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 it 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 Hydrogeologist 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 is that they are usually working with limited space and are affected by pipelines, electrical cables, telephone cables, and structures that interfere with accurate results.
• Water divining/dowsing is an age-old “art” and has been practiced throughout history. Various methods, such as forked sticks and copper wires, are used. 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. JAM Water Services has both geophysical equipment and can arrange for the water divining method and will gladly give an 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 or 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 about 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 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 neighbors 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 in optimum working order. 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 the portion of the borehole sidewall that 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, but high-yielding fracture zones (commonly associated with deep weathered and decomposed rock) may require the borehole to be cased throughout (top to bottom). In this case, perforated casing (casing slotted in such a way as to allow water in while 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 the borehole.

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 depending on:

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.