Bay Area Air District Proposed Amendments to Regulation 11 Rule 18: Reduction of Risk from Air Toxic Emissions at Existing Facilities

Environmental Consulting

10/22/2025

Share it with the world!

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.

Trinity has also developed a flow chart of the Rule 11-18 process based on the draft amendments.

Trinity attended the public workshop on the draft amendments to Rule 11-18 on October 2, 2025. Key highlights of the public workshop are summarized as follows:

The presentation slides summarizing the key changes are published for review.
There will be two “phases” to the amendments. Phase 1 is focused on efficiency and expediting implementation. The District plans to bring the Phase 1 amendments proposal package to the Board of Directors in Q2 2026. Accordingly, Phase 2 of proposed amendments, which will focus on stringency, will follow after the Phase 1 amendments are adopted.
The public comments verbally received after the presentation and from the Q&A chart were as follows:

Question	Answer
If the Preliminary HRA incorporates revisions as a result of the public comments, will there be another 90-day public review period to review the revised Preliminary HRA?	The District confirmed that in this situation there would only be one 90-day public comment period. The District acknowledged the concern that if changes are incorporated to the HRA after the public comment period, the public would not have another opportunity to review and comment on the revised Preliminary HRA.
Please clarify what a Legacy vs Non-Legacy facility means?	Legacy facilities are those that already have a District-approved modeling protocol in place. The District also made the comment that this only applies to Chevron. The District also clarified that anyone that has submitted a modeling protocol at this point but has not heard back from the District will be treated as Non-Legacy.
What happens if a facility has performed a recent source test to revise the emissions inventory but does not hear back from the District’s source test division approving the results by the time the draft preliminary HRA is due?	The District has added procedures for this situation within the amendments. Refer to Section 11-18-405 for additional details on how to incorporate this flexibility within the draft preliminary HRA report and what the potential outcomes may be. There is a situation in which two versions of a Risk Reduction Plan may need to be prepared (one that includes additional emissions data and the other under the assumption the additional emissions data is denied).
Who will be preparing the emissions inventory and which party is providing comments on the emissions inventory?	The District will share its emissions inventory to the facility when the notification to prepare an HRA is sent. Facilities may then request for changes to the emissions inventory, which the facility can propose as part of the draft preliminary HRA report. The District will then review the draft preliminary HRA in tandem with the revised emissions inventory.
Since the HRA is sensitive to the emissions inventory, wouldn’t the described process result in multiple rounds of review?	The District acknowledged that multiple rounds of review may be needed. The District anticipates that the draft Preliminary HRA results will be needed to determine whether to approve the requested emission inventory changes. Trinity commentary: We have submitted a comment to the District to consider reviewing requested changes to the emission inventory as part of the draft modeling protocol instead of the draft preliminary HRA.
How is the District going to prioritize the notifications to subject facilities?	The District plans to stagger notifications to account for load-balancing of the District's staff. The District will generally send out notifications for Phase I facilities located in AB617 communities first.
When will tailpipe emissions from non-motor vehicles need to be included?	Non-motor vehicles will be assessed if they are part of a facility’s normal, ongoing operations. Examples include locomotive engine emissions from on-site rail travel, hoteling emissions from ships while docked at a facility, emissions from 50 bhp or higher portable engines owned by a facility or remain for more than 12 months, and emissions from 50 bhp or higher portable engines that are operated for periods of 72 hours or more per event.
Where can the socioeconomic impact study of the Phase 1 amendments be found?	This will be published with the proposed rule amendment materials in the first half of 2026 as part of the final proposal submitted to the Board for their consideration.
What is the general guideline from the District regarding which operational year to use for the emission inventory?	District will first consider the most recent data but will compare the data with approved inventories from the previous five years in order to determine the trend to ensure representativeness.

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.

Interested parties can read the proposed amended rule language and accompanying documents on the Rule 11-18 2025 Amendments page.

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.

The level of stress within our organization has reduced dramatically since partnering with Trinity. They offer proactive support to our mission and are always available to answer questions, provide insights, and ensure that our business plays within the rules, en route to achieving profitable growth.

EHS Director /Large Packaging Company