Water as known is the most important life keeper. Groundwater is the major source of supply. This can only be achieved by effective and professional placement of a borehole.
Reaching underground reservoirs can sometimes prove to be very extremely challenging exercise. However, our proposed methodology and scope of work has been defined as being:-
Rig Set Up
The rotary rig will be moved into a position of the selected site by the consulting hydro geologist. The unit will be levelled into position using hydraulic jacks. This is on pre-positioned heavy-duty timber slippers. This is done in order to avoid any deviation in the borehole during drilling operations and also to achieve affective vertically of the borehole.
(A) Consolidated Formation
We shall deploy the use of hydraulic rotary rig namely DTH with Mission Hammer Bits. This combines the percussive action of cable tool drilling with the rotating action of rotary drilling. Its fast penetration rate in medium hard to very hard formations results from two important factors.
1. Since its bottom – hole tool, the piston blows are transmitted directly to the bit without losing energy through the drill string
2. The air is fully used for rapid impacting action and for lifting cuttings from the hole.
This tool is operated by high-pressure compressed air, injected through hollow drilling pipes by means of 1200cfm, 320 psi Ingersole Rand Screw Air Compressor. Compressed air ensures that the moment water is located, compressed air immediately lifts it to the surface.
We propose to drill sufficient diameter hole from ground level to final depth (s) using Down-The-Hole (DTH) hammer or Mud Drilling with air/Water and foam to have a recommended finished borehole.
We shall from time to time allow the consulting hydrogeologist if any to inspect our daily logs, geotechnical logs, water bearing strata, water rest level, estimation of yields, borehole plumpness etc.
(B) Unconsolidated Formation
Borehole drilling (unconsolidated formation) we propose to drill 10” or 12” hole up to overburden zone then install suitable surface casing then telescope the borehole to final recommended depth and then install 6” (152mm) or 8” (200mm) ID permanent casing.
Borehole Design & Construction
On completion of drilling works to the satisfaction of the consulting hydrogeologist if any or the Employer, we shall proceed with the borehole construction as shall be instructed and in accordance with the design specified.
The construction will involve installation of casings, screens, filter gravel pack all to the approval of the consulting hydrogeologist.
Borehole Chemical Development Works
Chemical development depends on the basis of observations made during drilling by the Supervisor. Depending on whatever the matter shall be, we shall carry with us the typical dosage rates e,g calgon injection and we shall use the chemical as per the instructions of the Supervisor. We shall use an air compressor of 1200 cfm, 320 psi to carry our chemical development works using air-lifting method. We will sodium hexameta phosphate,, 66% chlorine granular calcium hypo chlorite and chlorine as per the instruction of the supervisor.
Borehole Physical Development Works
On satisfactory completion of the borehole construction works, we shall use an IR Compressor of 1200 cfm, 320 psi to carry out physical development works using air-lifting method with occasional addition of biodegradable polymer or as will have been specified in order to achieve the desired goals of producing clean sediment-free and improving aquifer permeability.
Test Pumping & Discharge Measurements
Upon satisfactory construction of developments works, we shall use an electric submersible pump with fully functioning non-return valve in the pump itself. We shall then proceed with expeditious test pumping operations as shall be instructed by the consulting hydro geologist. This will have been specified and designed to test aquifer parameters such as hydraulic conductivities, transmissibility and storability from which design yield will be determined.
The test pump will consist of step draw down and constant drawdown test as per the instruction of supervisor.
We shall provide un-interruptible power generating set 20 to 82.5 KVA to efficiently run the pump set
Discharge measurement during constant drawdown test shall be done using a volumetric method of 20 litres, 50 litres or 200 litres depending with the yield of he borehole and the drum set horizontally on the ground. Time measurement shall be recorded by means of a stopwatch.
During testing, we shall monitor water level using electric sounding or lighting dipper. The dipper, will go in through a 1” piezometre tube installed alongside the test pumping rising main secured by insulation tape or cable clip.
We shall sample clean water in 1 litre jerry can and forward to the Government Chemist, Nairobi or any other competent authority for Chemical analysis.
Borehole Completion & Capping
We shall approximately construct suitable concrete plug around casing with dimensions specified in the Bill of Quantities after successful completion of test pumping works.
We shall compile a report after completion of the assignment, which will include:-
- Drilling operations (i.e penetration and geological logs), results and borehole design construction with drawings.
- Development and test pumping operations, results and analysis with graphs
- Water quality analysis
- Recommendations on groundwater abstraction and utilization, including submersible pump specifications
- Borehole Completion Certificate
We trust that you will find our proposed methodology acceptable.