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)