Effects of Solid Wastes on the Quality of Underground Water

Effects of Solid Wastes on the Quality of Underground Water

Chapter One

Aim and Objectives of Study

Aim of Study

This research aims to determine the impact of solid waste dumping on groundwater quality in selected dumpsites in Uyo, Ikot Ekpene, and Oron, Southeastern Nigeria

Objectives of the Study

The objectives of the study include to:

Carry out geophysical surveys to obtain vertical electrical-sounding data in the study areas.
Carry out a detailed interpretation of the vertical electrical sounding curves obtained and delineate the leachate/plume contaminated layers.
Delineate the migration paths.
Generate geoelectrical attributes of the area.
Correlate the geo-electric sections/VES curves with various lithologies using borehole logs.
Analyse for physicochemical and microbial parameters in the groundwater within the vicinity of the waste dumps.
Produce risk model maps of the leachate level.

CHAPTER TWO

LITERATURE REVIEW

Studies Related to Waste dumpsites

Karlik and Kaya (2001) combined the electrical and electromagnetic methods to investigate groundwater contamination at an open waste disposal site in Isparta, Turkey, with the objective of mapping the extent of contamination induced by the open waste-disposal site and thus, help to determine where future monitoring wells should be located. From their result, a good correlation between the Very Low Frequency-Electromagnetic (VLF-EM) and direct current (DC) resistivity methods employed for the study was observed, where soil chemical and previous hydrogeological surveys had indicated high levels of chemical concentration. They concluded the existence and spread of groundwater contamination and contributed to the efforts of groundwater protection and the assessment of installation sites for monitoring wells.

Soupios et al. (2007) carried out a study on estimation of aquifer hydraulic parameters from surficial geophysical methods around Keritis Basin in Chania, Greece, in order to know the aquifer parameters which are essential for the management of groundwater resources. The researchers applied geophysical methods in combination with pumping tests which provided a cost-effective and efficient alternative to estimate aquifer parameters. They used geophysical method to obtain aquifer characteristics that are previously estimated through pumping tests. They established a correlation among the parameters at other sites where pumping has not been carried out. In this way, the entire investigation area could be covered to characterize an aquifer system. They concluded that their study area is required for the management of groundwater in the region.

According to Dahlin et al. (2010), solid waste dumps constitute integral parts of the soil hydrological system and pose a serious pollution threat to both groundwater and downstream surface water. In a solid waste dump, high concentrations of materials such as heavy metals, nutrients, and organic substances lead to a risk of pollution to the surrounding environment. The pollutant load to the environment depends on the quantity and quality of the water that percolates through the waste dump and reaches the surroundings. It is related to this present study because the researchers evaluated the effect of solid waste dumps in relation to groundwater resources.

Awokunmi et al. (2010) conducted a study on the effect of leaching on heavy metals concentration at dumpsites by analysing samples of soil collected from different dumpsites located within Ikere and Ado Ekiti metropolis, South Western Nigeria. The samples were analysed for concentrations of Cd, Co, Cr, Cu, Fe, Pb, Mn, Ni, Sn and Zn. Control soil samples were taken at 200 m away from the last sampling point on each dump site down the slope and were also analysed for the presence of these heavy metals. The results of the analyses showed a significant difference in the concentration of these metals from the centre of each dumpsite at interval of 10 – 70 m down the slope (p < 0.05). The dumpsites were found to contain significant amount of toxic heavy metals.

Amadi (2011) assessed the effects of Aladimma dumpsite in soil and groundwater using water quality index (WQI) and factor analysis. The results suggested that the groundwater around the dumpsite is poor in quality while factor analysis revealed five sources of groundwater pollution. The poor quality of groundwater around the dumpsite was attributed to leachate percolating into the subsurface thus contaminating the groundwater.

CHAPTER THREE

MATERIALS AND METHODS

Materials

Equipment for Resistivity Survey

The geoelectrical resistivity survey within the study area involved the use of the GEOTRON (Model G41) resistivity meter and OHMEGA resistivity meter (Figs. 3.1a and b).

The GEOTRON (Model G41) resistivity meter has potential and current electrodes, 4 reels of cables of 700m long for current electrodes and 200m for potential electrodes, measuring tape, GPS, data reporting sheet, field note book, pen, pencil and geologic hammers for the collection of field resistivity data. The South African made resistivity meter (GEOTRON G41) has a very high precision in giving accurate results and has the advantage of instantly converting resistivity values to apparent values, making data collection easy and with less time. This is a great advantage over other resistivity meters where field resistivity values are multiplied with the Geometric factor (K) to obtain apparent values, which is usually time consuming.

CHAPTER FOUR

RESULTS AND DISCUSSION

Qualitative Interpretations of Geoelectrical Results

The geoelectrical curves generated across the study areas (Fig. 4.1 – Fig. 4.2), vary considerably throughout the entire areas. Uyo resistivity curves show typically H-curves which are quite common in a sedimentary environment for multilayer structures of three or more layers (Fig. 4.1a). At Ikot Ekpene, there are hybrid of K and H curves, A and K curves while one VES station has H-curve. At Oron, it is predominantly K-curves, with one VES station having A-curve and hybrid KHK-curve.

