 PSD rule preamble and EPA’s 1980 guidance. -- real concentrations reflect existing emissions -- existing emissions by existing sources should be used when modeling predicted concentrations -- predicted concentrations should resemble real concentrations (within a factor of +2 or better)

10. Normal Operations of Major Sources Current period – Two years preceding date of concern Baseline period – Two years preceding minor source baseline date unless earlier or later years ( ) better represent use of production capacity

11. Baseline Emission Rates Source-specific AP-42 sulfur dioxide emission factors, 30S, were developed from CEM data and used to calculate actual emissions during the baseline period for coal-fired power plants. -- S is coal sulfur content (%) -- the 30 factor assumed that 25% of sulfur adsorbed during combustion by sodium oxide, real data show the 30 varies among plants -- provided apples-to-apples (current versus baseline) rates

13. Model Performance ND’s modeling inputs, as applied to current- period emissions inventory, provided better agreement with real ambient concentrations. RUC/MM5 improved that agreement. Performance testing became the gateway to understanding model protocol bias.

13. continued Confounders in Calmet-Calpuff performance assessment were: – IWAQM settings – Choice of meteorological driver – Choice of major source emission rates – Background concentration

15. Increment Consumption Calculations 1.Model inventory of current-period emissions 2.Model inventory of baseline-period emissions 3.Establish the baseline concentration 4.Subtract the baseline concentration from current-period concentrations -- positive difference larger than the increment is an exceedance (one is allowed)

Conclusion and Status There are alternatives to several aspects of the historical EPA protocols that are consistent with law, rule, EPA’s interpretive preambles, EPA’s initial guidance, many court decisions, reasonable science & engineering, computer technology, etc. EPA acceptance of the these alternatives is pending.

End of Presentation Questions?