Which type of sampling combines multiple samples from a defined area?

Composite sampling is the correct answer because it involves the collection of multiple samples from a defined area, which are then combined into a single sample for analysis. This method is particularly useful in providing an average representation of the contaminant levels across a specific location, rather than relying on a single point measurement. By aggregating results in this way, composite sampling can help to smooth out any variations that might be present in individual samples, leading to a more accurate assessment of the contamination level over a broader area.

In terms of application, composite sampling is often utilized in environmental monitoring where pollutants can be distributed unevenly across a site. By averaging multiple samples, the analysis can be more representative of the overall conditions, allowing for better decision-making regarding safety and remediation efforts.

Discrete sampling refers to the collection of individual samples from specific points, which does not provide the averaged perspective that composite sampling achieves. Grab sampling is a method where a single sample is taken quickly from a location without prior planning of multiple locations, and surface sampling focuses specifically on the surface of materials or areas without the aspect of combining multiple samples. Thus, these alternative methods do not fulfill the requirement of combining samples from a defined area as effectively as composite sampling does.