Localized
significance thresholds (LST’s) were developed in response to Governing
Board’s Environmental Justice
Enhancement Initiative I-4. The LST
methodology was provisionally adopted by
the Governing Board in October 2003 (Appendix C of the LST methodology adopted by the Board is
outdated, the user is referred to the latest version of
Appendix C - Mass Rate LST Look-up Table below)
and formally approved by SCAQMD's Mobile Source Committee in February
2005.
On October 6, 2006, the
SCAQMD Governing Board unanimously adopted a methodology to calculate
PM2.5 and PM2.5 significance thresholds. The documentation that was
adopted in October 2006, also included PM2.5 LST look-up tables in support
of the LST program. Additional information, including final
methodology and the PM2.5 LST look-up tables, can be found on the
PM2.5 Significance Thresholds and
Calculation Methodology webpage.
LST Methodology
LSTs are only applicable
to the following criteria pollutants: oxides of nitrogen (NOX),
carbon monoxide (CO), and particulate matter less than 10 microns in
aerodynamic diameter (PM10). LSTs
represent the maximum emissions from a project that are not expected to
cause or contribute to an exceedance of the most stringent applicable
federal or state ambient air quality standard, and are developed based on
the ambient concentrations of that pollutant for each source receptor area
and distance to the nearest sensitive receptor. For PM10 LSTs were
derived based on requirements in SCAQMD Rule 403 – Fugitive Dust.
The use of LSTs is
voluntary, to be implemented at the discretion of local public agencies
acting as a lead agency pursuant to the California Environmental Quality
Act (CEQA). LSTs would only apply to projects that must undergo an
environmental analysis pursuant to CEQA or the National Environmental
Policy Act (NEPA) and are five acres or less. It is recommended that
proposed projects larger than five acres in area undergo air dispersion
modeling to determine localized air quality. Projects that are
statutorily or categorically exempt under CEQA would not be subject to LST
analyses. Projects exempt from CEQA also include infill projects that
meet the H&S Code provisions or projects identified by lead agencies as
ministerial.
Final LST Methodology Document
(PDF, 422k) (Appendix
C provided below)
Appendix C - Mass Rate LST Look-up Table
The mass rate look-up
tables were developed for each source receptor area (SRA) and can be used
on a voluntary basis by public agencies to determine whether or not a
project may generate significant adverse localized air quality impacts.
The LST mass rate look-up tables only apply to projects that are less than
or equal to five acres. Lead agencies may use the LST mass rate look-up
tables to determine localized air quality impacts or use the LST mass
look-up tables as a screening analysis. If the project exceeds any
applicable LST when the mass rate look-up tables are used as a screening
analysis, then project specific air quality modeling may be performed. In
the event that the project area exceeds five acres, it is recommended that
lead agencies perform project-specific air quality modeling for these
larger projects.
Appendix
C - Mass Rate LST Look-up Tables (PDF, 54k)
Source Receptor Area (SRA)/City Table
The following document can
be used to identify the appropriate SRA in which the project is located.
SRA/City
Table (XLS, 38k)
Sample
Construction Scenarios
Sample scenarios were
designed to be used by local lead agencies as models or templates for
analyzing construction air quality impacts for projects undergoing an
environmental analysis under CEQA or the National Environmental Policy Act
NEPA. The sample construction scenarios have been developed to
generically represent a broad range of project types that occur in the
district, e.g., commercial, residential, educational, etc.). Each sample
construction scenario is divided into five non-overlapping phases:
demolition, site preparation, grading, building, and architectural
coatings and paving. The construction scenarios can be used in their
entirety to represent similar construction for the project proposed in the
air quality analysis. Alternatively, the lead agency can use the
construction scenario spreadsheets and tailor them to fit the
characteristics of the project analyzed. The construction scenarios are
based on actual numbers of construction equipment and activity (hours of
operation, area disturbed, dirt and debris handled, etc.) obtained from
construction site surveys.
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