Marco Rotiroti

Origin of Arsenic in Groundwater from the Multilayer Aquifer in Cremona (Northern Italy)

An analysis of 70 wells that tap groundwater from depths of up to 260 m in and around the town of Cremona, N. Italy, shows that 50 of them contain more than 10 μg/L of arsenic. Concentrations of As >10 ppb are accompanied by concentrations of Fe ranging from <0.1 to 6 mg/L and high concentrations of NH4 and Mn (<19 and <1.3 mg/L, respectively). The associations suggest that the mechanism of mobilization of As is the reductive dissolution of Fe oxides driven by the degradation of peat, which is commonly found in the aquifer system. Groundwater in the aquifer has a component of downward flow via leakage through aquitards and flow through lateral discontinuities in them. Along these flow paths, As is released by reductive dissolution of Fe oxides in shallow and intermediate aquifers (0-85 m below surface), reaching up to 183 μg/L, and is attenuated (<95 μg/L) at greater depths (100-150 m). Coprecipitation in iron sulfides could play an important role in As attenuation at these depths. The lower As concentration (<37 μg/L) in the deepest aquifer (160-260 m) is less related to the As concentration of the overlying aquifers because the groundwater here has a component of upward flow.

Pollutant sources in an arsenic-affected multilayer aquifer in the Po Plain of Italy: Implications for drinking-water supply

In aquifers 160 to 260m deep that used for public water-supply in an area ~150km2 around the town of Cremona, in the Po Plain of Northern Italy, concentrations of arsenic (As) are increasing with time in some wells. The increase is due to drawdown of As-polluted groundwater (As ≤144μg/L) from overlying aquifers at depths 65 to 150m deep in response to large-scale abstraction for public supply. The increase in As threatens drinking-water quality locally, and by inference does so across the entire Po Plain, where natural As-pollution of groundwater (As >10μg/L) is a basin-wide problem. Using new and legacy data for Cl/Br, δ18O/δ2H and other hydrochemical parameters with groundwater from 32 wells, 9 surface waters, a sewage outfall and rainwater, we show that the deep aquifer (160-260m below ground level), which is tapped widely for public water-supply, is partly recharged by seepage from overlying aquifers (65-150m below ground level). Groundwater quality in deep aquifers appears free of anthropogenic influences and typically <10μg/L of As. In contrast, shallow groundwater and surface water in some, not all, areas are affected by anthropogenic contamination and natural As-pollution (As >10μg/L). Outfalls from sewage-treatment plants and black water from septic tanks firstly affect surface waters, which then locally infiltrate shallow aquifers under high channel-stages. Wastewater permeating shallow aquifers carries with it NO3 and SO4 which suppress reduction of iron oxyhydroxides in the aquifer sediments and so suppress the natural release of As to groundwater.

Determination of trigger levels for groundwater quality in landfills located in historically human-impacted areas

Landfills are one of the most recurrent sources of groundwater contamination worldwide. In order to limit their impacts on groundwater resources, current environmental regulations impose the adoption of proper measures for the protection of groundwater quality. For instance, in the EU member countries, the calculation of trigger levels for identifying significant adverse environmental effects on groundwater generated by landfills is required by the Landfill Directive 99/31/EC. Although the derivation of trigger levels could be relatively easy when groundwater quality data prior to the construction of a landfill are available, it becomes challenging when these data are missing and landfills are located in areas that are already impacted by historical contamination. This work presents a methodology for calculating trigger levels for groundwater quality in landfills located in areas where historical contaminations have deteriorated groundwater quality prior to their construction. This method is based on multivariate statistical analysis and involves 4 steps: (a) implementation of the conceptual model, (b) landfill monitoring data collection, (c) hydrochemical data clustering and (d) calculation of the trigger levels. The proposed methodology was applied on a case study in northern Italy, where a currently used lined landfill is located downstream of an old unlined landfill and others old unmapped waste deposits. The developed conceptual model stated that groundwater quality deterioration observed downstream of the lined landfill is due to a degrading leachate plume fed by the upgradient unlined landfill. The methodology led to the determination of two trigger levels for COD and NH4-N, the former for a zone representing the background hydrochemistry (28 and 9 mg/L for COD and NH4-N, respectively), the latter for the zone impacted by the degrading leachate plume from the upgradient unlined landfill (89 and 83 mg/L for COD and NH4-N, respectively).

Numerical Modeling of Groundwater Flooding in Urban Area: The Case of Polustrovo (St. Petersburg, Russia)

The present paper describes the implementation of a numerical model to simulate groundwater flooding in the Polustrovo urban area of St. Petersburg (Russia), characterized by a moraine aquifer system. The main purposes are to determine the causes of groundwater flooding and to simulate some examples of engineering solutions. The study concerns (a) data collection and processing also by means of geostatistical analysis, (b) conceptual model elaboration and (c) implementation of a 3D groundwater flow model (design, execution and calibration) using MODFLOW code. Results point out a shallow flow system governed by topography and by groundwater-surface water interaction. All surface water bodies collect water from the shallow aquifer. Flow direction is mainly W/E in the northern part of the area and N/S in the southern part. Hydraulic gradient of shallow aquifer (average of 0.4 %) varies depending on lithology distribution, whereas in the deep aquifer the gradient has a constant value of 0.3 %. In the southern part of the area, deep aquifer has artesian condition. Flooding results in the southern zone of study area, according to field observation. Likely cause of flooding is the quick decrease of hydraulic conductivity along flow direction in the shallow aquifer, in addition to the decrease of soil surface elevation. The rising of deep groundwater under artesian condition in the zones where the aquitard is eroded can increase the intensity of flooding. Finally, the modeling indicates that a passive drainage system or a hydraulic barrier (pumping wells) could represent some engineering solutions of the flooding problem.