Domenico Antonio De Luca

Nitrate contamination of groundwater in the western Po Plain (Italy): the effects of groundwater and surface water interactions

This study aims to investigate the physical and chemical effects of interactions between groundwater and surface water (GW–SW)—particularly in streams—on nitrate contamination. The effects of GW–SW interactions are briefly reviewed, with a particular emphasis on processes and environments that influence increases or decreases in nitrate concentration. Then, this paper analyses nitrate concentrations in groundwater and surface water in the western Po plain (Northwestern Italy); this analysis includes the nitrate concentration profiles across the shallow aquifer and intersecting the main streams on the plain. The investigation highlights how the concentration trends are similar, even when nitrate levels in rivers and groundwater are not comparable. The maximum nitrate concentrations in the surface water were generally measured in areas with high-nitrate levels in groundwater. An analysis of the nitrate concentration profiles highlighted the mutual influences of GW–SW. The most important streams on the plain (the Po River and Stura di Demonte River), both of them gaining streams, seem to reduce the nitrate concentrations of groundwater at a study scale. The proposed conceptual model indicates how the near-stream environment (the riparian zone, wetlands, hyporheic zone and shallow organic-rich soils in the near-stream environment) and the groundwater flow systems in shallow and deep aquifers, from the recharge zone to the streams, could dramatically affect the nitrate concentrations.

Effect of the dilution process on the attenuation of contaminants in aquifers

This paper discusses the effects of the dilution process on levels of aquifer contamination attenuation, developing analytical equations for application in theoretical and practical cases. The key finding is that, in aquifers, the dilution process causes a reduction of the contaminant concentration. Analytical equations for the assessment of the contaminant attenuation capacity, by means of the dilution process in an aquifer, are put forward. In particular, the attenuation of the contaminant concentration in an aquifer, and thus the dilution, is described by the volumetric flow rate per unit width perpendicular to the flow direction (qu). Moreover, a classification of qu was developed, considering six classes of attenuation capacity due to dilution. For the equations validation, nitrate contamination attenuation due to dilution was analysed in two sample areas in Piedmont (North-West Italy). The results confirmed the hypothesis, evidencing high nitrate concentrations in areas with low qu values, connected to low dilution rate of the contaminant in the groundwater; vice versa, low nitrate concentrations were evidenced in areas with high qu values, due to a high nitrate dilution rate.

The use of multilevel sampling techniques for determining shallow aquifer nitrate profiles

Nitrate is a worldwide pollutant in aquifers. Shallow aquifer nitrate concentrations generally display vertical stratification, with a maximum concentration immediately below the water level. The concentration then gradually decreases with depth. Different techniques can be used to highlight this stratification. The paper aims at comparing the advantages and limitations of three open hole multilevel sampling techniques (packer system, dialysis membrane samplers and bailer), chosen on the base of a literary review, to highlight a nitrate vertical stratification under the assumption of (sub)horizontal flow in the aquifer. The sampling systems were employed at three different times of the year in a shallow aquifer piezometer in northern Italy. The optimal purge time, equilibration time and water volume losses during the time in the piezometer were evaluated. Multilevel techniques highlighted a similar vertical nitrate stratification, present throughout the year. Indeed, nitrate concentrations generally decreased with depth downwards, but with significantly different levels in the sampling campaigns. Moreover, the sampling techniques produced different degrees of accuracy. More specifically, the dialysis membrane samplers provided the most accurate hydrochemical profile of the shallow aquifer and they appear to be necessary when the objective is to detect the discontinuities in the nitrate profile. Bailer and packer system showed the same nitrate profile with little differences of concentration. However, the bailer resulted much more easier to use.

The role of physical and biological processes in aquifers and their importance on groundwater vulnerability to nitrate pollution

Currently, diffuse pollution by nitrate is considered one of the main causes of groundwater quality deterioration. Many methodologies have been suggested to map aquifer vulnerability to nitrate pollution; however, no standard method has yet been established. Many proposed methods only take into account the aquifer’s protection and do not consider the physical or chemical processes in groundwater. More specifically, recent studies indicate that the fate and concentration of nitrates in aquifers mainly depend on the following: (a) the efficiency of natural attenuation (e.g. biological denitrification), (b) the physical processes of attenuation (e.g. dilution). Both the processes can lower the nitrate levels in groundwater. The aim of this research is to describe the features and role of these processes in aquifers. According to previous studies and our results, dilution and denitrification occurring in aquifers have a key role in the attenuation of nitrate. More specifically, the occurrence and effectiveness of denitrification were evaluated in a plain area in NW Italy through nitrogen isotopic fractionation analysis; the volumetric flow rate per unit width perpendicular to the flow direction, which is a function of the hydraulic gradient, hydraulic conductivity and aquifer thickness, was instead used for the assessment of nitrate attenuation capacity by means of the dilution process. Knowledge and understanding of these processes is essential to the identification of areas where groundwater is more prone to contamination. Thus, the evaluation of groundwater vulnerability to nitrate contamination cannot be separated from the comprehension of these processes.

Areal and Vertical Distribution of Nitrate Concentration in Piedmont Plain Aquifers (North-Western Italy)

Several areas in Piedmont plain (North-Western Italy) are characterized by nitrate concentrations higher than 50 mg/L, the maximum nitrate concentration accepted by Italian law. The Piedmont plain sector is the most important water reservoir of the Piedmont Region, due to its size, the characteristics of its deposits and the possibility of recharge. In the Piedmont plain groundwater, the origin of nitrate contamination is due to the increasing amount of synthetic nitrogenous fertilizers and organic manure used for agricultural purposes but also to septic tank effluents input. Univariate and bivariate statistics and concentration maps were used to describe the distribution of nitrate in Piedmont plain, both in shallow and in deep aquifers, to highlight the variation of nitrate levels from year 2000 to 2012 and to analyse the relation of nitrate versus well depth. The purpose is to create the basis for future investigations and insights about the nitrate sources and the attenuation processes in aquifers.

