Notice of Availability of Dispersion Modeling Analysis of PSD Class I Increment Consumption in North Dakota and Eastern Montana

AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Notice of availability.

SUMMARY:

The EPA announces the availability of a dispersion modeling analysis of Prevention of Significant Deterioration (PSD) increment consumption in North Dakota and eastern Montana. EPA's air quality modeling analysis is contained in a report titled Dispersion Modeling Analysis of PSD Class I Increment Consumption in North Dakota and Eastern Montana (May 2003 Version). The results of this analysis show numerous violations of the Class I PSD increments for sulfur dioxide (SO₂) in four Class I areas. These Class I areas are the Theodore Roosevelt National Park and the Lostwood Wilderness Area in North Dakota and the Medicine Lakes Wilderness Area and Fort Peck Indian Reservation in Montana. The EPA is soliciting additional public comments on this analysis before taking any further actions.

DATES:

Comments on the May 2003 version of the Report will be accepted for 30 days. Comments must be received in writing on or before June 23, 2003.

ADDRESSES:

Written comments may be mailed to Richard R. Long, Director, Air and Radiation Program, Mailcode 8P-AR, Environmental Protection Agency (EPA), Region VIII, 999 18th Street, Suite 300, Denver, Colorado 80202. The Report and supporting documentation are available on EPA's Web site at http://www.epa.gov/region8/air/ndair.html . Copies of the Report and supporting documentation and data are also available for public inspection during normal business hours at the Air and Radiation Program, Environmental Protection Agency, Region VIII, 999 18th Street, Suite 300, Denver, Colorado 80202. Interested persons should contact the person listed below to arrange a time to view the Report.

FOR FURTHER INFORMATION CONTACT:

Carl Daly, EPA, Region VIII, (303) 312-6416.

SUPPLEMENTARY INFORMATION:

I. What Are the PSD Increments?

The purpose of the Prevention of Significant Deterioration (PSD) program of the Clean Air Act (Act), 42 U.S.C. 7470-7479, is to ensure that the air quality in clean air areas remains clean and does not deteriorate to the level of the national ambient air quality standards (NAAQS). The mechanism created by Congress to meet this goal is the establishment of “PSD increments.” These increments define the maximum allowable increases over baseline concentrations that are allowed in a clean air area for a particular pollutant. Any increase above this level indicates that significant deterioration of air quality has occurred. Because only emissions increases above the baseline concentration are considered in determining how much increment has been consumed, the amount of increment consumed can only be determined through air quality dispersion modeling, not through direct monitoring of ambient concentrations.

The Act provides for three different classes of air quality protection, to reflect varying levels of protection from significant deterioration in air quality. In the 1977 Clean Air Act Amendments, Congress designated all international parks, national wilderness areas and national memorial parks which exceed 5000 acres in size, and all national parks which exceed 6000 acres in size as mandatory Class I areas. Congress also allowed States or Tribes to request redesignation of any area to Class I air quality protection status. Class I areas are to receive special protection from degradation of air quality, and the most stringent PSD increments apply in these areas. The Class I increments for SO₂ are defined in section 163(b)(1) of the Act, 42 U.S.C. 7473(b)(1), as follows:

Annual arithmetic mean—2 μg/m³

Twenty-four hour maximum—5 μg/m³

Three-hour maximum—25 μg/m³

These increments are also promulgated in EPA's PSD regulations at 40 CFR 52.21(c). North Dakota has adopted these increments as state regulation in section 33-15-15-01.2.b. of the North Dakota Administrative Code, which EPA approved as part of the State Implementation Plan (SIP) on November 2, 1979 (44 FR 63102).

For any averaging period other than an annual averaging period, section 163(a) of the Act allows the increment to be exceeded during one such period per year. Otherwise, section 163 of the Act provides that the increments are not to be exceeded and that the SIP must contain measures assuring that the increments will not be exceeded. Section 110(a)(2)(D)(i)(II) of the Act, 42 U.S.C. 7410(a)(2)(D)(i)(II), further requires the SIP to include provisions prohibiting any source or other emitting activity within the State from emitting air pollution in amounts that will interfere with measures to be included in any other State's implementation plan to prevent significant deterioration of air quality. EPA's PSD regulations also provide that the SIP must be revised whenever EPA or the State determines that an applicable PSD increment is being violated. (See 40 CFR 51.166(a)(3).)

II. What Is the Basis for EPA's Modeling Study and What Are the Next Steps?

The North Dakota Department of Health (NDDH) conducted a modeling analysis in 1999 and prepared a draft report that showed violations of the Class I PSD increments for SO₂ in four Class I areas. In a March 13, 2001 letter to EPA, the NDDH committed to refine this modeling analysis and to subsequently adopt revisions to the State Implementation Plan (SIP) as may be necessary to address the increment violations that may be shown by the revised analysis (see EPA's May 29, 2001 Information Notice for more details, 66 FR 29127). However, in developing a modeling approach to finalize the study, EPA and North Dakota could not fully agree on the appropriate data, or the emissions inputs that should be used in the final modeling. Therefore, EPA prepared a dispersion modeling analysis of PSD increment consumption in North Dakota and eastern Montana. On March 5, 2002 EPA released a draft analysis report (January 2002 Version) to interested stakeholders for review and comment. The draft modeling results showed numerous violations of the PSD increment for SO₂, both for the three-hour and twenty-four hour increments, in four Class I areas. Comments received on the January 2002 draft Report have been considered by EPA and incorporated as appropriate into this May 2003 version of the Dispersion Modeling Analysis of PSD Class I Increment Consumption in North Dakota and Eastern Montana Report. These public comments and the January 2002 draft Report are available for review on the Web site noted below.

As outlined in the May 2003 version Report, EPA's methodology follows EPA regulatory requirements and guidance as applied over the last 20 plus years. We believe this approach also best meets the intent of the increment modeling—to characterize the potential for increment violations under realistic emissions and meteorology conditions.

The results of this study are similar to those from the air quality modeling analysis completed by the State of North Dakota in 1999 and from EPA's January 2002 draft Report. EPA will consider all comments received before taking any further actions.

III. How Can I Obtain a Copy of and/or Provide Input on This Report?

The May 2003 version of the Report and supporting documentation are available on EPA's Web site at http://www.epa.gov/region8/air/ndair.html . Copies of the Report can also be obtained from the contact person listed above. Written comments may be mailed to Richard R. Long, Director, Air and Radiation Program, Mailcode 8P-AR, Environmental Protection Agency (EPA), Region VIII, 999 18th Street, Suite 300, Denver, Colorado 80202.

This notice today informs the public and identifies the appropriate EPA regional office from which the public may gain further information and view the Dispersion Modeling Analysis of PSD Class I Increment Consumption in North Dakota and Eastern Montana Report (May 2003 Version). This notice and the May 2003 version of the Report do not constitute final agency action. Such action may be taken at some point in the future, after notice and comment, as may be necessary to address any PSD increment violations.