Hydrogeochemistry of Ground Water in Mbeere South Sub-County, Kenya

Abstract

This paper presents the experimental and simulated results of ground water in Mbeere South Sub -County, Kenya. A total of 30 samples from 10 boreholes were collected and used to investigate the chemical characteristics of groundwater. The samples were analyzed for physicochemical characteristics such as pH, temperature and Total Dissolved Solids along with major cations and anions using standard analytical procedures. The laboratory data obtained was run into a hydrogeochemical computer model, PHREEQC for aqueous speciation modelling. Origin pro and AqQA computer software were also used to reveal more hydrogeochemistry of the groundwater in the area. The results showed that the Na+ ˃ Ca2+ ˃ Mg2+ ˃ K+> Fe3+were the dominant cations while HCO3-˃Cl->SO42->NO3-˃F- were the dominant anions. The hydrogeochemical facies indicated that 40% of the samples belong to the Ca2+-Mg2+-Cl--SO42- type, 40% belong to the Ca2+-Mg2+-HCO3-, 20 % are of the type Na+-K+-HCO3- with no Na+-K+-Cl--SO42- water type. The facies also illustrated atmospheric precipitation, dissolution of salt deposits within the vadose zones and weathering of halite, anhydrite, gypsum, huntite, hydromagnesite, artinite, dolomite and magnesite as the major contributors to the variation in Mbeere South groundwater chemistry. The Saturation Indices (SI) showed that the specimens were slightly saturated with aragonite, calcite, and dolomite; slightly under-saturated with anhydrite and gypsum; moderately under saturated with halite and under-saturated with hydromagnesite, trona and portlandite.