What criterion is used to determine purging and sampling equipment?

The criterion used to determine purging and sampling equipment primarily involves the volume depth to the top or bottom of the screen in relation to potential contaminants. This consideration is essential because the purpose of purging is to remove stagnant water from the well that may not represent the aquifer's current conditions, as well as to prevent the disturbance of contaminants that may be present near the screen. Depending on the specific depth and configuration of the well screen—how deep it is and its position concerning contaminants—different purging and sampling equipment may be employed to ensure that the samples collected are representative and accurate.

This factor greatly influences the choice of equipment and methodology for sampling to maintain the integrity of the data gathered, which is pivotal in groundwater monitoring and assessing water quality. The considerations regarding the type of well or its casing size, while important in other contexts, do not specifically address the connection between screen depth and contaminant interaction, emphasizing why the volume depth to the top or bottom of the screen to contaminant is the most relevant criterion in this scenario.