Borehole Drilling And Testing

The process involved with drilling a borehole.

Below is the process involved with drilling a borehole and what you can expect from Water pump Services cc. The drilling of a borehole is not something that you do every day and therefore you may have some concerns regarding what is involved. So we have put together something below that we hope will give you a better understanding of what is takes to drill a borehole and the provision of potable water. Drinking water (or potable water) is water safe enough to be consumed by humans or used with low risk of immediate or long term harm. In most developing countries, the tap water supplied to households, commerce and industry meets the water quality portability standards.

It is very important to fully understand the sequence of events and the possible consequences before you drill a borehole and also what takes place during the drilling process.

Borehole Siting (Survey)

The first decision once you have decided to drill a borehole is, where do you drill it? The drilling site has to be chosen and physically marked on the ground. This is usually done by a professional such as a Hydrogeologists or alternatively, a Water Diviner.

The Hydrogeologist uses various geophysical methods to survey the subsurface geology. In ideal conditions a Hydrogeologist's success rate is between 60% - 85%. One of the problems with using a Hydrogeologist in an urban setting with his geophysical equipment and methods to probe beneath the surface, is that he is usually working with limited space (not so on a farm or plot) and the other problem is all the pipelines, electrical cables, telephone cables and structures that interfere with an accurate result from the equipment used.

Water divining/dowsing is an age-old “art” and has been practiced throughout history. There are a variety of methods used like, forked sticks, copper wires and many other methods. There is no scientific explanation for water dowsing.

To sum up the siting of a borehole - the decision lies with the customer as to which method they choose. We are here to advise and guide the customer, however it is the customer choice as to which way to go. JAM Water Services has both the geophysical equipment and can arrange for the water divining method and will gladly give our opinion once the location has been visited.

Drilling & Construction of the borehole

Once the customer has decided on which method to use for siting (either the Hydrogeologist ot the Water Diviner) and the drilling target has been pegged the next task is the drilling of the borehole. The customer needs to obtain quotations from a number of drilling contractors and appoint one to undertake the job. Please note that the customer contracts the driller to drill the borehole to a required depth - not to find the water. The driller cannot be held responsible for the success of the borehole, the customer pays for the depth drilled at the agreed rate regardless of the amount of water or lack thereof.

There is a perception that you drill and suddenly there is water and that it is just depends on the depth. This is not the case. There are a percentage of boreholes that are drilled that are "Dry". The driller is being paid according to the depth of the borehole and not for a successful "wet" borehole.

Drilling Method

The drilling method used is known as "down-the-hole" (DTH) air flush rotary percussion. A pneumatic hammer and drill bit operated at the end of the drill pipe rapidly strikes the rock while the drill pipe is slowly rotated. The shattered pieces of rock are removed from the borehole by compressed air which is used to drive the hammer. The drilling process is very noisy and very messy. The process can either be very dusty or very muddy or both. JAM Water Services however takes measures to limit the dust and control the mud that is produced during the drilling process.

In urban areas we only drill during normal working hours and it is advisable to notify your immediate neighbours to close their windows the day drilling is to commence. The drilling process should only take a couple of hours depending on the depth, as JAM Water Services uses only the best equipment that is in optimum working order. Have a look at our website gallery (jwservices.co.za) to see the equipment we use. Drilling usually proceeds until either sufficient water is intersected or the client’s budget is exhausted.

Borehole Construction

Domestic boreholes are initially drilled 8.5" (215mm) in diameter through the topsoil and weathered overburden rock. This larger diameter facilitates the installation of steel casing (177mm OD). The borehole casing effectively stabilizes that portion of the borehole sidewall, which is unstable and prone to collapse. The average depth of overburden and hence casing required in the Gauteng area varies between 8m and 40m. Insufficient casing can result in borehole collapse with severe financial implications for the client (loss of pump, pipes and the entire borehole).

Usually casing is only required through the unstable overburden however high yielding fracture zones (commonly associated with deep weathered and decomposed rock) may require that the borehole is cased throughout (top to bottom). In this case perforated casing (casing slotted in such a way as to allow water in whilst keeping rock out) would be installed opposite the water bearing fractures. The amount of casing required is unique to each borehole and can only be deduced from the results of the drilling.

Assuming that the borehole is successful the driller will perform a blow yield and ‘guestimate’ the yield of thereof.

Cleaning Up After The Drilling

Drilling is a “dirty job”. Unfortunately we do make a mess. To reduce the mess we lay down plastic and shade cloth to protect plants where possible.

The price can escalate or plummet according to:

1. The depth that will have to be drilled.
2. The type of stone found in the area – the harder the stone the more difficult
the borehole drilling process.
3. The type of sand in the area – the number of casings used depends on this aspect.
4. The length of electrical cord used to get electricity to the pump.
5. The distance and the type of topography (terrain) the rig will have to travel through
to get to the drilling area.
6. The time it will take to complete the drilling.

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