Investigation of Groundwater Quality in parts of Onitsha, Southeastern Nigeria

Abstract

The physico-chemical and microbial characteristics of water defines its quality. The groundwater quality in Onitsha was investigation in the present study from the point-view anthropogenic interference. The concentrations of the major ions were found to be below the recommendations by Nigeria Standard for Drinking Water Quality (NSDWQ) and World Health Organization (WHO) except chloride. High chloride content in groundwater may be an indication of urban groundwater contamination as well as proximity to marine source. The water type in the area as revealed from Piper Diagram is calcium-chloride type. The pH of the groundwater is slightly acidic, and it explains the paucity of carbonates in the groundwater system in the area. Carbonates are easily converted to bicarbonates under acidic condition. The concentrations of iron, lead, manganese, chromium and cadmium in the groundwater were found to be 73.3%, 23.3%, 20.0%, 13.3% and 10.0% respectively higher than their maximum permissible limit by NSDWQ and WHO. The slightly acidic medium enhances the dissolution, release and migration of these metals into the auriferous system. Based on the Water Quality Index (WQI), the groundwater in the area was categorized into 5 ranging from excellent water (24%), good water (27%), poor water (17%), very poor water (24%) and water unsuitable for drinking (10%). High concentration of chloride, iron, lead, manganese, chromium and cadmium in the groundwater in some locations are responsible for the poor water quality in the area. It can be attributed for the huge human activities going on in the area. The spatial distribution of WQI shows that wells close to dumpsites or untreated industrial effluent are deteriorated with respect to quality. Metal pollution index (MPI) indicates that iron lead and manganese show moderate pollution status while chromium and cadmium reflect light pollution. The results MPI agreed with the findings of WQI, which confirms the efficacy of these models in groundwater pollution studies.