Which statement best describes a six-part composite sample?

• A. A single sample consisting of six equal portions collected during the composite period
• B. A composite sample formed by combining six equal portions collected at different times
• C. A single sample taken from the end of the sampling period
• D. Six separate samples collected daily and analyzed separately

Answer: (B)

In wastewater sampling, a composite sample is created by pooling several subsamples collected over a defined period to represent conditions across that entire interval. For a six-part composite, you take six equal portions at different times during the sampling window and combine them into one sample. This approach smooths out short-term fluctuations in concentration due to variable flow or diurnal patterns, giving a more accurate picture of typical wastewater characteristics over the period. The statement that best describes this is the one that specifies six equal portions collected at different times and then combined into a single composite sample. The other descriptions describe either a grab sample taken at one moment or six separate samples analyzed independently, which do not form a single composite representative of the period.