TIME-DEPENDENT METHODS TO EVALUATE THE EFFECTS OF URBAN SPRAWL ON GROUNDWATER QUALITY

As groundwater resources are becoming more vulnerable due to the increasing number of contamination sources in developed and developing countries (such as urbanization and agricultural activities), practical actions, strategies and solutions to protect the resource are widely required. The most efficient tool, which helps supporting land use development, while protecting groundwater from contamination, is represented by groundwater vulnerability assessment. European Directives require member states, for the protection of groundwater quality, to assess the current groundwater quality status, detect changes or trends in groundwater quality, assess the threat of deterioration and predict future changes in groundwater quality. In order to cope with the EU requirements, this study focuses on the development of a time-dependent approach, which could take into account both the current groundwater quality status and its changes, assessing groundwater vulnerability to nitrate contamination in the Po Plain area of Lombardy Region, through a Bayesian spatial statistical method (Weights of Evidence). In addition, an innovative dataset to delineate urban areas with satellite scatterometer data (QuikSCAT-DSM) is explored. To evaluate its reliability in groundwater vulnerability assessments, QuikSCAT-DSM dataset is compared with population density and land use derived from aerial images. Results showed that: a) urbanization prevails on agricultural activities in causing the degradation of groundwater quality; b) QuikSCAT-DSM data is a reliable variable to represent urban nitrate sources, with the advantages of a worldwide coverage, a continuous data collection and an adequate resolution; c) the time-dependent approach allows to identify areas both affected by nitrate contamination and characterized by an upward concentration trend of contamination; d) the time-dependent approach allows to determine what could happen to groundwater resources if land use policies are maintained or new ones will be proposed and/or if natural factors are changing under climatic or anthropogenic stresses

Evaluation of the deposition, infiltration and drainage of the atmospheric pollutants in the vadose zone

In the last decades, a large effort has been carried out to reduce atmospheric pollutant emissions in Europe. However, despite the progresses of the last 30 years (Rogora et al., 2016), water and soil acidification, nutrition unbalance in forest trees, and eutrophication in surface waters are still of great concern. In particular, nutrients that fall on the ground from the atmosphere represent a minor component of the total nitrogen input to soils, especially when compared to agricultural, civil and industrial inputs (EEA, 2005). Although often underestimated, this source apportionment becomes a part of leaching from the soil to groundwater. Therefore, the overarching goal of this study is to identify anthropogenic background values of pollutants in groundwater, not related to direct sources of contamination (e.g., industrial wastes, leakages from sewage systems, fertilizers)

Specific yield of aquifer evaluation by means of a new experimental algorithm and its applications

A simplified method to determine specific yield (i.e., effective porosity) from hydraulic conductivity data obtained through pumping tests is proposed. This new method derives from a reprocessing of literature data and a subsequent calibration with results from pumping tests performed in different hydrogeological contexts. The use of the algorithm allows obtaining values of specific yield (Sy), which could be useful for the resolution of problems concerning the water balance and the transport of contaminants in groundwater. The proposed algorithm is applied to a large-scale area (Milan and its suburbs, northwestern Italy) to determine a map of the specific yield of a sandy-gravel aquifer and the effects on the estimation of water volumes stored in the subsoil from a hydrogeological point of view, considering about seventy years of measures. It is demonstrated that the great variation in water volumes reflects the socio-economic history of the territory

Using statistical analyses for improving rating methods for groundwater vulnerability in contamination maps

With the aim of developing procedures coping with the disadvantages and emphasising the advantages of existing rating methods and the use of statistical methods for assessing groundwater vulnerability, we propose to combine the two approaches to perform a groundwater vulnerability assessment in a study area in Italy. In the case study, located in an area of northern Italy with both urban and agricultural sectors, keeping the structure of the DRASTIC rating method, we used a spatial statistical approach to calibrate weights and ratings of a series of variables, potentially affecting groundwater vulnerability. In order to verify the effectiveness of these procedures, the results were compared to a non-modified approach and to the map resulting from the ‘‘Time–Input’’ method, highlighting the advantages that can be obtained, and defining the general limit of these applications. The revised method shows a more realistic distribution of vulnerability classes in accordance with the distribution of wells impacted by high nitrate concentration, demonstrating the importance of taking into account the specific hydrogeological conditions of the area

Atmospheric nitrogen deposition in a highly human impacted area in northern Italy

