Addressing New Source Permitting and Visibility Issues

- By: ,

Courtesy of AECOM

Within the past decade-- and especially in the past year-- several important developments have occurred, which affect new or proposed emission sources in virtually every region of the country. These developments include the availability of new, more accurate techniques for assessing air quality impacts, significant increases in the areas subject to assessments of pollutant impacts on Class I, Prevention of Significant Deterioration (PSD) areas, and the increasing influence of Federal Land Managers.

Proposed facilities subject to PSD regulations are required to evaluate air quality at specially protected national parks, wilderness areas, and wildlife refuges (Federal Class I areas) in their permit applications. Because PSD Class I considerations have become the most critical and constraining aspects of permitting new sources, it is important for applicants to determine at the outset how these issues could affect a proposed project.

Until recently, however, Federal Land Managers (FLMs), responsible for protecting the environment Federal Class I pristine areas, have given little or no guidance regarding approved modeling techniques to assess effects of new emission sources or on threshold impact levels that would designate a project as having no significant impact.

For example, until the late 1990s, a PSD permit applicant only needed to address Class I areas within 100 km (65 miles) of a proposed facility. Before this period, visibility concerns focused on the presence of a visible plume ('plume blight'), with little attention paid to a facility's contribution to regional haze (reduction in visual range due to particulate concentrations). For acidic deposition, the application of crude screening tools was common practice.

Today, the role of the FLMs in reviewing PSD permit applications has increased significantly due to a number of developments:

  • Proposed rulemaking on reforms to New Source Review (July 23, 1996 Federal Register Notice) has affirmed the increased role of the FLMs in permit reviews.
  • An FLM workgroup on air quality related values (AQRVs) has formally proposed and published final guidance on assessment techniques for visibility and acidic deposition, so that impact assessments for these issues are now required.
  • An Interagency Workgroup on Air Quality Models (IWAQM) among the Environmental Protection Agency (EPA) and the FLMs has agreed upon a preferred dispersion modeling technique (the CALPUFF model) for long-range transport applications which increase the distance range where modeling results can be obtained.
  • The EPA has formally proposed that CALPUFF be the preferred air quality model for assessment of long-range transport modeling issues.

Now, the FLMs require that the effects of emissions on Class I areas must be addressed in areas within 200 km (130 miles) or, in some cases, up to 300 km (195 miles). As shown in Figure 1, this expansion of the area of influence affects new PSD sources over most of the United States.

Visibility Criteria: A New Hurdle

Assessments of the impacts of proposed projects on visibility have become more restrictive over the past 10 years. An important measure of existing visibility is the background visual range (maximum distance at which terrain features can be distinguished). Prior to the mid 1990s, changes in visual range associated with proposed emission sources were compared to the median visual range. A few years ago, once the FLMs had collected field data on visibility, they began to specify the 90th percentile 'best' background visual range as the basis for comparison. This change in policy from 50th to 90th percentile made it more difficult for a proposed project to show an insignificant visibility impact.

As a result of the finalization of the Regional Haze Rule (July 1, 1999 Federal Register), the FLMs have recently tightened the criteria even further for the background visual range. In late 2000, the Federal Land Managers' Air Quality Related Values Workgroup (FLAG) published Phase I guidance that now governs the FLM review of PSD permits. In a major policy shift, FLAG's guidance changed how FLM determines visibility impairment.

The FLAG guidance replaces the 90th percentile criterion with that of a 'natural' background. Citing the 1977 Amendments to the Clean Air Act, FLAG interprets natural background as the concentration level that would exist in the absence of human activity on earth. This is inconsistent with the purpose of National Parks, which have been established for the enjoyment of human visitors.

The new criteria are more restrictive to permitting, especially in the eastern United States. A proposed source that could have been permitted prior to the FLAG guidance now will have to reduce emissions by a factor of two or three to meet the new criterion. Furthermore, modeling will more often indicate that the project emissions are too high to pass the regional haze thresholds. Ironically, this could increase pollution, because procedures developed to protect Class I areas from further visibility degradation from new sources will hamper development of new, less-polluting power plants that would replace the generation capacity provided by older sources that are less efficient and emit more pollutants. Thus, in the near term, the FLAG guidance could aggravate rather than improve the regional haze conditions in PSD Class I areas.

Recommendations to Developers of New Emission Sources

In light of these emerging requirements, ENSR recommends the following strategies to developers of new emission sources:

  • Check the location of the source relative to the map that shows areas within 300 km of a Class I area. If the source is within range, assess the effect of the proposed source for PSD Increment consumption, visibility, and acidic deposition effects.
  • If the source is within 50 km of a Class I area, apply short-range dispersion modeling procedures that are used for the ambient air impact assessment surrounding the facility. If the source is farther than 50 km from the Class I area, apply CALPUFF.
  • The FLMs will closely scrutinize the emissions of a project relative to recent Best Available Control Technology assessments. Careful attention should be paid to this issue. One benefit of proposing lower emissions is that it is more likely the project will pass the modeling thresholds. 
  • The recommended model, CALPUFF, can first be run in a simple screening mode using a single meteorological station to determine if the project has an insignificant impact. While it is likely that well-controlled natural gas-fired projects have a chance to pass this test, a refined analysis using multiple meteorological stations is likely to be required for oil- or coal-fired sources.
  • Check with the FLMs to see if a refined analysis may already have been done for that area. If not, an experienced air quality meteorologist will be needed to conduct the required refined CALPUFF analysis. If the proposed source alone shows an insignificant impact within the Class I area, no further analysis is required. Otherwise, a cumulative analysis with all PSD sources within at least 100-200 km of the Class I area is necessary.
  • ENSR's experience indicates that cumulative analyses are most often triggered by two criteria, the PSD Increment for sulfur dioxide and regional haze, with the latter typically more constraining. In conducting the refined analysis, the meteorological conditions should be carefully scrutinized for factors that may negate visibility as an important air quality-related value. For example, because the modeled haze is very sensitive to relative humidity, periods of fog or inclement weather may be excluded because the visibility is already naturally reduced. 
  • Seek ways to refine estimates of natural background to include regional or local contributions. For instance, for coastal areas, include sea salt particles in the background. 
  • Because of the many complicated technical, regulatory and policy issues, ongoing communication with the permitting agency and the FLMs is essential for the expeditious and successful permitting of any new major emissions source.


In any fatal flaw assessment of a proposed project, the impacts of the project emissions on PSD Class I areas may result in constraints to the project. A thorough understanding of the issues associated with modeled impacts at these areas is essential to a successful permit.

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