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. KDM Drilling 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.

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 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" 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. KDM Drilling 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 KDM Drilling uses only the best equipment that is in optimum working order. 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.

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.

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.