Boreholes are generally drilled when ground water is not accessible by means of a wellpoint.
A borehole is drilled to a required depth and water level which will be continuously monitored during the drilling process. The ground structure that is found during the drilling process will determine whether the driller will continue mud drilling or move over to air drilling.
- Mud Drilling is used when formations that need to be penetrated are softer than sand stone and rock. A drag bit can be used with a slurry mixture to stabilize the drilling shaft once a certain depth is reached which will be determined by the driller. The hole will be sleeved and gravel packed once the drilling procedure has been completed and all the drilling equipment has been extracted from the borehole shaft. Equipping and completion of the borehole will commence shortly after drilling process has been completed. A Stand-time will take place to allow the slurry to decompose due to the drilling process.
- Air drilling is used to drill through hard substrata or sub formations such as sandstone that is generally found in the Western Cape area. The driller will determine what drilling equipment will be required to continue through the rock formation. Drilling equipment, like down the hole air hammers, will be able to brake through hard rock and sand stone layers. The air will drive the cuttings out the hole and when water is found the air will force the water to the surface. The driller will then be able to determine the volume of water, the availability, the quality and recharge rate of the borehole.