Rising groundwater levels in the Neapolitan area and its impacts on civil engineering structures, agricultural soils and archaeological sites

The rise of groundwater levels (GWLr) is a worldwide phenomenon with several consequences for urban and rural environment, cultural heritage and human health. In this thesis the phenomenon and its effects are analysed in two sectors of the Metropolitan City of Naples (southern Italy). These areas are the central sector of the eastern plain of Naples and the Cumae archaeological site in the western coastal sector of Phlegraean Fields. The triggering mechanism of GWLr is attributed to anthropogenic and natural causes, as the groundwater rebound (GR) process and the relative sea level rise due to volcano-tectonic subsidence of coastal areas. In the eastern plain of Naples, the interruption of pumping for public and private purposes occurred in 1990, leading to a progressive increase of piezometric levels with values up to 16.54 m. Since the end of 2000s, episodes of groundwater flooding (GF) have been registered on underground structures and agricultural soils. The historical piezometric levels and a comprehensive conceptual model of the aquifer have been reconstructed, as well as a first inventory of GF episodes and the hydrogeological controlling factors of GF occurrence have been detected. The economic consequences of GF have been analysed for an experimental building of study area, in which a sharp increment of expenditures has been registered. These costs include technical and legal support, construction and maintenance of GF mitigation measures and electricity consumption. Others GWLr-induced phenomena have been recognised, as ground vertical deformation and variations of the groundwater contamination. A relationship between GWLr and ground uplift emerges from the coupled analysis of piezometric and interferometric data, referred to the 1989-2013 period. The ground deformation occurs in response to the recovery of pore-pressure in the aquifer system, reaching an uplift magnitude up to 40-50 mm. In the 1989-2017 period, the piezometric levels and the concentrations of some natural contaminants in groundwater (Fe, Mn, fluorides) show opposite trends, conversely the same rising trend has been observed with nitrates. These different responses to piezometric rise are related to the lack of mobilization of deep fluids due to the interruption of pumping and to the reduction of the surficial contaminants' time travel caused by a shorter thickness of the vadose zone. In the western sector of Phlegraean Fields, the naturally triggered GWLr has caused GF in the Cumae archaeological site for the last decade, threatening safeguard and conservation of the archaeological heritage. From an integrated hydrogeological, hydrochemical and isotopic survey, a considerable contamination of groundwater resulted, due to the presence of rising highly mineralized fluids, mobilized during pumping periods, and others anthropogenic sources of contamination. Lastly, a novel methodology for groundwater flooding susceptibility (GFS) assessment has been developed by using machine learning techniques and tested in the eastern plain of Naples. Points of GF occurrence have been connected to environmental predisposing factors through Spatial Distribution Models' algorithms to estimate the most prone areas' distribution. Ensemble Models have been carried out to reduce the uncertainty associated with each algorithm and increase its reliability. Mapping of GFS has been realized by dividing occurrence probability values into five classes of susceptibility. Results show an optimal correspondence between GF points' location and the highest classes (93% of GF points falls into high and very high classes). The results of this research provide new knowledge on the GWLr phenomenon that has impacted a large territory of the Metropolitan City of Naples. The methodological approach used can be exported in others hydrogeological contexts to characterize GWLr and its impacts. In addition, the implemented GFS methodology represents a new tool to assist local government authorities, planners and water decision-makers in addressing the problems deriving from GF, and a first step for the evaluation of GF risk as required by Italian and European legislation

The survey of Italian springs by the National Hydrographic Service, a forgotten database. Structuring and analysis of a dataset of Campania springs (southern Italy)

