European Geologist Journal 58

Groundwater contamination and the invisible crisis of sustainability

 

by Ana Maria Antão 1*

1 Instituto Politécnica da Guarda, Escola Superior de Tecnologia e Gestão, Guarda, Portugal

Contact: anantao@ipg.pt

Abstract

Groundwater contamination poses a critical global challenge, often overlooked due to its invisibility and complexity. This silent threat compromises freshwater availability, vital ecosystems, and sustainable development. Unlike surface water, groundwater lacks self-purification, making contamination almost irreversible. This article explores the interplay between geological characteristics, legal frameworks, and public awareness in addressing groundwater contamination. Drawing on case studies from Portugal, it highlights the need for robust legislation, enhanced hydrogeological research, and proactive monitoring systems. The findings stress the urgency of preserving this finite resource through multidisciplinary approaches and education, ensuring future generations are equipped to manage and protect groundwater effectively. The article concludes by emphasising that safeguarding groundwater requires global collaboration and innovative policies to combat escalating environmental and climatic challenges.

Cite as: Antão, A. M. (2024). Groundwater contamination and the invisible crisis of sustainability. European Geologist, 58. https://doi.org/10.5281/zenodo.14840728

Creative Commons License This work is licensed under a Creative Commons Attribution 4.0 International License.

1. Introduction

The final decades of the 20th century and the early decades of the 21st century saw an abundance of news about accidents related to soil contamination. While such incidents had previously occurred, public opinion and the media were not fully attuned to this pressing reality that poses risks to the environment. The preceding centuries brought significant advances in research in chemistry, physics, biology, geology, anthropology, among other sciences, enabling us to pose critical questions about this ‘silent enemy’ that is threatening Earth’s future.

Until the mid-20th century, Europe endured two world wars on its territory. These conflicts were separated and followed by episodes of famine and air quality issues, ranging from the smog crisis in London during the 1950s to contemporary measures on combustion vehicles in major European cities. Emerging concerns regarding the quality and quantity of surface waters were increasingly attributed to the initial impacts of climate change. These challenges, combined with the conclusion of the Cold War and Europe’s drive to assert itself in a very competitive global landscape, resulted in the neglect of its soil and groundwater resources. It is urgent to start dealing with these critical issues now. Failure to act promptly risks irreversible damage.

Groundwater contributes around 25% to our planet’s annual freshwater consumption [1], underscoring the importance of groundwater contamination.

Groundwater does not exist in isolation from other terrestrial environments. It is intricately connected with specific terrains, such as soils and rocks, that facilitate its accumulation and preservation. One of the characteristics of groundwater is that, unlike surface water, it is not directly influenced by rainfall or the regional water system. Instead, its behaviour is governed primarily by geological, rather than morphological, characteristics. Understanding groundwater requires understanding of the geology and, more specifically, the hydrogeology of each region.

2. Contamination: a legal issue?

It is with this evolving context that questions arise about the health of our soil and its associated aqueous environment, specifically groundwater. On the scale of human life, groundwater is a finite resource. Its contamination often goes unnoticed, neither seen, felt, nor smelt, yet its challenges persist silently. Every instance of land development must account for this critical issue. In this regard, the European Union must intensify its efforts to address groundwater challenges.

For instance, Portugal enacted Law 58/2005 to transpose Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000, commonly known as the Water Framework Directive. However, specific provisions regarding groundwater were not introduced until 2006, when the EU established Directive 2006/118/EC, which created a legal framework for groundwater protection. This directive was later transposed into Portuguese legislation through Decree-Law 208/2008. A closer examination of this legislation reveals concerning oversimplifications of the protection requirements necessary for this essential resource.

Groundwater knows no human boundaries (Figure 1). It crosses countries, continents, and desert regions. Its borders are natural, marked by physicochemical and geologic parameters, and in this sense it does not (yet) have a defined “owner”. Understanding its characteristics and behaviour is crucial to preserving this vital reservoir of fresh drinking water. The contamination of groundwater is, without doubt, a global issue that demands global attention.

Figure 1: Groundwater resources of the world [7].

From a general point of view, groundwater is less contaminated than surface water. However, unlike surface water, it lacks the capacity for self-purification. As a result, once contaminated, the effects are often long-lasting, given the time scale required for recovery, and can therefore be considered nearly permanent.

The lack of self-purification capacity in groundwater can be explained by several factors related to its nature. Firstly, the flow of groundwater is extremely slow and, therefore, does not allow for the dilution and dispersion of contaminants that occur in more turbulent and dynamic flow systems. Secondly, aquifers are isolated from atmospheric oxygen, hence, there are no large populations of aerobic bacteria necessary to break down contaminants. Lastly, the low temperature to which groundwater is subject slows down decomposition reactions. The monitoring of natural attenuation, commonly employed in many hydrocarbon-contaminated sites, particularly in the United States, does not guarantee complete decontamination. Instead, it primarily reflects the gradual dissipation of hydrocarbon contaminants over time.

When groundwater is contaminated (Figure 2), the detection and monitoring of pollution is not only challenging but also expensive and time-consuming. Consequently, the most effective approach to protect this natural resource is by preventing contamination, through the implementation of targeted legislation and procedures.

Two recent cases in Portugal highlight the pressing issue of soil and groundwater contamination. One involves the former facilities of the GALP refinery, located in the sub-region of the Porto Metropolitan Area, in Matosinhos. In 2021, the former government decreed the extinction of this hydroskimming refinery, which had been operating continuously since 1970. It is currently being dismantled, and it is expected that the remediation of this soil and groundwater will take place once the demolition work has been completed. This process could take several years, pottentially jeopardising the area’s urban development in the short term.

