What is used to properly seal a drilled well to prevent contamination of the water supply?

To properly seal a drilled well and prevent contamination of the water supply, grouting is the preferred technique. Grouting involves filling the annular space between the well casing and the surrounding earth with a material, typically a type of cement, that creates an impermeable barrier. This barrier is crucial for preventing surface contaminants from traveling down the well and mixing with the groundwater, thereby ensuring the safety and quality of the drinking water.

By using grouting, you minimize the risk of pollutants, such as bacteria or chemicals, entering the well from the surface or from adjacent groundwater sources. It effectively seals off potential pathways for contamination, which is vital for maintaining the integrity of the water supply.

Concrete casing, while it provides structural support and can contribute to well sealing, does not independently prevent contamination without the additional step of grouting to seal the space around it. Filtration is a method for purifying water after it has been extracted but does not address the issue of preventing contaminants from entering the well in the first place. Covering with soil is not an adequate sealing method, as it does not create a reliable barrier to prevent the infiltration of contaminants. Thus, grouting stands out as the most effective means for sealing a drilled well to protect water quality.