A site assessment before permanent tank closure is required when:

A site assessment before permanent tank closure is crucial when evidence of a release is present. This requirement is part of the regulatory framework designed to protect the environment and public health. If there has been a release, it's important to determine the extent of contamination, the potential impact on groundwater, soil, and surrounding ecosystems, and to ensure that appropriate remedial action can be taken.

Conducting a site assessment in this situation allows for the identification of contaminants and their concentrations, which is essential for planning the next steps in remediation and ensuring that the area is safe for future use. The assessment will also provide necessary documentation to regulatory bodies, showcasing that proper procedures are being followed and that efforts to mitigate any environmental impact are being made.

In contrast, the presence of no evidence of a release, existing documentation of past tests, or the presence of external monitoring systems does not necessarily require a site assessment. These conditions may reflect sufficient management practices or monitoring that has rendered a more urgent assessment unnecessary. However, any clear indication of contamination mandates further investigation to safeguard environmental integrity.