Which type of well is least likely to be contaminated?

A drilled well is least likely to be contaminated because it typically extends deeper into the ground and penetrates through layers of soil and rock that can act as natural barriers to contaminants. These wells are constructed using large-diameter drilling equipment, ensuring a more controlled and sealed environment, which minimizes the risk of surface contaminants entering the water supply. The drilling process also allows for the installation of protective casings, which further reduces the potential for contamination from surface water and other pollutants.

In contrast, drivepoint wells and shallow wells are often more susceptible to contamination due to their construction methods and deeper proximity to surface sources of pollutants. Artisan wells, though they can provide a reliable water source, may also face contamination risks depending on the geological formations they tap. Thus, the design and construction characteristics of drilled wells give them an advantage in preventing contamination compared to the other well types listed.