Refuse dumpsite and its associated pollutants
Authors: Ojo-Awo Nicholas Adesina , Agbabiaka Hafeez Idowu , Ilesanmi Abiola O. 
Published: February 2018

Purpose
The purpose of this paper is to investigate the physico-chemical properties of the groundwater surrounding the Solous (solid waste dumpsite) at Isheri, Lagos, Nigeria.

Design/methodology/approach
In total, 40 groundwater samples were collected from ten pre-determined sampling stations. Three sample stations were established before the dumpsite; three sample stations were located in the vicinity of the dumpsite in the direction of the leachate plume, while the remaining four sample stations were situated further away and acted as a control. Sampling was carried out four times during the study period (twice each in the rainy and dry seasons). The parameters measured in situ were air and water temperatures (using mercury-in-glass bulb thermometer) and pH (using pH meter). Calcium and magnesium contents were measured using the Ca-Mg indicator; sodium content was measured using the flame emission spectrophotometry and phosphate was measured using the flame photometry. The selected heavy metals (copper, iron, lead, cadmium, zinc and manganese) were measured by using the atomic absorption spectrometer. The oxygen parameters, such as dissolved oxygen, biological oxygen demand, chemical oxygen demand and organic matter, were determined titrimetrically. The data obtained were subjected to descriptive statistics and analysis of variance (ANOVA).

Findings
The results showed that many 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 sulfate (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 (1,224.85±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 the values as one moved away from the dumpsite.

Practical implications
The implication of the findings is that human health is remarkably dependent upon safe and clean drinking water. Preserving the water resources and hindering them from pollution is preferred to the treatment of polluted water and rendering it suitable for consumption. The high electrical conductivity values obtained in the groundwater samples near the dumpsites are an indication of the effect of leachate on the groundwater quality. The high concentrations of dissolved solids in the groundwater may decrease the palatability and may cause gastro-intestinal irritation in humans, and laxative effect particularly on transits.

Originality/value
The pollutants from the various waste components disposed at the dumpsite percolate into the ground to pollute the groundwater. The groundwater is transported in the line of flow away from the vicinity of the dumpsite to pollute the groundwater in the area. The extent of contamination level of groundwater quality due to leachate percolation depends upon a number of factors like chemical composition of leachate, rainfall, depth and distance of the well from the dumpsite. Groundwater samples of different depths and distances from dumpsites were analyzed in the present study to understand the level of a combination.