GROUNDWATER VULNERABILITY TO POLLUTION IN OKIGWE AND UMUAHIA AXIS, SOUTH-EASTERN NIGERIA

GROUNDWATER VULNERABILITY TO POLLUTION IN OKIGWE AND UMUAHIA AXIS, SOUTH-EASTERN NIGERIA

As Human activities increase in the study areas, the need to protect groundwater becomes greater. Therefore a technique for monitoring and assessing groundwater vulnerability to contamination is established. Hence, this study examined groundwater vulnerability in Okigwe and Umuahia area, and information derived was useful for protecting groundwater resources in the area.

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CHAPTER ONE

INTRODUCTION

1.1   Background Statement

Groundwater is a precious source of drinking water in many parts of the world. If contaminated, groundwater may pose serious health hazards. Groundwater can be contaminated through a wide variety of human and other activities, which may include on-land disposal of waste materials and sewage and the leaching of fertilizer and pesticides. Since the late1970s, occurrences of nitrate, bacteria, and pesticides in groundwater have exhibited a significant increase in concentration and have stimulated research on the subsurface fate of contaminants. Prevention of groundwater contamination is the key to efficient and effective environmental management, as the groundwater remediation is expensive and slow. In order to protect groundwater resources, areas prone to contamination by human activity need to be delineated, which can be best accomplished through groundwater vulnerability assessment (National Research Council, 1993). Groundwater is the main source of water available for human consumption. Over the years due to the swelling population, increasing industrialization and expanding agriculture, the demand for water has multiplied. Simultaneously the available per-capita water resources have been reduced due to the declining groundwater table, combined with an inefficient use of water.

 1.2 Statement Of the Problem

Groundwater pollution is a growing environmental problem, especially in developing countries. Many major cities and small towns in Nigeria depend on groundwater for water supply due to its abundance, stable quality, and less cost of exploitation. This, in turn, results in aquifer deterioration. Once groundwater is contaminated, it is difficult, if not impossible, for the water quality to be restored. Thus, constant monitoring of groundwater quality is needed so as to record any alteration in the quality. Poor environmental management creates havoc in the water supply, hygiene and general public health (Okoro et al, 2009).

Okigwe and Umuahia are rapidly growing urban centers in South-Eastern Nigeria. As a result of increasing population, urbanization, poor agricultural practices, high reliability on groundwater, and uncontrolled dumping of refuse, the aquifer becomes deteriorated, and this tends to make the groundwater system of the area highly vulnerable to pollution.  Therefore, an assessment of the vulnerability of groundwater in the study area was conducted, using major geological and hydrogeological factors that affect and control groundwater vulnerability, in conjunction with Geographic Information System (GIS) to produce vulnerability map which will provide better information on the groundwater resource of the area for sustainable development.

1.3     Groundwater Pollution Pathway

As water moves through the ground, natural processes are responsible for attenuation of concentration of many contaminants including harmful micro-organisms. The degree to which attenuation occurs is dependent on the type of soil and aquifer characteristics, as well as the type of contaminant and the associated activity.

In general, the term groundwater vulnerability is used to represent the intrinsic characteristics of the aquifer which determine whether it is likely to be affected by an imposed contaminant load (National Research Council, 1993).

There are two categories of vulnerability via Intrinsic vulnerability, which depends solely on the properties of the groundwater system, and specific vulnerability; where these intrinsic properties are referenced to a particular contaminant or human activity.

Vulnerability assessment is based on the likely travel time for a contaminant to move from the ground surface to the water table. The greater the travel time, the greater is the opportunity for contaminant attenuation. Aquifer vulnerability can also be quantified by employing an appropriate mathematical framework and further subdivided into broad classes like very high, high, low and very low, depending upon the governing criteria.

1.4     Groundwater Vulnerability Considerations

The time element is an estimable factor in the vulnerability assessment of groundwater. When the static water level exists at a great depth, it will take pollutants a very long travel-time to reach the groundwater. If the pollutant travels relatively slowly within the aquifer (because of low hydraulic conductivity, or because of low groundwater velocities), then groundwater vulnerability is considered to below. If on the other hand, recharge reaches the water table within a relatively short time because the aquifer is shallow or because geologic materials above the aquifer are highly permeable, then vulnerability is considered to be high. Deep groundwater is considered less vulnerable than shallow groundwater, because of the longer travel times necessary for a pollutant to reach a well.

Time scales are also important when mapping vulnerability to specific pollutants that become less harmful over time. For example, vulnerability to pathogen contamination is only a concern where travel times to groundwater (or to groundwater wells) are less than a few months to a couple of years. Also, many organic chemicals degrade over long time periods, becoming less harmful substances. (For some pesticides, this time period may be on the order of weeks to months).

Vulnerability may or may not include an assessment of whether pollutants are present or absent in the region of interest. The vulnerability that is independent of whether or not contaminants (pollutants) are present and which focuses primarily on a description of natural environmental conditions is often (though not always) referred to as “susceptibility”, “natural vulnerability”, “aquifer sensitivity”, or “intrinsic vulnerability”. Vulnerability is also a function of pollutant type. Different pollutants (or contaminants) behave differently, depending on their chemical or microbiological make-up. Pollution-type-dependent vulnerability, or vulnerability to specific land uses, is sometimes referred to as “specific vulnerability” or “integrated vulnerability”.

When groundwater becomes contaminated, it is very difficult to remediate: it moves slowly, so flushing out an aquifer can take a very long time (Liggett and Talwar, 2009). Treatment of the groundwater is not as easy as surface water because of the movement ability of water underground. So that preventive actions for groundwater is much more important than surface water.

1.5     The Study Area

The study area: Okigwe and Umuahia axis is between longitude 7⁰17’E to 7⁰ 39’E and Latitude 5⁰ 32’N to 5⁰ 55’N and comprises of communities such as Agbobu, Achara, Ihube, Mbato, Leru, Isi-Ikwato, umuowaibu, Okigwe, Avutu, Obowo, Isuochi, Umunneochi, and many others. It is bounded by highlands and lowlands with elevation ranging from 50m to 270m.

Fig 1.Location map of Study Area (Source: Google Earth map, 2018)

1.6     Aim of Study

The aim of this study is to assess groundwater vulnerability to pollution in Okigwe and Umuahia axis, South-Eastern Nigeria, Using DRASTIC (Aller et al, 1987) and GOD (Foster,1987) model, to promote sustainable development.

1.7     Objective of Study

As Human activities increase in the study areas, the need to protect groundwater becomes greater. Therefore a technique for monitoring and assessing groundwater vulnerability to contamination is established. Hence, this study examined groundwater vulnerability in Okigwe and Umuahia area, and information derived was useful for protecting groundwater resources in the area.

Some specific objectives of this study include:

1. Determination of DRASTIC & GOD parameters of the study area that will be integrated into the GIS environment to produce groundwater vulnerability maps of the study area.
2. Making recommendations for further studies involving the assessment of groundwater pollution potential.

1.8     Significance of Study

Groundwater vulnerability maps are designed to show areas of great potential threats to groundwater safety on the basis of hydrogeologic and anthropogenic (human) factors. Based on the produced vulnerability maps, it is possible to point out priority areas where there is a significant risk of groundwater contamination.