Parts of a bore
Bores have four main parts as listed on this page.
All bores must be constructed with a surface collar at least 5m deep and a minimum annulus (space between the surface collar and the drill hole) of 20mm.
The annular space of cased boreholes must be grouted when the bore is finished to seal the surface collar.
Bores need a 1m squared concrete slab at surface level around the bore casing. The slab must be 75mm thick above the final ground surface and 25mm thick below the final ground surface.
The concrete slab must let water drain away from the finished bore casing.
Casing is a pipe that protects the borehole from collapsing.
The choice of material and size is based on a number of factors including all of the following:
- bore depth
- water quality
- potential yield of water.
Casings can be made from steel, plastic or fibreglass. Plastic is common as it is cheap and doesn't corrode.
The borehole must be larger than the casing you are using.
The space left, the annulus, may need to be filled with watertight materials like grout, concrete or bentonite to stop surface water contamination, transfer between zones and to protect the casing from soils and water.
The bore casing also needs be at least 300mm above the top of the concrete slab.
If the bore is in an area prone to flooding then the casing should extend above the potential flood height.
Screens are needed in bores within unconsolidated aquifers such as sand and gravel.
The bore screen lets water enter the bore, stabilises the formation and stops entry of unacceptable particles.