1,721,070 research outputs found
Attenuazione naturale controllata: una tecnica di bonifica innovativa ed economica
No full textIl presente lavoro trae spunto da un caso di studio inglese assai ben documentato, studiato da anni dal GPRG (Groundwater Protection and Restoration group, University of Sheffield) presso cui gli autori sono direttamente coinvolti in un progetto comune di ricerca, per dimostrare l'efficacia dell'attenuazione naturale e la sua natura fortemente basata sulla caratterizzazione idrogeologica ed idrogeochimica e sulla modellazione in antitesi alle tecniche di bonifica ingegnerizzate sovente adottat
Parametric and numerical modeling tools to forecast hydrogeological impacts of a tunnel
Full text linkThe project of interest involving a hydroelectrical diversion tunnel through a crystalline rock massif in the Alps required a detailed hydrogeological study to forecast the magnitude of water inflows within the tunnel and possible effects on groundwater flow. The tunnel exhibits a length of 9.5 km and is located on the right side of the Toce River in Crevoladossola (Verbania Province, Piedmont region, northern Italy). Under the geological framework of the Alps, the tunnel is located within the Lower Penninic Nappes in the footwall of the Simplon Normal Fault, and the geological succession is mostly represented by Antigorio gneiss (metagranites) and Baceno metasediments (metacarbonates). Due to the presence of important mineralized springs for commercial mineral water purposes, the abovementioned hydrogeological study focused on both quantity and quality aspects via rainfall data analysis, monitoring of major spring flow rates, monitoring of hydraulic heads and pumping rates of existing wells/boreholes, hydrochemical and isotopic analysis of springs and boreholes and hydraulic tests (Lefranc and Lugeon). The resulting conceptual model indicated dominant low-permeability (aquitard) behavior of the gneissic rock masses, except under conditions of intense fracturing due to tectonization, and aquifer behavior of the metasedimentary rocks, particularly when interested by dissolution. Groundwater flow systems are mainly controlled by gravity. The springs located near the Toce River were characterized by high mineralization and isotopic ratios, indicating long groundwater flow paths. Based on all the data collected and analyzed, two parametric methods were applied: 1) the Dematteis method, slightly adapted to the case study and the available data, which allows assessment of both potential inflows within the tunnel and potential impacts on springs (codified as the drawdown hazard index; DHI); 2) the Cesano method, which only allows assessment of potential inflows within the tunnel, thereby discriminating between major and minor inflows. Contemporarily, a groundwater flow model was implemented with the equivalent porous medium (EPM) approach in MODFLOW-2000. This model was calibrated under steady-state conditions against the available data (groundwater levels inside wells/piezometers and elevation and flow rate of springs). The Dematteis method was demonstrated to be more reliable and suitable for the site than was the Cesano method. This method was validated considering a tunnel through gneissic rock masses, and this approach considered intrinsic parameters of rock masses more notably than morphological and geomorphological factors were considered. The Cesano method relatively overestimated tunnel inflows, considering variations in the topography and overburden above the tunnel. Sensitivity analysis revealed a low sensitivity of these parametric methods to parameter values, except for the rock quality designation (RQD) employed to represent the fracturing degree. The numerical model was calibrated under ante-operam conditions, and sensitivity analysis evaluated the influence of uncertainties in the hydraulic conductivity (K) values of the different hydrogeological units. The hydraulic head distribution after tunnel excavation was forecasted considering three scenarios, namely, a draining tunnel, tunnel as a water loss source, and tunnel sealed along its aquifer sectors, considering 3 levels of K reduction. Tunnel impermeabilization was very effective, thus lowering the drainage rate and impact on springs. The model quantitatively defined tunnel inflows and the effects on spring flow at the surface in terms of flow rate decrease. The Dematteis method and numerical model were combined to obtain a final risk of impact on the springs. This study likely overestimated the risk because all the values assigned to the parameters were chosen in a conservative way, and the steady-state numerical simulations were also very conservative (the transient state in this hydrogeological setting supposedly lasts 1–3 years). Monitoring of the tunnel and springs during tunnel boring could facilitate the feedback process
Idrogeologia per la gestione integrata delle risorse idriche in aree costiere al di sotto del livello del mare: l’area deltizia padana
No full textLa ricerca mette in risalto l'importanza del monitoraggio idrogeologico di tipo discontinuo nel tempo, integrato da un monitoraggio in continuo, unito alla modellazione numerica con finalità previsionali, per la gestione integrata delle risorse idriche in aree "sensibili" quali le zone costiere del Delta Padan
Natural attenuation processes in the CORONA Protocol: application to the “NIT” field site
No full textThe contribution of the CORONA project (Confidence in fORecasting Of Natural Attenuation a research project supported by the European Commission under the Fifth Framework Programme) to the theoretical background and application principles of Monitoring Natural Attenuation (MNA) is presented. A detailed knowledge of hydrodynamical, hydrochemical and microbiological processes occurring inside and, particularly, at the interfacial fringe of the plume is put in evidence as the key factor in assessing the natural attenuation potential. The plume zonation (both in horizontal and vertical direction) in areas where different redox processes are acting is possible only with high resolution sampling devices such as Multi Level Samplers (MLSs).
