EPA proposes major changes to multiple rules

The Environmental Protection Agency (EPA) has been on a rulemaking roll! In recent weeks, the agency has published significant proposed rules in the Federal Register that affect coal-fired power plant wastewater, pre-construction air permits, and vehicle emission requirements.

Coal-fired power plants: Unmanaged CRL discharges

EPA proposes to revise the wastewater requirements established by a 2024 final rule (2024 Rule) for unmanaged combustion residual leachate (CRL) from coal-fired power plants.

Unmanaged CRL (a type of waste stream) is water that contains coal combustion residuals and leaks from landfills or surface impoundments (i.e., waste management units). Unmanaged CRL includes:

• Pumped unmanaged CRL (leached CRL that’s captured, pumped to the surface, and discharged directly to waters of the United States); and
• The functional equivalent of an unmanaged CRL direct discharge (determined by the permitting authority).

The proposed rule applies to coal-fired power plants with unmanaged CRL that are subject to the 2024 Rule’s technology-based effluent limitations guidelines and standards.

The agency proposes three options to revise the unmanaged CRL requirements:

• Option 1 (preferred by EPA) would maintain the 2024 rule’s mercury and arsenic numeric limits for pumped unmanaged CRL discharges, but it would delay the compliance deadline from December 31, 2029, to December 31, 2034. Additionally, the permitting authorities would determine best available technology economically achievable (BAT) limits for functional equivalents on a case-by-case basis.
• Option 2 would maintain the 2024 rule’s mercury and arsenic numeric limits for pumped unmanaged CRL discharges and functional equivalents. It would also maintain the original compliance timeline of December 31, 2029.
• Option 3 would impose zero-discharge limits for all pollutants in pumped unmanaged CRL discharges and functional equivalents. It would also establish interim BAT limits for mercury and arsenic. Facilities would have to meet the zero-discharge limits by December 31, 2034.

Public comments are due by June 17, 2026 (Docket ID No. EPA–HQ–OW–2009–0819).

Pre-construction air permits: Begin actual construction

EPA proposes to allow construction-related activities on components or structures that don’t emit air pollutants to start before obtaining a New Source Review (NSR) pre-construction permit to build or modify a stationary source. The proposed rule:

• Redefines “begin actual construction," and
• Adds “pollutant-emitting activities” to the regulatory definitions.

Both definitions list equipment, components, and processes that are excluded, meaning that construction on these activities may begin before obtaining an NSR permit. Examples of exempt activities include compacting and stabilizing soil, paving surfaces, and installing concrete pads.

If finalized, the proposed rule will distinguish between construction on stationary sources and construction on non-emitting components (e.g., utility infrastructure, certain building foundations) and codify that on-site construction of non-emitting components or structures can begin before getting an NSR permit.

Public comments are due by June 29, 2026 (Docket ID No. EPA-HQ-OAR-2025-0618).

Light- and medium-duty vehicle regulations: Tier 4 standards

EPA published Part 1 of a two-part rulemaking effort to revise the Tier 4 criteria air pollutant standards set in 2024 (Tier 4 Rule) for light- and medium-duty vehicles (LMDVs), which include:

• Light-duty vehicles and trucks,
• Medium-duty passenger vehicles, and
• Medium-duty vehicles.

In Part 1, EPA proposes to amend the phase-in schedule for Tier 4 criteria air pollutant requirements by:

• Extending the Tier 3 standards set in 2014 (Tier 3 Rule) for LMDVs to model years (MYs) 2027 and 2028,
• Delaying the start of phasing in Tier 4 standards for LMDVs from MY 2027 to MY 2029, and
• Removing the optional early phase-in of Tier 4 standards for LMDVs with a gross vehicle weight rating of more than 6,000 pounds from MYs 2027 and 2028.

The agency also proposes to delay changes to the test protocols for emissions performance certification evaluations to MY 2029.

In Part 2, EPA will reconsider the Tier 4 Rule for LMDVs, which may include changing emission standards, lead time and phase-in schedules, and test procedures.

Public comments are due by July 6, 2026 (Docket ID No. EPA–HQ–OAR–2025–3297).

Key to remember: EPA has issued a series of proposed rules that, if finalized, may have significant regulatory impacts on power plant wastewater, pre-construction air permits, and vehicle emission requirements.