Abstract:
The main objective of this project was to improve the success rate in the siting of
groundwater boreholes on a typical hard rock terrain. The study was done on a
1 OXl O km area, underlain by the Lebowa Granite Suite, covering villages in the GaMasemola
district in the Northern Province. This specific site has been declared as
unsuitable for groundwater development due to the fact that there wasn't enough
water in the existing boreholes to supply the villages even with their minimum
requirements. In order to improve the previously applied exploration approach of
siting boreholes within a specific radius of a village in need of water, a more regional,
exploration approach was investigated as an alternative. This included the use of high
resolution airborne geophysical data, structural mapping and ground geophysics to
follow up the main features identified from the regional data sets. Thirteen sites were
identified and 33 boreholes were drilled by the Department of Water Affairs and
Forestry in order to evaluate this approach. The results compared very well to the
holes that existed in the area prior to this investigation:
• 40 existing holes - total blow test yield/air lift = 5 .4 1/s
• 33 new holes - total blow test yield/air lift= 74 1/s
Although not all the holes or sites were high yielding, the regional approach has been
proven to be successful both in the more successful siting of water yielding boreholes,
and the yield per borehole. The optimum airborne geophysical data set and flight line
spacing has also been determined as 50-75m line spacing airborne magnetic data.
Furthermore, for this specific geological setting, the main aquifers were found to be
faults and shear zones rather than lithological contacts or weathered basins.