As a representative case study the NIT plant is been chosen as test site for the application of the Corona Protocol
The CORONA screening model and a 2D reactive transport model for a BTEX and styrene plume to evaluate natural attenuation potential
No full textThe CORONA Screening Model (CSM) is a new spreadsheet tool for the prediction of contaminant plume length in groundwater. The CSM has been used to predict the spreading of a BTEX and Styrene plume in an unconfined sandy aquifer. To test the reliability of this new software, the results gained by the application of CSM have been compared with the ones obtained with the implementation of a numerical model built using a world accepted and tested code like PMWIN.
In the numerical model a coupled reactive transport model PHT3D has been used to simulate the fate of dissolved BTEX and Styrene in the aquifer. The model grid was intensevely tested to avoid numerical dispersion. Calibration was achieved comparing 3 data sets sampled in different water table conditions coming from MLS located along a flow line
The use of monitored natural attenuation as a cost effective technique for groundwater restoration: the case study of REXCO (UK)
No full textTheoretical background and application principles of Monitoring Natural Attenuation (MNA) contaminated
aquifers not engineered remediation methodology are presented. A detailed knowledge of hydrodinamical,
hydrochemical and microbiological processes occurring inside and , particularly, at the interfacial fringe
(the so called “corona”) of the plume is put in evidence as the key factor in assessing the natural attenuation
potential. Chemical mass balance of plume and identification of chemical “footprints” reflecting that NA is
really working are the two most important tools to evaluate the processes. As a representative case study
the Rexco plant (Mansfield, UK) is considered. A phenols plume has been almost entirely attenuated by the
natural groundwater system avoiding so the contamination of wells located downgradient; at the same time
an ammonium plume, originating at the same plant, also if strongly retarded by the finer matrix of the
aquifer, has was recalcitrant to attenuation. The presented case study underlines the importance of a
combined use of both an experimental verification and a forecasting of the plume time-space evolution by
numerical models, being the first one necessary for the calibration and the progressive tuning of the second
one
Estimation of recharge in mountain hard-rock aquifers based on discrete spring discharge monitoring during base-flow recession
Full text linkEstimation of aquifer recharge is key to effective groundwater management and protection. In mountain hard-rock aquifers, the average annual discharge of a spring generally reflects the vertical aquifer recharge over the spring catchment. However, the determination of average annual spring discharge requires expensive and challenging field monitoring. A power-law correlation was previously reported in the literature that would allow quantification of the average annual spring discharge starting from only a few discharge measurements in the low-flow season, in a dry summer climate. The correlation is based upon the Maillet model and was previously derived by a 10-year monitoring program of discharge from springs and streams in hard-rock aquifers composed of siliciclastic and calcareous turbidites that did not have well defined hydrogeologic boundaries. In this research, the same correlation was applied to two ophiolitic (peridotitic) hard-rock aquifers in the Northern Apennines (Northern Italy) with well-defined hydrogeologic boundaries and base-outflow springs. The correlation provided a reliable estimate of the average annual spring discharge thus confirming its effectiveness regardless of bedrock lithology. In the two aquifers studied, the measurable annual outputs (i.e. sum of average annual spring discharges) could be assumed equal to the annual inputs (i.e. vertical recharge) based on the clear-cut aquifer boundaries and a quick groundwater circulation inferable from spring water parameters. Thus, in such setting, the aforementioned correlation also provided an estimate of the annual aquifer recharge allowing the assessment of coefficients of infiltration (i.e. ratio between aquifer recharge and total precipitation) ranging between 10 and 20%
Metodologia di redazione della Carta della Vulnerabilità intrinseca e del rischio d’inquinamento degli acquiferi del Valdarno medio.
