Eurípedes do Amaral Vargas

HCH distribution and microbial parameters after liming of a heavily contaminated soil in Rio de Janeiro

The closing down of a lindane factory near Rio de Janeiro, over 45 years ago, left an area heavily contaminated with hexachlorocyclohexane (HCH). Remediation by soil liming was applied by government authorities in 1995. This study aims to evaluate the HCH distribution and impact on soil microbiota due to contamination and liming. Microcosm experiments with uncontaminated soil mixed with HCH and lime indicated that lime-promoted dechlorination of HCH molecules led to leaching and volatilization of metabolites. The treatment applied transformed but did not solve the problem as most of the HCH remains in the soil. Reduced microbial respiratory activity was measured in contaminated field samples. Higher respiration rates in uncontaminated soil were reduced by HCH and lime addition; the sole addition of HCH caused a temporary increase in soil respiration, and stimulation occurred with oxygen and/or nutrient addition. A heterotrophic bacterial population around 10(9)CFU/g was found in polluted field soil, some well-known degraders having been isolated. Native soil microbiota showed resistance to high amounts of HCH and alkaline pH. The results allow considering bioremediation rather than chemical treatments to clean up the area.

Toward improved prediction of the bedrock depth underneath hillslopes: Bayesian inference of the bottom‐up control hypothesis using high‐resolution topographic data

PUBLICATIONS Water Resources Research RESEARCH ARTICLE 10.1002/2015WR018147 Key Points: We introduce an analytic formulation for the spatial distribution of the bedrock depth Bayesian analysis reconciles our model with field data and quantifies prediction and parameter uncertainty The use of a distributed parameterization recognizes geologic heterogeneities Toward improved prediction of the bedrock depth underneath hillslopes: Bayesian inference of the bottom-up control hypothesis using high-resolution topographic data Guilherme J. C. Gomes 1,2 , Jasper A. Vrugt 2,3 , and Eur ipedes A. Vargas Jr. 1 Departamento de Engenharia Civil, Pontif icia Universidade Cat olica do Rio de Janeiro, Rio de Janeiro, Brazil, 2 Department of Civil and Environmental Engineering, University of California, Irvine, California, USA, 3 Department of Earth System Science, University of California, Irvine, California, USA Abstract The depth to bedrock controls a myriad of processes by influencing subsurface flow paths, ero- Correspondence to: J. A. Vrugt, jasper@uci.edu Citation: Gomes, G. J. C., J. A. Vrugt, and E. A. Vargas Jr. (2016), Toward improved prediction of the bedrock depth underneath hillslopes: Bayesian inference of the bottom-up control hypothesis using high-resolution topographic data, Water Resour. Res., 52, 3085–3112, doi:10.1002/ 2015WR018147. Received 24 SEP 2015 Accepted 15 MAR 2016 Accepted article online 18 MAR 2016 Published online 22 APR 2016 sion rates, soil moisture, and water uptake by plant roots. As hillslope interiors are very difficult and costly to illuminate and access, the topography of the bedrock surface is largely unknown. This essay is concerned with the prediction of spatial patterns in the depth to bedrock (DTB) using high-resolution topographic data, numerical modeling, and Bayesian analysis. Our DTB model builds on the bottom-up control on fresh- bedrock topography hypothesis of Rempe and Dietrich (2014) and includes a mass movement and bedrock-valley morphology term to extent the usefulness and general applicability of the model. We recon- cile the DTB model with field observations using Bayesian analysis with the DREAM algorithm. We investi- gate explicitly the benefits of using spatially distributed parameter values to account implicitly, and in a relatively simple way, for rock mass heterogeneities that are very difficult, if not impossible, to characterize adequately in the field. We illustrate our method using an artificial data set of bedrock depth observations and then evaluate our DTB model with real-world data collected at the Papagaio river basin in Rio de Janeiro, Brazil. Our results demonstrate that the DTB model predicts accurately the observed bedrock depth data. The posterior mean DTB simulation is shown to be in good agreement with the measured data. The posterior prediction uncertainty of the DTB model can be propagated forward through hydromechanical models to derive probabilistic estimates of factors of safety. 1. Introduction The depth to bedrock (DTB) controls a large array of geomorphologic, hydrologic, geochemical, ecologic, and atmospheric processes, yet is large unknown as hillslope interiors are very difficult and costly to illumi- nate and access. The regolith thickness determines groundwater flow [Freer et al., 2002; Lanni et al., 2012], infiltration and redistribution [Kosugi et al., 2006], subsurface saturation [Tromp-van Meerveld and McDonnell, 2006b; Ebel et al., 2007; Liang and Uchida, 2014], runoff generation [Troch et al., 2002; Tromp-van Meerveld and McDonnell, 2006a], storage capacity [Ohnuki et al., 2008], the shape of the hydrograph [Hopp and McDonnell, 2009], and variably saturated water flow [Fujimoto et al., 2008]. The bedrock topography is also of paramount importance in geotechnical engineering as it determines slope stability [Mukhlisin et al., 2008; Ho et al., 2012; Kim et al., 2015], pore pressure responses to infiltration [Vargas Jr. et al., 1990; Askarinejad et al., 2012; Lanni et al., 2013], and landslide potential [Borja and White, 2010; Milledge et al., 2014; Bellugi et al., 2015]. An accurate characterization of the DTB is thus a prerequisite to describe adequately many dif- ferent Earth-surface processes. C 2016. American Geophysical Union. V All Rights Reserved. GOMES ET AL. Spatial patterns in the bedrock depth arise from complex interactions between a myriad of biologic [Jenny, 1941], (geo)chemical [Lebedeva and Brantley, 2013], and hydrologic [Rempe and Dietrich, 2014] processes, and factors including surface topography, lithology [Catani et al., 2010], climate [Anderson et al., 2013], and long-term human activities [Kuriakose et al., 2009]. As a consequence, the thickness of the regolith can vary considerably within a hillslope and watershed, thereby complicating tremendously the characterization and point prediction of the bedrock depth topography [Catani et al., 2010]. Until hillslope interiors are more readily accessible through geophysical imaging or extensive deep drilling, the transition of the underlying fresh bedrock will remain largely unknown [Rempe and Dietrich, 2014]. BAYESIAN INFERENCE FOR BEDROCK MAPPING

