Which statement best describes the purpose of a QA/QC plan in environmental sampling and explains why chain-of-custody is essential?

• A. A QA/QC plan is optional and chain-of-custody is used only for shipping samples.
• B. A QA/QC plan ensures data quality and integrity during sampling and analysis; chain-of-custody ensures samples are controlled and defensible results.
• C. QA/QC plans address only equipment calibration and do not affect data quality.
• D. Chain-of-custody is used to determine sampling locations.

Answer: (B)

In environmental sampling, having a QA/QC plan centers on protecting data quality and integrity from field collection all the way through laboratory analysis. It sets up the standards, procedures, and checks that ensure measurements are accurate, precise, and reproducible—things like field blanks, replicate samples, method validation, instrument calibration, and thorough data review. This makes the results trustworthy and defensible, which is crucial when decisions or regulatory actions depend on the data.

Chain-of-custody is essential because it documents every step of a sample’s journey: who collected it, who handled it, when and where it was stored, and how it was transferred. This trail preserves sample identity, prevents tampering, and helps detect mix-ups or contamination. With a clear chain-of-custody, you can defend the data in audits or legal contexts and trace any issues back to their source.

So, the plan ensures data quality and integrity across the process, while chain-of-custody protects the sample’s identity and provides a defensible record of who had it and when.