No full textViene presentata la carta, accompagnata dalle note illustrative, relativa alla valutazione della vulnerabilità intrinseca e del rischio di inquinamento degli acquiferi del bacino fluvio-lacustre del Valdarno Medio (pianura Firenze-Prato-Pistoia). Il lavoro rappresenta la sintesi finale di un lungo lavoro di censimento, prima elaborazione e georeferenziazione di tutti i dati, idrogeologici e territoriali, concernenti ed influenzanti il ciclo naturale e di sfruttamento dell’acqua sotterranea nel territorio indagato. La pianura del Valdarno Medio, di estensione pari a circa 350 km2, ha costituito un interessante test site per l’applicazione delle metodologie di valutazione adottate, caratterizzata come è da: una elevata variabilità idrogeologica del grado di protezione del primo acquifero, una presenza di acquiferi superficiali scarsamente protetti e profondi ben protetti, una elevata e diversificata pericolosità territoriale con compresenza di aree urbanizzate, industrializzate ed agricole intensive (trattasi in pratica di una estesa area metropolitana praticamente senza soluzione di continuità), un notevole interesse acquedottistico locale delle risorse idriche di sottosuolo sia in quanto attualmente sfruttate sia in quanto caratterizzate, in alcuni casi, da una produttività residua ancora elevata. Il quadro illustrato, unito alla notevole quantità di dati disponibili sia di tipo geologico (più di 2000 stratigrafie), pedologico, idrochimico e concernenti la pericolosità territoriale (circa 7000 punti di potenziale pericolo per la falda, differenziati fra sorgenti di tipo puntuale, lineare ed areale), ha fornito una elevata significatività, in termini di impiego operativo della cartografia realizzata, alle metodologie di valutazione adottate.
Per la valutazione della vulnerabilità intrinseca è stato adottato il modello parametrico a punteggio e pesi SINTACS con alcune integrazioni ed affinamenti giustificati dall’elevato dettaglio conoscitivo del sottosuolo e dalla specificità idrogeologica dell’area; oltre all’inserimento dei parametri tempo di arrivo e spessore dell’acquifero, sono state aggiunte, alle stringhe di pesi già codificate, alcune specifiche relative alle aree soggette a rischio idraulico (assai elevato in alcune aree del bacino), alle aree urbanizzate ed alle aree soggette a ricarica laterale per travaso dagli acquiferi fratturati del substrato pre-lacustre o per deflusso ipodermico dalle pendici delle colline. E’ stato anche valutato un’indice di vulnerabilità SINTACS relativo agli acquiferi profondi confinati.
Per quanto concerne la valutazione del rischio di inquinamento si è operato tramite un sistema parametrico a punteggio basato sull’incrocio, gestito da sistema informativo su piattaforma Intergraph, dell’Indice di Pericolo (Hazard Index), derivato dalla densità di distribuzione e dalla magnitudo di potenziale impatto dei centri di pericolo georeferenziati, e dell’Indice di Vulnerabilità SINTACS integrato dalla schematizzazione dei flussi orizzontali di falda; ai fini di una compiuta valutazione del rischio viene anche parametrizzato il valore idrogeologico e socio-economico della risorsa, assai diversificato nell’area. La metodologia proposta recepisce le esperienze degli autori, relative sia alla valutazione parametrica del rischio tramite sistema informativo ARC/INFO sia agli studi di idrogeologia urbana nell’area della città di Firenze
Groundwater flow modelling of a tunnel-drained fractured aquifer: validation through creek base-flow continuous monitoring
No full textThis paper concern the implementation and validation of a numerical flow model based on the data collected and related to the bored section of a base tunnel through the Appenninic chain (Veccione watershed, Upper Reno basin, Tuscany, Northern Italy). The hydrologic input data employed in the simulation are the results of an hydrogeological program based on a discontinuous monitoring of springs, creeks discharges and tunnel’s drainage rate from 1995 to 2001. Moreover a detailed geological survey of the area was developed to identify the main tectonic patterns.
Three different numerical models were set up, all based on the numerical code Modflow: the first one is a steady-state model calibrated on piezometric levels, springs and creeks discharge in undisturbed conditions; the second one is a transient model relative to the time span between 1999 and 2004 calibrated with the tunnel drainage to nowdays; the third is a transient model to verify the long term effects (till 2015). To improve the validation of the second transient model, were compared data coming from continuous stream stage monitoring systems with model outputs . The study focus on tunnel’s interference with groundwater flow system and the possibility to employ a finite differences code as a predictive tool in fractured aquifer
- …
