A time composite sample is defined as:

• A. Collected based on flow.
• B. Collected over time, typically at constant time intervals.
• C. Collected only during peak flow.
• D. Collected at random times.

Answer: (B)

A time composite sample is about averaging what the plant sees over a period by taking small portions at regular time intervals and combining them. This approach smooths out short-term fluctuations in concentration that happen as influent quality and flow change throughout the day, giving a representative picture of the period rather than a single moment. The key idea is collecting at fixed intervals—every so often—independently of how much flow is moving through the plant, then mixing those sub-samples into one. This is different from grabbing samples only during peak flow or collecting samples at random times, and it’s distinct from flow-proportional composites where the volume of each sub-sample depends on the flow. Typical practice uses constant intervals (like every 15, 30, or 60 minutes) over the chosen sampling period.