What type of well is considered least likely to become contaminated?

Drilled wells are least likely to become contaminated primarily due to their construction method, which involves penetrating deep into the ground to tap into aquifers that are less exposed to surface contaminants. This method typically results in a well that has a relatively small diameter and is often lined with casing to help prevent contamination from soil and surface water.

The process of drilling involves using machinery that creates a very precise and deep well, often reaching depths that access safer water sources, thereby minimizing the risk of contaminants from agricultural runoff, industrial pollution, or septic systems, which are more prevalent in shallower wells. Additionally, the casing used in drilled wells provides an extra layer of protection, sealing the well against the possibility of surface contaminants seeping into the water source.

In contrast, bored, driven, and dug wells are either shallower or do not have the same level of protective casing, making them more vulnerable to contaminants that may infiltrate from the surface. These types of wells can be significantly impacted by environmental factors and human activities nearby. This distinction is crucial in understanding groundwater protection and ensuring safe drinking water.