What should the diameter of the upper drill hole be when sealing in consolidated formations?

When sealing in consolidated formations, the diameter of the upper drill hole must be at least three inches greater than the diameter of the permanent casing. This requirement ensures that there is sufficient space around the casing for the proper placement and integrity of the sealing materials, which often include grout or other sealing compounds.

This additional space helps to accommodate the sealing materials, allowing for a complete fill that can effectively prevent the migration of water and contaminants. It is crucial to create a watertight seal in these formations to maintain the integrity of the well and protect groundwater resources. If the upper drill hole were the same size as the casing or only slightly larger, there would not be enough room to ensure a reliable seal, putting the well at risk for potential contamination or failure to retain water properly.