The investigation of the impact of leachate from Solous Waste Dumpsite, Isheri, Lagos, on the groundawater quality
This study investigated the physico-chemical properties of the groundwater surrounding the Solous Solid Waste Dumpsite at Isheri and determined the seasonal and spatial variations in the groundwater quality at selected distance intervals away from the dump site. This was with a view to determining the impact of percolating leachate from the dumpsite on the groundwater of the surrounding area. Forty groundwater samples were collected from ten pre-determined sampling stations. Three sample stations were established before the dumpsite. Three other sample stations were located in the vicinity of the dump in the direction of the leachate plume while the remaining four sample stations situated further away acted as control. Sampling was carried out four times during the study period comprising of twice each in the rainy and dry seasons. Samples were collected from wells with the aid of the equipment used by the residents. The parameters measured in-situ were air and water samples (using mercury-in-glass bulb thermometer) and pH (using pH meter). Calcium and Magnesium were measured by complexometric titration using Ca-Mg indicator; Sodium was measured using flame emission spectrophotometry and Phosphate using flame photometry. The selected heavy metals (Copper, Iron, Lead, Cadmium, Zinc and Manganese) were measured with an Atomic Absorption Spectrometer. The oxygen parameters such as dissolved oxygen, biological oxygen demand, chemical oxygen demend and organic matter were determined titrimetrically. The data obtained were subjected to descriptive statistics, regression, analysis of variance (ANOVA), cluster analysis, and principal component analysis (PCA). The study revealed that more parameters had higher values in the dry season than in the rainy season. Temperature (27.75±0.95°C), alkalinity (211.37±82.78 mg/LCaCO3), phosphate (0.30±0.07 mg/L) and sulphate (2.78±0.35 mg/L), sodium ion (41.95±18.86 mg/L), dissolved oxygen (2.98±0.57 mg/L) and COD (33.54±4.50 mg/L) had higher mean values in the dry season than in the rainy season. On the other hand the mean values of electrical conductivity (1224.85±370.63), nitrate (0.01±0.003 mg/L), chloride (98.76±21.58 mg/L), calcium ion (5.38±0.68 mg/L), Magnesium ion (3.05±0.05 mg/L), BOD (22.37±2.20 mg/L) and pH (6.31±0.18) were higher in the rainy season than in the dry season. The heavy metals (Iron 1.10±0.05 mg/L, Lead 0.12±0.07 mg/L, Manganese 0.01±0.004 mg/L, Copper 0.15±0.003 mg/L, Zinc 0.07±0.004 mg/L and Cadmium 0.02±0.02 mg/L) were fairly uniform all year round. There was also a marked decline in values as one moved away from the dumpsite. The differences in seasonal variations of measured parameters were not significant at p > 0.05 The study concluded that the leachate percolating from the Solous solid waste dumpsite at Isheri, Lagos, had negatively impacted the groundwater quality of the surrounding study area.