Groundwater contamination by organo-chlorinated compounds and its remediation is currently one of the main environmental problems in the management and remediation of contaminated sites. Among the different remediation technologies, bioremediation techniques are becoming increasingly important due to their cost-effectiveness and increasing effectiveness. These include Monitored Natural Attenuation (MNA), which is based on the constant monitoring of groundwater contamination and the demonstration of the presence of natural attenuation mechanisms, including biodegradation. Where MNA application is to be evaluated, a preliminary characterization study must be conducted in order to understand the importance of the natural implementation mechanisms present at the polluted site. In order to better understand and simulate these processes, in the last years have been developed codes able to simulate the reactive transport of solute, such as MODFLOW-USG transport and BIOCHLOR-ISO. In the present thesis they have been used to demonstrate the existence of degradative processes and to simulate the relative plume in a contaminated site by chloroethylenes (TCE, cis-DCE and VC) located in Southern Italy. After a proper calibration by PEST code, the model developed by MODFLOW-USG transport has been used for forecasting purposes to determine the period necessary for the detected concentrations to comply with the legal limits, established by the Legislative Decree 152/2006. Assuming a given remediation scenario of the contamination source, both an MNA and a bisotimulation process were simulated. Subsequently, in order to further support the existence of natural biodegradation processes, using a model implemented in BICHLOR-ISO developed for descriptive purposes, it was simulated both the reactive transport and the isotopic fractionation of carbon based on data extrapolated from a isotopic analysis campaign conducted at the site (13C/12C). Based on the results of the two models, it was possible to estimate a remediation time of about 22 years by exploiting the natural attenuation mechanisms active at the site and about 5 years by implementing biostimulation. Moreover, thanks to the results of the model realized with MODFLOW-USG, it was possible to define a monitoring network to support the MNA, a prerequisite for the application of this methodology. This paper demonstrates the potential of reactive transport models, which can be used for interpretive purposes to evaluate the active degradation conditions at a site, for forecasting purposes to obtain an estimate of the remediation time in different scenarios and to establish ad-hoc monitoring networks for the site under investigation.
La contaminazione delle acque di falda da composti organo-clorurati e il loro risanamento è attualmente uno dei principali problemi ambientali nella gestione e bonifica dei siti contaminati. Tra le varie tecnologie di bonifica, oggigiorno le tecniche di biorisanamento stanno assumendo sempre più importanza data la loro economicità e crescente efficacia. Tra esse rientra l’Attenuazione Naturale Monitorata (MNA), basata sul costante monitoraggio della contaminazione in falda e sulla dimostrazione della presenza di meccanismi di attenuazione naturale, tra cui la biodegradazione. Laddove si voglia valutare l’applicazione della MNA è necessario effettuare uno studio di caratterizzazione preliminare al fine di comprendere l’importanza dei meccanismi di attuazione naturale presenti nel sito inquinato. Per comprendere e simulare al meglio tali processi, negli ultimi anni sono stati elaborati codici in grado di simulare il trasporto reattivo di soluto, come MODFLOW-USG transport e BIOCHLOR-ISO. Questi sono stati utilizzati nel presente elaborato di tesi per dimostrare l’esistenza di processi degradativi e simulare il relativo plume in un sito contaminato da cloroetileni (TCE, cis-DCE e VC) ubicato nel Sud Italia. Una volta calibrato adeguatamente tramite il codice PEST, il modello realizzato tramite MODFLOW-USG transport è stato utilizzato a scopo previsionale per determinare il periodo necessario affinché le concentrazioni rilevate rispettino i limiti di legge, stabiliti dal D.Lgs. 152/2006. Ipotizzando un determinato scenario di bonifica della sorgente di contaminazione, sono stati simulati sia un processo di MNA che di bisotimolazione. Successivamente, al fine di supportare ulteriormente l’esistenza di processi biodegradativi naturali, tramite il modello implementato in BICHLOR-ISO elaborato a scopo descrittivo, è stato simulato sia il trasporto reattivo che il frazionamento isotopico del carbonio basandosi su dati estrapolati da una campagna di analisi isotopiche condotta nel sito (13C/12C). Sulla base dei risultati delle due modellazioni, è stato possibile stimare un tempo di bonifica di circa 22 anni sfruttando i meccanismi di attenuazione naturale attivi nel sito e di circa 5 anni implementando la biostimolazione. Inoltre, grazie ai risultati del modello realizzato con MODFLOW-USG, è stato possibile definire una rete di monitoraggio a supporto dell’MNA, prerequisito dell’applicazione di questa metodologia. Il presente elaborato dimostra la potenzialità dei modelli di trasporto reattivo, che possono essere utilizzati a scopo interpretativo per valutare le condizioni di degradazione attive in un sito, a scopo previsionale per ottenere una stima dei tempi di bonifica in diversi scenari e per la definizione di reti di monitoraggio ad-hoc per il sito in esame.
Modellazione numerica del trasporto reattivo in falda di composti organo-clorurati
CONSONNI, DANIELA
2020/2021
Abstract
Groundwater contamination by organo-chlorinated compounds and its remediation is currently one of the main environmental problems in the management and remediation of contaminated sites. Among the different remediation technologies, bioremediation techniques are becoming increasingly important due to their cost-effectiveness and increasing effectiveness. These include Monitored Natural Attenuation (MNA), which is based on the constant monitoring of groundwater contamination and the demonstration of the presence of natural attenuation mechanisms, including biodegradation. Where MNA application is to be evaluated, a preliminary characterization study must be conducted in order to understand the importance of the natural implementation mechanisms present at the polluted site. In order to better understand and simulate these processes, in the last years have been developed codes able to simulate the reactive transport of solute, such as MODFLOW-USG transport and BIOCHLOR-ISO. In the present thesis they have been used to demonstrate the existence of degradative processes and to simulate the relative plume in a contaminated site by chloroethylenes (TCE, cis-DCE and VC) located in Southern Italy. After a proper calibration by PEST code, the model developed by MODFLOW-USG transport has been used for forecasting purposes to determine the period necessary for the detected concentrations to comply with the legal limits, established by the Legislative Decree 152/2006. Assuming a given remediation scenario of the contamination source, both an MNA and a bisotimulation process were simulated. Subsequently, in order to further support the existence of natural biodegradation processes, using a model implemented in BICHLOR-ISO developed for descriptive purposes, it was simulated both the reactive transport and the isotopic fractionation of carbon based on data extrapolated from a isotopic analysis campaign conducted at the site (13C/12C). Based on the results of the two models, it was possible to estimate a remediation time of about 22 years by exploiting the natural attenuation mechanisms active at the site and about 5 years by implementing biostimulation. Moreover, thanks to the results of the model realized with MODFLOW-USG, it was possible to define a monitoring network to support the MNA, a prerequisite for the application of this methodology. This paper demonstrates the potential of reactive transport models, which can be used for interpretive purposes to evaluate the active degradation conditions at a site, for forecasting purposes to obtain an estimate of the remediation time in different scenarios and to establish ad-hoc monitoring networks for the site under investigation.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/187858