Groot Aub groundwater quality and its suitability for domestic purposes, Namibia

Abstract

The Groot Aub (GA) settlement depends entirely on groundwater for domestic purposes and other development activities. Development activities are mainly agriculture, such as animal husbandry, chicken farming and crop farming using irrigation. However, these activities have the potential to contaminate the groundwater system. A total of 87 groundwater samples were collected from the boreholes in the study area during the dry and wet season. Water quality parameters (pH, salinity, total dissolved solids (TDS), electrical conductivity (EC) and hydrochemistry (Na⁺ > Ca²⁺ > Mg²⁺ > K⁺, and HCO₃⁻  > SO₄²⁻ > Cl⁻) of 5 boreholes and 1 reservoir tank were analysed. The dominant cations were attributed to cation exchange processes as a coupled exchange of Na⁺ + K⁺ replacing Ca²⁺; and Na⁺ replacing Mg²⁺ ions in the rock–water interactions. The HCO₃⁻ anion is attributed to underlying rich carbonate rocks in the study area and chemical reactions between groundwater and silicate minerals.  TDS ranged from 639.01 to 1 998.96 mg/L. The microbial levels as indicated by heterotrophic plate count (HPC) values exceed the limits imposed by the local Namibian and WHO drinking water regulations. The Piper diagrams showed a mixed water type of mainly HCO₃⁻ and SO₄²⁻ anions and Na⁺ and Ca²⁺ > Mg²⁺ cations. The study shows that the elemental composition of the groundwater is impacted significantly by primarily anthropogenic activities and secondarily geogenic processes. Based on the results of this study it is recommended that a buffer zone be created between human activities and production boreholes to avoid further groundwater contamination.