EPA Updates Clean Air Act Standards Applicable to Small Waste Incinerators
On June 30, 2025, the U.S. Environmental Protection Agency (EPA) finalized updates to its New Source Performance Standards (NSPS) and Emission Guidelines for Other Solid Waste Incineration (OSWI) units under the Clean Air Act (CAA). These units — combustion systems that incinerate solid waste from commercial or institutional sources not otherwise regulated under specific incinerator categories — include very small municipal waste combustors and institutional incinerators. The final rule includes applicability-related and definitional changes expanding the class of incinerators subject to NSPS, revises the OSWI subcategories and tightens emission limits for key pollutants. It also adopts changes to startup, shutdown, and malfunction (SSM), and expands testing, monitoring, reporting, and recordkeeping requirements that will affect both existing and new OSWI units.
D.C. Circuit Largely Vacates EPA State Implementation Plan Call on Startup, Shutdown, and Malfunction Rules
In a 2–1 decision, the U.S. Court of Appeals for the District of Columbia Circuit (D.C. Circuit) largely vacated an Environmental Protection Agency (EPA) rule requiring 32 states to amend their Clean Air Act implementation plans (called State Implementation Plans, or SIPs) by removing provisions providing either exemptions or affirmative defenses to excess emissions from unit startups, shutdowns, or malfunctions (SSM) — times when pollution controls often cannot fully function as needed.[1] Sources in states that still have or revert to allowing an SSM defense may now have this important operational flexibility. However, stakeholders should track the actions of their individual states and keep close watch on whether EPA or environmental groups seek rehearing or appeal the ruling.
