Which of the following actions is a requirement before sampling groundwater?

Sampling groundwater effectively requires ensuring that the sample accurately represents the aquifer's conditions. Pumping the well to remove stagnant water is essential because it helps eliminate any water that may have been sitting in the well casing for an extended period, possibly leading to contamination or a misrepresentation of the water quality. By doing this, the technician ensures that the sample collected reflects the true characteristics of the groundwater from the aquifer rather than being influenced by water that has been stagnant or affected by the well environment.

Measuring water temperature and calibrating the pH meter are important steps in the overall process of water analysis, but they do not directly pertain to the preparatory actions required before taking a sample. Collecting surface water samples, while an important part of a comprehensive water quality assessment, does not relate to the specific actions needed before groundwater sampling. Thus, the requirement to pump the well ensures that the groundwater sample is not compromised by prior conditions, making it the crucial first step before sampling.