The present work shows a discussion about the problematic related to the anomalies of fluoride concentrations in groundwaters intended for human provisioning and also about the public health issues and financial waste generated by them. As a contribution, a map was elaborated containing the spacing of the occurrences of anomalous fluoride in the states of Rio Grande do Sul and Santa Catarina. Taking in to account the importance of understanding a little more about the behavior of the waters which suffer this anomaly of fluoride concentration, we have carried out a detailed description of the compositions and of the polytypes of water, verifying what tendencies they present. For that, the area of study has been split in three zones composing the Gurany Aquiferous System: Zones of Blooming, Confinement and Strong Confinement, with a greater emphasis to the Blooming Zone, once that the later presents the greatest amount of wells with excessive fluoride concentrations in the same area, which coincides with the Central Depression of Rio Grande do Sul. After evaluating the typologies of the analyzed waters it was possible to verify the occurrence of a higher tendency in the three zones for the polytype of the sodic Bicarbonate waters. On the basis of the verifications of previous studies attesting the existence of flotations of chemical parameters in underground areas this study has evaluated and identified its percentage of variation in 17 physical-chemical parameters. For that, multivariate data analyses were accomplished for 13 water samples of a deep tubular well (276m), monitored during a six months period, reaching variations of 1,5 200%. The most variable pattern was color. In it was possible to verify that during the pumping period of 15 minutes there has been a coloring variation of water of six different colors attesting how important it is to consider same water taking in order to monitor deep tubular wells because it can receive several water contributions with differentiated characteristics among each other. The pH has shown the smallest percentage of variation, always remaining with the characteristics of neutral pH. / Este trabalho apresenta uma discussão sobre as problemáticas relacionadas às anomalias de concentração do fluoreto em águas subterrâneas destinadas ao abastecimento humano e os problemas de saúde pública e desperdício de finanças que podem proporcionar. Como contribuição, elaborou-se um mapa com a espacialização das ocorrências anômala de fluoreto nos Estados do Rio Grande do Sul e Santa Catarina. Considerando a importância de entender um pouco mais sobre o comportamento das águas que sofrem essa anomalia de concentração de fluoreto, efetuou-se um detalhamento das composições e dos polítipos das águas verificando-se quais as tendências que elas apresentam. Para isso a área de estudo, foi dividida em três zonas que compõem o Sistema Aquífero Guarani: Zonas de Afloramento, Confinamento e Forte Confinamento, tomando uma ênfase maior para Zona de Afloramento, devido a esta apresentar a maior quantidade de poços com concentrações excessivas de fluoreto em uma mesma região, que coincide com a Depressão Central do Rio Grande do Sul. Após avaliar quais as tipologias das águas analisadas foi possível constatar que houve uma maior tendência nas três zonas, para o polítipo de águas bicarbonatadas sódicas. Com base nas verificações de estudos anteriores que atestam a existência de flutuações de parâmetros químicos em águas subterrâneas, o estudo avaliou e identificou qual o seu percentual de variação em 17 parâmetros físico-químicos. Para isto foram realizadas análises multivariadas de dados, para 13 amostras de água de um poço tubular profundo (276 m), monitorado por uma período de 6 meses, chegando-se a variações na ordem de 1,5 a 200%. O parâmetro que mais apresentou variação foi a cor, nela pode-se verificar que no período de 15 min de bombeamento do poço houve uma variação de coloração da água em cinco cores distintas, podendo atentar-se o quanto é importante considerar-se uma mesma tomada de água para monitorar poços tubulares profundos, pois ele pode receber diversas contribuições de água com características diferenciadas entre si. O pH foi o que apresentou a menor (percentual) variação, permanecendo sempre com as características de pH neutro.

