The District assists project applicants and lead agencies to prepare environmental documents under the California Environmental Quality Act (CEQA) by providing air quality data and other needed information. The District has prepared the following guidelines for the Lead Agencies to consider for calculating emissions, performing air dispersion modeling and conducting health risk assessment in preparation of CEQA documents for projects in San Diego County. The District also recommends using the County of San Diego  thresholds of significance  when evaluating air quality impacts for a project.   District staff are available for consultation at any time in the project review process.

CEQA provides governmental decision makers and the public with information about the potential, significant environmental effects of proposed projects. Projects are classified as either discretionary or ministerial.

CEQA applies to all discretionary activities proposed to be carried out or approved by California public agencies, unless an exemption applies. When a public official in a governmental agency can use its judgment in deciding whether and how to carry out or approve a project, it is a discretionary project. If the public official of the governmental agency merely applies the law to the facts as presented, but uses little or no personal judgment, the project is ministerial, and exempt from CEQA.

The goals of CEQA are for California’s public agencies to identify the significant environmental effects of their actions; and, either avoid those significant environmental effects, where feasible; or mitigate those significant environmental effects, where feasible. By identifying and discussing all significant impacts, CEQA allows the project applicant to change the project to mitigate adverse effects; lead agencies to be provided the information necessary to impose conditions on the project to mitigate adverse effects; the public access to information about the effects of projects; and policy boards to receive important information for determining whether the project “protects the public health, safety and welfare.”


It is recommended that the Lead Agency use the calculation methods and emission factors published by the SDAPCD for equipment, processes and operations used at stationary sources, found at the SDAPCD’s website www.sdapcd.org . Other calculation methods can be used if documentation is provided regarding the validity, appropriateness and applicability to the project.

Emissions associated with mobile sources should utilize the most recent EMFAC(on-road) and OFFROAD (off-road) emission factors published by the California Air Resources Board (CARB) found at www.arb.ca.gov .The District recommends using only approved and up to date models for calculating emissions from land use projects, such as the CalEEMod model.


To complete an air quality impact assessment (AQIA) and health risk assessment (HRA) for the CEQA process, modeling is usually required.  The SDAPCD requires that AERMOD, the EPA approved regulatory air dispersion model, be used to perform the air dispersion modeling for AQIAs and HRAs.  The AERMOD executable is available for free from EPA at:


The AERMOD user’s guide is at:


There are also fee-based software options available that incorporate a user-friendly interface. The SDAPCD does not endorse any specific interface, but one such product is Lakes Environmental AERMOD View software, which is used by SDAPCD modeling staff for all modeling projects using AERMOD.  Lakes AERMOD View software can be obtained at the Lakes website at:


 The use of Lakes AERMOD view by the Lead Agency may help with the ease of review and sharing of files.  AERMOD contains several regulatory options, include default options, and non-regulatory options.  For most modeling projects, the regulatory default options should be used in the modeling.

Emission Sources

AERMOD requires the input of emission source information.  There are four different types of sources - point, area, volume, and line. 

·        Point Sources – A point source is the most common type of release and is characterized by a stack or vent.  Examples of point sources are exhausts from emergency engines, stacks coming off combustion equipment, and roof vents.  There are different types of point sources that can be modeled in AERMOD including non-capped vertical stacks, a stack with a flapper valve, and stacks with a fixed rain cap.  Point sources can also be modeled as having a horizontal orientation.  Point sources have stack parameters associated with them including exhaust temperature, stack diameter, flow rate, and stack height.

·        Area Sources – Area sources are used to model releases that occur over an area.  Examples of area sources include landfills and open tanks and stockpiles.  Different types of area sources are rectangular, circular, and polygonal (to represent an area that is irregularly shaped and has up to 20 sides).  For an area source, you must determine the release height above ground.  For example, a tank open to the atmosphere would have a release height equal to the tank height.  For a landfill surface, the release height would be zero.

