GROUNDWATER POTENTIALS OF THE NANKA SANDS AROUND NANKA-OKO AND ITS ENVIRONMENTS, ANAMBRA STATE

posted on August 13, 2019

ABSTRACT

Investigations were carried out for groundwater potentials and hydro-geochemical characteristics of the Nanka-Oko area and environs, southeastern, Nigeria. The areas are underlain by the Nanka Sands Formation. Data from 14 vertical electrical soundings were interpreted using computer aided techniques (IPI2win software). A total of 16 borehole groundwater samples, were also analyzed for their physiochemical and biological properties with the aim of assessing their characteristics and quality for domestic and agricultural purposes. The results of the interpretation of the geophysical data show that the area is characterized by variable subsurface layering ranging from six layers to eight layers.Lithologic logs, geoelectric sections and static water levels data reveal that the area is characterized by two aquifer horizons (upper and lower) and two aquifer types (confined and unconfined).Based on the estimated hydraulic conductivity, transmissivity and specific yield, two groundwater potentials zones (low and high) were defined. Results also show that the order of magnitude of the ionic species of groundwater of the area is > Na⁺> Ca²⁺>> Cl^–> Mg²⁺>> Fe^2-/3-. Only among the major ions (, Cl^–,,Ca²⁺,Mg²⁺ and Na⁺) shows a pronounced difference in concentrations from the two aquifer types. The chemical composition of the groundwater is controlled mainly by weathering processes with little contribution from dilution processes. Three hydro-geochemical facies were deduced from the Piper diagram namely, CaHCO₃, mixed CaMgCl and CaCl₂. The geochemical data also reveal that the groundwater from the area is potable as drinking water and suitable for irrigation purposes.

CHAPTER ONE

INTRODUCTION

1.1 General Information

The Nanka Sandstone has proven to be a prolific aquifer with intriguing hydraulic and challenging geotechnical properties. The characteristic nature of the sandstone continues to attract the interest of researchers in the fields of hydrogeology, geotechnical engineering, and environmental geology among others for obvious reasons. Dozens of works have been done on the Nanka Sandstone in recent times, but none so far has holistically treated all the challenges posed by this litho unit as each work has concentrated on a particular/peculiar challenge. In general, increased urbanization with its attendant increase in demand for potable water for domestic and agricultural purposes has increased interest in the study area. With the presence of Federal Polytechnic at Oko, and a perennial expanding Ekwuluobia Market for example, more groundwater exploration has become necessary.

Thisresearch project reports the groundwater potentialsof the Nanka Sands using vertical electrical soundings (VES), geologic logs of boreholesand hydrochemical data of the groundwater.

1.2 Objectives

The objectives of this study were to determine the groundwater potentials as well as the hydrochemical characteristics of the aquifers in the study area.

1.3 Location of the study area

The study area (Nanka-Oko and environs) lies within latitudes 6⁰00’ and 6⁰08’North, and longitude 7⁰00’ and 7⁰08’ East. Some of the towns include Nanka, Ekwuluobia, Oko, Obeledu and Agulu (Fig 1).

Climate And Physiography

The climate of the area is tropical with an average yearly rainfall of 1478mm, daily minimum and maximum temperatures of 22⁰ and 33⁰C, respectively. Relativehumidity ranges from 60% (at dry seasons) to 90 % (at rainy seasons). Two seasons exist namely, wet season (March to October) and dry season (November to February).