At a minimum, how often should QC check samples be analyzed?

The frequency at which quality control (QC) check samples should be analyzed is critical to ensuring the reliability and accuracy of water quality testing results. The correct answer emphasizes that QC checks should be performed at least quarterly. This approach helps to maintain the integrity of the testing process over time by allowing for the identification of trends or issues that could affect data quality in a timely manner.

Analyzing QC samples quarterly provides a balance between sufficient oversight and resource management, allowing analysts to ensure that the methods and equipment being used are still performing accurately and reliably without overburdening the laboratory with excessive testing. Regularly scheduled QC checks can reveal drifts in measurement or indicate the need for maintenance on instruments, thus enhancing the overall confidence in the data produced.

In contrast, while testing with each batch or daily may seem valuable for continuous monitoring, it is often more practical to enforce a minimum standard of quarterly checks. Monthly checks may be excessive for some laboratories, given the resources required, and quarterly checks offer a reasonable compromise to ensure quality without compromising operational efficiency.