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Significance Criteria and Determinations

Once the air quality (including health risks and/or odors) and climate change analyses are completed, Yorke will prepare an Air Quality Technical Report that will be written in a format for easy inclusion into the Environmental Impact Report (EIR) or other California Environmental Quality Act (CEQA) document. The report will establish the baseline air quality conditions and regulatory setting that will define what analyses are required and how the impacts will be addressed. The report will identify each of the Lead Agency’s defined significance thresholds for evaluating emissions of criteria pollutants (e.g., ozone precursors, particulates, carbon monoxide, sulfur oxides), toxic air contaminants (TACs), odors, and/or greenhouse gases (GHGs) for construction and operation, as applicable. The main thresholds and standards that may need to be addressed are as follows:

  • Regional Mass Emissions Thresholds;
  • Emissions Standards by Regulation;
  • Local Significance Thresholds (LSTs);
  • California and National Ambient Air Quality Standards;
  • Health Risk Assessment (HRA) Thresholds;
  • Carbon Monoxide Hotspots (if applicable);
  • Cumulative Impacts Analysis;
  • Off-Road and Portable Equipment Regulations; and
  • Permitting Consistency – Best Achievable Control Technology, Modeling, and Health Risk.

Although the State clearinghouse provides guidance on significance criteria for CEQA analyses, each Lead Agency may have slight variations and additional criteria that must be addressed. A summary of some typical significance criteria and technical analyses Yorke would use to evaluate project impacts with respect to each criteria is shown in Table 1.

Table 1: Significance Criteria and Evaluation Method

Significance Criteria Evaluation Method
Air Quality
Conflict with or obstruct implementation of the applicable air quality plan Qualitatively compare project activities and emissions to the Air District’s Air Quality Management Plan (AQMP)
Violate any ambient air quality standard or contribute substantially to an existing or projected air quality violation Compare project emissions to the mass daily significance thresholds and LSTs or conduct air dispersion modeling if warranted
Result in a cumulatively considerable net increase of any criteria pollutant for which a region is nonattainment Compare project emissions and emissions from other new projects in the area to the mass daily significance thresholds and LSTs
Expose sensitive receptors to substantial pollutant concentrations Conduct a project-level health risk assessment (screening or refined as applicable)
Create objectionable odors affecting a substantial number of people Discuss the potential for malodorous emissions and perform an ambient air quality impact analysis
Greenhouse Gas Emissions
Generate GHG emissions, either directly or indirectly, that may have a significant impact on the climate Compare project emissions to applicable mass significance thresholds
Conflict with any applicable plan, policy, or regulation of an agency adopted for the purpose of reducing the emissions of GHGs Qualitative comparison of project activities and emissions to the overall goals of AB 32

The CEQA analysis is used as a tool to assist decisionmakers with whether or not to approve a project or suggesting changes that would allow approval. If a project is determined to have a potentially significant impact, additional mitigation measures can be evaluated to determine whether the impact can be reduced. If all feasible mitigation measures have been incorporated and the impact is still expected to be significant, then it is the prerogative of the Lead Agency and other responsible agencies to decide if a project should nevertheless be approved in spite of the significant impacts. In that case, a statement of overriding considerations must be prepared by the Lead Agency which justifies approval of the project.

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