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U.S. EPA Proposes PSD/NSR Clarifications to Increment Modeling Procedures


By Jennifer Thompson, Attorney, Bingham Greenebaum Doll LLP

On May 24, 2007 U.S. EPA proposed to clarify existing New Source Review (“NSR”) Prevention of Significant Deterioration (“PSD”) regulations regarding how States and regulated sources calculate increases in concentration for increment consumption analysis purposes. Because the Clean Air Act (“CAA”) does not directly specify how to determine an increase, and U.S. EPA never adopted regulations establishing a specific methodology to calculate an increase, States and U.S. EPA Regional Offices have had to rely on guidelines while conducting increment analysis.

Most of U.S. EPA’s clarifications have been proposed through a new definition of “actual emissions” at 40 C.F.R. § 51.166(f) and 40 CFR § 52.21(f) that will only apply to methods for determining increment consumption and through exclusions to methods for determining increment analysis. U.S. EPA seeks comment on whether it could also repeal the existing definition of “actual emissions” in 40 C.F.R. § 51.166(b)(21) and § 52.21(b)(21) without affecting other elements of the PSD program.

Generally, U.S. EPA’s proposal regarding calculating increases in concentration includes, but is not limited to the following:

Data Used to Estimate Emissions
To address uncertainty, U.S. EPA proposes to codify a policy that gives the reviewing authority discretion to select the data and emission calculation methodologies that are reliable, consistent, and representative of actual emissions for increment consumption purposes. U.S. EPA also seeks comment on whether additional guidance or limitations should be included for estimating emissions that make up the baseline concentration or consume increment.

Time Period of Emissions Used to Model Pollutant Concentrations
U.S. EPA proposes to clarify the circumstances when it is permissible in the context of an increment consumption analysis to determine actual emissions for increment consuming sources using a period of time other than the two years immediately preceding the relevant date. Specifically, U.S. EPA intends to clarify three primary issues:

1. one is not required to demonstrate the occurrence of a catastrophic event in order to determine actual emissions on the basis of a period other than the two years immediately preceding the date in question;
2. there can be circumstances where emissions increases occurring after the baseline date or due to increases in hours of operation or capacity utilization may be more representative of normal source operation; and
3. when an alternative (more representative) time period other than the two years before the particular date is used to reflect actual emissions, that alternative time period must be representative of source emissions (within an expected range of variability) as of the particular date and cannot be based on emissions experienced because of a change in the normal operations of that source after that date.

Actual Emission Rates Used to Model Short-Term Increment Compliance
U.S. EPA proposes to include how to come up with short term emission rates when modeling the change in the concentration for the 24-hour and 3-hour averaging period used in increments for some pollutants. Additionally, it seeks comment on whether U.S. EPA should expand the proposed options for short-term emissions rate calculations to include the following permissible data sources and methods recommended by the Western States Air Resources Council.

Where CEMS data is available:

  • Use of short-term maximum emissions for the entire plant over a 2-year period;
  • Determine maximum short-term emissions from each source at the facility;
  • Determine short term emission rates and sort them, then determine representative rates, such as upper percentile, as the single short-term emission rate for modeling;
  • Use CEMS data to determine actual emissions as defined by rule and explained by U.S. EPA in the preamble to the 1980 PSD rule revisions; or
  • Use hour-by-hour CEMS data in the model.

In situations where CEMS data is not available:

  • Average two years of actual annual emissions representing normal operations surrounding the baseline date and date of analysis for current emissions, and divide by annual operating hours;
  • Calculate emissions from production data for the two years prior to the baseline date or date of analysis for current emissions (emissions calculated using valid emission factors and methods);
  • Use two years of emissions data, which may be before or after the baseline dates, which have a similar facility configuration that would be representative of baseline emissions; or
  • Use of allowable emission rates, including use of regulatory limits, where appropriate.

Meteorological Data and Processing
U.S. EPA proposal also recognizes the need to clarify guidance for determining the appropriateness of prognostic meteorological model output data for use in dispersion models and is seeking comment on: (1) the selection of geographic domains and time periods; (2) technical options governing the meteorological model calculations; (3) data assimilation parameters; and (4) other factors.

Years of Meteorological Data
U.S. EPA seeks to clarify guidance on the number of years that prognostic meteorological model output data is necessary for a representative dispersion model simulation. U.S. EPA proposes to allow States when developing a set of data years for dispersion modeling to use data years that were not produced by the exact same meteorological model configuration and simulation. However, the State must further determine that a particular set of data years can be modeled to produce an appropriate depiction of the air quality.

Treatment of Sources That Have Previously Received a Class I area FLM Variance
U.S. EPA’s proposed regulations include a new provision stating that the emissions of any source that was permitted after receiving a Class I increment variance from a Federal Land Manager (“FLM”) need not be included in the consumption analysis for a Class I area increment for the area for which the variance was issued.

Documentation and Data Software Availability
U.S. EPA believes the current text of 40 CFR Part 51, Appendix W, adequately defines the documentation and software availability requirements related to both preferred and alternative modeling techniques, but seeks comment on whether additional guidance is needed to clarify these requirements as they apply to the use of proprietary software and/or data to develop input for an Appendix A modeling application for PSD increment consumption.

Effect of the Draft 1990 New Source Review Workshop Manual
In addition to the proposed changes to the PSD/NSR regulations, U.S. EPA also clarifies in the Preamble that the Draft 1990 NSR Manual is not a NSR Program binding regulation and that the Draft NSR Manual does not by itself establish final EPA policy or authoritative interpretation of EPA regulations.

U.S. EPA is encouraging States to incorporate the regulations once they are finalized and believes it should be relatively easy task given that SIP changes resulting from other upcoming NSR rulemakings (e.g. rules for electric generating units, corn milling, potential to emit, and aggregation, debottlenecking, and project netting) will likely be required during the same time period.

However, U.S. EPA stresses that SIP changes may not be necessary (before relying on the proposed PSD increment analyses) because U.S. EPA’s prior recommendations have not been binding on States. U.S. EPA, however, seeks comment on the need for SIP revisions or any viable alternatives for implementing the changes for these proposed increment analysis provisions.

U.S. EPA’s proposal was included in the June 6, 2007 Federal Register and is available for viewing or printing here. Comments are due to the U.S. EPA Docket Center on or before August 6, 2007 and should identify Docket ID No. EPA-HQ-OAR-2006-0888.


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