Tennessee Wastewater Operator Practice Exam

What type of sample should be collected when immediate analysis is not possible?

1. Composite sample

2. Grab sample

3. Preserved sample

4. Integrated sample

The correct answer is: Preserved sample

When immediate analysis is not possible, the best choice is to collect a preserved sample. This type of sample is treated with preservatives immediately after collection to prevent any changes in the water quality parameters over time. Preservatives may include acids, heat, or specific chemicals that inhibit biological activity or chemical reactions that would otherwise alter the sample's integrity. This method is crucial in ensuring that the sample remains representative of the original conditions at the time of collection, as it allows for accurate analysis to occur at a later date. For example, if a sample contains biodegradable materials, preserving it will prevent the breakdown of these materials that could lead to misleading analytical results. The other sampling types, while useful in certain situations, do not adequately address the issue of anticipated delays before analysis. A composite sample is taken over time or at different locations to provide an average concentration but is usually not intended for delayed analysis without preservation. A grab sample reflects a single moment in time and is not suitable if it cannot be analyzed soon after collection, as it may not accurately represent the conditions later. An integrated sample, which combines multiple sub-samples into one, also does not focus on preservation and may still experience changes before testing.