Groundwater geochemical characteristics and its suitability for drinking and irrigation in Ventersdrop, North West Province, South Africa
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Date
2019
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University of Zululand
Abstract
Groundwater is major source of freshwater in regions devoid of surface water resources. The dependence on groundwater is increasing worldwide. South Africa is no exception. Groundwater resource has been identified as the main and reliable water resource for human consumption and agricultural practice in the Ventersdorp area, South Africa. Assessment of groundwater quality is necessary for safe usage for drinking and for irrigation purposes so as to boost the socio-economic wellbeing of the region. One such study was taken in Ventersdorp area, Schoonspruit Catchment, South Africa. The groundwater samples were collected from forty boreholes in 2015 as well as seventy boreholes in 2017 and was analysed for major ions and nitrate. The physical and chemical parameters of groundwater namely EC, pH, TDS, Ca2+, Mg2+, Na+, K+, Cl-, SO42-, HCO3-and NO3- during 2015 and 2017 were analysed. The concentration of major ions chemistry in groundwater was within the permissible limits of South African National Guidelines and World Health Organisation and for drinking use. The overall pH values for both sample periods represent slightly acidic to alkaline in the study area. Based on DWAF (1996) approved limit of drinking (EC <450), 45% of groundwater samples in 2015 and 13% samples in 2017 exceeded the limit in the study area. The classification of groundwater based on total hardness (TH) in the study area shows that majority of groundwater samples fall within the hard water category and the major groundwater types were Ca–HCO3 and Ca-SO4. The affluence of the major ions in the groundwater of the study area was found to be in the order of Ca>Na>Mg>K and HCO3>Cl> SO4>NO3. Several correlation diagrams between the major ion and other plots like the Gibbs, Chadha, Piper, Durov’s were prepared to ascertain the sources of ions in the study area. Gibbs plots have revealed that groundwater in the study area for both year 2015 and 2017 is of rock water interaction dominance. Similar inferences were obtained from Chadha plot. High correlation between calcium and bicarbonate, chloride with sodium, nitrate and sulphate and nitrate and potassium. Further, in order to ascertain the irrigation water quality, Kelly’s ratio, Sodium percent, residual sodium carbonate, sodium absorption ratio and permeability index were calculated for the groundwater samples in the study area. The IWQI as well as DWQI was calculated to get a snap shot of the region and it confirmed that most of groundwater samples in the study region fall between the range of suitable for both drinking and irrigation purposes in 2015 and 2017. The impact of heavy metal pollution index (HPI) in groundwater was ascertained. The coefficient variation of Zn was found to be higher than that
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of Cu, Cr, Cd, Ni and Pb in groundwater of the study area. The results suggest that Zn concentration has a high probability of being influence by human activities.
Apart from this groundwater quality, rainfall data and groundwater level data from 1974 to 2014 was collected from National Department of Water and Sanitation of South Africa. The analysis of the data revealed that shallow aquifers are easily affected by local climate changes while deep aquifers are dependent only on regional changes. Thus, shallow aquifers are more vulnerable to climate variability. The recharge of shallow aquifer is brief as compared to recharge of deep aquifer. In the study area, shallow wells are more likely to be affected by irrigation flow compared to deep wells and inferred from high correlation between Ca and HCO3. Cl was correlated with K and Na. NO3 and Cl are highly correlated. Variables correlating with Cl, SO4 and NO3 are partly derived from agricultural activities. Nitrate concentration in the study area shows strong positive relationship with five major ion and EC for last three decades from 1994 to 2014.
In general, the quality of groundwater is suitable for both drinking and irrigation needs. This study helped to comprehend the present state of groundwater chemical composition in Ventersdorp and to assess its fitness for irrigation and drinking uses.
Description
A dissertation submitted to the Department of Hydrology in fulfilment of the requirements of Master of Science Degree in the Faculty of Science and Agriculture at the University of Zululand, 2019.
Keywords
Groundwater, Geochemical