School of Civil, Environmental and Mining Engineering

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Carlos Descourvieres Joiko


Start date

Mar 2007

Submission date

Nov 2011

Carlos Descourvieres Joiko

Carlos Descourvieres Joiko profile photo

Thesis

Quantifying water quality changes during managed aquifer recharge in a physically and chemically heterogeneous aquifer

Summary

In many parts of the world, depleting water resources and their management are recognised as a fundamental problem. The impact of this problem is enhanced by seasonal as well as long-term imbalances between fresh water supply and demand. Managed aquifer recharge (MAR) is increasingly used to mitigate these imbalances. MAR operations often involve the injection of oxic waters into anoxic media, which will generally trigger a wide range of mineral dissolution/precipitation, ion exchange and complexation reactions that can alter the water quality. However, while the influence of physical heterogeneity on MAR processes is increasingly recognised, little attention has been devoted to the superposed impact of physical and geochemical heterogeneity on water quality. A comprehensive series of experiments, at both laboratory and field scale, were conducted in the context of a pilot aquifer storage and recovery (ASR) implementation in Perth, Western Australia, to develop a quantitative understanding of the coupled physical and hydrogeochemical processes that affect the quality of the recovered water.

In the first part of this study a detailed aquifer characterisation was carried using high-resolution sediment sampling. The minerals that were likely to act as reductants for the oxygen introduced by the injection water and participate in the redox chemical reactions during a MAR operation were identified and quantified. These minerals included: pyrite, sedimentary organic matter (SOM), Fe(II)-carbonates and Fe(II)-silicates. The sediment characterisation was used in conjunction with incubation experiments to investigate correlations between reactive and physical parameters of the aquifer material. Subsequently, long-term batch and column experiments were performed to quantify the kinetics of the reactive processes that emerge under MAR conditions. The different contributions of the reductant and of the different lithologies to the oxygen consumption measured during sediment incubation experiments were quantified. This geochemical characterisation showed that grain size fractionation and hydraulic sorting were the main controlling processes that determined the geochemical signature of the sediments.

The aerobic reductive capacity, as defined by the rate of oxygen consumption, was found to be dependant on the reductant concentration but also on the variability in reductant composition and availability. The mineral that acted as the main oxygen reductant was pyrite, followed by SOM, despite SOM being much more abundant in the the proposed operating conditions the recovered water would not experience any deterioration in its quality

Why my research is important

One of the fundamental water resource management problems that are apparent in many parts of the world is the seasonal, but also longer term, imbalance between freshwater supply and demand (Maliva et al., 2006). While the average rainfall at these locations may be sufficient to fulfil the existing and projected average demands of freshwater, existing natural and anthropogenic reservoir systems do often not provide sufficient storage capacity to meet temporary freshwater demands at all times. This water deficit is aggravated where the continuous increase in water demand, especially in many arid or semi-arid regions that rely on groundwater resources, has over-stressed aquifers, leading to their depletion and/or salinisation (Custodio, 2002).


 

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