The process involved with drilling a borehole.
Below is the process involved with drilling a borehole and what you can expect from JAM Water Services. 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.
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.
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.
Determining the yield of the borehole
The accurate yield of a borehole can only be determined by means of an aquifer test (pumping test). These tests involve installing a test pump and pumping the borehole for a period of time at a given rate (yield) whilst recording the drawdown (lowering of water level in the borehole as a result of abstraction). Simply put, the maximum yield of the borehole is achieved by increasing the abstraction rate to a yield, which results in the maximum drawdown of water in the pumping borehole without resulting in pump suction in a given period of time. Aquifer tests are valuable in determining optimum abstraction rates, which in turn allow for correct sizing of the pump (prevent over abstraction and pump burn out) and in determining optimum pumping schedules.
An alternative and less accurate method for determining the yield of a borehole is to quantify the BLOW YIELD whilst drilling or air flushing. A blow yield usually realizes a conservative estimate i.e. as a rule of thumb a blow yield represents approximately 60% of the maximum yield of the borehole. Unfortunately blow yield testing has limitations. Blow yields are not considered reliable if small (<1000 l/hr) volumes of water are intersected. The reason for this being that the volume and pressure of compressed air being introduced into the borehole partially inhibits water entering the borehole. A 4 hour test pump not only realizes an accurate water yield, but it also further cleans out debris from the borehole accumulated during the drilling process.
We recommend that whilst conducting the water yield test, we take a water sample which will be sent to the laboratory. An analysis of the water drawn from the borehole will determine if the water needs to be treated in any way.
Equipping of the borehole
The final stage of the sequence of events is to pump and pipe (reticulate) the water from the successful borehole. The end use of the water will to a large extent determine what type of pumping and reticulation system is to be installed. Of paramount importance to the pump installer
are the results of the pumping tests - how much water can be pumped out the borehole for how long a period? There are too many variations on the nature and type of pump installation to adequately cover all the options in this document. Suffice it to say that a correctly sized and installed pump should last for many years with a minimum of maintenance and that the extra cost of having a system professionally installed will pay for itself time and time again.
It is very important to check that the drilling company that you appoint has serviced equipment that will not break down, that they use good quality casing (steel 4 mm thickness is our standard with laser cut slotted casing) that they install a quality pump. Make sure that the company that you use has a good health & safety record and are continuous of conserving our environment. Insist on your contractors being members of the Borehole Water Association (011-447 0853) and check their reputation with the association. You have no recourse with a contractor who is not a member of the BWA should a problem arise.
Some Points We Consider Important When Drilling Your Borehole
- We have to beat the hectic traffic in the morning, so we generally like to get an early start. We may need to ask you to move your cars into the street if needed as we would not like to block them into your yard.
- When we arrive at your property, we are going to make as little noise as possible – no shouting at each other and we do not permit our staff to play music onsite. We promise to be considerate.
- We have well serviced equipment and vehicles which are in top condition and will not arrive with oil or diesel leaking.
- The drill rig & compressor trucks are very big and heavy (usually in excess of 20 tons) and are very difficult to manoeuvre in confined spaces and may also cause damage to lawns and paved areas. JAM Water Services will make every effort to avoid any damage to your garden.
- Our team are well trained, dress neatly and work safely. Our team will not wonder around your premises. We recognize that your property is your private space and respect that. In turn we ask that the space we need to work in be kept out of bounds for any children & pets. We work with heavy equipment and very high pressure!
- We’ll cover the area under the drill rig with a plastic liner in case of an oil leak developing during work in progress.
- Our team are not permitted to smoke or consume alcohol onsite. We have a no foul language policy in our company.
- For your dog’s sake as much as for our team's sake, we’ll ask you to make provision for your pets to be kept separate from our area of work. We don’t want to get bitten and nor do we want your dog running out into the street or under our equipment.