Groundwater Vulnerability to Pollution Assessment

Water scarcity and pollution have arisen as global issues in the twenty-first century. Groundwater quantity and quality protection are crucial challenges to ensuring access to fresh water, which is seriously threatened by overexploitation and contamination caused by anthropogenic activities, as well as the effects of climate change [1]. In the last decades, the increase in water demand on a global scale has exceeded twice that of population growth. This has resulted in more and wider regions of the world experiencing water stress, where the present restricted rates of water use and consumption are unsustainable [2,3]. Water availability became an important challenge for most countries in which human pressures such as industry and agriculture development, urbanization, demographic growth, increased tourism, and climate change are responsible for the evident change in the groundwater quantity and quality that also causes critical effects on public health [4,5,6].

Coastal and inland porous, karst, and fissured carbonate rock aquifers are threatened by groundwater pollution, and this trend is expected to continue in the future due to the increasingly intense and unplanned anthropogenic activities and water exploitation under the climate change impacts. The scientific community has recognized the assessment and mapping of an aquifers’ vulnerability to pollution and related risk as to the most effective prevention tools for groundwater protection and management strategies.

In this frame, we encouraged submissions of original contributions dealing with groundwater vulnerability topics, including the application of methods and models for intrinsic vulnerability to pollution assessment related to the groundwater quality, the prevention of pollution risks, sustainable groundwater management, and the effects of climate change.

In the Special Issue “Groundwater Vulnerability to Pollution Assessment”, after a rigorous editorial check and peer-review process, which involved external and independent experts, nine papers have been published. In the following paragraphs, a short presentation of each is given.

Addison et al. [7] focused on the characterization of the hidden hot springs that probably impact rural water supplies in Malawi’s Rift Valley, with excess dissolved fluoride leading to localized endemic severe dental fluorosis. A multidisciplinary approach was applied to predicting hidden hot spring locations using a synthesis of proxy indicators (geological, geochemical, dental). Thirteen hidden hot springs were identified. The collaboration between geoscientists and dentists allowed the authors to define a vulnerability prediction map for the region. It allows improved groundwater fluoride prediction in Malawi’s rift basin, which hosts the majority of hot springs, and allows dentists to recognize geological control over community oral health.

Živanović et al. [8], using two methods, COP + K and the Time-Dependent Model (TDM), assessed groundwater vulnerability, to obtain the most suitable vulnerability map that can be easily used to define sanitary protection zones. Both methods were tested in Blederija karst spring, Eastern Serbia. The vulnerability maps show that the highest vulnerability classes were identified in the areas near the spring Blederija and the immediate area of ponor Cvetanovac. The COP + K method clearly defines three vulnerability classes, whereas the TDM method shows the groundwater vulnerability through water travel time, where each point in the spring’s catchment shows how much time is needed for surface water to reach the spring. The results highlighted that the delineation of sanitary protection zones is much easier with the application of the TDM method.

Ślósarczyk et al. [9] presented the potential presence of pesticides within the catchment areas of Goczałkowice and Kozłowa Góra reservoirs (Southern Poland) that are destined for drinking water supply. Agricultural and rural areas dominate both catchments. This indicated the possible presence of pesticides in shallow groundwater. The study outcomes showed that pesticides were not detected above the detection limits in any of the samples. Due to variations in the persistence and degradation rates of pesticides, the occurrence of these substances in the groundwater environment and the possibility of their migration to aquifers should not be completely excluded. Natural processes and factors (e.g., sorption, biodegradation, hydrolysis, and redox conditions) may gradually reduce the pesticide concentrations in groundwater. The chemical analyses revealed high groundwater nitrate concentrations. This suggests the possible influence of agriculture and fertilizer application on groundwater quality; however, a proportion of NO₃⁻ ions may be connected with improper sewage management within the two catchments. The absence of pesticides in groundwater impacted by agriculture may result from processes occurring in the aquifer and the rapid degradation of these compounds due to photolysis and prevailing weather conditions. In the vicinity of dwellings, nitrates also originate from domestic wastewater. Thus, the occurrence of pesticides in groundwater contaminated with NO₃ cannot always be expected.

Mester et al. [10] highlighted the environmental hazards of an abandoned and unrecultivated liquid waste disposal on soil and shallow groundwater contamination of the settlement at Báránd located in the eastern part of the Great Hungarian Plain in the Nagy-Sárrét region. The soil and water sample analysis showed a high level of contamination in the area. In the borehole profile of the infiltration basin, a well-developed leachate nitrate profile was observed, with a high concentration of NO₃⁻. The soil phosphate content was also significant. Extremely high concentrations of ammonium and organic matter were detected in the groundwater of the basins, indicating that contaminated soil remains a major source of pollutants more than ten years after closure. For all micro- and macroelements present in detectable concentrations, a significant increase was observed in the infiltration basin. The results revealed that the surroundings are also heavily contaminated. NO₃⁻ concentrations above the contamination limit were measured outside the basins. The recultivation of liquid waste disposal sites of similar characteristics is therefore strongly recommended.

