SCS Technical Bulletin 2026: California AB 28: Subsurface Elevated Temperature Events At Solid Waste Landfills

OVERVIEW OF AB 28

Assembly Bill 28 was signed by the Governor on September 20, 2026, and is now law in California. The bill adds Sections 43031 and 43031.2 to the Public Resources Code and establishes a notification, corrective action, and penalty framework for solid waste landfills experiencing a subsurface elevated temperature event.

Some elements of AB 28 are directly referenced in the revised California Air Resources Board (CARB) Landfill Methane Regulation (LMR). Where the LMR governs monitoring and operating standards, AB 28 gives regulators authority to compel corrective action, require financial assurance, and assess civil penalties when elevated temperature conditions exist.

Key impacts include:

• Trigger is 131°F wellhead or waste temperature “over a substantial areaˮ
• Mandatory notification to eight state and local agencies
• Agency-directed corrective action plans, cost assessments, and financial assurance
• Administrative civil penalties of up to $100,000 per day
• Authority to pursue parent companies for unrecovered costs
• Community health assessments and air monitoring funded by the owner or operator

Implementing guidance and possible companion regulation(s) are still pending. Landfill owners are recommended to screen their wellfield temperature data against the 131°F threshold now and evaluate whether notification criteria may apply at their sites, especially where multiple gas wells are showing elevated temperatures.

About SCS Engineers

As an environmental engineering, consulting, and contracting firm with a strong portfolio in landfill gas collection and control systems (GCCS), SCS Engineers (SCS) can help California landfill owners and operators evaluate and respond to AB 28. We have extensive experience with elevated temperature landfill events, corrective action programs, closure and post-closure cost estimating, financial assurance, and multiagency regulatory coordination. In California, SCS has assisted over 80 landfills with LMR compliance and participated in industry discussions during the development of AB 28.

Because AB 28 and the LMR both key off wellhead temperature, the two are best addressed together. As an initial step, we recommend reviewing your wellfield data to identify wells persistently above 131°F, the extent and clustering of those wells, and the operational factors driving the temperatures, followed by a combined AB 28 and LMR compliance strategy.

For more information, contact:

Pat Sullivan, REPA, CPP, BCES, Senior Vice President, , www.scsengineers.com

SUMMARY OF AB 28

Effective Date and Implementation

AB 28 was signed on September 20, 2026, and is effective now. Unlike many bills, it carries no deferred January 1 operative date. But it also does not have specific requirements that must occur on a defined schedule.

The statute leaves significant details unwritten. CalRecycle is authorized to adopt regulations, and emergency regulations filed under this authority remain in effect for two years or until revised. Additional guidance is anticipated on the definition of “substantial areaˮ and on how remediation cost assessments are to be prepared. Whether the framework ultimately arrives as formal regulation or as agency guidance is not yet clear.

Applicability

The law applies to solid waste landfills as defined in Section 40195.1, with the following exclusions:

• Landfills receiving only hazardous waste
• Landfills containing only construction and demolition wastes, inert wastes, or non-decomposable wastes
• Landfills with fewer than 450,000 tons of waste-in-place

The 131°F Trigger

A subsurface elevated temperature event is defined as an event where subsurface gas or waste temperatures persistently exceed 131 degrees Fahrenheit (°F) over a substantial area, together with other performance criteria to be determined by CalRecycle.

Two points deserve attention:

• 131°F is not an LMR violation. Under the LMR, 145°F is the compliant temperature and 131°F drives enhanced Under AB 28, 131°F is the entry point to a far more consequential process.
• “Substantial areaˮ is: The statute does not state a well count, a percentage of the wellfield, or whether affected wells must be contiguous.

AB 28 is separate from the air regulations and does not recognize approved higher operating values (HOVs). Sites relying on HOVs should not assume those approvals offer protection under this law, especially since the LMR will require all previous HOVs and alternatives to be reconsidered.

Notification Requirements

If a subsurface elevated temperature event occurs, the owner or operator must notify all of the following agencies:

• CalRecycle
• State Water Resources Control Board
• CARB
• The local enforcement agency (LEA)
• The local air pollution control district
• The local health department
• State Department of Public Health
• The appropriate regional water quality control board

The owner or operator must also provide subsurface gas and waste temperature data to these agencies when requested by CalRecycle. In practice, a notification should be expected to generate a broad follow-on data request covering gas data, water levels, and leachate information.

Corrective Action

The owner or operator must take the actions CalRecycle deems necessary to mitigate and resolve the event, which may include developing a corrective action plan. If a corrective action plan is also required under Section 95469 of Title 17, the plan adopted under AB 28 may not conflict with it.

If a Corrective Action Plan Is Required

CalRecycle may require the owner or operator to do one or more of the following:

• Complete a cost assessment for fully implementing the plan, including cleanup, abatement, other remedial actions, and reimbursement of the multiagency coordination group
• Provide evidence of financial ability sufficient to address implementation costs, in addition to existing Title 27 of California Code of Regulations (CCR) financial assurance requirements
• Revise the closure and post-closure maintenance plan to account for the added costs

The statute does not prescribe a methodology for the cost assessment. Financial assurance is expressly tied to Title 27, which carries very different practical consequences for large private operators able to post a letter of credit compared to smaller private owners required to fund an account. It is unclear if this new cost of corrective action will be covered by existing financial assurance mechanisms or if it requires something different.

