Water borehole drilling involves creating a 150mm diameter borehole, with depth depending on geology. Air flush drilling, the most common method, uses compressed air to remove drilling residue and monitor water levels. The installation includes slotted pipe for water entry, a filter pack for stability and filtration, and a submersible pump for water supply.

1. Water BoreholeDrilling and Installation

2. What does drilling a water borehole involve?A water borehole is usually drilled to 150mm in diameter. The depth depends on the geology.The drilling equipment used to drill a borehole varies depending on the geology. Anything from a drag bit to a high impact air hammer is used.

3. Air flush water borehole drillingAs the borehole is drilled to depth, water levels within the borehole are monitored. Air flush drilling is now the most common method of drilling, the alternative being mud flush. Air flush drilling uses compressed air to drive the drilling tools. The air enables the drilling residue to be driven out of the hole to enable continual drilling. An advantage of air flush drilling is that once water is reached, it is also driven out of the hole, allowing the driller monitor the water flow and calculate the water level, quantity and re-charge rate of the borehole.

4. Maintaining borehole stabilityBorehole wall collapse can occur in certain geologies if the borehole has been improperly designed. To prevent the borehole wall from falling into the well during drilling temporary steel casing can be inserted. These sections of steel casing are screwed together to form an uninterrupted tube of casing that supports the sidewall of the borehole, allowing drilling to continue into harder, more stable geology.

5. Installing the water boreholeWith the drilling completed, the lower parts of the borehole are created using screen. These are 3 meter lengths of Water Regulation Advisory Scheme (WRAS) approved slotted pipe. The pipe’s 1mm wide slots allow water to percolate into the borehole. The top sections of pipe are solid WRAS-approved pipe which prevent any surface water or polutants entering the water supply. The gap between the 150mm hole and the 100mm installation is filled with a glass media filter pack made from recycled glass and gravel. This acts as an initial water filter and also supports the borehole wall. The filter pack is inserted to a depth of 6m below the surface. The top of the borehole is double lined with a 125mm diameter WRAS approved pipe which is inserted over the 100mm install and acts as a further barrier to prevent surface contamination. This pipe is grouted into place with a bentonite grout.

6. Sealing the boreholeThe borehole is finished with a poly well head sump approximately 600mm x 450mm in diameter, which is covered with a manhole cover. These may be anything from lightweight steel covers through to reinforced weight rated covers to allow traffic to pass over the borehole.

7. Installing the water borehole pumpA submersible pump is installed into the borehole to supply water for any number of applications from domestic supply to commercial irrigation. Water borehole systems use direct pressure pumps providing water on demand at 3–4bar into a network of new or existing pipe work. These systems can also pump into holding tanks with the water then pumped around a pipe network.

8. For more information:To find out more about water borehole drilling and installation, visit:www.geologicboreholes.co.ukOr contact us:Geologic Boreholes & Systems LtdTel: 01404 851459e-mail: info@geologicboreholes.co.uk