Establishment of the relationship between the sediments mineral composition and groundwater quality of the primary aquifers in the Maputaland coastal plain
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Date
2010
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Abstract
The Maputaland coastal plain has the largest primary aquifers in South Africa. It
has highly permeable sediments that promote rapid recharge to the aquifers and
strong interactions with wetlands in the region. The hydrochemical study of the
Richards Bay aquifers suggested that there is rising levels of dissolved minerals
in the Science Center aquifer. This study was designed to determine the
relationship between sediment mineral composition and the groundwater quality
of the selected primary aquifers of the Maputaland coastal plain.
The aquifers of interest were classified into Cretaceous, Miocene, Pleistocene
and Holocene Units, depending principally on a specific type of rock Formation
penetrated during the drilling process. The sediments of the aquifers were
classified into the Kwambonambi, Sibaya, Kosi Bay, Port Durnford, Uloa and St
Lucia Formations, according to the established lithological Units, using the grain
size, texture and colours of the sediments.
Water samples taken from the boreholes were assumed to represent all aquifers
intersected during the drilling process.
Maputaland aquifers are low in potassium, sulphate and magnesium ions.
Sodium and chloride ions remain unevenly distributed throughout the entire
selected Maputaland coastal plain aquifers. The Miocene Unit is characterized by
two chemical signatures, calcium and bicarbonate ions dominance and sodium,
calcium and bicarbonate ions dominance. The Pleistocene Unit is characterized
by three chemical signatures, sodium and bicarbonate ions dominance, calcium
and bicarbonate ions dominance and sodium and chloride ions dominance. The
Holocene Unit is characterized by two chemical signatures, sodium and chloride
ions dominance and calcium and bicarbonate ions dominance.
The Richards Bay sediments of the shallow Units are predominantly acidic with
high clay minerals, while the deep Units are mostly neutral or alkaline. It was concluded that the sediments in the shallow aquifers are acidic due to high
rainfalls that leaches calcium and carbonate ions from the sediments resulting in
weathering of the sediments to high clay minerals. Sodium and chloride ions
were assumed to be contributed by marine sediment deposits, coastal-influence
precipitation or direct recharge from surface water resources. These ions are
exchanging sites with calcium and bicarbonate ions resulting in sodium and
chloride ions dominance.
Although the groundwater quality of the Maputaland region has elevated total
dissolved solids with unevenly distributed sodium and chloride ions, low calcium
and bicarbonate ions in the shallow aquifers, the chemical composition of the
groundwater is still suitable for potable purposes, except in areas where the pH is
low with elevated dissolved ferrous, fluoride, aluminium and manganese ions.
Description
Submitted to the faculty of Science and Agriculture in partial fulfillment
of academic requirement for the Degree of Masters of Science in
the department of Chemistry, University of Zululand, 2010.
Keywords
Maputaland coastal plain, Aquifers -- South Africa, Sediment mineral composition, Groundwater quality