ABSTRACT
The study aimed at investigating groundwater pollution in the vicinity of a municipal solid waste (MSW) dumpsite in order to reduce the risks of groundwater contamination and spread of water-borne diseases. To achieve this, the research tools used include model formulation, finite volume analysis, field collection of soil samples at Enugu Waste Management Authority (ESWAMA) dumpsite at various depths along radial sampling lines during wet and dry season periods. Heavy metals (Cu, Fe, Zn, Pb, Cd, Cr, As, Ni, Co, and Mn) concentrations at various distances and depths were determined using an atomic absorption spectrophotometer (AAS model: AA320N). Soil samples were also analysed in the soil mechanics laboratory of the Department of Civil Engineering in the University of Nigeria, Nsukka for soil parameters viz. moisture content, densities, specific gravity, porosity, permeability, advective velocities, dispersion coefficients etc. By the method of finite volume analysis, one symmetric half of the study area was discretised into 160 nodes and all the nodal concentrations were determined through MATLAB solution of a 160 x 160 square matrix (for each heavy metal) arising from a two-dimensional solute transport equation. The predicted heavy metal concentrations from finite volume analysis were then compared with the laboratory results from field investigations. Baseline concentrations (ppm) of the heavy metals increased in dumpsite soils as follows: Cu: 0.167 – 1.351, Fe: 0.043 – 1.558, Zn: 0.257-0.688; Pb: 0.26 – 1.082; Cd: 0.267 – 1.448; As: 0.093 – 0.776; Ni: 0.057 – 0.444, Co: 0.267 – 1.448; Mn: 0.01 – 0.1403. The field results showed marked differences between the minimum and maximum heavy metal concentrations (ppm) respectively as follows Cu: 0.03 and 1.244; Fe: 0.01 and 2.82; Zn : 0.05 and 1.727; Pb: 0.072 and 1.43; Cd: 0.01 and 0.77; Cr: 0.01 and 0.422; As: 0.01 and 0.99; Ni 0.01 and 0.97; Co: 0.01 and 1.90; Mn: 0.01 and 0.39. From the finite volume analysis, the minimum permissible distance from the dumpsite required to site a well and the coefficient of correlation of the curve were computed and showed respectively as follows: Cu: 350m, 0.593; Fe : 140m, 0.583; , Zn; 2816m, 0.573; Pb: 833m, 0.59; Cd: 263m, 0.596; Cr: 470m, 0.570; As: 328m, 0.595; Ni: 351m, 0.594; Co: 550m, 0.590; Mn: 185m, 0.597. Both field results and finite volume analysis showed that the concentration of pollutants decreased with distance and depth from the dumpsite. The recommended minimum permissible distance from the dumpsite to site a well was 2.82 kilometers which corresponds to the distance from the most persistent heavy metal. Long term dumping of municipal wastes can increase the risks of groundwater pollution and spread of water-borne diseases and therefore continuous assessment and control measures should be put in place
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background Of Study
In Nigeria today, the government is unable to meet the ever increasing water demand. Thus individuals have had to look for alternative groundwater sources such as shallow wells and boreholes. The quality of these underground water are affected by the characteristics of the media through which the water passes on its way to the underground water zone of saturation (Adeyemi et al, 2007). Thus the pollutants discharged by industries, traffic, municipal, hazardous waste sites, landfills as well as from fertilizers for agricultural purposes and accidental oil spillages from tankers can result in a steady rise in contamination of ground water (Vodela et al., 1997; Igwilo et al., 2006).
1.2 Research Problem
Individuals in rural and urban areas nationwide complement governments efforts in the water sector, by providing private water supply schemes mostly shallow boreholes and hand dug wells with their attendant high risks of contamination from waste disposal sites, septic tanks and soak away pits, untreated industrial effluents, storm water runoffs from agricultural cultivated fields, leakages from municipal sewers etc. This study is therefore undertaken as a contribution to government mitigation measures in solving the problem of groundwater contamination that threatens the teeming population of our rural and urban dwellers living without adequate and safe drinking water, but meet their water supply requirements through underground water sources.
1.3 Scope Of Study
The study used a two-dimensional solute transport equation to investigate the spatial variation of the concentration distributions of heavy metals in the vicinity of a dumpsite by finite volume analysis. Soil samples were collected during the months of August 2012 (wet season) and February 2013 (dry season) within 80 meters radius along sampling lines from the boundaries of the dumpsite. The soil samples were analysed using atomic absorption spectrophotometer in order to determine the pollutants’ concentrations and compare same with the predicted values from finite volume analysis. A laboratory model was constructed and used to determine the transport parameters (advective velocities and coefficients of hydrodynamic dispersion). Other parameters determined included soil permeability, porosity, densities, specific gravity and moisture content. The heavy metals tested were Cu, Cr, Ni, Pb, Co, Fe, Cd, As, Zn and Mn. The minimum permissible distance to site a well on a lateritic soil from a dumpsite was also recommended.
1.4 Aims and Objectives of Study
The study is undertaken with the following aims and objectives :
- To determine, by field study, the variation of pollutants concentrations with distance from the dumpsite.
- To model the distribution of heavy metals around the dumpsite by finite volume method.
- To determine the minimum allowable or permissible distance of a water supply well from a point source of pollution.
- To compare predicted pollutant concentration values with the corresponding laboratory test values.
- To rank pollutants in order of risk of groundwater contamination.
1.5 Significance of Study
From this study, it is possible to predict with great accuracy, the variation of concentration of pollutants in time and space from a dumpsite, and to determine the minimum permissible distance from a dumpsite to site a safe water drinking well.
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