Eutrophication of Piedmont Quarry Lakes (North-Western Italy): Hydrogeological Factors, Evaluation of Trophic Levels and Management Strategies

Quarry lakes resulting from alluvium extraction have excavation depths that can reach the shallow aquifer and extend beyond the piezometric surface. Similar to natural lakes, pit lakes are subject to eutrophication process, both during and after quarrying activity; during mining activity, the eutrophic level is strongly controlled by the excavation method. The present study describes the trophic status of several quarry lakes in the Piedmont plain (north-western Italy) that were evaluated by applying classifications from scientific literature. Most of the studied quarry lakes were mesotrophic or eutrophic, and a slight worsening of water quality was observed over time. In addition, the paper focuses on the pit lake water quality and pit dimension; it was shown that lakes with a larger depth and volume generally had a lower tendency towards eutrophication. At last some management strategies were suggested to achieve environmental sustainability.

Simulation modelling for groundwater safety in an overexploitation situation: the Maggiore Valley context (Piedmont, Italy)

The Maggiore Valley well field plays a fundamental role in supplying drinking water to a large territory of the Piedmont (north-western Italy). However, an increasing demand for water has led to the overexploitation of the groundwater resources. This situation has caused a progressive drawdown of the piezometric level (locally, up to 0.8 m/year), a spatial reduction in the artesian zone, localised land subsidence and damage to wells. The main purpose of this study was the development of a groundwater flow model of the area for analysing the aquifer response to various pumping strategies. Initially, the groundwater flow simulation (achieved by the application of the MODFLOW code) was calibrated satisfactorily. Then, the groundwater response to four scenarios was simulated to explore the best option to mitigate the problem. In three of the scenarios, a withdrawal reduction of 110 l/s was simulated, whilst considering various relocation options for extraction within the well field. The fourth scenario simulated a withdrawal reduction of 150 l/s; this option also assumed a supplementary water supply from the Monferrato Aqueduct, located north of the study area. All the simulations provided an increase in the piezometric level; in some instances, up to 30 m. Based on these simulations, the most promising management strategy for the Maggiore Valley well field would seem to be the option using a supplementary feed from the Monferrato Aqueduct. In this instance, the predicted piezometric level rise would be up to 25 m; this option also precludes the need for drilling additional wells.

Environmental Issues Connected to the Quarry Lakes and Chance to Reuse Fine Materials Deriving from Aggregate Treatments

Nowadays the number of quarries below water table is increasing due to the raising demand of aggregates. This kind of quarry implies an irreversible change of land use, since it forms artificial lakes which remain also when the activity is over. Quarry lakes are particularly numerous in alluvial plains, as we can find in Northern Italy, along the main streams of the Po plain. A quarry lake alters the pre-existent piezometric water table morphology and there is the possibility of a mixing between shallow aquifer and deep aquifers. Furthermore, a quarry lake creates an area of high vulnerability, especially because potential contaminants could reach the aquifer. The presence of a quarry lake can affect the local hydrological balance due to a high evaporation in the quarry. At last, the working activities connected to aggregate exploitation cause the production of fine materials (silt and clay) potentially employable in quarry rehabilitation. Most of time, these materials are used in quarry lake backfilling with a consequent hydrogeological alteration. This research deals with a study and an analysis of problems concerning quarry lakes in plain areas, their relationship with the hydrogeological setting and the issues connected to the production of fine waste. These problems are examined both from a theoretical point of view and from the analysis of real contexts, focusing on the legislation in force in Italy.

Preliminary results on temperature distribution in the Quaternary fluvial and outwash deposits of the Piedmont Po Plain (NW Italy): a statistical approach

We propose a statistical approach to the study of subsoil thermal data in order to find an equation able to describe the temperature distribution in the underground of the Piedmont plain sectors (NW Italy). The analytical model here proposed, can be used during the preliminary stage of investigation for the exploitation of subsoil by means of low enthalpy geothermal plants. The statistical analysis was performed using groundwater thermometric data from thermal logs collected in boreholes crossing the Quaternary fluvial deposits hosting a shallow aquifer.

Industrial Chance to Recover Residual Sludge from Dimension Stones in Civil and Environmental Applications

Residual sludge coming from dimension stones working plants represents a problem for European Stone Industries. The difficulties to opportunely exploit such waste are related to their chemical and physical characteristics. Moreover the management of sludge is subject to periodic updating regulatory developments (DLgs 152/06, DLgs 13/09 and DLgs 61/2012 in Italian legislation) which can complicate their correct management. The topic of the research, financed by Camera di Commercio VCO (Verbano Cusio Ossola—Piedmont Region—NW Italy), is the evaluation of the best methodologies for residual sludge treatment and exploitation. A chemical and physical characterisation on the sludge as such, and on several mixes produced to individuate the more suitable recycled products, was foreseen. Laboratory and in situ tests are in progress (2012–2014). The paper aims to demonstrate that, on the basis of a strict characterisation, appropriate treatment and correct management it is possible to turn residual sludge (waste) into resources (potentially alternative to the natural ones).