NDLI: Modeling of transient groundwater flow, pollutant transport, and biodegradation in an aquifer with large hydraulic head variations

Content Provider	Springer Nature Link
Author	Rinaldi, Sandro Louati, Sihem Bendjoudi, Hocine Marsily, Ghislain
Copyright Year	2014
Abstract	Industrially sourced dense non-aqueous phase liquids (DNAPLs) contaminated an alluvial aquifer in France decades ago. The location(s) and nature of the pollution source zone(s) were unknown, and the dissolved concentrations of volatile organic compounds in the monitoring wells varied greatly with time. The aquifer was in hydraulic equilibrium with an artificial canal whose water level was highly variable (up to 5 m). These variations propagated into the aquifer, causing changes in the groundwater flow direction; a transient numerical model of flow and solute transport showed that they correlate with the concentration variations because the changes in the flow direction resulted in the contaminant plume shifting. The transient hydrogeological numerical model was built, taking into account solvent biodegradation with first-order chain, since biodegradation has a significant influence on the pollutant concentration evolution. The model parameterization confirms the position of the source zones among the potential troughs in the bedrock where DNAPLs could have accumulated. The groundwater model was successfully calibrated to reproduce the observed concentration variations over several years and allowed a rapid validation of the hypotheses on the functioning of the polluted system.Depuis plusieurs décennies, un aquifère alluvial français est contaminé par des produits industriels denses et non solubles (DNAPL). La position et la composition exacte des zones sources de la pollution étaient inconnue, et les concentrations en composés organique volatils dissous dans les piézomètres de contrôle étaient très variables au cours du temps. L’aquifère est en équilibre hydraulique avec un canal artificiel, dont le niveau est très variable (jusqu’à 5 m). Ces variations de charge, se propageant dans l’aquifère, entraînaient des variations de la direction d’écoulement ; un modèle numérique transitoire d’écoulement et de transport de solutés a montré que ces variations étaient corrélées aux variations de concentrations parce que la variation de la direction d’écoulement déplaçait le panache de pollution. Ce modèle transitoire inclut une biodégradation des contaminants en chaîne avec une cinétique du premier ordre, en raison de l’influence importante de ce mécanisme sur l’évolution des concentrations. Le calage du modèle sur les données disponibles a permis de déterminer la position de la zone source parmi les différentes « cuvettes » du substratum de la nappe, susceptibles d’avoir accumulé des DNAPLs. Le modèle calé reproduit bien les variations observées de concentrations dans la nappe, sur plusieurs années, et a permis de valider les hypothèses faites sur le fonctionnement du système.Líquidos densos de fases no acuosas provenientes de fuentes industriales (DNAPLs) contaminaron un acuífero aluvial décadas atrás en Francia. La ubicaciones y naturaleza de las zonas de fuentes de contaminación eran desconocidas, y las concentraciones disueltas de compuestos orgánicos volátiles en los pozos de monitoreo varió grandemente con el tiempo. El acuífero estaba en equilibrio hidráulico con un canal artificial cuyo nivel de agua era altamente variable (hasta de 5 m). Estas variaciones se propagaban dentro del acuífero, causando cambios en la dirección del flujo de agua subterránea; un modelo numérico transitorio de flujo y de transporte de soluto mostró que ellos se correlacionaban bien con las variaciones de concentración debidas a que los cambios en la dirección de flujo provocaban el desplazamiento de la pluma contaminante. El modelo numérico hidrogeológico transitorio fue construido, tomando en cuenta la biodegradación de solventes con cadenas de primer orden, puesto que la biodegradación tiene una influencia significativa en la evolución de la concentración de contaminantes. La parametrización del modelo confirma la posición de las zonas fuentes entre las depresiones potenciales en el basamento donde el DNAPLs podría haberse acumulado. El modelo de agua subterránea fue calibrado exitosamente para reproducir las variaciones observadas de concentración a lo largo de varios años y permitió una validación rápida de las hipótesis sobre el funcionamiento del sistema contaminado.