Ducci and Sellerino [11] presented the groundwater vulnerability assessment in three different areas of southern Italy by the application of the DRASTIC and AVI methods. The study highlighted the limitations of the AVI method in alluvial aquifers and the differences with other methods. AVI and DRASTIC are both suitable for predicting the pollution potential for porous aquifers, but AVI tends towards a higher class of vulnerability than DRASTIC, especially in shallow aquifers, exaggerating the degree of susceptibility. To reduce this difference in outcome and obtain more reliable results when compared with the DRASTIC method, a new classification for the AVI method was developed using a statistical approach. The modified AVI method was applied to three porous alluvial aquifers. The comparison between the outcomes showed that in the AVI modified method the same areas are highlighted as the more vulnerable areas, although the vulnerability map obtained using the AVI method remains more severe than using the DRASTIC method. The major novelty of the modified method consists of having deduced the class limits from the distribution of log₁₀C values (where C is the hydraulic resistance) in the three aquifers, clearly distinguishing three slope changes. Among many methods, AVI appears to be a valuable approach to be implemented worldwide, particularly if the project scale is wide, data availability is limited, and only a few hydrogeological characteristics are available.

Šrajbek et al. [12] presented a study on the groundwater quality at the Varaždin wellfield in the northern part of Croatia, characterized by high concentrations of nitrates. Nitrates are among the most common groundwater pollutants, especially in areas with agricultural and zootechnical activities. The numerical models of groundwater flow and pollution propagation were carried out with MODFLOW and MT3DMS codes, respectively. By using statistical and geostatistical methodologies, the sources of nitrate pollution in the influential wellfield zone were located and quantified. The simulations highlighted that to obtain reliable outcomes is necessary to locate all the pollution point sources in the vicinity of the wellfield since the absence of a single source significantly reduces the accuracy of the results. According to the results of the performed analyses, the point sources of pollution are dominant; in particular, the poultry landfill on the southwest side of the Varaždin wellfield is the main source of nitrate pollution.

Barmakova et al. [13] presented the findings of a detailed analysis of the groundwater chemical composition in the Karatal massif, Southeastern Kazakhstan. On cultivated lands, irrigation can significantly impact the chemistry of groundwater, and the increasing salt concentration is one of the most relevant environmental problems. A correlation analysis between chemical parameters was performed to establish the relationships between ions in groundwater. A seasonal pattern of variations in the groundwater chemical composition was distinguished. Soil samples and data on irrigation and drainage waters within the Karatal River basin highlighted that the presence of saline soil-forming rocks, the groundwater depth, the volume and the quality of irrigation waters, the characteristics of the natural drainage, and evaporation processes all impact the hydrochemical regime of groundwater. The results showed that the hydrogeological conditions and drainage availability influence the salinization processes; in particular, a high risk of soil salinization was observed in the northeastern part of the massif.

Fang et al. [14] highlighted the importance of the pollution risk assessment in oilfield drilling sites, which are potential dispersive pollution sources of groundwater. Combining groundwater vulnerability, pollution source hazard, and groundwater value function, a comprehensive groundwater pollution risk assessment method was developed and applied in Yitong County, China. The DASTIC-LD_R system was developed to assess groundwater vulnerability. To analyze the transport characteristics of pollutants in the porous medium, the Groundwater Modelling System software was utilized. MODFLOW and MT3DMS codes were applied separately to simulate groundwater flow and the influence range of benzene series when pollutants are released. The oilfield drilling and centralized water supply wells for human habitation and groundwater function value were assessed by groundwater quality and groundwater storage. The results showed that areas classified as high risk are mainly distributed around the center position of the oil drilling site, floodplains, and reservoir. The authors highlighted that the proposed method can be suitable for the comparative assessment of a large number of dispersive pollution sources on a regional scale.

Canora et al. [15] focused their attention on the intrinsic groundwater vulnerability assessment of the Metaponto coastal aquifer (Italy) by the application of the classic and modified SINTACS methods. Indeed, the anthropogenic influence in the area was considered by applying the SINTACS-LU method, in which the land use parameter was added because of its impact on groundwater vulnerability. The research enhanced understanding of the coastal plain, characterized by intensive agriculture, leading to new considerations concerning the link between the aquifer’s hydrogeological behavior and anthropogenic activities. The sensitivity analysis performed both for SINTACS and SINTACS-LU showed that hydrogeological features, expressed by water table depth and effective infiltration parameters, and land use significantly influence the intrinsic vulnerability. The study highlighted that knowing the intrinsic vulnerability of an aquifer system and the problems associated with the groundwater quality is essential to prevent and control the potential contamination of resources. Identifying highly vulnerable areas is crucial both in efficiently managing groundwater resources and in increasing community awareness of environmental issues.

The Special Issue includes nine research papers on a variety of aquifers typologies ranging from coastal and inland porous, karst, and fissured carbonate aquifers. The chosen articles help to recognize the importance of assessing and mapping the aquifers’ vulnerability to pollution and related risk. The objective is that the presented studies would promote attention to the development and application of methodologies and models for intrinsic vulnerability assessment, pollution risk prevention, and sustainable groundwater management.