Assessment of Groundwater Chemistry and Quality Characteristics in an Alluvial Aquifer and a Single Plane Fractured-Rock Aquifer in Bloemfontein, South Africa
Authors: Modreck Gomo
The evolution of groundwater chemistry and its quality is largely controlled by hydrogeochemical processes and their understanding is therefore important for groundwater quality assessments and protection of the water resources. A study was conducted in Bloemfontein town of South Africa to assess and compare the groundwater chemistry and quality characteristics in an alluvial aquifer and single-plane fractured-rock aquifers. 9 groundwater samples were collected from monitoring boreholes drilled into the two aquifer systems during a once-off sampling exercise. Samples were collected through low-flow purging technique and analysed for major ions and trace elements. In order to describe the hydrochemical facies and identify dominant hydrogeochemical processes, the groundwater chemistry data are interpreted using stiff diagrams and principal component analysis (PCA), as complimentary tools. The fitness of the groundwater quality for domestic and irrigation uses is also assessed. Results show that the alluvial aquifer is characterised by a Na-HCO3 hydrochemical facie while fractured-rock aquifer has a Ca-HCO3 facie. The groundwater in both aquifers originally evolved from the dissolution of calcite rocks that are common on land surface environments. However the groundwater in the alluvial aquifer further goes through another evolution as driven by cation exchange process in which Na in the sediments exchanges with Ca2+ in the Ca-HCO3 hydrochemical type to result in the Na-HCO3 hydrochemical type. Despite the difference in the hydrogeochemical processes between the alluvial aquifer and single-plane fractured-rock aquifer, this did not influence the groundwater quality. The groundwater in the two aquifers is very hard as influenced by the elevated magnesium and calcium ions that evolve from dissolution of carbonate minerals which typically occurs in surface environments. Based on total dissolved levels (600-900 mg/L), groundwater quality of the two aquifer systems is classified to be of fair quality. The negative potential impacts of the groundwater quality for domestic uses are highlighted.
Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1314783Procedia APA BibTeX Chicago EndNote Harvard JSON MLA RIS XML ISO 690 PDF Downloads 561
 G. Sawyer, and D.L. McMcartly, Chemistry of Sanitary Engineers, 2nd Edition. McGraw Hill, New York, 1967, p. 56.
 W. Stumm, and J.J. Morgan, Aquatic Chemistry - Chemical Equilibria and Rates in Natural Waters, 3rd Edition. Wiley & Sons, New York, 1996, p. 214.
 M. Gomo, G.J. van Tonder, and G. Steyl, “Investigation of the hydrogeochemical processes in an alluvial channel aquifer located in a typical Karoo Basin of Southern Africa,” Environmental Earth Science, vol. 70, pp. 227-238, 2013.
 S. Selvakumar, N. Chandrasekar, and G. Kumar, “Hydrogeochemical characteristics and groundwater contamination in the rapid urban development areas of Coimbatore, India”, Water Resources and Industry, vol. 17, pp. 26-33, 2017.
 A. Rezaei, and H. Hassani, “Hydrogeochemistry study and groundwater quality assessment in the north of Isfahan, Iran,” Environmental Geochemical Health, https://doi.org/10.1007/s10653-017-0003-x, June 2017.
 J.F. Botha, J.P. Verwey, I. Van der Voot, J.J.P. Vivier, J. Buys, W.B. Colliston and J.C. Loock, “Karoo Aquifers: Their Geology, Geometry and Physical Properties,” Water Research Commission of South Africa, Pretoria, 1998.
 M. Gomo, “A groundwater-surface water interaction study of an alluvial channel aquifer,” Ph.D. thesis, University of the Free State, Bloemfontein, South Africa,” 2011.
 M.P. Kearl, E.N. Korte, M. Stites, and J. Baker, “Field comparison of Micropurging vs. Traditional Ground Water Sampling,” Groundwater Monitoring and Remediation, vol. 4, no. 4, pp. 83-190, 1994.
 R.W. Puls, and M.J. Barcelona, “Low flow (minimal drawdown) ground-water sampling procedures,” U.S. Environment Protection Agency, EPA/540/S-95/504, 1996.
 U.S. Geological Survey, “National Handbook of Recommended Methods for Water Data Acquisition,” January, Reston, Virginia, USA, 1996.
 D.L. Parkhurst and C.A. Appelo, “Description of input and examples for PHREEQC version 3-A computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations,” U.S. Geological Survey Techniques and Methods; United States Geological Survey (USGS): Reston, VA, 2013.
 WHO, “Total dissolved solids in drinking-water. Background document for development of WHO Guidelines for Drinking-water Quality”. WHO/SDE/WSH/03.04/16. Geneva, Switzerland, 2003.
 W. McGowan, “Water Processing: Residential, Commercial, Light-Industrial,” 3rd Edition. Water Quality Association, Lisle, Illinois, USA, 2000.
 K.G. McQueen, “Calcrete geochemistry in the Cobar-Girilambone region,” Cooperative Research Centre for Landscape Environments and Mineral Exploration (CRC LEME), New South Wales, 2006.
 J.A. Schraut Jr, “The occurrence and association of millerite and fluorite in limestone quarries of the St. Louis, Missouri area,” Rock and Mineral, vol. 25, pp. 3-4, 1950.
 WHO, “Guidelines for Drinking-water Quality,” 4th Edition. ISBN 978 92 4154815 1, Geneva, Switzerland, 2011.