ABSTRACT

This research work presents findings of the extent and distributions of saline zone and the hydrochemical characteristics of the groundwater of Awe, Keana and Giza areas in the Middle Benue Trough of Nigeria.Staticwater levels(swl) of hand dug wells were measured andthe results used to generate hydraulic head data and hydraulichead map. The static water levels range from 1.0m to 13.5m at Awe, 1.0m to 4.5m at Keana and 2.2m to 9.2m at Giza. The hydraulic head maps for the three areas show different patterns/directions of groundwater flow for each area. Geophysical investigations, mainly vertical electrical sounding (VES) using Schlumberger electrode configuration array were performed at 47 locations spread across the entire study areas. Results of the VES revealed that the study areas are characterized by 3, 4 and 5 geo-electrical layers with 9 different curve type signatures. Also, results of the VES show that Awe area has the highest occurrence of saline zone, followed by Keana and Giza respectively. Multi-layer saline zones were observed only at Awe. Thirty (30) groundwater samples (10 each from the 3 areas) were analyzed for physiochemical parameters (rare earth elements, heavy metals, major cations and major anions).Results of hydrochemical analysis revealed five (5) hydrochemical facies namely,Ca-HCO₃, NaCl, NaHCO₃, Ca-Na-HCO₃ and Ca-Mg-Cl facies. Principal component analysis of the hydrochemical data revealed that the groundwater chemistry of the areas is controlled by the mineralization of the host rocks, weathering of galena, uranite, felsds pathic minerals and dissolution of limestone and dolomite. The spatial distribution pattern of the rare earth elements of groundwater of the study areas showed a strong positive correlation exists between brine and the elements. Uranium, however, showed a district distribution pattern which may indicate a distinct source from the other elements. Of the three areas studied, Keana has the most potable water supply.  Awe and Giza groundwater have chloride (Cl), nitrate (NO₃) and lead (Pb) contaminations. It was observed that the groundwater quality of the study areas is not only salinity dependent, but also influenced by anthropogenic activities such agricultural wastes and domestic waste released into the environment.Based on the irrigation water quality indexes employed, groundwater of the areas range from unsuitable to suitable for irrigation purposes.

CHAPTER ONE: INTRODUCTION

1.0       INTRODUCTION

1.1       BACKGOUND OF STUDY

The Benue Trough of Nigeria is one of the most prominent geologic features in West Africa. It extends over a length of 800km trending NNE-SSW from the Niger Delta to the south-west of Lake Chad basin and ranges in width from 130 to 250 km (Figure 1.1).  Due to the large regional extent, studies in the Trough are often divided geographically (though arbitrarily) into upper, middle and lower regions (the approximate boundaries of these regions are given in Figure 1.1. No concrete line of subdivision can be drawn to demarcate the individual regions, but major localities (towns/settlements) that constitute the depocenters of the different regions have been well documented (Obaje et al., 1999). The depocenters of the Lower Benue Trough comprise mainly the areas around Nkalagu and Abakaliki, while those of Middle Benue Trough comprise the areas around Makurdi through Yandev, Lafia, Obi, Awe, Keana, Giza, Jangwa to Wukari. In the Upper Benue Trough, the depocenters comprise Pindiga, Gombe, Nafada, Ashaka (in the Gongolaarm) and Bambam, Tula, Jessu, Lakun and Numan in the Yola arm.  

The origin of the Trough (which is still controversial in details) has long been associated with the breakup of Gondwana – the separation of Africa from South America and the opening of the South Atlantic Ocean. 

Occurrences of saline groundwaters as springs, ponds or in dug wells and boreholes are common in parts of the Trough. Prominent outcrops (which commonly support local salt industries) are found in the Lower Benue Trough and Middle Benue Trough (Figure 1.2). Brine is saline or salty water, particularly a highly concentrated solution of common salt (sodium chloride). It occursnaturallyas an underground salt lake and is one of the commercially important sources of common salt in the world (Leford and Jacoby, 1983).  Thesaline groundwaters in the Lower and Middle Benue Trough are frequently associated with tectonic elements such as intrusive and mineralized veins (Uma, 1998).

The presence of brine constitutes a serious hydrogeological problem on groundwater and as noted by Adeoti et al. (2010), saltwater intrusion into aquifers has become a major concern in most of the areas around brine fields as it constitutes the commonest of all the pollutants in freshwater.Therefore, understanding the point of saline intrusion is essential for the management of groundwater in such areas.Awe, Keana and Giza brine fields inAweand Keana Local Government Areas (LGAs) of Nasarawa State are some of the brine fields

located within the Middle Benue Trough.

            According to Offodile (1983), the saline ponds in the areas appear to originate from underground brine issuing from the western flanks of Keana anticline and perhaps also from the interbedded shale of fractured sandstone of Awe Formation and feeding the Awe and the other brine fields in the Middle Benue Trough.

1.2       STATEMENT OF THE PROBLEM                          

The presence of salt ponds in Awe, Keana and Giza areas is suspected to have led to an inflow of saltwater into the fresh aquifers of the areas, thereby resulting in serious groundwater contamination. Thus there is increasing demand for potable water supply in these areas. 

1.3       OJECTIVES OF THE STUDY

The primary objective of this work is to investigate the saline water intrusion into the freshwater aquifers of the areas. The outcome of the investigation is considered important for management of water resources of the areas.

            The secondary objectives/scope of this study is:

1. To investigate the extent and distribution of brine in each of the study areas.
2.  To delineate saline/brackish and freshwater zones of each of the study areas; this would be useful for groundwater management with minimum risk of saline contamination.
3. To investigate the geochemical properties of the waters in the various areas and determine the suitability of the waters for various purposes.

1.4       STUDY AREAS DESCRIPTION    

1.4.1   Location                                    

The areas, Awe, Keana and Giza are politically located in Awe and Keana local government areas(LGAs) in the south-eastern part of Nasarawa State. They are located between Awe lies between latitude 8° 06’ – 8° 12’N and longitude 8° 38’ – 9° 09’E. The major localities are in Awe and Keana local government areas(LGAs) of Nasarawa State.