The analysis of groundwater resources is a particularly significant aspect of the economic, social and environmental development of the national territory. This is particularly relevant for the Campania region which, although characterized by the most significant aquifer systems of southern Italy, suffers from critical issues related to the progressive increase in demand and climatic variability at different time scales. In this framework, the lack of data concerning the survey of springs, including the minor ones, and of historical discharge measurements represents the main limitation to a more comprehensive regional hydrogeological characterization. The only source of historical data regarding the systematic and comprehensive survey of springs and discharge measurement is the Publication No. 14 of the National Hydrographic Service of the Ministry of Public Works "The Italian springs. List and description" reporting measures made between the 1920s and 1940s which was published in distinct volumes for each compartment. Despite its potential relevance, this source has so far been little used in regional hydrogeological studies. In this paper, a comparative analysis among data of springs derived from the Publication No. 14 and from measurement campaigns made by the Cassa per il Mezzogiorno (Special Project 26), between the 1960s and 1980s for main springs, was carried out for the Campania region. The information available from each source was validated through a cross-check, by means of a comparison of coordinates and a statistical analysis of the characterizing parameters. The new dataset allowed to expand the hydrogeological regional characterization with a higher number of springs, including the minor ones. The results obtained recognize the Publication No. 14 of the National Hydrographic Service as an important source of data to not be overlooked, especially in a condition of historical data shortage, by which can be both carried out regional hydrogeological and temporal analyses as well as identified integrative groundwater resources

Hydrogeological and hydrogeochemical monitoring in the Cumae archaeological site (Phlegraean Fields, southern Italy)

Phlegraean Fields, hydrogeological model, hydrochemical facie

Groundwater rebound and flooding in the Naples' periurban area (Italy)

Groundwater bodies in the urbanized and densely populated aquifers or coastal floodplains may be subjected to groundwater rebound (GR), often causing serious risks of groundwater flooding (GF) to underground structures and infrastructures. This paper shows the results of a study carried out in the Naples' periurban area (Italy) to: investigate the dynamics and features of GR and GF phenomena, map flooded sites during 2013–2015 period, and provide an interpretative analysis of the factors that control the GF of private buildings and agricultural lands. At the municipality scale, since 1990 and until 2015, a remarkable and widespread GR was observed, with magnitude up to +16.54 m, triggering an unexpected GF of basements of buildings and agricultural soils. Field surveys proved that there is a time delay of the GF, ranging from 17 to 20 years, compared to the start of GR. Moreover, inhomogeneous distribution of flooding episodes is controlled by anthropogenic and natural factors. The obtained results are fundamental to design mitigation measures to GF hazard, and offer new perspectives to make Naples' periurban area more robust, smart and resilient against this new hydrogeological risk, undervalued by Italian legislation and local authorities

Rising groundwater levels and impacts in urban and semirural areas around Naples (southern Italy)

The rising of groundwater levels in urban and rural areas is a relevant topic of the Urban Hydrogeology because it affects different areas of the world requiring specific analyses and mitigation measures by the institutions involved in the protection and security of the territory. In the last century, in many developed countries processes of deindustrialization and urban transformation have caused the rising of groundwater levels and severe economic and social impacts. The aim of this paper is to analyse the rising of groundwater levels in a multi-layered pyroclastic-alluvial aquifer, located in the coastal plain eastward of Naples (southern Italy) and its interactions with buildings and agricultural lands. The research has been carried out by means of: i) analysis of stratigraphic settings by 86 boreholes and reconstruction of hydraulic conductivity logs; ii) reconstruction of a 2D hydrostratigraphic model of the multi-layered pyroclastic-alluvial aquifer; iii) slug test and multitemporal hydrogeological monitoring of 83 wells, 9 piezometers and 12 river water levels; iv) analysis of daily rainfall time series; v) hydrogeological monitoring of impacted buildings and agricultural lands. For the monitored period (November 2013-March 2015), the groundwater table showed a generalized rise, although with a spatial variability. The rise of groundwater levels ranged from a minimum of 0.10 meters, in the central and eastern sector of the study area, to a maximum of 2.05 meters, in the south-western sector, with an average growth rate of about 0.16 m. The distribution of the impacted areas is not spatially homogeneous, and it was observed to vary over time. The hydrogeological interactions between groundwater and urban and rural areas are affected by: i) foundation types of buildings and the depth of the underground structures; ii) presence of shallow aquicludes (marshy clay-sands, clay-silts and peat levels) that determine local conditions of confinement for groundwater; iii) hydraulic efficiency and maintenance state of the dense network of drainage channels and micro-channels, which were historically built to drain surface water and groundwater in rural areas. The obtained results provide the basic data to set up a numerical groundwater flow model, which is an indispensable tool to simulate and predict the hydrogeological effects of possible safeguard actions on urban and agricultural areas

Uplift Evidences Related to the Recession of Groundwater Abstraction in a Pyroclastic-Alluvial Aquifer of Southern Italy