<p> Speleothems are calcium carbonate deposits, such as stalagmites, stalactites and flowstones, formed in a cave environment by loss of carbon dioxide from saturated groundwaters. Variations in the 18o/16o ratio of calcite are related to changes in depositional temperature provided that the speleothem formed in isotopic equilibrium with its seepage water (conditions characterised by slow coloss and no evaporation of seepage water). Variations in 18o/16o of the seepage water will also be reproduced in the calcite but allowance for this effect can be made if 18o/16o ratio of the source (ocean water) can be estimated (from deep sea sediment cores) and if the influence of temperature on 18o/16o ratio of precipitation at the site can be determined. Because cave temperatures closely approximate mean annual surface temperature, the axial 18o/16o record of a speleothem is therefore an indication of paleoclimate and of temperature change over the period of its growth. </p> <p> The frequency distribution of age measurements for several speleothems from an area may also be used as a paleoclimatic indicator because cold or glacial conditions above the cave will inhibit speleothem growth by freezing water at the surface and removing vegetation and soil cover, the main source of CO2 for the limestone dissolution-reprecipitation process. </p> <p> Pure, non-porous calcite speleothems from several limestone regions have been dated in this study by the 230Th/234U method, and in cases of uranium-rich speleothems, by the 231Pa/230Th method also. For ten such cases, examined, good agreement of ages determined by both dating methods was found. </p> <p> Relatively few deposits however, have shown deposition under isotopic equilibriwn conditions, due probably to the well-ventilated nature of the caves studied. </p> <p> The age distribution for speleothem from Cascade Cave on Vancouver Island, B.C., indicates growth during the mid-Wisconsin interstadial dated as 65 -30,000 yrs. B.P. Stable isotope profiles for two speleothems which grew over this period both show values of 18o/16o ratios of calcite which are significantly lower than calcite growing in the cave today. This is the first clearly-defined record of such an occurence (in previous work, 18o/16o of fossil speleothem was generally greater than modern). Using estimates of the change in 18o/16o of ocean water from a Pacific deep sea core, and the value determined by Dansgaard (1964) for the temperature dependence of 18o/16o of precipitation for oceanic sites, a realistic paleotemperature record is derived. The results indicate that temperatures at the Cascade Cave site were about 4.0°C , 64,000 yrs. ago· and gradually declined to 0°c by 35,000 yrs. ago. These data are consistent with the findings of Canadian workers from 14c and palynological studies of fossil organic matter in the area, and do not support the proposal by some American workers of a major glaciation occurring between 35 - 40,000 yrs. B.P. </p> <p> The age distribution for 140 analyses of 82 speleothems collected from caves in north-west England show abundant deposition during the periods 130 -90,000 yrs. B.P. and 13,000 yrs. B.P. to present, with limited growth over the periods > 350 -170,000 yrs. B.P. and 70 -35,000 yrs. B.P. No ages were found to lie within the periods 170 -140,000 yrs. B.P. and 35-15,000 yrs. B.P. These intervals are correlated to the Wolstonian and Devensian glaciations respectively. </p> <p> Only four speleothems were found to have grown in isotopic equilibrium with their seepage waters, and one of these showed periods of non-equilibrium deposition. In contrast to the Vancouver Island results, 18o/16o all ratios were found to be greater than or equal to modern, indicating that the apparent oceanic location of this site is not expressed in the on the value for temperature dependence of 18o/16o precipitation. </p> <p> An oxygen isotope profile for a flowstone dated between 126,000 and 109, 000 yrs. B.P. shows 18o/16o ratios commencing at values slightly lower than for modern calcite and shifting to still lower values at about 112, 000 yrs. B.P. This shift may indicate a cooling event perhaps carrelative with the isotope stage 5e-5d transition seen in the deep sea core record. A profile for a flowstone over the period 290 -190,000 yrs. B.P. shows excellent correlation to interglacial stages 9e and 7c seen in the deep sea core record, and a pronounced growth hiatus dated at about 250 210,000 yrs. B.P. correlates with glacial stage 8. These are the first speleothem results to show a climatic record beyond 200,000 yrs. B.P. </p> <p> The differences in 18o/16o behaviour for speleothems from the two locations (N .E. Pacific and ..E. Atlantic) are interpreted in terms of their relative proximity to the ocean, potential for exchange of water vapour and 'rainout' by airmasses moving towards the cave sites, and possibility of change in