Final answer:
Under Dispenser Containment was mandated by environmental regulations such as the Oil Pollution Act and the Spill Prevention, Control, and Countermeasure Rule (SPCC), which require facilities with large capacities of oil to have spill prevention and containment plans.
Step-by-step explanation:
Under Dispenser Containment, which refers to systems designed to prevent leaks from underground storage tanks (USTs) from contaminating the environment, was mandated as a result of a series of environmental regulations. Among these regulations, the Oil Pollution Act and the Spill Prevention, Control, and Countermeasure Rule (SPCC) play significant roles. The SPCC applies to facilities that handle oil products and mandates that facilities with large oil storage capacities have written plans to prevent and handle potential spills, which would include secondary containment measures. Another key piece of legislation is the Safe Drinking Water Act of 1974, which allowed the Environmental Protection Agency (EPA) to regulate public water systems and set national standards for safe drinking water, impacting how facilities deal with potential contaminants and leakage.