Cumulative Air Toxics – South Coast AQMD is Developing New CEQA Methods Impacting New Construction, Major Projects and Permitting

Environmental Consulting

10/02/2025

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Introduction

Cumulative air toxic impacts are defined as the total burden to local communities, including long-term exposure from multiple air toxins and hazardous pollutants. Communities which suffer from exposure to cumulative air toxins also tend to have low incomes and minority populations, referred to as disadvantaged communities. Regulations which look at managing cumulative air toxic impacts are evolving at the local and national level and tend to be intertwined with environmental justice and public health concerns. This article reviews new California Environmental Quality Act (CEQA) methods under development with South Coast Air Quality Management District (South Coast AQMD).

These new cumulative air toxics methods could cause more complex evaluations for some new constructions, major projects and permit applications, adding time and costs to the CEQA process. While this regulation is currently under development, once adopted it could apply to a range of major industrial permit applications as well as major land use projects triggering CEQA in the South Coast Air Basin.

Background – Air Toxics Monitoring

In the 1980s, South Coast AQMD started collecting regional air toxics data with their first Multiple Air Toxics Exposure Study (MATES), published in 1987. This was the first major data collection effort on cumulative air toxics in the US and initiated the investigation into the relationship between public health and environmental justice. In 1996, the US EPA started collecting and assessing national air toxics data, then called National Air Toxic Assessment or NATA, now AirToxScreen.

By the 2000’s, South Coast AQMD were tying their MATES investigations into their environmental justice workplan. This tied key impact and permit thresholds to their goal of reducing health risk impacts on disadvantaged communities. They continue to collect data and document the substantial reductions in air toxics between the 1980s and today. Initially, cancer risk levels were 4000 or more in a million in the 1990s; risk levels have come down to 600-1,000 in a million for MATES V (See Figure 1 below). Even so, the regional emissions show the cumulative risk levels continue at well above the 10 in a million-cancer risk threshold.

Figure 1. MATES V Cancer Risk Levels

Background – State and Local Air Toxics Reporting Regulations

In parallel to the air toxics monitoring described above, the California Air Resources Board (CARB) and local air districts have developed the following air toxics reporting regulations:

Annual Emissions Reporting or Inventories – required at local air district level and may include reporting of some air toxics
AB 2588 – established in 1987, the Air Toxics Hot Spot Information Act requires stationary sources to report the types and quantities of certain substances their facilities routinely release into the air.
AB 617 – Also known as the Community Air Protection Program (CAPP), established in 2017, and includes fenceline monitoring and emission reduction programs in designated disadvantaged communities with strategies to reduce health impacts.
Criteria Pollutant and Toxics Emissions Reporting (CTR) – effective in 2020, supports the mandates of AB 617, AB 2588, and other emissions reporting requirements; requires annual reporting of criteria pollutants and toxic emissions from subject facilities; and provides the public access to air toxics emissions data.

These reporting programs are used to support rule development to reduce public health impacts from air toxics emissions. With the implementation of these recent air toxics programs, South Coast AQMD started to review their cumulative CEQA impacts methods and question if it was still relevant for air toxics, as discussed in the next section.

New CEQA Policy Development for Cumulative Air Toxics Assessment

As part of the process of updating its 1993 “Air Quality Guidance Handbook,” South Coast AQMD staff is updating existing and developing new air quality analysis guidance to address CEQA requirements for direct, indirect and cumulative impacts. South Coast AQMD developed a white paper that historically supported the rationale that if a project’s incremental impacts were below the thresholds of significance for that resource category, then the project’s incremental contribution was not cumulatively considerable (White Paper on Potential Control Strategies to Address Cumulative Impacts for Air Pollution).
In 2003, this was considered a forward-looking comprehensive strategy for addressing cumulative impacts of air pollution at the regional and local level. Born out of South Coast AQMD’s adoption of Environmental Justice Initiatives, the intent of 2003 White Paper was to identify both regulatory and policy options to address cumulative impacts from air toxics.

However, South Coast AQMD has since found that although a project’s environmental effects may be individually limited, in some circumstances, its incremental effect may be cumulatively considerable (CEQA Guidelines Section 15064(h)). And the on-going MATES data illustrates concerns about high levels of cumulative health risks in some locations. Further, a legal challenge in the South Coast Air Basin revealed deficiencies in the 2003 white paper (People of the State of California v. City of Fontana, San Bernardino Superior Court, Case No. CIVSB2121829, referred to as the CA Department of Justice case). The South Coast AQMD has been working with a stakeholder group since 2022 to collect input and explore enhanced qualitative cumulative analysis and new quantitative cumulative analysis as part of its process to update its cumulative air toxics analysis thresholds and methods. Further, South Coast AQMD has an existing mapping tool for looking up cancer risk levels within MATES V.

Development of New Policy

As part of the analysis deliberations, some project and land use types have lower potential cancer risk impacts than other others, and thus have been split into three groups:

Low Cancer Risk Impacts (residential, commercial, recreational, educational, and retail)
Medium Cancer Risk Impacts (truck yard, gas station, linear roads)
High Cancer Risk Impacts (Heavy industrial, major transportation activities, and major planning projects)

From these groupings, those projects which do not require a cumulative air toxics impact analysis can be identified and include:

Land use projects with low or no air toxic emissions
Projects which qualify for a CEQA statutory, ministerial, or certain categorical exemptions
Individual projects tied to a larger regional project (e.g., general plan, specific plan and others)
Projects for a lead agency with its own cumulative impact guidance

The goal of the new cumulative air toxics policy is to provide a multilayered and streamlined qualitative and quantitative analysis for those CEQA projects that warrant more analysis. Further, an updated cumulative air toxics guidance will provide a resource for lead agencies in the air basin, address the CA Department of Justice CEQA case law, ensure that cumulative air toxics will be assessed adequately, and promote equity. This updated cumulative air toxics guidance is not intended to stop projects or require Environmental Impact Report (EIR) for all CEQA projects.

New project-level methodology and criteria are being tested, and stakeholder comments are welcome. The current proposed process for project-level analyses is as follows. First, one needs to determine the initial cumulative threshold, which will be determined based on the MATES percentile for the project location. Then, identify if the project triggers any of the following:

Criterion #1: High Volume Diesel-Fueled Trucks along truck route
Criterion #2: Sensitive Receptor Population – AB 617 communities or SB 535

For Criterion 1, truck trips are estimated at the nearest truck route as follows: [most recent Caltrans truck trips + Proposed Project truck trips + future truck trips (if known) – 2018 Caltrans truck trips]. Where the truck trips are 951 or greater, this criterion is triggered. South Coast AQMD provided a map showing where the AB 617 and AB 535 communities are located. The cumulative cancer risk is recalculated for each project to then determine if the project’s contribution is cumulative significant. If yes, then an EIR and a health risk assessment would be required.

As South Coast AQMD is proceeding with developing a draft guidance document to implement the proposed revised policy/methodology for analyzing cumulative impacts from air toxics, they are soliciting stakeholder feedback. For more information, check out this CEQA Policy Development (New) webpage.

In conclusion, South Coast AQMD is a leader in developing new policies and programs and typically influences the eventual development of new state and federal air pollution control policies and programs. If you are planning to develop a major project in the South Coast Air Basin with sources of air toxics, high levels of diesel truck movements, and/or in an AB 617 or SB 535 community, this emerging policy could affect your permitting budgets and schedules.

If you would like to discuss and review how this developing cumulative air toxics requirement may impact your upcoming facility permitting, please contact Valerie Rosenkrantz.