Nitrogen can enter the water cycle through atmospheric depositions on ground and water surfaces, leakages from point and diffuse sources (i.e., sewage treatment plants or sewage systems, fertilizer and manure applications), and erosion processes affecting nitrogen rich soils (EEA, 2005). However, integrating all nitrogen forms, processes and scales is still a major challenge for the understanding and the management of the nitrogen cycle

A Bayesian approach for the assessment of shallow and deep aquifers susceptibility to point sources contamination in the Province of Milan, Italy

In densely populated areas, urban and industrial activities are responsible for groundwater quality deterioration due to point sources contamination (Kuroda and Fukushi, 2008). In the Province of Milan (Northern Italy), the available water-quality data indicate the occurrence of high PCE+TCE and chromium concentrations in the unconfined shallow as well as in the confined deep aquifers. To cope with this problem, statistical methods can represent reliable tools to provide key information for groundwater management and protection

A Bayesian approach for the assessment of shallow and deep aquifers susceptibility to point sources contamination in the Province of Milan, Italy

In densely populated areas, urban and industrial activities are responsible for groundwater quality deterioration due to point sources contamination (Kuroda and Fukushi, 2008). In the Province of Milan (Northern Italy), the available water-quality data indicate the occurrence of high PCE+TCE and chromium concentrations in the unconfined shallow as well as in the confined deep aquifers. To cope with this problem, statistical methods can represent reliable tools to provide key information for groundwater management and protection

An Enhanced Approach to the Spatial and Statistical Analysis of Factors Influencing Spring Distribution on a Transboundary Karst Aquifer

Karst aquifers are indispensable, yet vulnerable, resources; therefore, they require a comprehensive protection strategy. Since springs are the terminal points of the karst flow systems, knowledge of their distribution is a key element for the better understanding of groundwater flow, availability and vulnerability. The present study aims to introduce a data-driven analysis by the application of a spatial statistical technique (Weights of Evidence (WofE)) for the evaluation of factors influencing spring distribution in karst areas. A workflow was developed for investigating two questions: where will the springs locate, and where will the permanent springs evolve? This workflow has the potential for application to unconfined karst areas. This enhanced approach was applied to an unconfined transboundary aquifer, the G\uf6m\uf6r\u2013Torna Karst (HU and SK). The roles of five factors was statistically investigated: terrain elevation, distance to faults, distance of the carbonate\u2013non-carbonate rock contact, distance to sinkholes, and precipitation distribution. The validation procedures confirmed the effectiveness of the approach. The resulting predictive maps are useful for decision-makers to delineate areas holding potential karst springs and to address water availability problems and protection measures. In addition, the WofE technique improved the comprehension of the geological conditions favourable for the formation of the springs

Implementation of satellite-based data for improving predictions of arsenic contamination in groundwater in the Red River Delta in Vietnam

Natural arsenic contamination of groundwater aquifers is globally widespread, and particularly poses a problem in regions where groundwater is the main source of drinking and cooking water. Arsenic poisoning can lead to a myriad of serious health effects such as diseases of blood vessels, diabetes and cancers. The aquifers of the Red River Delta in Vietnam are highly contaminated with arsenic and it has been estimated that in this area, around 3 million people are affected by high arsenic concentrations (> 10 \ub5g/L, WHO guideline value; Winkel et al., 2011). Previously, predictions of arsenic contamination in the Red River Delta were established via geospatial modelling using arsenic measurements, as well as surface and 3D-geology. Based on these predictions, probability maps of arsenic at specific depths were created. By comparing these depthresolved probabilities to measured arsenic concentrations, a drawdown of arsenic-enriched waters from Holocene aquifers to previously uncontaminated Pleistocene aquifers was observed. This finding indicated that arsenic contamination has been exacerbated by excessive groundwater pumping rates (Winkel et al., 2011). Furthermore, in a study conducted in the Mekong delta, it was hypothesized that groundwater extraction causes interbedded clays to compact, thereby releasing water containing dissolved arsenic that is subsequently transported to deeper aquifers (Erban et al., 2013). Such human-induced changes cannot be captured by the previous predictive models based on natural predictive parameters mentioned above, leading to erroneous predictions of the arsenic content in areas affected by urbanization, especially in deeper aquifers. To improve predictions in human-affected regions we are using satellite data and remote sensing techniques that enable detection of changes of urban and suburban extents (Nghiem et al., 2009) and vertical build-up (Mathews et al., 2019). Those data and techniques in combination with geochemical and environmental data can help in i) resolving mechanisms behind arsenic mobilization in aquifers due to increased pumping rates and ii) making predictions of arsenic contamination more accurate, especially in areas characterized by increased groundwater pumping