OSWI Redefined: U.S. EPA’s Final Amendments on Waste Combustion Regulations

On June 30, 2025, the U.S. Environmental Protection Agency (U.S. EPA) announced multiple final amendments to the Other Solid Waste Incinerators (OSWI) standards based on its review of 40 CFR Part 60, Subparts EEEE and FFFF required by Clean Air Act (CAA) section 129(a)(5). These guidelines cover new and existing “other” solid waste incineration units not otherwise governed by CAA section 129.

What Units do These Rule Changes Affect?

• Very small municipal waste combustors (VSMWC) used by any state, local, or tribal governments, and industrial or commercial facilities
• Institutional waste incinerators (IWI) used by correctional institutions
• OSWI units used by any of the following: nursing or residential care facilities, federal government agencies, educational institutions, churches and convents, and civic or religious organizations

These changes do not affect any other incineration or combustion units referenced in CAA section 129.

What are the Key Changes?

In the final amendments, the focus of the “municipal solid waste” definition shifts from where waste is collected to the source and type/nature of the waste. This change allows for small commercial or industrial incinerators that combust a minimum of 30% municipal solid waste (MSW) to be held to OSWI requirements, and not the MSW rules. Similarly, small remote incinerators that combust 30% or more MSW are now subject to OSWI standards. The final rule also defines “rudimentary combustion devices” to address common challenges with operating small, primitive incinerators that cannot adhere to the latest emissions and testing standards (most are not equipped with stacks). However, the rule does not set standards for these devices, meaning any state or local standards will continue to apply.

The final rule creates additional subcategories for VSMWC and IWI units based on combustion capacity in tons per day (TPD). The units that have a capacity below 10 TPD can use Substitute Means of Compliance Demonstration (SMCD) to reduce the financial and technical challenges associated with testing some smaller units. The finalized SMCD includes an option for using a “representative” initial compliance demonstration, found in U.S. EPA’s WebFIRE Database. Continuous compliance for VSMWC and IWI units with a capacity less than 10 TPD can be demonstrated using an Alternative Waste Characterization (AWC) option, also finalized in this rule, that requires additional recordkeeping and reporting. See the following table for a breakdown of the new subcategories and the respective capacities.

New Subcategories for VSMWC and IWI Based on Combustion Capacity

The new subcategories also include new emissions limits for units with a capacity less than 10 TPD of solid waste. The emissions limits were published by U.S. EPA in These updated emissions limits better reflect actual emissions data provided by industry.

What Can ALL4 Do to Help?  

Navigating changes to and applicability of regulatory proceedings can be a difficult task, but ALL4 is here to help. For assistance with or questions in regard to the amended OSWI standards, please contact Molly Palmer at mpalmer@all4in.com or Amy Marshall at amarshall@all4inc.com.