What construction material is isolated by tank-top sumps from corrosive underground environments?

The correct answer highlights that steel, which is commonly used in the construction of underground storage tanks (USTs), is particularly susceptible to corrosion when exposed to underground environments, especially when interacting with moisture, soil chemicals, and other corrosive agents. Tank-top sumps are designed to isolate and protect these steel tanks by providing a barrier that prevents substances from reaching the steel surface directly.

By using tank-top sumps, the corrosive elements in the underground environment are kept away from the steel, thus extending the life of the tank and maintaining the integrity of the storage system. This protection is vital for ensuring safety and compliance with environmental regulations regarding hazardous materials.

In contrast, while concrete and plastic can also be used in construction materials for tanks, they have different properties with respect to corrosion resistance and may not require such isolation measures to the same extent as steel. Wood, due to its inherent characteristics, is not used for constructing tanks meant to hold potentially hazardous materials underground, as it does not provide the necessary durability and resistance to environmental factors.