There are a number of aspects that needs to be taken into consideration when testing a borehole. According to Prof van Tonder at the Institute for Groundwater Studies (Free State University) there are two important rules that needs to be kept in mind when determining the sustainable yield I.e.: The total abstraction from a borehole should be less than the natural groundwater recharge, and secondly, a borehole should be pumped in such a manner that the water level never reaches the position of the main water strike (normally associated with a fracture). Should this happen the yield will inevitably be affected and the borehole would eventually dry up.

Specific information is required to properly test a borehole, these can be listed as follows: what is the rest water level before the start of the test, how does the water level change over time once pumping has started, how long does it take for the water level to recover after the pump has been stopped to recover to the original level – or how far does the water level recover after the same amount of time allowed as for pumping – leaving a residual drawdown.

Test pumping of boreholes is normally carried out to meet two main objectives:

To establish borehole potential. To estimate the sustainable yield and hydraulic erformance of individual boreholes for water supplies.

 To establish aquifer potential. To assess the hydraulic characteristics of the aquifer.

Drilling and production of boreholes

Drilling Methods
Considering the nature of the regional geology-that is mainly hard rock, the rotary air flush percussion drilling method is suspected to be sufficient in the majority of the project areas. The objective of drilling is to establish a borehole in the identified area that will be sustainable in the
long-term.

Borehole Construction
The drilling should be carried out according to the Development, Maintenance and Management of Groundwater Sources – SA Code of Practice Ref SABS 0299 1,2 &3 – Design and Construction of Groundwater Boreholes & Drilling of Groundwater Boreholes. The following
details are highlighted: –

Borehole diameter:
Rotary air flush percussion drilling will be done using one of the following procedures: –

(1) drilling of a 165mm diameter borehole through the weathered overburden until the hard rock Formation (unweathered material) has been penetrated for at least 3m. The borehole is then reamed to a diameter of 219mm and the weathered material cased off, using normal 3mm thick
solid 165mm diameter mild steel casing, to prevent the collapse of the (unstable) overburden. Drilling is then continued with the 165mm diameter hammer to the borehole’s completion depth.

(2) The drilling is initiated using a 219mm diameter hammer until the more stable rock formation has been penetrated for at least 6m, followed by the installation of 3mm thick 165mm diameter solid mild steel casing, piloting the 165mm diameter borehole to the final depth.

Borehole Development:
This is done by flushing drill fluids, fines and debris from the borehole on completion of drilling. The method used is that of plunging and surging – using compressed air, flushing the debris from the borehole. On completion, a blow yield can be determined, which gives an indication of the potential yield of the borehole.

Borehole Protection:
The borehole is capped with a steel plate welded flush to the protruding borehole casing.

Formation sampling:
During the drilling process, a lithological sample for each meter drilled, will be taken by the drilling contractor and placed on a cleared patch for the geohydrological consultant to inspect and describe and to discuss and eventually decide the depth of casing installation.

Water strike depth
The depth of each water strike is recorded by the drilling contractor, inclusive of seepage. Several water strikes may occur in one borehole and it is therefore important to determine the blow yield of each individual strike. This information is used when the borehole is tested and is vital for equipping of the borehole.

Blow Yield
On completion of drilling, the final blow yield of each borehole is measured and recorded.

Borehole Test Pumping

The efficient operation and utilization of a borehole requires insight into and an awareness of its productivity and that of the groundwater resource (aquifer) from which it draws water. This is best achieved by borehole test pumping. This activity provides a means of identifying potential
constraints on the performance of a borehole and on the exploitation of the groundwater resource. The recognition and understanding of these constraints promote the proper, judicious and optimum exploitation of the groundwater resource. Ignorance and disregard of these
constraints can lead, at best, to the uneconomical operation of the borehole and, at worst, to overexploitation of the source. Over-exploitation of the groundwater resource can have adverse affects such as depletion of the aquifer.

As the aim of the boreholes is to supply water for domestic purposes, the testing of the borehole for at least 12 hrs is recommended and 24 hrs for higher yielding boreholes. At the same time water will be extracted for chemical analysis purposes.

Test pumping procedure will include:
i.) A four-hour stepped discharge test followed by a 12hr or 24hr constant discharge test.
ii.) Recovery tests
iii.) Collection of a water sample.

Groundwater Sampling

Two water samples of each borehole drilled and/or tested will be taken, simultaneously, at the
end of the stepped discharge or constant discharge test and conveyed to an approved laboratory
(Talbot&Talbot Laboratory) in Pietermaritzburg for analyses.

The samples will be analysed for the following parameters:
– Physical analysis – that is turbidity and colour
– Macro analysis – that is the chemical constituents
– Bacteriological analysis – that is the detection and quantification of Feacal Coliforms.

Water Quality

The results of the chemical analysis will be classified by the geohydrological consultant according
to The SABS specifications for Domestic Water Supplies. According to these criteria, the water
quality of a borehole can be classified in terms of health or general use or aesthetic reasons.