Investigation of hydrochemistry and uranium radioactivity in the groundwater of Namaqualand, Northern Cape, South Africa
Date
2012-06-21
Authors
Leshomo, Joyce Tryphina
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The demand for groundwater in South Africa has increased over the years,
mainly in the arid, semi-arid and rural areas of the country. Groundwater is
generally considered a safe and viable option to untreated surface water.
Groundwater samples analyzed were limited to inorganic chemicals, stable
isotopes and radiological constituents. Dissolved inorganic constituents and
parameters analyzed included major anions and cations, trace metals, and
physico-chemical parameters. Inorganic constituents were analyzed to provide
basic information pertaining to water chemistry.
The hydrochemistry of the area indicates that groundwater evolution is taking
place and dissolution, ion exchange and mixing processes are the driving
processes. Br-/Cl- ratio show that the salinity in the area is derived from seawater
mixing, halite dissolution and atmospheric deposition/sea aerosol spray. Under
excessive evaporative regimes, as experience in the study area some of the
groundwater is heading towards hypersaline waters.
Isotopes analyses disclosed two groundwater flow types, deep and shallow
groundwater flow. The data further revealed groundwater mixing within the
aquifer where there is no direct infiltration (the samples have undergone
fractionation due to evaporation before infiltration), recharge in the area results
from regional flow from the neighboring catchments. . The age of the
groundwater calculated from average tritium of the local rainfall of 28.32 TU,
ranges from 87.01 to 174.02 years.
Gross alpha and beta emitters were detected in the water samples and are likely
attributed to naturally occurring uranium isotopes present in the water. The
radioactivity in the area is background activity, i.e. it is very low and is from the
rock material.
Uranium occurs in high concentrations in the groundwater of the study area,
ranges from 1 μg/l to 146 μg/l, which is above the WHO drinking water standard.
Data analysis show that uranium occur as UO2
+(c), UO2OH+, and U(OH)5
-
complexes in the absence of other complexing agents. In the presents of
carbonates uranium is found in solution as UO2
+, UO2CO3 and UO2(CO3)2
2- and
UO2(CO3)3
4- complexes.