HYDROGEOCHEMICAL ASSESSMENT OF GROUNDWATER BASED ON AQUIFER LITHOLOGY AROUND NCHALO, CHIKWAWA
Abstract
This study focused on analyzing and correlating the chemical composition of groundwater to aquifer lithology, in an area underlined by superficial (alluvial) deposits with subsurface extensions of Cretaceous Lupata sediments and Basement complex.
To achieve the main objective, the following specific objectives were carried out: (1) to analyze and interpret the water quality parameters of groundwater resource sample data; (2) to determine hydrogeochemical water types of each sampled groundwater resource; and (3) to use HCA and PCA to divide groundwater samples into different groups. Multivariate statistical analyses (PCA and HCA) combined with Piper trilinear graphical analysis were used to assess groundwater quality and understand the local hydrogeology on the groundwater hydrochemistry, The study involved collecting 8 groundwater samples from 4 different borehole sites.
The analytical results of groundwater chemistry indicated that the order of abundance of cation concentration was Ca>Na>Mg>K, while those of anions were HCO3>SO4>Cl.
The hierarchy cluster analysis (HCA) transformed the groundwater samples into three groups, and principal component analysis (PCA) identified that the major chemical variables governing PC1 and PC2 were (Ca, Mg, K, SO4, HCO3) and Cl respectively, and these explained most of the hydrogeochemistry. The hydrogeochemical facies observed from the piper plot were mostly of Ca-HCO3 types whereas some were of mixed Ca-HCO3-Cl type. These facies were seen to have originated from aquifer lithology through (1) the water-rock interactions to the phases of carbonate rocks (i.e. limestone and dolomites), gypsum, evaporate minerals (halite), calcite, silicates, and mafic minerals; (2) ion-exchange between Ca and Mg with Na in clayed sediments; and (3) mixing with fresh water. Generally, the groundwater is slightly saline or blackish
and can be safe for human consumption. For further studies, the determination of seasonal variations of hydrogeochemical parameters in these groundwater resources is recommended.
Research summary
This study focused on analyzing and correlating the chemical composition of groundwater to aquifer lithology, in an area underlined by superficial (alluvial) deposits with subsurface extensions of Cretaceous Lupata sediments and Basement complex. To achieve the main objective, the following specific objectives were carried out: (1) to analyze and interpret the water quality parameters of groundwater resource sample data; (2) to determine hydrogeochemical water types of each sampled groundwater resource; and (3) to use HCA and PCA to divide groundwater samples into different groups. Multivariate statistical analyses (PCA and HCA) combined with Piper trilinear graphical analysis were used to assess groundwater quality and understand the local hydrogeology on the groundwater hydrochemistry, The study involved collecting 8 groundwater samples from 4 different borehole sites. The hierarchy cluster analysis (HCA) transformed the groundwater samples into three groups, and principal component analysis (PCA) identified that the major chemical variables governing PC1 and PC2 were (Ca, Mg, K, SO4, HCO3) and Cl respectively, and these explained most of the hydrogeochemistry.