What should be done if water returns to an excavation after being pumped out?

When water returns to an excavation after being pumped out, collecting a representative water sample as soon as enough water returns is essential for evaluating the water's quality and managing its impact on the excavation site. Sampling the water allows for the analysis of potential contaminants or characteristics that could affect safety and compliance with environmental regulations.

This approach is crucial because it helps determine if the water poses any risks that must be addressed before proceeding with further work. It also ensures that appropriate actions can be taken based on the findings, whether it involves treating the water or implementing additional safety measures.

The other options focus on stopping work or just draining the water without first understanding its quality or risks, which may lead to overlooking environmental regulations or safety concerns. Leaving the water alone until the excavation is complete could expose workers to hazards or violate local regulations governing water quality and its management. Therefore, sampling to assess the water quality is the most responsible and regulatory-compliant action.