When a tank has been permanently closed and left in the ground, it must be _______.

• A. Drained of all liquids
• B. Sealed with concrete cap
• C. Removed completely
• D. Filled with inert solid material

Answer: (D)

When an underground tank is permanently closed and left in place, the goal is to stabilize the void and prevent future hazards. Filling the remaining space with inert solid material achieves this by immobilizing any residual contents, eliminating voids that could collapse or allow groundwater to move through the tank, and reducing the risk of vapor buildup or leak pathways over time. Draining liquids alone doesn’t address the empty space or potential residuals inside, and sealing the top without filling the void doesn’t prevent movement or intrusion. Removing the tank would eliminate the structure, but the scenario specifies it’s left in the ground. Filling with inert material provides a safe, long-term closure.