In what scenario is it most appropriate to use grab sampling?

Grab sampling is most appropriate for specific pollutant detection because it allows for the collection of a concentrated sample at a particular moment in time. This method is beneficial when there is a need to identify the concentration of a specific contaminant within a wastewater sample. It provides a snapshot of the water quality and can capture fluctuations in pollutant levels that might occur due to various operational conditions or events.

When focusing on specific pollutants, grab sampling effectively helps in pinpointing issues or verifying compliance with regulatory limits for those particular substances. For instance, grab samples might be taken when there is suspicion of a spike in a certain toxic compound entering the treatment facility, thereby allowing for targeted analysis and rapid response.

In contrast, continuous monitoring relies on constant data collection over time and would not effectively provide the specific snapshots needed for targeted pollutant analysis. Similarly, assessing treatment efficiency often requires composite sampling, which averages out changes over time rather than focusing on a singular event or condition. Trend analysis typically demands repeated measurements over time to observe changes, making grab sampling less suitable in this context.