Two-Dimensional Conservative Contaminant Transport Modeling of the Akaki Wellfield
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Date
2009-11
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Addis Ababa University
Abstract
This thesis work focuses on non-reactive solute transport modeling of the akaki wellfield
for two selected groundwater contaminants (chloride & fluoride) for the 25 operating
boreholes administered by Addis Ababa Water & Sewerage Authority (AAWSA). The
work is conducted based on laboratory analysis of groundwater samples from selected
boreholes and based on historical data of the wellfield boreholes.
The widespread use of chemical products, coupled with the disposal of large volumes of
waste materials, poses the potential for widely distributed groundwater contamination.
Because such contaminations can pose a serious threat to public health, prediction of the
degree of contamination by appropriate numerical modeling tools is vital to aware the
end user from possible risks. Mathematical models solved numerically are the subject of
this thesis work focusing on conservative solute transport in the Akaki well field.
Chloride & fluoride ions predictive modeling of the wellfield for the next ten years
(2007-2017) is made first by calibrating the model input parameters using the available
historical solute concentration data for selected boreholes at various periods. For
calibration purpose, initial solute concentration was taken as 3 mg/l for chloride and 0.51
mg/l for fluoride and MATLAB simulation of chloride & fluoride ion concentration is
done.
The simulation results show that while chloride concentrations in the wellfield get
increased; fluoride, however, is getting decreasing through out all of the boreholes in the
wellfield. This is in agreement with the actual observed pattern of solute load of the
wellfield revealing chloride is being introduced in to the wellfield by one or more
mechanisms somewhere in the vicinity of the akaki river catchment (ARC) while fluoride
is not.
Keywords: aquifers, breakthrough curves, initial conditions, boundary conditions,
calibration, prediction, conservative contaminant transport, hydraulic conductivity,
porosity.
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Keywords
aquifers; breakthrough curves; initial conditions; boundary conditions; calibration; prediction; conservative contaminant transport; hydraulic conductivity; porosity.