meteorological conditions (principally storm track) over the periods studied. </p> <p> In a subsidiary study, evidence for major sea level lowering during the Illinoian glaciation is recognised by age determinations on the calcite core of speleothems collected at 45m below present sea level from a 'blue hole' near Andros Island in the Bahamas. </p> <p> The possibility of applying the 234U/238U dating method to speleothem is also investigated in this work, by the analysis of modern calci tes and their seepage waters, using a new method for uranium extraction from groundwater. However the variations in 234U/238U ratios observed over short distances in the same cave demonstrate that estimation of initial fossil 234U/238U in the speleothem cannot simply be made by averaging modern ratios for the cave. </p> <p> Consideration is also given to the temperature dependent distribution of trace elements in calcite, particularly magnesium and strontium. Analyses of modern calcites and waters show that Mg incorporation is strongly temperature dependent whereas Sr is not. The possibility of using Mg variations in fossil speleothem as indication of temperature change is briefly examined but the results for one sample are found to be inconclusive. </p> / Thesis / Doctor of Philosophy (PhD)

La caractérisation géochimique et isotopique des eaux souterraines de la « zone minéralisée de l’Entre-Deux-Mers » indique une origine commune de la minéralisation, directement liée à la minéralogie des formations captées par les forages.La géochimie montre que les interactions eau-roche sont majoritairement influencées par la présence d’évaporites, mais que d’autres interactions mettant en jeu des carbonates, des silicates et des argiles existent. Un modèle géochimique d’acquisition de la minéralisation reconstitue parfaitement la chimie des eaux souterraines à l’échelle de la zone d’étude. Ce modèle, construit en se basant sur la géochimie des eaux et sur la minéralogie des formations tertiaires du nord du Bassin aquitain, met à l’équilibre des eaux avec des formations carbonatées et évaporitiques. Afin de mieux comprendre la distribution latérale et verticale des formations tertiaires et leur minéralogie, une approche paléogéographique et sédimentologique a permis de localiser les différents horizons riches en sulfates et/ou en fluorures, mais aussi de comprendre leur origine de dépôt. En se basant sur l’hydrogéologie, la paléogéographie, la minéralogie et la géochimie, des hypothèses de répartition de la minéralisation à l’échelle du forage ont pu être testées. Les résultats de la modélisation couplée hydrodynamique–transport reconstituent la chimie des eaux prélevées par les forages de la « zone minéralisée de l’Entre-Deux-Mers ». Au vu de ces résultats, un modèle avec obturation des horizons riches en sulfates et en fluorures a été testé et les résultats obtenus ouvrent des perspectives pour des futures recherches. Ce travail a donc permis de comprendre l’origine de la minéralisation des eaux de « la zone minéralisée de l’Entre-Deux-Mers », mais aussi de proposer des améliorations et des perspectives pour une meilleure gestion d’une des principales ressources en eau potable de la Gironde. / Geochemical and isotopic characterizations of groundwaters in the "mineralized Entre-Deux-Mers area" indicate a common origin of the mineralization, directly linked to the mineralogy of the formations abstracted by drilling.Geochemistry shows that water-rock interactions are mainly influenced by the presence of evaporites, and that but that other interactions involving carbonates, silicates and clays exist. A geochemical model based on the water geochemistry and mineralogy of the Tertiary formations of northern Aquitaine Basin fix waters in equilibrium with evaporitic and carbonated formations. This model reconstitutes perfectly the groundwaters’ chemistry across the study area and explains the mineralization acquisition. Improving the understanding of the lateral and vertical distribution of tertiary formations and their mineralogy requires a sedimentological and paleogeographical approach. This approach allowed to locate the different layers rich in sulphates and/or fluoride and to understand also their origin.Based on hydrogeology, paleogeography, mineralogy and geochemistry, the distribution of the mineralization has been tested at the borehole scale. The results of this coupled hydrodynamic-transport modeling reconstitute the chemistry of the groundwaters in the "mineralized Entre-Deux-Mers area." A model, that considers the sealing of sulphates- and fluorides-rich layers has been tested and its results highlights future research perspectives. This work has allowed understanding the origin of the mineralization of the waters "of the mineralized Entre-Deux-Mers area" and also suggests improvements and prospects for sustainable management of a major drinking water resource in Gironde.

