Contamination is the presence of harmful substances in soil, water, or air. Contaminated land is land where those substances pose a serious or material risk to health or the environment. In contrast, clean earth is natural soil, rock, or sand free from waste or hazardous contaminants—safe for reuse and exempt from regulation.

Having a clear and simple definition of what constitutes clean earth or clean fill seems like a no-brainer, but it is something that has...