Grab samples are typically used when testing for which of the following?

Grab samples are commonly used in wastewater testing for dissolved gases because they provide a snapshot of the water's quality at a specific moment in time. Since dissolved gases can fluctuate rapidly due to various factors such as temperature changes, biological activity, and water movement, a grab sample captures these transient conditions effectively.

In the context of dissolved gases, such as oxygen and carbon dioxide, it is essential to obtain a sample that reflects the immediate content of these gases in the water. The nature of grab sampling allows for quick collection and subsequent analysis, which is crucial for gaining insights into the gas concentrations that can impact aquatic life and the overall health of the water system.

Total suspended solids, heavy metals, and pH levels may also be assessed using grab samples; however, they are often better evaluated through composite sampling methods, particularly when assessing average concentrations over time. Composite samples can provide a more representative measure of these constituents, as they account for variations in concentration that may occur over extended periods or various conditions. Thus, the specificity and immediacy of grab sampling make it particularly suitable for evaluating dissolved gases.