How long must records of repairs and maintenance for a UST system be kept?

The requirement to retain records of repairs and maintenance for a UST (Underground Storage Tank) system until the system is permanently closed or transferred is rooted in the need for accountability and ensuring compliance with regulatory standards. Keeping these records allows for a comprehensive history of the tank's operation, including any issues that may have arisen and the corresponding actions taken to address them.

This practice aids in understanding the condition of the system at the time of closure or transfer, which is crucial for both safety and environmental considerations. For instance, if a tank is closed and there were unresolved issues, having a full record could influence future environmental assessments or potential liabilities. Moreover, thorough documentation can assist regulatory bodies in evaluating past compliance and ensuring that all necessary protocols were followed throughout the tank's operational life.

The other choices suggest a finite time frame for record retention, which would not provide the same level of detail or protection for entities involved with the UST system. Thus, maintaining records until the moment the system is no longer in service ensures that all necessary information is available for any subsequent procedures or evaluations.