Sanitary Seal

In order to prevent ingress to the aquifer of any potential contaminants from the surface via the borehole itself, it is necessary to seal the uppermost section of the annulus between the outermost casing string and the wall of the borehole. The sealing material commonly used is cement grout or a bentonite mixture. It is also prudent to ensure that no potential contaminants can enter the borehole from the surface via the space between any other internal casing strings.