Aquifer mismanagement is a common anthropogenic cause of subsidence and uplift phenomena in alluvial plains, representing one of the main natural hazards in urban areas due to related damage to urban structures and infrastructures. In this work, the groundwater rebound phenomenon that occurred in the last decades of the 20th century in the Lufrano area (Metropolitan area of Naples, Southern Italy) has been studied by integrating geological data, hydrogeological continuous monitoring and spaceborne SAR information derived from ERS-1/2 and ENVISAT satellites. In the period of 1989–2006, the Lufrano area, which hosts an important well field made up of 180 wells extracting groundwater for drinking use, suffered an initial over-exploitation of the aquifer which was followed by a sudden and severe decrease of the volume abstraction, resulting this last in a rapid ground uplift. The coupled analysis of hydrogeological and DInSAR data have shown a correspondence between piezometric level rise (up to 15 m) and ground uplift (up to 50 mm) trends in the period 1989–2006. In order to examine the spatio-temporal evolution of the phenomena and the cause-effect relationships, showing the link between the two phenomena and their rates, longitudinal cross-sections were carried out and comparisons between piezometric level rise and time-series of displacements were reconstructed. The obtained results represent an initial contribution to the definition of ground deformation related to groundwater level rise phenomena, providing a basis for future studies focused on the modelling of the hydro-mechanical properties of the aquifer

Environmental effects of the groundwater rebound in the eastern plain of Naples (Italy)

Since 1990, in the eastern plain of Naples a generalized groundwater rebound phenomenon has occurred, caused by the sharp reduction of the withdrawals which had overexploited the plain aquifer until 1989. The present study aims to investigate, for 1989-2013 period, the groundwater flooding and ground uplift related to the groundwater rebound, by a coupled analysis of multi-temporal hydrogeological and DInSAR data of this area. Results show a generalized rise of groundwater levels from 1990, varying from 6.0 to 16.0 m, whereas localized impacts of groundwater flooding on buildings and agricultural soils have started since 2006. An uplift trend is observed in ground deformations (up to +40 mm), caused by the increase of pore water pressure in the aquifer system, following to groundwater rebound. This result opens new perspectives in assessment, mitigation and management of geohazards not considered by the Italian legislation

Quantitative Assessment of Specific Vulnerability to Nitrate Pollution of Shallow Alluvial Aquifers by Process-Based and Empirical Approaches

Shallow aquifers of coastal and internal alluvial plains of developed countries are commonly characterized by the challenging management of groundwater resources due to the intense agricultural and industrial activities that determine a high risk of groundwater contamination. Amongthe principal origins of pollution in these areas are agricultural practices based on the amendment of soils by nitrate fertilizers, which have been recognized as one of the most severe environmental emergencies for which specific policies and regulations have been issued (e.g., EU Directive 2006/118/EC). In such a framework, the results of research aimed at assessing the specific vulnerability of shallow alluvial aquifers to nitrate fertilizer pollutants by coupled process-based and empirical approaches are here proposed. The research focused on assessing the specific vulnerability to nitrate pollution of a shallow alluvial aquifer of the Campania region (southern Italy), which was selected due to its representativeness to other recurrent hydrogeological settings occurring in alluvial plains of the region and worldwide. In this area, 1D hydro-stratigraphic models of the unsaturated zone were reconstructed and applied for simulating the transport of nitrate pollutants at the water table and estimating the associated travel times. Numerical modeling was carried out by the finite dierences VS2TDI code and considered a 10-year time series of rainfall and evapotranspiration as well as typical local farming practices of nitrate fertilizer input. Results of the travel time calculated for the 1D hydro-stratigraphic models considered and at dierent depths were recognized as a proxy to assess the specific vulnerability to nitrate fertilizer pollution. Among the principal outcomes is an empirical multiple correlation between the travel time of the nitrate fertilizer pollutant, water table depth, and equivalent saturated hydraulic conductivity of the unsaturated zone or hydraulic resistance, which was used to assess the travel time at the distributed scale over the whole area studied as well as the related specific vulnerability. Given such results, the coupled process-based and empirical approach is proposed as generally applicable for assessing and mapping groundwater vulnerability in shallow aquifers, for which detailed stratigraphic and piezometric data are available