1,720,978 research outputs found
Tecniche e metodologie per la caratterizzazione idrodinamica degli acquiferi fessurati
No full textL’attività di ricerca che è stata sviluppata durante il dottorato ha approfondito ed affinato
metodiche che hanno visto l’impiego di traccianti di comune utilizzo in idrogeologia e di
nuova generazione, verificandone eventuali interazioni/assorbimento con materiali
rappresentativi degli acquiferi di differenti domini idrogeologici dell’Italia centrale. In
particolare l’utilizzo di un biotracciante (molecole di DNA), sperimentato in ambito
scientifico internazionale fino ad ora solamente nello studio di acque superficiali, ha
consentito di mettere a punto una nuova metodologia nello studio delle acque sotterranee.
Tale metodica è stata sperimentata in un laboratorio appositamente realizzato per
confrontare diversi traccianti e diversi materiali acquiferi, ed è stata poi applicata con
successo in campagna, in una struttura idrogeologica della dorsale carbonatica umbromarchigiana.
Una parte non trascurabile dell’attività di ricerca è stata infine rivolta alla
ricostruzione dettagliata dei modelli idrogeologici concettuali ed alla parametrizzazione
idraulica degli acquiferi carbonatici.
I risultati ottenuti da prove di laboratorio in colonna e su batch test con diversi traccianti
sono: le differenze dei tempi di arrivo dei picchi, a parità di condizioni idrauliche, sono
dovuti alla diversa geometria delle colonne; i valori di porosità efficace sono molto vicini ai
valori effettivamente ricavati indirettamente; i valori di velocità effettiva ottenuti con prove
di tracciamento sono simili a quelli ottenuti per via indiretta.
La sperimentazione con il biotracciante DNA nei test di colonna e di campagna ha mostrato
la sua efficacia in acquiferi carsici caratterizzati da condotti o doppia porosità, ma meno in
acquiferi porosi se l’obiettivo è la determinazione della porosità efficace; un flusso quasi
esclusivamente convettivo nei test su colonna; l'adsorbimento del DNA sulla roccia
calcarea è trascurabile, così il biotracer si comporta come un tracciante conservativo
rispetto a materiali carbonatici
Best tracer selection for hydrogeological investigations: preliminary results from laboratory test
No full textTracers techniques are a good tool to investigate groundwater dynamics; they are essential to perform measurement of hydrogeological parameters of aquifers. This study was aimed at characterizing adsorption, effective porosity and pore water velocity in soil samples collected in a hydrographic basin of Marche Region (Italy). This basin has the typical geologic and hydrogeological features of many basins in Central Italy. Therefore. the principal aim is to evaluate the best tracer to be used for hydrogeological purpose (i.e. groundwater tracer test and aquifer parameter estimation). Adsorption has been investigated by means of laboratory batch tests using different tracers and involving different soils. In literature some application of tracers both to laboratory scale and to field scale can be found. Column tests have been performed also to test the effectiveness of different test equipment and to investigate the influence of some test parameters on the calculation of effective porosity and pore water velocity. These considerations and test results are very useful to advise the choice of the best tracer to be used in tracer field tests
Determinazione rapida della migrazione di contaminanti organici nei terreni: prospettive per la bonifica
No full textEvaluation of saline tracer performance during electrical conductivity groundwater monitoring
