Abstract
The geochemical evaluation of carbonate aquifers in Ngbo and environs has been executed to ascertain the major ion chemistry and quality of waters for domestic and drinking uses. Ten water samples were gathered from pit lakes, hand dug wells, boreholes and rivers. The collected samples were analysed for pH, EC, TDS, Ca2+, Mg2+, Na+, K+, HCO3−, Cl−, SO42−, NO3− and PO42− in the laboratory using the standard methods. The results were compared with NDWQS and WHO standards. The physical parameters varied from pH (6.2–8.4), temp. (25.0–26.0 °C), electrical conductivity (4.9–102 µS/cm) and total dissolved solids (25.5–214.2 mg/l). The analysed results revealed the mean concentration of cations and anions in the following order: Ca2+ > Mg2+ > Na+ > K+ > Fe2+ and HCO3− > CO32− > SO42− > Cl−, respectively. Based on the standard limits, about 90% of the waters in the study area is suitable for domestic and drinking purposes. The Piper trilinear, Stiff and Durov diagrams showed that water samples from various locations fall into mixed CaCO32−+HCO3 type. Various ionic ratio plots show that water sources are from dissolution of minerals in the aquifer media. Geochemical parameters such as Cl−, Na+ and K+ show good interrelationship with positive factor loadings among the ions.
Highlights
Water is considered as fresh water exclusively if it generally contains Ca2+ as primary cation and H CO3− as principal anion
The pH value of water samples in the study ranged from minimum 6.2 to 8.4 with the least value observed in Ogwurube River (RS 1), while the maximum value was recorded at Stone Pile Mining Pit (PL 4)
The pH of the water samples indicates mildly acidic to alkaline in nature. pH was within the NDWQS (2007) and WHO (2011) acceptable level
Summary
Water is considered as fresh water exclusively if it generally contains Ca2+ as primary cation and H CO3− as principal anion. Most of the groundwater resources rich in C a2+ ion concentrations are considered safe for drinking (Castanier et al 1999). The chemistry of groundwater in carbonate aquifers has received considerable attention from researchers all over the world due to its heterogeneity and susceptibility to chemical pollution from human activities (Field 1988; White et al 1995; Romanov et al 2003). Owing to the modification in development of groundwater in carbonate aquifer, Hughes et al (1994) stated that geological structures and hydrogeological systems within carbonate aquifers are extremely complex. On the other hand, Plummer et al (1990) opined that dedolomitization influenced by gypsum dissolution is a major factor controlling the origin of water chemistry in the carbonate aquifers. On the other hand, Plummer et al (1990) opined that dedolomitization influenced by gypsum dissolution is a major factor controlling the origin of water chemistry in the carbonate aquifers. Hanshaw and Back (1979) stipulated the geochemical changes in carbonate aquifer systems and their hydrogeological deductions. Jalali (2005) reported that the dissolution of carbonate minerals, cation exchange and weathering
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