The Bay Area Air District (the District) adopted amendments to Regulation 11, Rule 18: “Reduction of Risk from Air Toxic Emissions at Existing Facilities” (Rule 11-18) on June 3, 2026.
A Quick Refresher
What is Rule 11-18 and Who is Subject?
Rule 11-18 is the Bay Area Air District’s Facility Risk Reduction Program for reducing public exposure to toxic air contaminant (TAC) emissions from existing facilities. Facilities with elevated health risks may be required to conduct a Health Risk Assessment (HRA) and, if necessary, implement a Risk Reduction Plan (RRP). The District identifies facilities subject to Rule 11-18 through a risk-based prioritization process and publishes affected facilities on its Phase I and Phase II facility lists. The rule applies broadly to toxic risk facilities that must report TAC emissions under California’s Air Toxics “Hot Spots” Information and Assessment Act. Facilities can review the current lists on the Air District’s Facility Risk Reduction Program webpage to determine whether they may be subject to Rule 11-18 requirements. Examples of facilities exceeding the Rule 11-18 prioritization score thresholds include petroleum refining, electric power generation and cogeneration, waste management and landfills, wastewater treatment, chemical manufacturing, metals and materials processing, semiconductor and advanced manufacturing, and large institutional facilities such as universities and laboratories.
Exemptions under Rule 11-18 are limited. Facilities are exempt only if they consist solely of emergency-use stationary diesel generators and have a prioritization score below 250, or if they are a retail gasoline dispensing facility (GDF) with a prioritization score below 250.
Key Changes Included in the Final Rule
Since the October 2025 release of the proposed amendments, the District received comments from regulated facilities, community organizations, industry groups, and other stakeholders. Following consideration of stakeholder feedback, the District adopted the final amendments on June 3, 2026. Several notable changes were made between the initial proposal and the final adopted rule, as summarized below:
- Health Risk Assessments (HRAs) will generally be prepared by facilities. The final amendments maintain the proposed shift from District-led HRAs to facility-prepared HRAs, although the District will continue to review and approve submitted assessments and has committed to conducting HRAs for qualifying small businesses. A Rule 11-18 HRA requires substantial technical resources, including detailed emissions inventory development, site-specific dispersion modeling, risk assessment expertise, and preparation of modeling protocols and HRA reports that can be independently reproduced and reviewed by the District.
- Dispute Resolution Panel (DRP) eligibility was significantly narrowed. The DRP was initially established as part of a settlement agreement with the Western States Petroleum Association to provide independent technical review of disagreements regarding emissions inventories, HRA, and risk reduction requirements. The final adopted Implementation Procedures limit DRP eligibility to disputes between refineries and the District and allow each request to raise no more than three technical issues. Non-refinery facilities do not have access to the DRP and must address technical comments or concerns through the District’s standard HRA review process.
- Updated compliance deadlines. Following stakeholder feedback regarding the feasibility of the proposed schedule, the District revised several key implementation deadlines in the final rule. The final adopted timelines are summarized below:
- 60 days to complete site-specific modeling protocol after receipt of District notification.
- 30 days to implement revisions to site-specific modeling protocol.
- 90 days to submit draft Preliminary HRA Report after approval of site-specific modeling protocol.
- 30 days to implement revisions and resubmit draft Preliminary HRA Report.
- 90 days public comment period for the Preliminary HRA Report.
- 30 days to implement and resubmit the draft final HRA report if public comments necessitate further revisions.
- District notifies Facility of final HRA results and publishes Final HRA on District’s website.
- District review timelines were removed. While the final rule establishes deadlines for facility submittals and responses, it does not impose corresponding deadlines for the District to complete its review or provide comments on submitted materials.
What Facilities Should Do to Prepare?
Affected facilities should begin preparing before receiving a District notification. Facilities currently listed on the District’s Phase I or Phase II lists may have limited time to validate emissions data, resolve data gaps, develop a site-specific modeling protocol, run and refine dispersion models, interpret risk results, and prepare a reproducible HRA once the formal schedule begins. Early planning can reduce the risk of compressed schedules and avoidable revisions during District review.
Trinity recommends facilities consider taking the following steps:
- Reviewing current toxic emissions inventory and supporting documentation.
- Evaluating whether updates to emissions data could affect Prioritization Score or future HRA results.
- Identifying potential data gaps, modeling needs, or other technical issues before receiving a District notification.
- Conducting preliminary planning for HRA development to better understand potential compliance obligations and avoid compressed project schedules.
Trinity can help facilities proactively prepare for Rule 11-18 requirements through emissions inventory reviews, Prioritization Score evaluations, air dispersion modeling, HRAs, RRPs, and overall compliance strategy development. By beginning the evaluation process early, facilities can gain a better understanding of potential HRA outcomes, identify opportunities for refinement, and approach the Rule 11-18 process with confidence rather than reacting to results and deadlines after receiving a District notification.
If you would like to discuss the how Rule 11-18 may affect your facility or are interested in any of the services described above, please contact Emily Wen and/or Jessica Evangelista in Trinity’s Oakland office or call 510.285.6351.