几十年前工业源的稠密无水相液体(DNAPLs)污染了法国一个冲积含水层。污染源带的位置和特性依然未知,监测井中的挥发性有机物溶解含量随时间变化很大。含水层与水位变化很大的(达5 米)人工运河处于水力平衡。这些变化传播到含水层中,引起地下水流方向的改变;水流和溶质运移瞬时数值模型显示它们与含量变化相关,因为水流方向改变导致污染物羽状转移。建立了瞬时水文地质数值模型,考虑到了具有一级链的溶解能力的生物降解,因为生物降解对污染物含量演变有重要影响。模型参数化确认了基岩势阱中源区的位置,在此(DNAPLs)可能已经积累。对地下水模型成功进行了校准,再现了观测到的几年含量变化,使污染系统的运作的假定能得到快速验证。Delle sostanze organiche liquide più dense dell’acqua (DNAPL) di provenienza industriale hanno contaminato una falda freatica situata Francia diverse decine di anni fa. Prima del nostro studio né la posizione né la composizione chimica esatta delle zone inquinate erano conosciute e le concentrazioni di composti organici volatili disciolti nei piezometri di controllo erano molto variabili nel tempo. La falda freatica é in equilibrio idraulico con un canale artificiale il cui livello d’acqua varia bruscamente (fino a 5 m). Tali variazioni di livello si propagano nella falda freatica causando delle variazioni di direzione del flusso sotterraneo; un modello numerico di flusso sotterraneo in regime transitorio e con trasporto di soluti mostra che queste variazioni di livello d’acqua e della concentrazione di contaminanti disciolti sono tra loro correlate poiché le variazioni di direzione del flusso sotterraneo determinano uno spostamento dell’acqua contaminata. Durante l’adattamento del modello ai dati disponibili è stato anche necessario includere una biodegradazione sequenziale dei contaminanti con una cinetica di primo ordine. L’adattamento del modello ha permesso di determinare la posizione delle zone d’origine della contaminazione tra le differenti depressioni del substrato della falda freatica, dove i DNAPL sono suscettibili di essersi accumulati. Il modello adattato riproduce in modo soddisfacente le variazioni delle concentrazioni di contaminanti osservate nella falda freatica su diversi anni e permette di convalidare le ipotesi fatte sul funzionamento del sistema.Há algumas décadas atrás, líquidos densos de fase não aquosa (DNAPLs) de origem industrial contaminaram um aquífero aluvial em França,. A localização(ões) e a natureza da fonte(s) de poluição eram desconhecidas, e as concentrações dissolvidas de compostos orgânicos voláteis nos furos de monitorização variaram muito com o tempo. O aquífero estava em equilíbrio hidráulico com um canal artificial cujo nível de água era altamente variável (até 5 m). Estas variações propagavam-se ao aquífero, causando alterações na direção de fluxo de água subterrânea; um modelo numérico de fluxo e de transporte de solutos em regime transitório mostrou que essas variações no nível da água se correlacionam com as variações de concentração, uma vez que as alterações nas direções de fluxo resultaram no desvio da pluma contaminante. O modelo hidrogeológico em regime transitório foi construído considerando a biodegradação dos solventes como cadeia de primeira ordem, uma vez que a biodegradação tem uma influência significativa na evolução da concentração de poluentes. A parametrização do modelo confirma a posição da zona das fontes entre as depressões potenciais no substrato rochoso onde os DNAPLs se possam ter acumulado. O modelo de água subterrânea foi calibrado com sucesso para reproduzir a concentração observada ao longo de vários anos e permitiram uma rápida validação das hipóteses no funcionamento do sistema poluído.
Starting Page	943
Ending Page	956
Page Count	14
File Format	PDF
ISSN	14312174
Journal	Hydrogeology Journal
Volume Number	22
Issue Number	4
e-ISSN	14350157
Language	Portuguese
Publisher	Springer Berlin Heidelberg
Publisher Date	2014-01-10
Publisher Institution	International Association of Hydrogeologists
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Transient groundwater modeling Groundwater/surface-water relations Chlorinated hydrocarbons contamination Geophysical surveys France Hydrogeology Hydrology/Water Resources Geology Waste Water Technology Water Pollution Control Water Management Aquatic Pollution
Content Type	Text
Resource Type	Article
Subject	Earth and Planetary Sciences Water Science and Technology

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