Modelagem da contaminação de aqüíferos livres por NAPLs residuais na zona não-saturada

Este trabalho aborda a modelagem de áreas de NAPLs ("Non-Aqueous Phase Liquids" - Fase Líquida Não-Aquosa) residuais, localizadas na zona não-saturada, com o objetivo de auxiliar na avaliação do impacto dessas áreas na qualidade dos aqüíferos freáticos. Dentro deste enfoque, foram desenvolvidos os seguintes pontos: * Implementação de um modelo numérico de fluxo de água e transporte de contaminantes, para ambas as zonas não-saturada e saturada, baseado na conexão entre um modelo unidimensional de zona não-saturada com um modelo multidimensional de zona saturada. * Avaliação da sensibilidade da simulação de transporte de contaminantes em zona nãosaturada ao uso do fluxo da fase aquosa em regime permanente e com perfis de saturação e descarga específica uniformes. * Inclusão, no modelo de transporte desenvolvido, da dissolução de fontes de NAPLs residuais na zona não-saturada através de diferentes abordagens de literatura para a estimativa do coeficiente de transferência de massa. Um trabalho experimental foi elaborado para gerar dados de dissolução, em condições de fluxo não-saturado, de NAPLs compostos por substância pura e por misturas binárias. A forma mista da equação de Richards e a equação de transporte advectivo-dispersivo foram implementados em diferenças finitas, constituindo o modelo unidimensional FflD, que simula o fluxo de água e transporte de contaminantes na zona não-saturada. Este modelo foi conectado aos modelos multidimensionais de fluxo e transporte em zona saturada, MODFLOW e MT3D. A abordagem de substituir a zona não-saturada multidimensional por domínios unidimensionais foi bem sucedida. Comparativamente aos modelos integrados multidimensionais FEMWATER (fluxo) e LEWASTE (transporte), foram obtidos resultados equivalentes e com um tempo computacional bastante inferior. Para a conexão do módulo de fluxo de FTlD e o modelo MODFLOW, foi desenvolvida nova metodologia para simular a elevação do nível do freático em resposta à recarga, que demostrou ser numericamente mais estável do que a metodologia citada na literatura. Dentro da faixa de valores avaliados, o modelo de transporte demonstrou grande sensibilidade quanto ao uso dos dados de fluxo em regime permanente, principalmente em solos com características mais arenosas. Além disso, a obtenção dos dados de fluxo em regime permanente não foi possível, em alguns casos, devido à não-convergência do método numérico. Neste caso, a solução permanente pode ser obtida estendendo-se a simulação transiente até que os resultados não mais se alterassem, mas às custas de maior tempo computacional. A simulação de transporte utilizando perfis uniformes de saturação e descarga específica também mostrou grande sensibilidade à escolha do valor de saturação. Para baixos valores de saturação, a estimativa utilizando este método gerou valores da massa de contaminante que atravessa determinada profundidade do domínio não-saturado até 88 vezes maiores do que utilizando os dados de fluxo transiente. Na modelagem da dissolução de zonas de NAPLs residuais, três formulações empíricas para a estimativa do coeficiente de transferência de massa foram adicionadas ao módulo de transporte de FflD. Os dados de dissolução não-saturada obtidos experimentalmente não foram conclusivos, uma vez que, na maioria dos ensaios realizados, a concentração na fase aquosa atingiu valores próximos à solubilidade. Além disso, a metodologia empregada não levou em consideração a interferência da partição com a fase gasosa. Nos ensaios com misturas binárias de NAPLs, foram observadas evidências de que a transferência de massa pode ser limitada pela difusão do contaminante dentro da fase NAPL, com redução da ordem de 20% na concentração atingida com relação à solubilidade efetiva.The subject of this work is the modeling of residual NAPLs (Non-Aqueous Phase Liquids) areas located in the vadose zone, with the objective to improve the evaluation of the impact of this areas on the quality of phreatic aquifers. The following points have been developed: * lmplementation of a water flow and contaminant transport numeric model for both vadose and saturated zones, based on the approach of using a unidimensional model in the unsaturated zone connected to a multidimensional saturated model. * Sensitivity evaluation for the unsaturated zone transport model due to the use of the steady state flow solution and uniform saturation and specific discharge profiles. * The dissolution of NAPLs residual sources in the unsaturated zone, using different approaches for the mass transfer coefficient estimation, is introduced on the transport model. An experimental work was developed to generate dissolution data on unsaturated conditions, with single and binary mixtures NAPLs. The mixed form of Richards equation and the advective-dispersive transport equation were implemented using the finite differences technique, resulting the FflD model. It simulates the unidimensional flow and contaminant transport in the unsaturated zone. This model was linked to the flow and transport multidimensional models for the saturated zone, MODFLOW and MT3D. The approach of replacing a multidimensional unsaturated zone by unidimensional domains was successful. The results obtained were quite similar to those of the integrated multidimensional models FEMW ATER (water flow) and LEWASTE (contaminant transport), with the advantage of being much less time consuming. For the connection between the FTlD flow module and the MODFLOW model, a new methodology was developed to simulate the water table levei elevation due to the recharge and it has shown to be numerically more stable than the literature methodology. Within the range of evaluated data, the transport model has shown a large sensitivity due to the use of steady state flow data, mainly in sandy soils. Besides, the achievement of steady state flow data was not possible, in sarne cases, due to the numerical solution methods non-convergence. ln these cases, it is still possible to obtain the steady state solution by extending the transient solution until the results stops changing, but it's a more time consuming process. The transport simulation using uniform saturation and specific discharge vi profiles also showed a large sensitivity to the choice of the saturation value. For small values of saturation, the estimation using these methods generated contarninant arnounts crossing a certain deep of the unsaturated domain that it is 88 times larger than using transient flow data. On the simulation of the dissolution of residual NAPL zones, the estimation of the mass transfer coeficient was made by three empirical formulations, being added to the transport module of the FflD model. The experimental unsaturated dissolution data were not conclusive since, in the major part of the experiments, the aqueous phase had reached the solubility levei. Besides, the used methodology did not consider the influence of the gas phase partition. For the tests using binary NAPLs, it was found evidences that the mass transfer rate can be lirnited by diffusion inside the NAPL phase, with a redution of about 20% in the concentration of the aqueous phase regarding the effective solubility