Analysis of water control in an underground mine under strong karst media influence (Vazante mine, Brazil)

This work presents analysis of groundwater flow conditions and groundwater control measures for Vazante underground mine located in the state of Minas Gerais, Brazil. According to field observations, groundwater flow processes in this mine are highly influenced by the presence of karst features located in the near-surface terrain next to Santa Catarina River. The karstic features, such as caves, sinkholes, dolines and conduits, have direct contact with the aquifer and tend to increase water flow into the mine. These effects are more acute in areas under the influence of groundwater-level drawdown by pumping. Numerical analyses of this condition were carried out using the computer program FEFLOW. This program represents karstic features as one-dimensional discrete flow conduits inside a three-dimensional finite element structure representing the geologic medium following a combined discrete-continuum approach for representing the karst system. These features create preferential flow paths between the river and mine; their incorporation into the model is able to more realistically represent the hydrogeological environment of the mine surroundings. In order to mitigate the water-inflow problems, impermeabilization of the river through construction of a reinforced concrete channel was incorporated in the developed hydrogeological model. Different scenarios for channelization lengths for the most critical zones along the river were studied. Obtained results were able to compare effectiveness of different river channelization scenarios. It was also possible to determine whether the use of these impermeabilization measures would be able to reduce, in large part, the elevated costs of pumping inside the mine.RésuméCe travail présente l’analyse des conditions d’écoulement des eaux souterraines et des mesures de contrôle des eaux souterraines pour la mine souterraine de Vazante située dans l’état de Minas Gerais, au Brésil. Selon les observations de terrain, les processus d’écoulements d’eau souterraine dans cette mine sont fortement influencés par la présence de phénomènes karstiques situés dans les terrains proches de la surface près de la rivière Santa Catarina. Les phénomènes karstiques, tels que les grottes, pertes, dolines et conduits, sont en contact direct avec l’aquifère et contribuent à augmenter les écoulements d’eau dans la mine. Ces effets sont plus prononcés dans les zones sous influence du rabattement du niveau des eaux souterraines par pompage. Des analyses numériques de cette condition ont été effectuées à l’aide du code informatique FEFLOW. Ce code permet la représentation des phénomènes karstiques tels que les conduits d’écoulement discrets unidimensionnels au sein d’une structure tridimensionnelle à éléments finis représentant le milieu géologique selon une approche continuum discret pour représenter le système karstique. Ces phénomènes créent des voies de circulation préférentielle entre la rivière et la mine; leur incorporation signifie que le modèle est d’avantage en mesure de représenter de manière réaliste l’environnement géologique de la mine environnante. Afin d’atténuer les problèmes d’afflux d’eau, l’imperméabilisation de la rivière par la construction d’un chenal en béton armé a été incorporée dans la modèle hydrogéologique développé. Différents scénarios de longueurs d’imperméabilisation du lit de la rivière pour les zones les plus critiques le long de la rivière ont été étudiés. Les résultats obtenus ont permis de comparer l’efficacité de ces différents scénarios de canalisation de la rivière. Il a également été possible de déterminer si l’utilization de ces mesures d’imperméabilisation pourrait permettre de réduire, en grande partie, les coûts élevés de pompage à l’intérieur de la mine.ResumenEste trabajo presenta un análisis de las condiciones del flujo y de las medidas de control del agua subterránea para la mina subterránea Vazante ubicada en el estado