SCAQMD Localized Significance Thresholds Staff Proposal for Discussion

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SCAQMD Localized Significance Thresholds
Staff Proposalfor Discussion

• March 5, 2003

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Localized Significance Thresholds - Background

• EJ Initiative 4 Establish Stakeholder Working
  Group to revise Handbook
• Stakeholder Working Group identified localized
  significance thresholds (LSTs) as a topic to
  include in the Handbook
• Developed concept of LST Lookup Tables
• February 1, 2002 Governing Board directed staff
  to continue developing LST
• September 13, 2002 Governing Board adopted EJ
  Enhancements Enhancement I-4 directs staff to
  continue developing LSTs

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Intent of Localized Significance Thresholds
Tables

• Provides another indicator of A.Q. significance
  for CEQA analysis
• Similar to Rule 1401/212 guidance, users will
  have the option of using conservative screening
  tables or performing project-specific modeling
  (Tier I)
• Users of criteria pollutant screening tables
  would need less resources

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Significance Threshold - Approaches
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Localized Significance Thresholds - Methodology

• AAQS Exceedance Approach for Attainment
  Pollutants - NO2 CO
• Emissions contribution from the project added to
  ambient concentrations
• Localized thresholds in mass daily emissions
  developed by SRA, size of emissions source,
  receptor distance

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Localized Significance Thresholds - Methodology
(Cont.)

• CO Basis
• Highest 1-hr 8-hr CO background conc. over
  3-year rolling average (1999-2001)
• Single table developed from the lower emissions
  allowed by either the 1- or 8-hr conc.

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Localized Significance Thresholds - Methodology
(Cont.)

• NOx Basis
• Highest 1-hr NOx background conc. over a 3- year
  rolling average (1999-2001)
• Gradual NOx to NO2 conversion

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Localized Significance Thresholds - Methodology
(Cont.)

• PM10 - Construction
• Applicable primarily to fugitive dust activities
• Would encompass PM10 from all emission sources
  dust and combustion
• Significance threshold consistent with Rule 403
• Back calculates mass emission that cause an
  exceedance of Rule 403-equivalent threshold of
  10.4 µg/m3 (24-hour average)

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Localized Significance Thresholds - Methodology
(Cont.)
 

• PM10 - Operation
• Significance threshold consistent with Rule 1303
  modeling requirement of 2.5 µg/m3
• Back calculates mass emissions that cause an
  exceedance of 2.5 µg/m3
• Applies to all emission sources

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Localized Significance Thresholds - Conclusion

• Staff proposal for LSTs would implement EJ
  enhancement I-4
• Tiered approach to assess localized impacts
• Lead agencies can use LSTs or perform
  site-specific modeling

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Localized Significance Thresholds Conclusion
(Cont.)

• Using LST Tables
• Requires less resources
• Can use mass emission estimate results
• More conservative
• Site specific modeling
• Requires more resources
• More flexibility
• More precise results