Multiagency Coordination

The Secretary for Environmental Protection may select and coordinate a multiagency coordination group to investigate and recommend a path to resolution. The group may include CalEPA and its boards, departments, and offices, the State Department of Public Health, the local air quality management district, the local health department, the LEA, and U.S. EPA.

CalRecycle may also, at its sole discretion, become the enforcement agency for all or part of a landfill and recover its reasonable and necessary costs from the owner or operator.

Jurisdiction returns to the LEA when CalRecycle determines whether the event has been satisfactorily mitigated or resolved, or sooner at its discretion.

Health Assessment and Air Monitoring 

Health Assessment

If the coordination group recommends a health assessment, the owner or operator must fund the local health department to conduct it, covering all reasonable and necessary anticipated expenses. The assessment is informed by the CDC CASPER Toolkit.

• The local health department must initiate the assessment within 60 calendar days of receiving recommendations
• Findings are posted on the health department website and on the facility website
• Findings are reported to the county board of supervisors or city council in a public meeting, with opportunity for public comment
• Subsequent assessments may be requested no sooner than two years after the most recent one, while the event continues

Air Monitoring

Upon request of the coordination group, the owner or operator must:

• Submit an onsite and offsite air monitoring and sampling plan within 30 days of the request
• Revise and resubmit within 30 days of a request from the local air district or the coordination group
• Begin implementation no later than 30 days after submittal, unless an extension is granted in writing

Penalties and Cost Recovery

Administrative Civil Penalties

CalRecycle or the LEA may impose administrative civil penalties of up to $100,000 per day for failure to comply with the notification, data, or corrective action provisions, or with any implementing regulation. No penalty accrues before the 31st day after a notice of violation is issued. These penalties are used as described below.

Landfill Subsurface Fire Mitigation Community Fund

Penalties are deposited into a newly created fund in the State Treasury and are continuously appropriated to the California Alternative Energy and Advanced Transportation Financing Authority. Funds are paid to counties where an event occurred to compensate affected residents for loss, damages, expenses, relocation, suffering, reduced real property value, closing costs, and inconvenience.

Agency Cost Reimbursement

The owner and operator must reimburse members of the multiagency coordination group and the local health department for all reasonable and necessary costs, on a monthly basis, including hourly staffing and overhead rates. Reimbursement is made directly to each agency that incurred the cost.

Parent Company Liability

If the owner and operator cannot sufficiently cover corrective action and reimbursement costs, the Attorney General may pursue an action against the parent company. The statute states that this provision does not itself create a cause of action or liability.

Key Operational Implications

• A temperature threshold that is not a violation under the LMR becomes the entry point to an enforcement process with substantial financial exposure
• Eight agencies receive notification and data, each with its own information requests and cost recovery
• Corrective action costs, financial assurance, and revised closure and post-closure plans can follow quickly once a plan is required
• Corporate structures separating subsidiary operators from parent companies provide less insulation than under prior law
• The absence of implementing guidance means near-term notification decisions are site-specific judgments

Strategic Recommendations

Immediate Actions

• Screen wellfield data to identify wells persistently above 131°F, how far above the threshold they run, and whether they cluster
• Build a watch list of wells in the mid-to-high 120°F range so rising trends are caught early
• Evaluate, on a site-specific basis, whether notification criteria may be met
• Review reliance on higher operating values and plan for their loss

Operational Adjustments

• Determine the source of elevated temperatures and plan corrective action accordingly.
• If the source is a subsurface oxidation event, focus on limiting oxygen intrusion into the affected area.
• If the source is a potential subsurface reaction, focus on heat
• Address liquids as a heat retention driver, recognizing that pumping down a well may cause a short-term temperature increase before temperatures decline
• Review and document any leachate or liquids reinjection practices
• Evaluate wellfield adjustments, including opening wells and well inserts, to draw heat out of affected areas

Planning and Budgeting

• Incorporate AB 28 into LMR gap assessments so both rules are addressed in a single compliance strategy
• Confirm that closure and post-closure cost estimates can be updated on short notice
• Assess financial assurance capacity against a potential corrective action obligation
• Track CalRecycle guidance, workshops, and any companion rulemaking

Conclusion

AB 28 carries considerably more enforcement weight than the monitoring and corrective action provisions of the LMR alone. It is effective now; its central trigger sits below the LMR-compliant temperature, and certain key terms remain undefined pending guidance.

Landfill owners and operators with wells persistently above 131°F should treat temperature management as a near-term priority rather than a deferred capital decision. Early data review, a clear understanding of what is driving elevated temperatures, and a documented mitigation approach will place a facility in a far stronger position if an agency inquiry and enforcement of AB 28 arrives.

For more information, contact:

Pat Sullivan, REPA, CPP, BCES, Senior Vice President, , www.scsengineers.com