Which of the following well types is most protected from surface contamination?

• A. Artesian well
• B. Infiltration gallery
• C. Rock well
• D. Shallow well

Answer: (A)

Protection from surface contamination is greatest when the water comes from a confined aquifer tapped by an artesian well. In a confined aquifer, an impermeable layer above traps the water under pressure, and the well is typically sealed within that barrier. This setup means surface contaminants would have to penetrate the confining layer and travel through the aquifer system to reach the water, making contamination entry much harder. The natural hydraulic pressure also often causes the water to rise in the well, reducing the direct exposure of the intake to surface infiltration.

By contrast, shallow wells and infiltration galleries draw from near the surface or permeable zones, where contaminants can more easily move down with infiltrating water. Rock wells depend on fractures in the rock, which can serve as straightforward pathways for contaminants from the surface or polluted zones. So the artesian well’s confined, pressurized nature provides the best protection against surface contamination.