Environmental Protection Agency (EPA) Lead Risk Assessor Practice Exam

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How many spike samples are needed per 50 samples analyzed?

1 per 20 samples
1 per 50 samples
2 per 50 samples
1 per 100 samples

The correct answer is: 1 per 50 samples

The correct number of spike samples needed per 50 samples analyzed is one. This requirement ensures that the results obtained from the sample analysis can be reliably assessed for accuracy and precision. A spike sample is used as a reference check, where a known quantity of a substance (in this case, lead) is added to an environmental sample to evaluate the performance of the analytical method being used. By including one spike sample for every 50 samples, it provides a balance between ensuring quality control and managing the costs and resources associated with analyzing spike samples. This frequency allows for reasonable monitoring without overwhelming the analysis process or introducing significant bias into the results. In higher frequencies, such as one per 20 samples or one per 100 samples, may either overburden the testing process or lead to infrequent assessment of accuracy, reducing the overall reliability of the testing outcomes. Hence, the choice of one spike sample per 50 samples strikes a practical and effective balance.