A Comparative Study on the Effects of Leachate on Groundwater in Selected Dumpsites in Rivers State, Nigeria

The health and environmental risk associated with unlined open waste dumpsites are worrisome. This study, therefore, evaluated the leachate and its final fate on groundwater pollution at selected solid wastes dumpsites in Rivers State. Leachate samples collected near the dumpsites were analyzed to determine the physical and biochemical characteristics. The two studied dumpsites indicated that the computed TCB were 296.33±6.22 cfu/100 ml and 182.68±21.33 cfu/100 ml respectively which were within the permissible limits of 400cfu/100 ml specified by World Health Organization (WHO) and Federal Ministry of Environment (FMEnv); which suggest low quantities of disease-causing agents in the groundwater. The total heterotrophic bacteria (THB) were 21x104 cfu/ml and 17x104 cfu/ml. These high values of THB may not be an indication of contamination of groundwater but it indicates a gradual decline in raw water quality. The values of SO42-, PO43-, TDS, DO, BOD and COD at the dumpsites were 196.52±6.26 mg/l and 9.12±0.59 mg/l, 139.23±3.19 mg/l and 3.81±0.68 mg/l, 5952.23±72.52 mg/l and 12663.33±490.95 mg/l;1.51±0.42. mg/l and 2.02±0.16 mg/l; 31.22±4.12 mg/l and 21.33±3.51 mg/l, and313.30±6.57 mg/l and 270.33±26.16 mg/l respectively which exceeded the standards of the WHO and FMEnv. The high values of analyzed parameters were an indication of the groundwater contamination. Heavy metals in the Rumuosi dumpsite indicated 11.31±1.33 mg/l, 11.01±0.67 mg/l, 361.84±12.31 mg/l, 118.03±5.74 mg/l and 84.77±4.84 mg/l for Pb, As, Mn, Fe and Zn respectively. While Heavy metals thresholds at Igwuruta were 0.004±0.005 mg/l, 0.04±0.07 mg/l, 0.05±0.08 mg/l, 0.08±0.14 mg/l and 0.15±0.04 mg/l respectively. Rumuosi thresholds exceeded the standards, indicating that the exposed local people in the nearby communities may experience cases of non-carcinogenic and carcinogenic health risk by drinking the groundwater. The leachate pollution index (LPI) at the studied dumpsites indicated 13.58 and 12.9 which exceeded the internationally accepted benchmark of 7.38; indicating that the Rumuosi leachate was more polluted than Igwuruta leachate. The analysis of variance (ANOVA) of the pollutant characteristics indicated a significant difference at p=0.05 across the physicochemical and biological indicators at Rumuosi dumpsite over Igwuruta dumpsite. The researcher recommended the practice of sanitary landfill which may reduce the risk of leachate percolation, a primary source of groundwater contamination.