Letizia Fumagalli

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).

Classifying zones of suitability for manual drilling using textural and hydraulic parameters of shallow aquifers: a case study in northwestern Senegal

A method is proposed that uses analysis of borehole stratigraphic logs for the characterization of shallow aquifers and for the assessment of areas suitable for manual drilling. The model is based on available borehole-log parameters: depth to hard rock, depth to water, thickness of laterite and hydraulic transmissivity of the shallow aquifer. The model is applied to a study area in northwestern Senegal. A dataset of boreholes logs has been processed using a software package (TANGAFRIC) developed during the research. After a manual procedure to assign a standard category describing the lithological characteristics, the next step is the automated extraction of different textural parameters and the estimation of hydraulic conductivity using reference values available in the literature. The hydraulic conductivity values estimated from stratigraphic data have been partially validated, by comparing them with measured values from a series of pumping tests carried out in large-diameter wells. The results show that this method is able to produce a reliable interpretation of the shallow hydrogeological context using information generally available in the region. The research contributes to improving the identification of areas where conditions are suitable for manual drilling. This is achieved by applying the described method, based on a structured and semi-quantitative approach, to classify the zones of suitability for given manual drilling techniques using data available in most African countries. Ultimately, this work will support proposed international programs aimed at promoting low-cost water supply in Africa and enhancing access to safe drinking water for the population.RésuméUne méthode est. proposée utilisant l’analyse des logs stratigraphiques des forages pour la caractérisation des aquifères peu profonds et pour l’évaluation des zones favourable pour le forage manuel. Le modèle repose sur l’analyse des paramètres extraits des logs de forage disponibles: profondeur au socle, profondeur au niveau piézométrique, épaisseur de la latérite et transmissivité hydraulique de l’aquifère peu profond. Le modèle est. appliqué à une zone d’étude dans le nord-ouest du Sénégal. Un ensemble de données de logs de forages a été traité en utilisant l’application informatique TANGAFRIC développée au cours de la recherche. Après une procédure manuelle pour attribuer une catégorie standardisée décrivant les caractéristiques lithologiques, l’étape suivante et une extraction automatique des différents paramètres texturaux et l’estimation de la conductivité hydraulique en utilisant des valeurs de référence disponibles dans la littérature. Les valeurs de conductivité hydraulique estimées à partir des données stratigraphiques ont été partiellement validées, en les comparant aux valeurs mesurées à partir d’une série de pompages d’essais réalisés sur des forages de grand diamètre. Les résultats indiquent que cette méthode permet de produire une interprétation fiable du contexte hydrogéologique peu profond en utilisant des informations généralement disponibles dans la région. La recherche contribue à améliorer l’identification de régions pour lesquelles des conditions sont en faveur de forages manuels. Ceci est. réalisé en appliquant la méthode décrite, basée sur une approche structurée et semi-quantitative, pour classer l’aptitude de zones à des techniques données de forage manuel en utilisant les données disponibles dans la plupart des pays africains. En fin de compte, ce travail appuiera les programmes internationaux proposés visant à promouvoir l’approvisionnement en eau potable à un faible coût en Afrique et à améliorer l’accès à l’eau potable pour la population.ResumenSe propone un método que utiliza el análisis de registros estratigráficos de pozos para la caracterización de acuíferos poco profundos y para la evaluación de áreas aptas para la perforación manual. El modelo se basa en el análisis de parámetros extraídos de registros de pozos disponibles: profundidad de la roca dura, profundidad del agua, espesor de laterita y transmisividad hidráulica del acuífero poco profundo. El modelo se aplica a un área de estudio en el noroeste de Senegal. Un conjunto de datos de registros de perforaciones se ha procesado utilizando un paquete de software (TANGAFRIC) desarrollado durante la investigación. Después de un procedimiento manual para asignar una categoría estándar que describe las características litológicas, el siguiente paso es la extracción automatizada de diferentes parámetros texturales y la estimación de la conductividad hidráulica usando los valores de referencia disponibles en la literatura. Los valores de conductividad hidráulica estimados a partir de datos estratigráficos han sido parcialmente validados, comparándolos con valores medidos de una serie de ensayos de bombeo realizados en pozos de gran diámetro. Los resultados muestran que este método es capaz de producir una interpretación confiable del contexto hidrogeológico superficial usando información generalmente disponible en la región. La investigación contribuye a mejorar la identificación de áreas donde las condiciones son aptas para la perforación manual. Esto se logra aplicando el método descrito, basado en un enfoque estructurado y semicuantitativo, para clasificar la idoneidad para determinadas técnicas de perforación manual utilizando datos disponibles en la mayoría de los países africanos. En última instancia, este trabajo apoyará los programas internacionales propuestos para promover el suministro de agua a bajo costo en África y mejorar el acceso al agua potable para la población.摘要提出了一种利用井孔地层测井资料分析浅层含水层的分析方法,并对适合人工钻孔的区域进行评估。该模型基于从可用井眼测井中提取的参数分析:浅层含水层深度与硬岩,水深,红土厚度和液压透过率。该模型适用于塞内加尔西北部的一个研究区域。钻孔日志的数据集已经使用研究期间开发的软件包(TANGAFRIC)进行处理。在指定描述岩性特征的标准类别的手动程序之后,下一步是使用文献中可用的参考值自动提取不同的结构参数和水力传导率的估计。通过与大直径井进行的一系列泵送试验的测量值进行比较,已经部分验证了从地层数据估算出的水力传导率值。结果表明,该方法能够利用该地区通用的信息,对浅层水文地质环境产生可靠的解释。该研究有助于改善条件适合手动钻孔的区域的识别。这是通过应用所描述的方法,基于结构化和半定量方法,使用大多数非洲国家可用的数据对给定的手动钻孔技术进行分类。最终,这项工作将支持旨在促进非洲低成本供水和提高人民获得安全饮用水的拟议国际方案。ResumoUm método é proposto usando análise estratigráfica de perfis de poços para a caracterização de aquíferos rasos e avaliação de áreas favoráveis para perfuração manual. O modelo é baseado na análise dos parâmetros extraídos de perfis de poços disponíveis: profundidade da rocha dura, profundidade da água, espessura da laterita, e transmissividade hidráulica do aquífero raso. O modelo é aplicado a uma área de estudo no noroeste do Senegal. Os perfis dos poços foram processados usando o programa de computador (TANGAFRIC) desenvolvido durante a pesquisa. Após um procedimento manual para assinalar uma categoria padrão descrevendo as características litológicas, o próximo passo é a extração automática de diferentes parâmetros texturais e a estimativa da condutividade hidráulica usando os valores de referência disponíveis na literatura. Os valores de condutividade hidráulica estimados de dados de estratigrafia foram parcialmente validados comparando estes com valores medidos através de uma série de testes de bombeamento realizados em poços de grande diâmetro. Os resultados mostram que este método é capaz de produzir uma interpretação confiável do contexto hidrogeológico raso usando informações disponíveis na região. A pesquisa contribui para promover a identificação de áreas onde as condições são favoráveis para perfuração manual. Isso é obtido aplicando o método descrito, baseado no processo estruturado e semiquantitativo para classificar a favorabilidade para uma certa técnica de perfuração manual usando os dados disponíveis na maioria dos países Africanos. Por último, este trabalho suportará programas internacionais propostos com o objetivo de promover o abastecimento de água a baixo custo na África e aumentar o acesso seguro a água potável para a população.

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.