de Minas Gerais, Brasil. De acuerdo con las observaciones de campo, los procesos de flujo de agua subterránea en esta mina están fuertemente influenciados por la presencia de características kársticas ubicadas en el terreno cercano a la superficie junto al río Santa Catarina. Las características kársticas, como cuevas, sumideros, dolinas y conductos, tienen contacto directo con el acuífero y tienden a aumentar el flujo de agua en la mina. Estos efectos son más agudos en áreas bajo la influencia del abatimiento del nivel del agua subterránea por bombeo. Los análisis numéricos de esta condición se llevaron a cabo utilizando el programa FEFLOW. Este programa representa características kársticas como conductos de flujo discretos de una dimensión dentro de una estructura tridimensional de elementos finitos que representa el medio geológico siguiendo un enfoque combinado de continuo discreto para representar el sistema kárstico. Estas características crean trayectorias de flujo preferenciales entre el río y la mina; su incorporación significa que el modelo tiene una mayor capacidad para representar de manera realista el ambiente hidrogeológico del entorno de la mina. Para mitigar los problemas de infiltración de agua, se simuló numericamente la impermeabilización del río mediante la construcción de un canal de hormigón armado en el modelo hidrogeológico desarrollado. Se estudiaron diferentes escenarios para longitudes de canalización para las zonas más críticas a lo largo del río. Los resultados obtenidos pudieron comparar la efectividad de diferentes escenarios de canalización fluvial. También fue posible determinar si el uso de estas medidas de impermeabilización podría reducir, en gran parte, los elevados costos de bombeo dentro de la mina.摘要本研究工作分析了位于巴西Minas Gerais州Vazante地下矿地下水流条件和地下水控水措施。根据野外观测结果,这个矿的地下水流过程受到Santa Catarina河附近近地表地形中的岩溶特征的强烈影响。岩溶特征,诸如洞穴、落水洞、溶斗和管道与含水层直接相连,使流进矿的水流增加。这些结果在抽水导致地下水位下降的影响下尤为突出。采用计算机程序FEFLOW对这种情况进行了数值分析。在代表岩溶系统的综合离散-连续统方法之后,这个程序把岩溶特征描述为一个代表着地质介质的三维有限元构造中的一维离散水流通道。这些特征在河流和矿之间产生优先流通道,其合并意味着模型更能真实地表现矿周围的水文地质环境。为了缓解水的流入问题,通过建设钢筋混凝土渠道河流的防渗并入到开发的水文地质模型中。对沿河流最关键地带渠道化长度的不同方案进行了研究。获取的结果能够比较不同河流渠道化方案的有效性。还有可能确定这些防渗措施的使用是否能够很大程度上减少矿内抽水已经升高的成本。ResumoEste estudo apresenta uma análise das condições de fluxo das águas subterrâneas e medidas de controle das águas subterrâneas para a mina subterrânea de Vazante, localizada no estado de Minas Gerais, Brasil. De acordo com observações de campo, os processos de fluxo das águas subterrâneas nessa mina são altamente influenciados pela presença de feições cársticas localizadas próximas à superfície do terreno próximo ao Rio Santa Catarina. As características cársticas, como cavernas, sumidouros, dolinas e condutos, têm contato direto com o aquífero e tendem a aumentar o fluxo de água na mina. Estes efeitos são mais agudos em áreas sob a influência da redução do nível do lençol freático por bombeamento. As análises numéricas desta condição foram realizadas utilizando o programa FEFLOW. Este programa representa características cársticas como condutos de fluxo discretos unidimensionais dentro de uma estrutura de elementos finitos tridimensional representando o meio geológico seguindo uma abordagem combinada discreta-contínua para representar o sistema cárstico. Essas feições criam caminhos de fluxo preferenciais entre o rio e a mina; sua incorporação significa que o modelo é mais capaz de representar realisticamente o ambiente hidrogeológico do entorno da mina. A fim de mitigar os problemas de infiltração de água, a impermeabilização do rio através da construção de um canal de concreto armado foi simulado numnéricamente no modelo hidrogeológico desenvolvido. Diferentes cenários para comprimentos de canalização para as zonas mais críticas ao longo do rio foram estudados. Os resultados obtidos foram capazes de comparar a eficácia dos diferentes cenários de canalização fluvial. Também foi possível determinar se o uso dessas medidas de impermeabilização seria capaz de reduzir, em grande parte, os elevados custos de bombeamento dentro da mina.