CHAPTER FIVE

SUMMARY, CONCLUSIONS, SUGGESTION FOR FURTHER WORK AND CONTRIBUTION TO KNOWLEDGE

Summary

This research work is summarized as follows:

The results of qualitative interpretation reveal that the VES curves generated at Uyo dumpsite is basically H-curves. The VES results in conjunction with the borehole logs showed mainly three or four lithologic layers namely: top lateritic sand, leachate contaminated sand, dry, fine to medium-grained sand and medium to coarse-grained sand layers. The leachate contaminated layer has thickness range of 0.64-22.20m and resistivity values range from 4.06 -20.0_Ωm. The computed layer parameters show that the values of various parameters range from low to high: longitudinal conductance (0.204500-2.636580S); transverse resistance (15.3468 – 186.9240_Ωm²) and leachate thickness (2.85 – 22.20m). The hydraulic conductivity of the leachate at Uyo dumpsite ranges from 23.62639 – 104.56490m/day while the transmissivity ranges from 96.6319 – 1175.5230m²/day. The hydrogeochemical analyses revealed that all water samples from boreholes proximal to Uyo dumpsite had low pH while few water samples exhibited elevated total dissolved solids (TDS), Cadmium, electrical conductivity and dissolved oxygen. The leachate migration path around Uyo dumpsite trend predominantly in NW- SE direction.

The VES curves generated at Oron dumpsite are K, A, and the hybrid curve KHK. The interpretation showed three to five layers, the leachate contaminated layer being the third layer. The computed layer parameters range as follows: leachate thickness (18.86 – 62.90m); longitudinal conductance (1.410526 – 13.186580S); transverse resistance (143.4344 – 509.2000). The hydraulic conductivity of leachate at Oron dumpsite ranges from 24.78434 – 99.97812m/day while the transmissivity ranges from 664.2203 – 5659.0750m²/day. Water samples from boreholes proximal to Oron dumpsite exhibited low pH, high electrical conductivity and dissolved oxygen. The leachate migration path trend predominantly in the NE-SW direction. The result reveals intersecting pattern such that the static water level crisscrosses the leachate level surface at 35m.

Conclusions

This study reached the following conclusions:

Vertical electrical sounding (VES) has guided the estimation of leachate resistivity, thickness, hydraulic conductivity, transmissivity, longitudinal conductance and transverse resistance
Oron dumpsite is more contaminated than Uyo. This is buttressed by the following:

At Oron dumpsite, the leachate level actually meets the static water level.
Oron dumpsite has lower resistivity values.
Oron dumpsite has lower erodibility.
Oron dumpsite has higher leachate transmissivity
Oron dumpsite has greater leachate thickness than Uyo.
Geologically Oron is underlain by Alluvial Sand while Uyo is underlain by more consolidated materials of lower porosity and permeability

The risks associated with the present poor system of waste management is very high as it constitutes threat to surface and groundwater resources. The groundwater of the study area may not have been seriously contaminated as at the time of study; but there is no guarantee that this may not reverse in the future.

Suggestions for further Work

There is a growing need for characterization of the near-surface region, with information required about the physical, chemical, and biological properties and processes in the subsurface. While traditional methods of drilling and direct sampling can provide highly accurate information, they are limited in terms of spatial coverage, in both the size of the sampled volume and the density of the sampling. In addition, when dealing with contaminated sites where there is a great need for accurate characterization, all methods of direct sampling run the risk of further spreading the contaminant, a potential hazard to both workers and to the environment.

Groundwater protection policy and strategy should be based on the concept that prevention of pollution is always less expensive than aquifer rehabilitation, which is a costly, time- consuming and technically demanding task. It may often be more efficient to invest in preventive processes within the catchment than to invest in major treatment infrastructure to manage a hazard. As it is neither physically nor economically feasible to test for all drinkingwater quality parameters, the use of monitoring effort and resources should be carefully planned and directed at significant or key characteristics. However, it is anticipated that in the future much more use may be made of geophysics for monitoring contamination of the groundwater using permanently installed geophysical sensors in water boreholes and perhaps both within and on the ground surface.

One public health implication of this work is that no new water supply wells should be placed in areas of abnormally low resistivity until the reason for this low resistivity can be resolved.

Contribution to Knowledge

The study evaluated layer parameters including Dar Zarrouk parameters of the Study Area.
The study allows for comparative assessment of data in geographically different, but geologically similar areas of Uyo, Ikot Ekpene and Oron.
The Risk Map Model is a very significant tool for assessing the contamination status in the Study Area.
The study has also designated areas affected and not affected by the dumpsites.
The data generated in this study, will guide planners and managers of environment in the future siting of waste ‘facility’ in the State.

REFERENCES

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