Another case pertains to the EXPO zone in Lisbon’s urban area, where recent work has shown that decontamination efforts carried out in the 1990s required monitoring. Portugal currently lacks comprehensive legislation on soil contamination. Historically, it has used the Ontario guidelines (Soil, Ground Water, and Sediment Standards for Use Under Part XV.1 of the Environment Protection Act, Ontario Ministry of the Environment, 2011) as a reference for soil and groundwater contamination standards. Recently, in 2020, the Portuguese Environmental Agency (APA), introduced new guidelines to replace these earlier standards. The updated guidelines were necessitated by shortcomings in fully decontaminating the  EXPO site under outdated national legislation related to groundwater management.

Figure 2: The most common sources of groundwater pollution [4].

Groundwater is an invaluable resource and is extensively exploited across diverse regions of the world. Recognising its critical importance, international organisations like the FAO and UNESCO have been adressing this issue for years and compiled substantial data leading to the following conclusions [2,3]:

  • Global groundwater extraction has grown more than fourfold in the last 50 years;
  • The most intense extractions occur in large areas of China, India, Pakistan, Bangladesh, Iran, the United States, Mexico and Europe;
  • There is overexploitation of aquifers in many places, resulting in their permanent depletion (Figure 3).

Figure 3: The global distribution of groundwater depletion is depicted as a three-dimensional topography, creating “mountains of groundwater depletion,” particularly evident in the United States, Mexico, Saudi Arabia, Pakistan, India, and China. The colour scale distinguishes between “blue water” (renewable surface water and groundwater) and “dark blue water” (non-renewable groundwater) [3].

3. Groundwater climate change and education

Given the recent climatic extremes affecting our planet, including major hurricanes, torrential rains, and the increasing frequency of wildfires in non-urban areas, it is imperative to highlight serious concerns about the quality of existing groundwater resources.

The groundwater governance framework [4], aims to improve groundwater governance, halt the current trend of resource depletion and degradation, and deliver positive environmental, social, and economic benefits. However, the framework has not produced the desired effects.

The increasing reliance on groundwater (Figure 4) [5,6] has resulted in significant adverse impacts on many aquifers, including land subsidence, seawater intrusion, stream depletion, deterioration of groundwater-dependent ecosystems, declining groundwater quality, and aridification.

Figure 4: Index depicting the ratio of total water withdrawals to available renewable surface and groundwater reserves. The withdrawals encompass domestic use, industry, irrigation, and livestock [5].

Chronic run-off from roads can have serious impacts on groundwater quality. This is mainly due to the concentration of pollutant loads generated by heavy traffic in urban areas and, in some cases, natural biosphere reserves [7,8] that warrant further studies. The growing trend of “urban gardens” in large municipalities introduces both challenges and benefits. One concern is the potential contamination of plants cultivated in these gardens with traffic-derived pollutants [9,10], which are particularly prevalent in urban settings with continuous, high-intensity traffic, contrasting rural areas, where such pollution is often negligible.

People often raise critical questions about the specific nature of groundwater, such as: Why is there no water in this area? What happens if I dig a well or drill deeper? Is the water quality safe? Why is groundwater available in some regions but not in others? Addressing these concerns promptly is essential to avoid the risk of contaminating what we cannot see.

Figure 5: Percentage of irrigated area serviced by groundwater [11].

4. Conclusion

Groundwater is the largest source of water supply and accounts for 30% of the freshwater resources available on Earth, but its distribution is extremely uneven. In addition, it can be found at variable depths, from near the surface to depths of over 1000 meters. It is this enormous variability that makes it fragile, as it can be found in the most varied environments and locations, but always with a strong umbilical link to geology. The disparity between total water withdrawals and available renewable surface and groundwater supplies highlight the uneven distribution of this vital resource. There is no doubt that climate change will intensify groundwater exploitation, especially in regions where its use is currently low. Changes in agricultural practices and livestock management [11], driven by climate change, will significantly contribute to this growing reliance (Figure 5).

Environmental education should emphasise the importance of groundwater and highlight that its presence is fundamentally a geological phenomenon (Figure 6) [12]. Groundwater availability is not determined by governments or policies, but rather a natural characteristic unique to each region, absent in neighbouring regions. It is not directly dependent on rainfall or climate. As such, understanding, studying, and preserving groundwater is essential for future generations. Achieving this will require a deeper focus on hydrogeological knowledge, with academia playing a more prominent role in educating and equipping the next generations with the tools and knowledge necessary to address this issue and ensure sustainable survival on our planet.

Figure 6: Hydrogeological conceptual model of a system requiring numerical modelling of the hydrological cycle. This involves a fully integrated, geologically and physically based, distributed groundwater–surface water model. The model is designed to evaluate the impacts of land use and climate change on water resources and ecosystems across various spatial and temporal scales [11].

Funding: The author acknowledges funding from the Foundation for Science and Technology, I.P., Portugal, through the strategic projects UIDB/00073/2020 and UIDP/00073/2020 of the R&D Unit Geosciences Centre (University of Coimbra, Portugal), as well as support from the Polytechnic Institute of Guarda, Portugal.

Conflicts of Interest: The author declares no conflict of interest.

References

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This article has been published in European Geologist Journal 58 – Water – making the invisible visible

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