The paper presents analytical methods and results for assessing the variation in the concentration of sulphate (and other ions) over space and time in groundwater flowing through a soluble evaporite terrain beneath a dam. The influence of effective porosity, groundwater flow velocity and the specific rate of dissolution (K′) are considered. The theoretical analysis was tested in a scale model simulating a dam constructed on heavily karstified bedrock. A simple and useful method for assessing how much material is lost through dissolution and how the rate of dissolution changes over time is considered in the context of the Caspe Dam, Spain. L’article présente des calculs analytiques et des méthodes d’évaluation de la concentration en sulfates (et d’autres ions) d’eaux s’écoulant au travers de formations évaporitiques sous un barrage, concentrations variables dans l’espace et dans le temps. Les rôles de la porosité effective, de la vitesse d’écoulement de l’eau et du rapport de solubilité (K′) sont analysés. L’étude théorique a été testée pour un modèle à l’échelle représentant un barrage construit sur un substratum fortement karstifié. Une méthode simple et utile pour évaluer quelle quantité de matière est évacuée par dissolution et comment le taux de dissolution évolue en fonction du temps est présentée dans le contexte du barrage de Caspe en Espagne.

Many of the large number of underground works constructed or under construction in recent years are in unfavorable terrains facing unusual situations and construction conditions. This is the case of the subject under study in this paper: a tunnel excavated in evaporitic rocks that experienced significant karstification problems very quickly over time. As a result of this situation, the causes that may underlie this rapid karstification are investigated and a novel methodology is presented in civil engineering where the use of saturation indices for the different mineral specimens present has been crucial. The drainage of the rock massif of El Regajal (Madrid-Toledo, Spain, in the Madrid-Valencia high-speed train line) was studied and permitted the in-situ study of the hydrogeochemical evolution of water flow in the Miocene evaporitic materials of the Tajo Basin as a full-scale testing laboratory, that are conforms as a whole, a single aquifer. The work provides a novel methodology based on the calculation of activities through the hydrogeochemical study of water samples in different piezometers, estimating the saturation index of different saline materials and the dissolution capacity of the brine, which is surprisingly very high despite the high electrical conductivity. The circulating brine appears unsaturated with respect to thenardite, mirabilite, epsomite, glauberite, and halite. The alteration of the underground flow and the consequent renewal of the water of the aquifer by the infiltration water of rain and irrigation is the cause of the hydrogeochemical imbalance and the modification of the characteristics of the massif. These modifications include very important loss of material by dissolution, altering the resistance of the terrain and the increase of the porosity. Simultaneously, different expansive and recrystallization processes that decrease the porosity of the massif were identified in the present work. The hydrogeochemical study allows the evolution of these phenomena to be followed over time, and this, in turn, may facilitate the implementation of preventive works in civil engineering.

The Sustainable Development Goals promulgate access to sanitation and hygiene for all and the end to open defecation in the framework of the human right to sanitation. Tanzania has one of the lowest levels of access to sanitation, with increasing open defecation. Ending open defecation has been identified as a top priority for reducing global inequalities in WASH (water, sanitation and hygiene). In this context, the coordinated work of NGOs, universities and governments developed a hygiene and sanitation programme (UMATA), whose methodologies and lessons learnt are ready to be scaled up. This research analyses the information collected from more than 21,000 households and discusses the challenges of monitoring and tracking the degree of achievement of the Sustainable Development Goals and the human right to sanitation. A characterisation of the hygiene and sanitation situation and the degree of adoption of different latrine types was assessed before (baseline) and after (follow-up) the implementation of the UMATA programme using the WHO/UNICEF JMP (Joint Monitoring Programme for Water Supply, Sanitation and Hygiene) metrics and approach. This allowed evaluating the efficacy of the strategy implemented in Tanzania to reduce open defecation that led to a decrease from 40.7% to 9.70% in the monitored period. Finally, we discuss the critical economic factors affecting the adoption and sustainability of improved sanitation systems.