Groundwater quality assessment in the Ngaka Modiri Molema District using the Water Quality Index

Abstract

In the conducted research, the groundwater quality of different boreholes located in the Ngaka Modiri Molema District (NMMD), more specifically Ratlou, Ditsobotla, and Tswaing local municipalities (LM), for drinking, livestock, and irrigation purposes were assessed. The obtained water quality results were also presented in straightforward and understandable form, along with a developed water purification technology decision tree in order to assist policymakers and/or concerned citizens with the evaluation and improvement of the water sources. It was found that the NMMD not only lacks a water management plan but also that irregular and ineffective groundwater monitoring is taking place. Furthermore, concerns were raised that the obtained results from the analysis would be rich in data, but poor in information for the necessary personnel. The objectives were therefore to not only effectively assess the groundwater quality of the specific area, but to also present the data in an easily understandable form for the necessary personnel by using the Water Quality Index (WQI) model. The WQI model used in the research was constructed by integrating the variable weights of several WQI studies. A final water quality class classification, ranging between Class I and V, was allocated to the individual water sources. 90 boreholes were evaluated, where the assessed parameters for drinking purposes include, Escherichia coli (E. coli), Faecal coliform, total dissolved solids (TDS), electrical conductivity (EC), pH, nitrate, sulfate, fluoride, chloride, manganese, iron, zinc, and copper. For livestock purposes TDS, EC, pH, nitrate, sulfate, chloride, calcium, magnesium, sodium, and copper were evaluated and for irrigation purposes, TDS, EC, pH, chloride, permeability index (PI), Kelly ratio (KR), sodium percentage (%Na), sodium adsorption rate (SAR), magnesium adsorption rate (MAR), and potential salinity (PS) were evaluated. For drinking purposes, the majority of the boreholes shifted from Class I to the unacceptable Class V when microbial contaminants were included in the evaluation, placing 51.1% of the boreholes in Class V. For livestock purposes, the majority of the boreholes (90%) had a WQI rating of Class I. The majority of the boreholes (66.7%) were classified as acceptable for irrigation purposes, with 27.8% and 38.9 of them classified as Class I and Class II, respectively. Further investigation was conducted on the investigated parameters that were proven to have elevated levels. It was found that nitrate, manganese, fluoride, EC, Faecal coliform, and E. coli had levels too high for drinking purposes. Only EC has proven to be a problem for livestock purposes and the levels of EC, calcium, magnesium, nitrate, sulfate, and chloride were too high for irrigation purposes. Water purification technologies were

recommended for each of the investigated boreholes in order to bring the water quality to the recommended standard. It was therefore concluded that the majority of the boreholes in the NMMD area had a water quality that is unsuitable for drinking purposes, however suitable for both livestock and irrigation purposes. Water management strategies, as well as effective and regular groundwater monitoring, are of utmost importance, especially for drinking purposes in the NMMD area.