No full textSaline solutions are the most commonly used hydrological tracers, because they can be easily and economically monitored by in situ instrumentation such as electrical conductivity (EC) loggers in wells or by geoelectrical measurements. Unfortunately, these low-cost techniques only provide information on the total concentration of ions in solution, i.e., they cannot resolve the ionic composition of the aqueous solution. This limitation can introduce a bias in the estimation of aquifer parameters where sorption phenomena between saline tracers and sediments become relevant. In general, only selected anions such as Cl− and Br− are recognised to be transported unretarded and they are referred to as conservative tracers or mobile anions. However, cations within the saline tracer may interact with the soil matrix through a range of processes such as ion exchange, surface complexation and via physical mass-transfer phenomena. Heterogeneous reactions with minerals or mineral surfaces may not be negligible where aquifers are composed of fine alluvial sediments. The focus of the present study was to examine and to quantify the bias between the aquifer parameters estimated during model-based interpretation of experimental data of EC measurements of saline tracer relative to the aquifer parameters found by specific measurements (i.e. via ionic chromatography, IC) of truly conservative species. To accomplish this, column displacement experiments with alluvial aquifer materials collected from the Po lowlands (Italy) were performed under water saturated conditions. The behaviour of six selected, commonly used saline tracers (i.e., LiCl, KCl, and NaCl; LiBr, KBr, and NaBr) was studied and the data analysed by inverse modelling. The results demonstrate that the use of EC as a tracer can lead to an erroneous parameterisation of the investigated porous media, if the reactions between solute and matrix are neglected. In general, errors were significant except for KCl and KBr, which is due to the weak interaction between dissolved K+ and the sediment material. The study shows that laboratory scale pre-investigations can help with tracer selection and to optimise the concentration range targeted for in situ multilevel monitoring by unspecific geoelectrical instrumentation
Monitoring and Modelling Interactions between the Montagna dei Fiori Aquifer and the Castellano Stream (Central Apennines, Italy)
No full textGroundwater is the most used water resource around the world, but due to population growth and climate change the alluvial lowland aquifers are often polluted and over-exploited. Thus, more and more frequently water managers need to shift their attention to mountain regions to identify groundwater resources for drinking purposes. This study presents a monitoring and modelling approach that allowed to quantify the inflow from the "Montagna dei Fiori" fractured aquifer to the Castellano stream. Continuous monitoring of flow discharge and temperature during an entire hydrological year (2018-2019) at two monitoring stations along the stream allowed to discriminate between the baseflow (on average, 0.891 m3/s) and the run-off (on average, 0.148 m3/s) components. A hydrogeological basin-wide numerical flow model (using MODFLOW-2005) was set up using information from hydrogeological and geomechanical surveys. The model was calibrated using the daily baseflow observations made in the Castellano stream (R2 = 0.75). The calibrated model allowed to quantify groundwater/surface water interactions. After an automated sensitivity analysis (using MODFLOW-2000), the recharge was found to be the most uncertain parameter, followed by the hydraulic conductivity zonation. This methodology could be applied in other mountain regions where groundwater monitoring networks are usually lacking to improve water resources management
THE CONTRIBUTION OF DNA AND FLUORESCENT TRACER FOR THE IDENTIFICATION OF CONNECTIONS IN KARST AND FISSURED AQUIFERS
No full textThe investigated area, located in the inner part of the Marche region (central Italy) and belonging to the
carbonate Umbria-Marche ridges in the central Apennines, is characterised by very complex geo-structural settings
and widespread karst phenomena. Hence, the definition of the relation among the aquifers basing only on the
hydrogeological survey is very difficult. The presence of different flowpaths (supposed from the observation of the
springs hydrograph) and of hydraulic contact among the aquifers is proved using tracer tests. In particular, the
Calcare Massiccio and the Maiolica aquifers are connected under certain tectonic conditions.