·        Volume Sources – Volume sources are used to model releases that occur over a three-dimensional volume.  Examples of volume sources include fugitive leaks, multiple vents, gas stations, wipe cleaning and solvent use.  Volume sources require a release height which is the height above ground at the center of the volume.  An irregularly shaped volume can be represented by dividing the volume source into multiple smaller volume sources.

·        Line Sources – Line sources are used to model releases from a variety of sources including roads, rail lines, and conveyor belts.  AERMOD also allows line volume sources, which are volume sources arranged in a line.  The SDAPCD typically uses this source type to represent heavy duty truck travel on unpaved haul roads as they are good at simulating the kicking up of dust by the trucks’ wheels.

Meteorological Data

SDAPCD-processed meteorological data should be used.  The SDAPCD has processed meteorological data with the latest version of the EPA AERMET preprocessor that converts the raw data into an AERMOD-ready meteorological data input file.  For more information on AERMET the user’s guide is at:


Please contact the SDAPCD to get the meteorological data for the site most appropriate for a modeling project.


The receptor network must include adequate coverage to capture the maximum ground level concentration.  The receptor network should include a regularly spaced grid and include property boundary receptors.  To limit the total number of receptors in a modeling, there is the option to have a denser grid of receptors closer to the source, and a coarser grid further away from the source.

A Health Risk Assessment (HRA) takes the expected airborne concentrations of toxic air contaminants from the project being evaluated and calculates the potential health risk to the surrounding population due to the project.  The California Air Resourced Board (CARB) has developed the HARP program (Hotspots Analysis and Reporting Program, available for free at: https://ww2.arb.ca.gov/our-work/programs/hot-spots-analysis-reporting-program) to take the concentrations from the air dispersion modeling software and calculate the health risks.  This program incorporates the California Office of Environmental Health Hazard Assessment’s (OEHHA’s)  Risk Assessment Guidelines for determining the risks (available at: https://oehha.ca.gov/air/crnr/notice-adoption-air-toxics-hot-spots-program-guidance-manual-preparation-health-risk-0).  In addition to the OEHHA Guidelines, the SDAPCD has published Supplemental Guidelines for how dispersion modeling and risk assessments should be conducted for projects within San Diego County (available at: https://www.sdapcd.org/content/dam/sdapcd/documents/permits/air-toxics/Hot-Spots-Guidelines.pdf). 

The types of health risk that must be calculated include the residential 30-year cancer risk, the occupational 25-year cancer risk, the non-cancer chronic health hazard index (HHI), the non-cancer 8-hour chronic HHI, the non-cancer acute HHI and the cancer burden (70-year exposure).  These risks shall each be made for the maximally exposed individual resident (MEIR), the maximally exposed individual worker (MEIW), the maximally exposed short-term receptor (if different than the MEIR or MEIW), as well as at nearby sensitive receptors.  If the project will have lead (Pb) emissions, the non-cancer sub-chronic (30-day average) lead risk must also be determined, following the CARB Lead Risk Management Guidelines (available at: https://ww2.arb.ca.gov/resources/documents/lead-risk-management-guidelines).

District Comment Letters

Commenting Agency

The District may provide comments on projects in which there is no District approval necessary as a commenting agency. Comments are prepared when it would be beneficial to protect public health, improve air quality or if inaccuracies are found in the document.   Comments are submitted to the Lead agency responsible for the project.

Responsible Agency

When the District proposes to carry out or approve a project, for which a lead agency is preparing or has prepared an EIR or negative declaration. For the purposes of CEQA, the term “responsible agency” includes all public agencies other than the lead agency which have discretionary approval power over the project.

Lead Agency

When the District is the public agency which has principal responsibility for carrying out or approving a project which may have a significant effect upon the environment, CEQA documents are prepared and other agencies and or the public may provide comments.



2024 Lead Agency Letters

Silver Lining Cremations 1/9/24

2022 Lead Agency Letters

Silver Lining Cremations 3/1/22

Stay Informed

The California Environmental Quality Act statute and guidelines are available from the Governor's Office of Planning & Research website.

Questions for the District should be sent via email or phone (858) 586-2600.