Investigating the possibility of using groundwater associated with dolerite structures to augment the municipal water supply to the city of Bloemfontein: investigations in the central business district
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Date
2018-01
Authors
Makoae, Manthofeela Christinah
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
This study investigates the potential of using groundwater resources associated with an intrusive
dolerite ring-dyke underlying the central business district (CBD) of Bloemfontein to augment the
current water supply to the Mangaung Metro Municipality (MMM). The current water supply to the
municipality is wholly dependent on surface water sources, which have proved to be unreliable and
insufficient to meet the increasing water demand in the municipality.
During the investigations, ground geophysical methods were used to detect and delineate the ringdyke
in areas within the CBD where the surface infrastructure allowed the geophysical surveys. The
magnetic and electrical resistivity (ERT) methods were used during the surveys. The magnetic
method is sensitive to both the presence of metallic infrastructure at surface or in the shallow
subsurface and to the presence of electromagnetic noise generated where electrical currents flow.
Since urban and industrial environments are characterised by such sources of noise, the magnetic
survey was severely restricted in terms of the locations available for the recording of reliable data.
The ERT survey, in turn, was severely restricted in terms of the space available within the CBD, as
well as the presence of hard surface covering (roads, pavements, concrete slabs) prohibiting the
installation of electrodes into the ground. Despite these limitations, the geophysical surveys were
successful in detecting the presence of the ring-dyke at certain positions within the CBD.
Based on the results of the geophysical investigations, positions for the drilling of investigative and
production boreholes were proposed. The drilling of these boreholes was to form part of the current
investigations, but due to factors beyond the control of the researcher, these boreholes are yet to be
drilled. These boreholes would have allowed the researcher access to the aquifers system associated
with the ring-dyke in order to perform hydraulic tests and assess the groundwater quality. The fact
that these boreholes were not drilled in time should be seen as a significant limitation of the current
study.
A limited hydrocensus was conducted in the vicinity of the ring-dyke. The purpose of the hydrocensus
was to locate points of groundwater abstraction near the ring-dyke in order to obtain information on
the use and quality of the groundwater, as well as to investigate the aquifer system(s) hosting the
groundwater. During the hydrocensus, several boreholes were located within 300 m from the ringdyke.
Of these boreholes, access to only three could be obtained as the owner of the properties on
which the remaining boreholes were located would not allow access to these boreholes. The
hydrocensus revealed that the boreholes near the ring-dyke are currently mostly used for irrigation.
No hydraulic tests could be performed on the boreholes identified during the hydrocensus due to the
presence of infrastructure. Hydraulic tests were, however, performed on a single borehole located on the premises of the Central University of Technology (CUT). Analyses of the results of the hydraulic
tests indicated transmissivity values in the order of hundreds of metres squared per day, indicating
that the aquifer system associated with the ring-dyke can be expected to be high-yielding.
Hydrochemical analyses of the groundwater samples collected from the boreholes identified during
the hydrocensus showed that the groundwater quality ranges from good to ideal. No clear evidence
for contamination was visible in the results of the inorganic analyses. The good quality of the
groundwater suggests that it can be incorporated into the municipal water supply without requiring
too much treatment. However, the investigations into the groundwater quality did not consider
hydrocarbon or bacteriological contamination of the groundwater. No conclusions can therefore be
drawn on the groundwater quality in terms of possible organic and bacteriological contaminants.
The results of the investigations indicate that that groundwater associated with the ring-dyke could
successfully be used to augment the municipal water supply. Depending on the quality of the
groundwater, it may find different applications in the municipality, including: domestic water,
irrigation, and industrial use. However, each of these applications has its own challenges in terms of
monitoring, aquifer management, water treatment and infrastructural requirements. To ensure the safe
and sustainable use of the groundwater resource, a groundwater monitoring and management
programme should be implemented. Such a programme will aim to ensure that the volumes of
groundwater abstracted do not exceed the long-term capacity of the aquifer system to deliver water,
while ensuring that the quality of the water delivered to the municipal supply system is of a suitable
quality for the its intended purpose. Routine monitoring of the water quality should be done to detect
possible contamination with organic compounds and bacteria, as well as industry-specific
contaminants.
Description
Keywords
Groundwater, Dolerite dykes, Ground-water management, Dissertation (M.Sc. (Institute for Groundwater Studies))--Unversity of the Free State, 2018