Certified Hazardous Materials Manager (CHMM) Practice Exam

A UST, or Underground Storage Tank, is defined as a tank that has 10 percent or more of its total volume beneath the surface of the ground. This definition is crucial because it helps establish regulatory guidelines for monitoring and managing the storage of hazardous substances. By requiring only 10 percent of the tank to be underground, the definition captures a broader range of installations while focusing on potential environmental risks associated with leaking fluids.

When a tank is mostly buried, there is a higher potential for leaks to go undetected, which can lead to groundwater contamination and environmental harm. Therefore, having this threshold is essential for regulatory purposes, ensuring that tanks that potentially pose a risk are monitored appropriately. The other options provide higher percentages of tank volume that need to be underground, which could exclude tanks that still present significant risk despite having less than those specified percentages buried. This inclusion promotes a proactive approach to environmental protection and hazard management associated with underground tanks.