MAPPING GROUND WATER VULNERABILITY & RISK OF HYDROCARBON CONTAMINATION IN A SEMI-ARID REGION OF NORTHERN NIGERIA

: MAPPING GROUND WATER VULNERABILITY & RISK OF HYDROCARBON CONTAMINATION IN A SEMI-ARID REGION OF NORTHERN NIGERIA

Abstract

Groundwater is a critical resource for people relying on it for drinking water, agricultural needs, industry, and many other applications. However, groundwater aquifers are highly susceptible to contamination from anthropogenic impacts. Understanding the risk and potential extent of contamination is key to protecting precious groundwater supplies. Among the numerous groundwater vulnerability assessment methodologies and tools, is the Geographical Information System GIS-based DRASTIC and GOD models, which are the most widely used and have been found to achieve reliable results even in hydro-geologically complex systems. In semi-arid regions, many areas heavily dependent on and susceptible to groundwater contamination face water scarcity. However, prevailing research utilizing vulnerability models has predominantly concentrated on temperate and wet regions, such as those found in the USA and the United Kingdom. Moreover, the majority of groundwater vulnerability modeling efforts have primarily centred on nitrate contamination. Notably, there exists a dearth of studies evaluating the inclusion of hydrocarbon point sources of contamination within the frameworks of these models.
This doctoral investigation centered on two main objectives: firstly, the assessment and comparison of the performance of the DRASTIC and GOD models in identifying regions susceptible to contamination; and secondly, the quantification of hydrocarbon contamination in the Kano region, coupled with visualization through model-derived groundwater vulnerability maps. More precisely, the study therefore aimed to delineate vulnerable zones within the semi-arid landscape of Kano, Nigeria, specifically addressing hydrocarbon contamination. This was achieved through the application of a GIS-based spatial analysis approach, integrating the vulnerability models DRASTIC and GOD.
The paramount parameters characterizing groundwater vulnerability were discerned as the depth of water (22.92%), net recharge (25.98%), impact of the vadose zone (27.07%), and groundwater confinement (53.47%).Field monitoring conducted for this study involved spatial analysis of borehole data for groundwater samples, specifically targeting benzene, ethylbenzene, and xylene (Betex) hydrocarbon components found in crude oil. The findings reveal elevated levels of hydrocarbons in the groundwater of Kano, with the highest recorded concentration (35 mg/l) identified in Dala, located in western Kano. This heightened concentration can be attributed to numerous point sources of pollution, notably under-storage tanks at petroleum stations and automobile garages, as pinpointed through field-based GPS data.To enhance the identification of groundwater vulnerable zones, a more adaptable approach was achieved by integrating sensitivity analysis principles into the model results. This involved supplementing the existing DRASTIC and GOD parameters with additional input data, serving as an optimiser to enhance the model's performance.

Date of Award	17 Jan 2024
Original language	English
Awarding Institution	University of Bath
Sponsors	Technology Development Fund (PTDF), Nigeria, 2018 - 2022.
Supervisor	Lee Bryant (Supervisor) & Thomas Kjeldsen (Supervisor)