L'exploitation des réserves d'eau douce, principalement contenues dans les aquifères est une préoccupation croissante dans les zones où elle se traduit par une baisse des niveaux piézométriques.Ce travail de thèse propose de caractériser l'évolution du Système Aquifère du Saharan Septentrional (SASS), et plus particulièrement le Continental Intercalaire (CI) à l'aide d'un couplage entre des outils de modélisation hydrogéologique et de traceurs géochimiques (36Cl, 234U/238U). Situé dans une région semi-aride à aride et s'étendant sur plus d'un million de km2, le CI présente un potentiel d'enregistrement d'une variabilité climatique à grande échelle en plus des baisses piézométriques anthropiques.Nous avons amélioré la définition de la recharge moderne du SASS à l'aide d'une méthode basée sur des données de télédection (entre 0 et 6.75 mm an−1 sur la période 2003-2010) ainsi que de la localisation zones de recharge du Sud Tunisien à l'aide de traceurs isotopiques (14C, 36Cl, 234U). Ces traceurs fournissant un lien évident mais complexe entre les conditions hydrodynamiques présentes et passées, nous nous sommes efforcés d'interpréter les informations paléoenvironnementales apportées par le 36Cl et le 4He sur l'ensemble de la zone tunisienne du CI. Introduites dans un modèle hydrogéologique du CI, les données de 36Cl nous ont permis d'améliorer des hypothèses sur des scénarios de recharge (variant entre 0.5 et 60 mm an−1) pendant les huit derniers cycles interglaciaires-glaciaires (0-775 ka).A partir d'informations complémentaires (échantillons d'eau, affleurements, zone climatique) nous avons finalement construit une représentation "hydro-climato-geochimique" du CI. / Concerns about freshwater availability increase with the rise of populations demands and decrease of piezometric levels in some aquifers. However, this "instantaneous" variability is complicated by a long-term climatic variability that impacts hydrodynamics on timescales of thousands to hundred of thousands of years.This study characterizes the evolution of a large aquifer (extending over more than a million of km2), the Continental Intercalaire (CI), from hydrogeological and geochemical viewpoints, over several hundreds thousand years. For this purpose, we combined hydrogeologic modeling and geochemical tracing methods (36Cl, 234U/238U. . .).The CI is the main aquifer of the North Western Saharan Aquifer System (NWSAS). Located in a semi-arid to arid region, its presence suggests potential records of climatic variability on large temporal and spatial scales. Our results corroborate previous assessment of the modern recharge, which fluctuates between 0 and 6.75 mm yr−1, over the entire NWSAS. We also improve the understanding of previously poorly characterized recharge areas in the South of Tunisia. Isotopic tracers can provide a strong but complex link between past and present hydrodynamic conditions, so we struggled to investigate chlorine-36 and helium-4 paleorecords. In our hydrogeologic model of the CI, chlorine-36 data allowed us to propose some hypotheses about recharge scenarios (varying between 0.5 and 60 mm yr−1) during height of the last interglacial-glacial cycles (0-775 ky). By using multi-scale information (groundwater samples, outcrops and climatic areas), we developed a "hydro-climatic-geochemical" representation of the CI.