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The aim of this work is to assess the risk of groundwater contamination associated with BTEX dissolution from fuels as a residual phase. Numerical simulations of sixty scenarios were carried out with the software HYDRUS 2D/3D. Groundwater contamination risk was analyzed given the combination of different porous media textures (silt loam, sandy loam and clay), water fluxes (0.5%, 1% or 3% Rainfall), water table depths (1.5, 2.5, 5 or 8 m below ground surface) and biodegradation rate (active or null). Risk was calculated comparing leachate concentrations to the aquifer and limits established by an international guideline for human drinking water. In all cases, benzene and toluene had the highest mobility in the dissolved phase. Contrary, xylene and ethylbenzene tended to concentrate close to the source zone. These two compounds predominantly concentrated in the solid phase. Calculated risk was proportional to the water flux rate and inversely proportional to the unsaturated thickness. Without biodegradation, in fine-grained sediments risk was very high for shallow aquifers (> 1.5 m depth) and moderate or low for deeper aquifers. However, in sandy loam sediments risk was classified as very high for aquifers up to 8 m deep. When biodegradation was considered, leached concentrations were greatly reduced in the three textures. BTEX concentration in Bahía Blanca City´s aquifer showed acceptable agreement with simulated scenarios. The most sensitive parameters to model results were biodegradation > foc > water table depth > Ks. This study is important for assessing the risks and developing management strategies for fuel contaminated sites.

O  setor sudoeste da cidade de Bahia Blanca, Argentina é caracterizado pela presença de solos de textura fina e um aquífero hipersalino raso, condições que causam a acumulação de sais nos níveis superficiais do solo. Este estudo tem por objetivo determinar os principais mecanismos de mobilidade e acumulação de sais em um solo limo-argiloso, aplicando o software HYDRUS 2D/3D. O movimento de sais no perfil do solo está ligado à hidrodinâmica naturais da zona não saturada, onde os processos de capilaridade e evapotranspiração são o principal acumulador de agentes solutos. Os períodos de maior acumulação correspondem aos meses quentes e secos, com alta demanda de umidade na atmosfera. Nestas condições, concentrações salinas são geradas nos níveis superficiais do solo de até 18.000 mg.L-1. A precipitação pluviométrica permite o ingresso de água de baixa salinidade ao perfil do solo, causando os processos de lavagem e diluição. Os sais são transportados para os níveis mais baixos da zona não saturada, efeito visível em anos pluviométricamente húmidos. As concentrações simuladas na franja capilar manteve-se na gama de entre 3000 mg.L-1 e 10 000 mg.L-1. Conhecer o processo de salinização do solo em áreas urbanas é fundamental para mitigar as consequências das áreas afetadas.

O objetivo deste trabalho é comparar o uso da solução inversa na estimativa das propriedades hidráulicas do solo com a análise tradicional de dados por infiltrômetro de disco de tensão (IDT), dados de retenção em campo e funções de pedotransferência (FPTs) comumente usadas. Os dados de campo foram coletados em uma parcela experimental localizada em Bahía Blanca, Argentina. A infiltração no campo sob condições saturadas foi medida pelo método do furo inverso e a infiltração sob condições insaturadas foi realizada com IDT. Os dados de retenção de campo (θ(h)) também foram coletados periodicamente. O software HYDRUS 2D/3D foi utilizado para otimizar os parâmetros hidráulicos do solo por solução inversa, de acordo com os dados do IDT. A condutividade hidráulica saturada medida pelo método do furo inverso (5.53 cm.h-1) e calculada pela abordagem analítica de Wooding (5.35 cm.h-1) e simulações numéricas inversas (5.36 cm.h-1) mostraram valores muito próximos. Segundo estimativas de macroporosidade, a água infiltrada é conduzida principalmente através de microporos e mesoporos do solo. Os macroporos canalizaram apenas 15.9% do fluxo total infiltrado. As curvas de retenção previstas pelos FPTs não representaram corretamente os dados de retenção em campo. O melhor ajuste entre o teor de água nas tensões específicas previstas pelas curvas de retenção e o teor de água medido no campo foi alcançado pela abordagem de solução inversa de IDT (RMSE: 0.050 cm3.cm-3). A abordagem de solução inversa demonstrou ser um método simples e prático para obter uma estimativa precisa de curvas de re-tenção e de condutividade hidráulica.

