What is the purpose of a collocation period in monitoring programs?

• A. To run two monitors side-by-side for a defined time to assess instrument agreement and quality of the data.
• B. To test a single monitor in isolation.
• C. To adjust the site's GPS coordinates.
• D. To perform annual maintenance.

Answer: (A)

A collocation period is about ensuring measurement quality by running two monitors side-by-side for a defined time to see how well they agree and to evaluate the quality of the data. By comparing the colocated instruments, you can detect biases, assess precision, and confirm that the data are consistent and reliable before they’re used for reporting or analysis. This approach provides a practical check against a reference standard and helps establish any needed calibration or quality-control adjustments.

The other options don’t fit because collocation isn’t about testing a single monitor in isolation, which wouldn’t reveal how measurements compare between devices. It isn’t about changing GPS coordinates, which isn’t related to instrument performance. And it isn’t a stand-alone maintenance activity, which focuses on keeping equipment running rather than evaluating how two monitors align.