Under which Subtitle are the ash produced by waste-to-energy (WTE) plants regulated?

The correct choice is based on the regulatory framework established by the Resource Conservation and Recovery Act (RCRA), which governs the management of hazardous and non-hazardous waste. Waste-to-energy (WTE) plants generate ash that can contain heavy metals and other contaminants, making it important to regulate this ash properly to protect public health and the environment.

RCRA Subtitle C specifically addresses hazardous waste management, establishing a system for tracking, treating, and disposing of hazardous waste. Ash produced by WTE facilities often falls under this Subtitle because it can be classified as hazardous waste if it contains harmful substances above certain thresholds. Thus, ash management must comply with stringent regulations outlined in Subtitle C to ensure that it is handled safely and effectively.

In contrast, the other options do not pertain to the management of hazardous waste. For example, Subtitle A mostly provides the fundamental framework for the RCRA itself, while Subtitle B outlines regulations for non-hazardous wastes. Subtitle D focuses on non-hazardous solid waste management, which does not adequately cover the specific concerns associated with potentially hazardous materials like ash from waste-to-energy plants. Therefore, Subtitle C is the appropriate regulatory designation for ash from WTE facilities.