A new tracer given by a single stranded DNA molecule and a traditional fluorescent dye have been injected into
the Montelago sinkhole in different periods (from the recharge to the discharge of the karst system) and recovered
in several points along the expected hydrogeological basin, using either manual and automatic sampling and
fluorescent traps positioned in creeks, rivers and springs. The DNA molecule is useful to trace surface water and
groundwater, is detectable even at very low concentrations, no significant change in water density and viscosity
can be observed and its use is not dangerous for the environment (Aquilanti et al. 2013; Sabir et al. 1999). However,
DNA is insoluble in groundwater and acts as a particle/colloidal tracer, so it shows a breakthrough curve
characterised by higher or lower pulses. The results stress the suitability of DNA as hydrogeological tracer, capable
to identify connections among aquifers and study different flowpaths even in high flow conditions when
traditional tracers are more and more diluted and often under the instrument detection limit. What is more,
Fluorescein tracer allowed for the transport parameter determination, giving mean velocities ranging from 100 to
3000 m/day and mean residence time from some tens to hundreds of hour
Caratterizzazione del campo di permeabilità di falde acquifere eterogenee tramite tecniche idrogeologiche e geofisiche
No full textPresso la Fondazione per l’agricoltura Fratelli Navarra a Malborghetto (FE), è stata
caratterizzata una porzione di terreno di circa 15000 m2 con la tecnica geofisica della
tomografia di resistività elettrica, con la quale sono stati individuati dei corpi sabbiosi
(paleoalvei) sede di falde acquifere. Grazie alla caratterizzazione geofisica è stata
installata una maglia regolare di circa 200 m2 costituita da 13 piezometri, perforati
all’interno del corpo sabbioso di maggiori dimensioni. In ogni piezometro sono state
effettuate prove di permeabilità in foro di tipo “slug test” a diverse profondità. La
comparazione fra valori puntuali di resistività elettrica e permeabilità ha permesso di
ricavare una relazione empirica di tipo bi-logaritmico fra questi due parametri.
Applicando la relazione empirica tra i valori di resistività elettrica stimati
dall’inversione 2D ed i valori misurati di permeabilità alle corrispondenti profondità,,
si è potuto estrapolare il campo di permeabilità all’intera zona indagata
DNA and Fluorescein tracer tests to study the recharge, groundwater flowpath and hydraulic contact of aquifers in the Umbria-Marche limestone ridge (central Apennines, Italy)
No full textThe purpose of this paper is to highlight the hydrogeological contact among aquifers in
karst and fissured systems and study the different flowpaths present in the aquifers;
given the complex hydrogeological and tectonics settings, a detailed hydrogeological
and geo-structural survey in a selected area of the Umbria-Marche limestone ridges
(central Apennines), supported by tracer field tests, was used to achieve this goal.
DNA and fluorescent tracers were injected into a sinkhole located in the Montelago
karst high-plain (Umbria-Marche ridge) and recovered at different points, thus allowing
for the identification of effective hydraulic contact among aquifers belonging to both
the same and different hydrogeological complexes, and to identify the main and
secondary direction of the groundwater. Moreover, tracer tests, highlighting the role
that tectonics play in the groundwater circulation, have shown that the majority of
groundwater flow is directed towards the axis of the tectonic structures, emerging in the
more depressed areas. In addition, they have demonstrated the influence of
karstification on the aquifer recharge and shallow flowpaths, allowing for a more
detailed characterisation of water circulation in the unsaturated zone of the Maiolica
and the Calcare Massiccio aquifers. In conclusion, the tracer tests confirmed the
hydrogeological survey results, while providing additional previously unknown
information. Furthermore, the DNA tracer (recently tested in a preceding study)
provided good results in the field especially in karst systems and fissured rocks, thus
confirming its appropriacy for flowpath investigations and vulnerability analysis of
springs
Fertilizers mobilization in alluvial aquifer: laboratory experiments
No full textIn alluvial plains, intensive farming with conspicuous use of agrochemicals, can cause land pollution and groundwater contamination. In central Po River plain, paleo-channels are important links between arable lands and the underlaying aquifer, since the latter is often confined by clay sediments that act as a barrier against contaminants migration. Therefore, paleo-channels are recharge zones of particular interest that have to be protected from pollution as they are commonly used for water supply. This paper focuses on fertilizer mobilization next to a sand pit excavated in a paleo-channel near Ferrara (Italy). The problem is approached via batch test leaking and columns elution of alluvial sediments. Results from batch experiments showed fast increase in all major cations and anions, suggesting equilibrium control of dissolution reactions, limited availability of solid phases and geochemical homogeneity of samples. In column experiments, early elution and tailing of all ions breakthrough was recorded due to preferential flow paths. For sediments investigated in this study, dispersion, dilution and chemical reactions can reduce fertilizers at concentration below drinking standards in a reasonable time frame, provided fertilizer loading is halted or, at least, reduced. Thus, the definition of a corridor along paleo-channels is recommended to preserve groundwater quality. © 2008 Springer-Verlag
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