Effect of partial lockdown due to Covid-19 pandemic on PM10 concentration in Belo Horizonte, Brazil

Despite their proven effectiveness in combating the pandemic of COVID-19, measures of social isolation, quarantines, and lockdowns have drastic consequences in the social and economic spheres. This paper presents results from an ongoing study in Belo Horizonte, Brazil, to evaluate the effect of social isolation on MP10 concentration. The monitoring point was chosen in a wooded area within a university campus. Social isolation was analyzed in terms of vehicle movements recorded by speed cameras, during all phases following the partial lockdown (PL) instituted in the city. The social isolation index (SDI) showed a maximum isolation percentage of 49.5%, reached in the first week of the PL, with a subsequent continuous downward trend. The results showed a 65.2% reduction in PM10 due to the PL, when comparing the mean values monitored before (22.2 ± 3.0 µg m-3) and during (7.7 ± 4.2 µg m-3) the PL. The relationship between vehicle movement and PM10 concentrations in the monitoring region was evidenced and found to be significant (r(XY) = 0.782, p-value = 0.000). Such reduction, observed in such a short term, but due to force majeure, certainly has beneficial effects on the population's health, reinforcing the reflection about the positive impacts that could come with policies that favor the reduction of vehicle movement in the cities

Avaliação do uso de poli(tereftalato de etileno) (PET) como matriz de imobilização de cinzas de incineradores Assessment of the use of polyethylene terephthalate (PET) as matrix for immobilization of incinerator ash

<abstract language="eng">Industrial hazardous wastes must receive appropriate treatment to ensure a safe disposal to humans and environment. One of the techniques adopted for this purpose is the stabilization/solidification in polymer matrices. This paper evaluated the use of recycled polyethylene terephthalate as an incorporation matrix of incinerator ash. The polymer and the ash were submitted to an extrusion process in different percentages. The final product was evaluated through thermal and leaching tests and the leachate extracts constituents were determinated by atomic absorption spectrophotometry. The results showed a reduction in the release of substances up to 99% by mass for the conditions used

Impact of an Alkaline Solution on the Chemistry, Mineralogy, and Sorption Properties of a Typic Rhodudult Soil

<div><p>Abstract The preferred option for disposal of short-lived low and intermediate level radioactive wastes is a near surface disposal facility in which soil is one of the barriers that avoid radionuclide migration outside the controlled area. For construction of that kind of facility, concrete is widely used, and its interaction with water induces its degradation, resulting in a high pH solution. The alkaline solution may affect the near-field environment of radioactive waste repositories, including the soil, promoting mineralogical alterations that result in significant changes in key properties of materials, compromising their performance as safety components. In this study, a sample of a Brazilian Typic Rhodudult soil, previously investigated concerning its performance for Cs sorption, was subjected to interaction with the alkaline solution for 24 h and for 7, 14, and 28 days in order to evaluate the impact on its chemical, mineralogical, and sorption properties. X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), atomic absorption spectrometry (AAS), scanning electron microscopy (SEM), and electron microprobe analysis were performed before and after each alteration period. Results indicated dissolution of minerals, such as kaolinite and quartz, associated with incorporation of K and Ca from the alkaline solution, likely resulting in the formation of hydrated calcium silicate phases (CSH), which are expected to be worse sorbents for alkaline elements (e.g., Cs) than the original minerals. The Kd values for Cs in the altered samples also decreased according to the alteration period, demonstrating that alkaline interaction effectively modifies the soil sorption properties for Cs.</p></div