GEOCHEMICAL AND MINERALOGICAL ASSESSMENTS OF WATER ROCK INTERACTION AND ITS IMPLICATIONS ON THE GROUNDWATER QUALITY IN AN AQUIFER: A CASE STUDY OF T/A CHIMALIRO AREA
Abstract
Contamination of groundwater is a widespread issue around the globe and the water quality is highly dependent on the geology as well as anthropogenic interventions in the area (Hellens, 2013). Groundwater is used intensively for domestic purposes in rural areas of Malawi where Over 82% of burgeoning 17.5 million of the country’s population live in rural areas that are heavily dependent upon groundwater for drinking water supply (Upton, Dochartaigh, Chunga, & Bellwood-Howard, 2020) of which T/A Chimaliro in Thyolo district is one of them. Six groundwater samples and 2 rock samples were collected to evaluate the hydro-chemical characteristics and the impact of water–rock interaction on the chemistry of groundwater using classical geochemical and statistical tools. The total dissolved solids (TDS) are all fresh water (below 530ppm).
The distribution of the major ions is the order of Ca2+> Mg2+ > Na+> K+ and HCO3 −> Cl−>SO42−. The entire water samples were collected from boreholes which draw groundwater from the fractured basement aquifer. Ionic abundance plot is of high Ca2+ + Mg2+ over alkalis and high weak acids over strong acids is suggestive of CaMg(HCO3−) type trends of concentrations (Piper, 1944). Gibbs ratio’s showed that two main processes prevailed, chemical weathering (carbonate dissolution) of rock-forming minerals, especially the carbonates (in five samples shown by the use of a piper diagram and scatter plots) and evaporation (on one sample). This is also proved by the hydro-chemical signatures and correlation relationships of the different elements. The obtained results revealed that about 100% of the samples are suitable for drinking purposes with respect to Malawi standards but according to WHO 33.33% of the samples with respect to iron concentrations. After all the analysis the fractured basement aquifer has not affected the hydro-geochemistry of the groundwater for it to have calcium and magnesium bicarbonate type because it is made up ferromagnesian minerals according to (Envans, 1965) and (Habgood, Holt, & Walshaw, 1973) which was also verified by the rock samples which were collected along the Luchenza River.
Research summary
Groundwater is used intensively for domestic purposes in rural areas of Malawi where Over 82% of burgeoning 17.5 million of the country’s population live in rural areas that are heavily dependent upon groundwater for drinking water supply (Upton, Dochartaigh, Chunga, & Bellwood-Howard, 2020) of which T/A Chimaliro in Thyolo district is one of them. Gibbs ratio’s showed that two main processes prevailed, chemical weathering (carbonate dissolution) of rock-forming minerals, especially the carbonates (in five samples shown by the use of a piper diagram and scatter plots) and evaporation (on one sample). The obtained results revealed that about 100% of the samples are suitable for drinking purposes with respect to Malawi standards but according to WHO 33.33% of the samples with respect to iron concentrations. After all the analysis the fractured basement aquifer has not affected the hydro-geochemistry of the groundwater for it to have calcium and magnesium bicarbonate type because it is made up ferromagnesian minerals according to (Envans, 1965) and (Habgood, Holt, & Walshaw, 1973) which was also verified by the rock samples which were collected along the Luchenza River.