How many side walls must soil samples be collected from if excavating one tank?

When excavating a heating oil tank, the requirement for soil sampling is crucial to ensure environmental safety and compliance with regulations. The correct response indicates that soil samples must be collected from two side walls of the excavation.

Gathering samples from two side walls is standard practice because it ensures that the assessment of potential contamination is thorough. It allows for a representative understanding of the soil conditions surrounding the tank, addressing any potential leaks or spills that may have occurred on different sides of the tank, which may not be captured if only one side wall is sampled.

Sampling from two side walls provides better data for evaluating contamination and helps ensure that any necessary remediation actions are appropriately directed. This approach aligns with best practices in environmental management and risk assessment.

While the other options suggest different numbers of side walls, they do not account for the standard procedures that aim to optimize safety and environmental protection during the excavation process.