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<p>Recharge environmental conditions and residence time, can be studied by the application of different tracers. Several tracers are useful as proxies of the environmental recharge conditions, such as water stable isotopes deuterium and oxygen-18, and the dissolved noble gases. Other tracers are applied in order to know when the recharge occurred. Carbon-14 dating is a widely applied method for dating old groundwater, having an application range up to around 30 ky. Noble gases, as non-reactive and water-soluble substances, constitute useful tracers for studying different processes in hydrologic cycles. One of the applications is dating very old groundwater beyond the range of <sup>14</sup>C. It can be done in a semi-quantitative way by the accumulation of <sup>4</sup>He, and quantitatively through the radionuclide <sup>81</sup>Kr (t<sub>1/2</sub> = 229,000 y), a more robust method for dating groundwater up to 1.3 million years.</p><p>The province of Buenos Aires, Argentina, hosts three deep sedimentary basins, from north to south, Salado, Claromecó and Colorado, with areas of 85,000 km<sup>2</sup>, 3,100 km<sup>2</sup> and 125,000 km<sup>2</sup>, respectively. In these basins, a thick continental sequence of Neogene sediments contains confined thermal aquifers, at depths from hundreds meters to more than 1 km. The recharge conditions and the water age of the Neogene aquifers are studied through water stable isotopes, <sup>4</sup>He and <sup>81</sup>Kr tracers.  10 deep wells were sampled for δ<sup>2</sup>H, δ<sup>18</sup>O, <sup>3</sup>H, <sup>14</sup>C, for noble gases using clamped copper tubes, and for <sup>81</sup>Kr with a gas extractor. <sup>4</sup>He analyses were performed at the IAEA laboratory by mass spectrometry, and <sup>81</sup>Kr at the ATTA laboratory of USTC.</p><p><sup>3</sup>H contents were not detectable in all of the cases, thus no young water components exist. By plotting the isotopic results in a δ<sup>2</sup>H vs δ<sup>18</sup>O diagram, four groups of samples can be recognized. Group 1 includes Colorado basin isotopically depleted samples (δ<sup>18</sup>O from -6.5 to -7.5 ‰) along a line parallel to the GMWL and the present LMWL, but with a higher deuterium-excess (<em>d</em>). Samples in G1 have a Ne/He ratio around 0.6. <sup>14</sup>C and <sup>81</sup>Kr ages were from 10 ky to 40 ky. Group 2 includes the samples of the borders of the Salado basin, being isotopically more enriched (δ<sup>18</sup>O from -3 to -4.5 ‰) and with a lower <em>d</em> than present precipitation, a Ne/He ratio from 0.2 to 0.8 and one sample with <sup>81</sup>Kr age of 640 ky. Group 3 is formed by brines from the Colorado basin, a Ne/He ratio in the range of 1E-02 to 1E-04, and <sup>81</sup>Kr in ages around 900 ky, and are along a line of slope 1.9, showing a <sup>18</sup>O shift. Finally the Group 4 formed by samples at the axis of Salado basin, are isotopically enriched (δ<sup>18</sup>O from -0.5 to -3.7 ‰) along a line of slope 3.9 resembling and evaporation line. However, these samples of <sup>81</sup>Kr ages of 1000 ky and Ne/He ratio of 2E-03, showed a high correlation Cl- vs δ<sup>18</sup>O, with increasing values from West to East. This suggest a mixing with a brine or an increasing water-rock interaction.</p>

Gas stations are one of the most important sources of soil and groundwater contamination in urban areas around the world. In this work, a mathematical model was applied to assess the risk of the physical media contamination. The model is based on the chemical properties of fuels and site-specific hydrological properties. The group of hydrocarbons selected were the monoaromatic: benzene, toluene, ethylbenzene and xylene (BTEX). The mathematical model was used to evaluate the behaviour of each compound in each partitioning phase (dissolved, volatile, solid and non-aqueous liquid phase). Furthermore, mass flux of BTEX reaching groundwater was calculated according to steady flow under two different conditions: (1) considering only sorption and volatilization, and (2) adding biodegradation. In all cases, the total mass of BTEX leachate was greater when biodegradation was not considered. In areas with unsaturated zone thickness greater than two meters, sorption is the main process affecting BTEX transport. Otherwise, when water table is placed at shallower depths, contaminants are predominately dissolved. In all cases, the lowest proportion of BTEX were in the volatile phase. The model presented in this work proved to be an interesting tool to evaluate the behaviour of BTEX in soil and groundwater and its applicability being directly related to environmental and urban management of pollution from gas stations. The methodology applied in this work could be extrapolated to any site of the world with the same problematic. Particularly, the theoretical model allowed to defined zones with high and low risk of contamination in Bahia Blanca, Argentina.