Groundwater Quality Assessment in Eti-Osa, Lagos-Nigeria using Multivariate Analysis

Abstract

Groundwater quality in Eti-Osa was assessed. 18 water samples were collected from hand dug well and measured for 3 physical (pH, EC and TDS) and 9 chemical parameters (Ca, Cl, Fe, TH, Mg, NO3, SO4,TSS and Zn) after standard procedures (APHA).The results show that pH of groundwater samples indicates a neutral condition (7.01).TH was slightly hard (37.11mg/l).TDS, Fe and Mg concentrations were above the NDWQS limit of (500, 0.3 and 0.2mg/l) respectively for drinking water purpose. The Coefficient of variation shows that all the groundwater parameters with the exception of pH, Ca, Cl and Fe are highly heterogeneous. The correlation among the groundwater parameters shows that pH has a negative correlation at with Ca and TSS (r=-0.49).TH and Ca showed a positive correlations with Cl (r=0.51), EC (r=0.58).The factor analysis employed indicates four factors. Factor I, explains 27.73% of the total variance, with a strong positive loading on EC, TDS, Ca and a negative loading on pH. Factor II accounts for 21.35% of the total variance, and was characterized by strong positive loading of Zn and negative loading of Fe and TDS.Factor III was characterized by high positive loading of Cl and TH and accounts for 15.98% of the total variance while factor IV accounts for 14.05% of the total variance and was characterized by a strong positive loading of NO3.The paper recommended routine monitoring and thorough treatment before consumption. The study demonstrates the effectiveness of factor analysis in assessing the hydrochemical processes of groundwater in the area. @JASEM Groundwater constitutes an important source of water for drinking, agriculture and industrial production. The use of groundwater has increased significantly in the last decades due to its widespread occurrence and overall good quality. The contribution from groundwater is vital; because about two billion people depend directly upon aquifers for drinking water, and 40 percent of the world's food is produced by irrigated agriculture that relies largely on groundwater (Morris et al., 2003).Despite its importance, contamination from natural, human activities, steady increase in demand for water due to rising population and per capita use, increasing need for irrigation, changes in climates and over-exploitation etc)among others has affected the use of groundwater as source of drinking water. In Nigeria, regulatory agencies (Standard Organization of Nigeria (SON), Federal Ministry of Environment (FME) among others are established for the enforcement of national water quality and emission standards in order to protect human health and aquatic ecosystems. In term of effectiveness of these agencies, the decree that established them can be described as stale judging from the punitive contents which can best be described as a disincentive and invitation to chaos. The penalties for defaulters are cheaper and paying such a pittance as fine saves them more money than the actual objective for which the decree was made. Access to sources of water in Nigeria shows that 48% (about 67 million Nigerians) depend on surface water for domestic use, 57% (79 million) use hand dug wells, 20% (27.8 million) harvest rain, 14% (19.5 million) have access to pipe borne water, and 14% have access to borehole water sources (FGN,2007).Globally, about 80% of all diseases and death in developing country are water-related as a result of polluted water (Ayeni et al; 2011, Aderibigbe et al; 2008). Among the multivariate techniques, R-mode factor analysis has been widely employed for understanding hydrogeochemical association and processes controlling them (Briz-kishore and Murali, 1992; Ravi, 1999 and Rao, et al., 2001). As a first step, correlation analysis that reveals the relationship between two variables was calculated for the major ion in groundwater samples in the study area. Though factor analysis reduces the dimensionality of the problem, the meaning of these factors may sometimes be difficult to deduce (Davis, 1986). In this study, Kaiser varimax rotation was applied for the multivariate analysis of groundwater quality parameters. The final step of the factor analysis projected the data on the rotated significant factors and the scores obtained by this projection (factor scores) are used to understand the nature of variables. According to Dalton and Upchurch (1978) factor scores are related to the intensity of the chemical processes described by each factor. Negative numbers reflect areas unaffected by the process, positive numbers indicate areas most affected and near-zero numbers affect to an average degree (Lawrence and Upchurch, 1982). This study examined the governing factors of groundwater quality based on multivariate analysis technique in the study area. The Study Area: Eti-Osa Local Government Area is located between latitude 6 0 15 ' and 16 0 17' and longitude 3 0 3' east and 3 0 35' east. It is bounded in the south by Atlantic Ocean, in the east by Ojo local government, north by Lagos lagoon and part of Mainland and Island local government and in the