The Bay Area Air District (the District) released draft amendments, draft implementation procedures, and a preliminary staff report for Regulation 11, Rule 18: Reduction of Risk from Air Toxic Emissions at Existing Facilities (Rule 11-18) on August 28, 2025. The amendments aim to expedite the Health Risk Assessment (HRA) and Risk Reduction Plan (RRP) approval steps and expedite implementation within the District. Rule 11-18 was originally adopted in 2017 to align with Assembly Bill 2588 (AB 2588), aiming to provide a mechanism to evaluate, and reduce if needed, the impact of toxic air contaminant (TAC) emissions from existing facilities. Subject facilities are categorized as Phase I and Phase II facilities, based upon their Prioritization Score. Rule 11-18 as adopted allows the District to evaluate the effects of all higher risk permitted operations alongside the scope of New Source Review (NSR) regulations.
The timeline below demonstrates the key milestones in the Rule 11-18 process.
Rule 11-18 Implementation Overview
Rule 11-18 Draft Amendments
The key proposed amendments to Rule 11-18 include the following:
Reconsideration of Prioritization Score
The District added Section 11-18-404 which allows a Facility to request that their prioritization score be reevaluated using a revised toxic emission inventory. The Facility must submit this request within 30 days of the District’s notification that an HRA is required. In this request, the Facility must provide the District with a recalculated prioritization score, calculated in accordance with Rule 11-18, Appendix A. The District may or may not withdraw the requirement for the Facility to prepare an HRA as a result. A request for reevaluation of the prioritization score does not alter the HRA preparation timeline outlined above.
Health Risk Assessments (HRAs)
Upon notification from the District, subject facilities are required to prepare preliminary HRAs. HRA procedures are outlined in the proposed Section 11-18-402 and are summarized below. The largest update is allowing third-party contractors to conduct HRAs on behalf of facilities and allowing for reconsideration of Prioritization Score.
- The District will notify the Facility that the Facility must prepare an HRA based on their Prioritization Score calculated using data submitted during permitting and the annual data update.
- The Facility or its contractor must prepare and submit a site-specific modeling protocol, within 45 days of receiving the notification above.
- The District will review the modeling protocol and provide approval or request revisions. The Facility will then have 14 days to implement requested revisions.
- Following approval of the site-specific modeling protocol, the Facility has 90 days to conduct and submit the preliminary HRA report, along with information necessary to reproduce the preliminary HRA results, including:
- District-provided toxic emissions inventory and documentation and rationale of any updates,
- Toxic release data and source parameters,
- Facility boundaries and surrounding receptors,
- Air dispersion modeling files, and
- Supporting electronic files.
- The District will review the preliminary HRA report and provide approval or request revisions. The Facility will then have 14 days to address and implement any requested revisions. There may be multiple round of revisions needed, as determined by the District, which each have a 14-day timeline.
- The finalized preliminary HRA will be subject to a 90-day public comment and review period, after which the District can request additional revisions which must be addressed and implemented within 14 days. The Facility can request an additional 30 days with sufficient justification.
- The District will notify the Facility of its final HRA results and determine if the facility’s health risk equals or exceeds any risk action level (RAL) set forth in Section 11-18-217.
Risk Reduction Plans (RRPs)
Facilities that exceed at least one RAL must submit a draft RRP within 180 days of notification from the District. The District may allow additional time upon request. The contents of the RRP, as outlined in Section 11-18-403.2, have not been amended. The draft RRP review timeline, outlined in the proposed Sections 11-18-403.3 through 11-18-403.7, are summarized below.
- After the Facility has submitted the draft RRP, the District has 60 calendar days, previously 20 business days, to review.
- The Facility will have 45 days to implement requested revisions. If the District determines the revised plan is still inadequate, the Facility has one additional opportunity to revise the plan in 45 days.
- The finalized preliminary RRP will be subject to a 45-day public comment and review period, after which the District can request additional revisions which must be addressed and implemented within 45 days.
- The District will publish the approved RRP on the District’s website within 30 days of approval.
Rule 11-18 Draft Implementation Procedures
In addition, the District published amendments to the draft 2024 implementation procedures, which are non-binding procedural guidelines developed to support uniform implementation of Rule 11-18. The amendments focused on aligning the procedures with Rule 2-5 and
CAPCOA Prioritization Score procedures, identifying that facilities would be responsible for HRAs instead of the District, and revising Section 5, Dispute Resolution Panel (DRP). The DRP is a panel of technical experts that will advise the District regarding technical disputes that may arise from the implementation of Rule 11-18. Revisions to DRP implementation procedures include:
- Limiting DRP eligibility to disputes between the District and refineries
- Requiring submission content to identify specific disagreements, propose specific remedies, and include supporting documents.
- Limiting the scope of disputes
- Limiting the Facility to one request to convene a DRP for the HRA and one request for the RRP. Each request is limited to three issues.
Future Rule 11-18 Amendments
The District plans to make additional amendments to Rule 11-18 focused on increasing rule stringency, such as reevaluating risk action levels, and making general rule improvements to improve rule clarity, transparency, and implementation. The District does not have a timeline for initiating these additional amendments.
The public workshop will be held virtually via
webcast (links and other information are provided under the “Public Workshop” section). Interested parties can read the proposed amended rule language and accompanying documents on the
Rule 11-18 2025 Amendments page. Written comments can be submitted via email at
[email protected] or via mail to 375 Beale St., Suite 600, San Francisco, CA 94015 by 5:00 PM on October 13, 2025. Comments will also be accepted during the public workshop.
Trinity is Available to Help
If the proposed Rule 11-18 amendments impact your Facility, Trinity is available to support, which may include the following:
- Review and prepare toxic emission inventories, air dispersion modeling files, and gap assessments;
- Recalculate prioritization scores;
- Prepare site-specific modeling protocols and HRAs;
- Prepare RRPs;
- Evaluate control technologies to reduce emissions and risk; and
- Address questions regarding Rule 11-18 requirements and timelines.
If you would like to discuss the amendments to Rule 11-18 and how they may impact your facility or are interested in any of the aforementioned support, please contact
Stephen Cao and/or
Emily Wen in Trinity’s
Oakland office or call
510.285.6351.
