Analysis of Subsurface Contaminant Transport in Akaki Well Field and surrounding areas, Central Ethiopia
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Date
2007-08
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Addis Ababa Universty
Abstract
The acute need for water in big cities like Addis Ababa calls for an
integrated water resources development approach that considers the
entailing environmental factors. This task becomes even more pressing
as industrialization and development advances. In view of this, the
current study aims to identify potential movement of pollutants in a wellfield,
and specifically to identify the pathways of pollutants and their
spatial movement in the aquifer.
The study area, the Akaki well field and surrounding areas including the
towns of Kality and Akaki, is located in the Awash drainage basin,
southeast of the Addis Ababa city centre. The well field provides more
than 30 % of the drinking water supply of Addis Ababa.
A groundwater flow model was constructed to analyze contaminant
transport in a fractured system. The model was then calibrated with both
under steady state and transient state flow conditions, in order to prove
that the model represents the actual conditions. Modeling tools have
been eventually used to calculate path lines and travel times of
contamination. This approach involved the introduction of particles at
contaminant sources upstream of wells and at the well field it self, then
identifying the path lines, and determining the spatial distribution of the
contaminants through steady state flow field at initial step and finally
through transient state flow field.
The individual measured data for nearly 120 wells were interpolated
using kriging method and each cell in the model was assigned its value.
The well data base is obtained from AAWSA. The physical parameters are
well organized; however, the Hydrochemical data are too old and does not
indicate real sign of pollution. The results revealed that the flow lines intersect with the Akaki River in
numerous places. Furthermore, the flow lines converge towards Akaki
well field from all directions, implying that any contaminated water from
the upper part of the aquifer will be pulled into the wells, indicating a
high risk of vulnerability of the well field to pollution.
The following recommendations are helpful in curbing the risks posed.
Manufacturing activities having pollution potential must be limited in
special areas sufficiently far from water supply wells; the chemical
quality of groundwater must be monitored and Environmental policy
must be implemented with particular emphasis for the protection zones
around the well field.
This study generated a model and recommendations that allows decision
makers to establish a framework for regulating contaminants that are
likely to pose risks to drinking water in the well-field.
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Keywords
Akaki Well Field and Surrounding Areas