A third party evaluation is necessary for which type of tanks when using SIR?

In the context of using Statistical Inventory Reconciliation (SIR) for underground storage tanks (USTs), a third-party evaluation is specifically required for Category 1 tanks. Category 1 tanks are defined as those that are subject to stringent regulations due to the higher potential for leaks and environmental impact. These tanks typically have certain criteria such as being located in high-risk areas or containing hazardous substances.

The requirement for a third-party evaluation ensures that the SIR calculations and methodologies used to monitor these tanks meet regulatory standards and accurately reflect the tanks' performance. This helps to identify leaks more efficiently and provides an added layer of accountability.

Category 2 tanks, on the other hand, may not have the same stringent requirements for third-party evaluations, as they might not present the same level of risk. Similarly, classifying tanks solely based on size or other categorical distinctions does not govern the need for a third-party evaluation in the same way. The necessity of third-party involvement is more closely related to the tank category and associated risks rather than size alone.