What is defined as "regulated substances" in the context of Underground Storage Tanks (USTs)?

In the context of Underground Storage Tanks (USTs), "regulated substances" are specifically defined as liquids that include hazardous substances, petroleum products, or other substances outlined by regulations. This classification is crucial because it helps to identify which materials require stringent management and regulatory oversight due to their potential environmental impact and risk to human health. The definition focuses on the nature of the substances and not their safety or disposability in other contexts. Thus, recognizing these substances is essential for operators to ensure compliance with federal and state laws, focusing on environmental protection and public safety.

The other options do not align with the regulatory definitions: safe liquids or only water-based liquids do not encompass the broader array of regulated substances that include hazardous materials. Similarly, liquids that can be disposed of in landfills do not necessarily reflect the regulatory context or identify the specific risks associated with USTs. Therefore, the delineation in option B is critical for understanding what substances must be managed according to UST regulations.