What is the maximum allowable residue for a UST to be considered "empty"?

In the context of underground storage tank (UST) regulations, a UST is considered "empty" if it has a maximum allowable residue of 2.5 cm (one inch) or less of product in the bottom of the tank. This standard is established to ensure that the tank is either ready for closure or can be adequately inspected and maintained without the risk of hazardous materials leaking into the environment.

The 2.5 cm threshold allows for a small amount of residual product to remain, acknowledging that complete removal can be impractical in certain situations. This measurement is crucial for compliance with environmental regulations and safety protocols, ensuring that the tank is not posing a risk to the surroundings even when it is deemed "empty."

Understanding this standard is vital for professionals involved in UST management, as it guides them in making decisions related to tank closure, maintenance, and environmental protection measures.