Stage 1: Site survey (Groundwater Investigations)
This is the first stage in the process of constructing a borehole. Depending on the geologist contracted to carry out the survey (Geophysical assessment), various techniques will be applied to sound (scan) the subsurface mainly to pick data from site for a technical analysis. This stage determines and answers the following questions;
a) Is there groundwater potential at site?.
b) Geological formation and setup of the area in question.
c) Recommended drilling depth required. This will influence the cost of drilling.
d) Likely challenges and possible solutions during the drilling exercise.
Stage 2: Drilling
The drilling stage is the actual exploration exercise carried out using a rig operated on site. Borehole drilling is the process of punching a hole in the ground to extract groundwater. Everything that happens at this point is in reference and under the guidance of the surveyor’s report. The drilling exercise is usually completed by installing casings and well screens to keep the borehole from caving in yet allowing water to percolate into the well. This also prevents surface contamination, sand and other sediments from drawing into the well
After the drilling is completed, the drilling supervisor will provide a report with all the drilling logs mainly reporting on the following.
a) Total drilled depth
b) Depth to the water strikes
c) Driller’s estimated yield
d) Well design and depth to screened water strikes etc.…
Stage 3: Test pumping.
Aquifer Tests also referred to as Test Pumping is done after the drilling exercise is completed. This is a scientific process that experiments the performance of a borehole. This is done by pumping groundwater from a well, usually at a controlled rate and measuring change in water level (drawdown) during and after pumping.
If this stage is poorly handled, can lead to under pumping or total malfunctioning of the well. And worst-case scenario would be over pumping the well leading to a chain of problems like draining the well and eventually spoiling the submersible pump and its installed components. The aquifer test report will provide the following information that is later used to size a proper pump and power supply during the installation phase.
a) Static water level what some people prefer to term as the water table.
b) Dynamic water level
c) Safe abstraction or recommended pump installation depth.
d) Recommended pumping duration and rest interval to allow for recovery.
e) Discharge rate. This is the actual yield of the well measured as m3/hr. (liters per hour) which is very crucial while sizing a pump.
Stage 4: Installations
Typically, what renders a borehole useful and complete is the installation of a submersible pump and all the accessories that come along. The most important information needed for a successful installation process, is expected from the aquifer test (Test pumping) report. This includes the drawdown and rest water level, the safe abstraction or recommended pump installation depth, percentage of recovery versus recommended pumping duration time. This information helps to implement the right specifications for both the submersible pump and the capacity of the power source.
The stages as identified above can only be implemented one after the other. It would be a gamble to cost a single part of the process ahead without completion of the previous step. For example, you wouldn’t know the right size of the pump to install without knowledge of actual discharge rate, and recovery rate of the well.