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Subsidies on Geomorphological and Geological-Structural Elements for the Knowledge of Deep Aquifer Systems of Hot Sulphurous Groundwaters in the Meda Region (Portugal)

Coelho-Ferreira P. J., Ferreira-Gomes L. M., Sousa-Oliveira A.

Inżynieria Mineralna

2024

Vol. 1, no. 2

art. no. 35

The Meda region is a territory in the interior of Portugal, made up of essentially rocky terrain of the Hercynian granite type and the ante-Ordovician schist type. The local population lives mainly from agriculture; only a small percentage lives from services, commerce, and other residual activities. The supply of drinking water to the population is provided from surface water, rainwater, stored in the Ranhados Dam, on the Torto River. The most common groundwater is essentially used for agricultural activities and is abstracted from surface aquifer systems, mainly in granite massifs, up to around 100m deep. The waters of these systems have hydrogeochemical characteristics typical of short underground circuits, shallow, with an acidic pH of around 6, total mineralization generally less than 300 mg/L, with the dominant anion being bicarbonate and the dominant cation being sodium and/or calcium. However, there are some occasional occurrences of groundwater, which although very rare, are very important due to their specific characteristics These rare groundwaters are sulphureous, with the presence of reduced Sulphur species, are alkaline due to their pH generally being higher than 8, have total mineralization between 300 mg/L and 600 mg/L, belong to the sodium bicarbonate facies, have significant concentrations of silica, with SiO2 between 25.0 mg/L and 63.5 mg/L, have fluoride values higher than 10 mg/L, and also have the presence of carbon dioxide (total CO2); present several trace elements with relevance to Boron (B), Rubidium (Rb), Strontium (Sr), Cesium (Cs), and Tungsten (W). There is also the particularity that the latter waters are warm, resurfacing to the surface at temperatures higher than normal in the region ( 15ºC), with the highest temperature at the Well AC1A of the Longroiva Medical Spa, with 47.4ºC. Geothermometer studies indicate reservoir temperatures of around 78ºC for Águas do Graben, 84ºC for Areola and 115ºC for Longroiva, which are the three main natural discharge sites for these deep aquifer systems. The potential use of these special waters is for thermalism activities and geothermal exploitation, as is already the case at the Longroiva Medical Spa. Therefore, in order to promote the exploration of those waters and new applications, it is necessary to know as accurately as possible the geohydraulic model of the circuit of those waters, and the geomorphological and geological-structural aspects are absolutely central to this process. So, this article, after a brief introduction, presents the main geomorphological and geological-structural characteristics of the region and explains the various details that led to the compartmentalization of the region into three potential exploitation poles: Longroiva Medical Spa, Areola Medical Spa, and Águas do Graben. Finally, some conclusions and final notes are presented on proposals for new studies to support detailed knowledge of the geohydraulic models of each Pole and other potential locations to explore water from the deep aquifer system.

Geotechnical Zoning Map for an Industrial Area in the Castelo Branco Region (Portugal)

Ferreira-Gomes L. M., Mendes E., Andrade Pais L. J., Maia Carvalho P. E., Coelho-Ferreira P. J., Gonçalves V.

Inżynieria Mineralna

2024

Vol. 1, no. 2

art. no. 36

Large-scale geotechnical zoning maps (  1/10 000) applied to Regional and Urban Planning (RUP), and also to the expansion of cities into new areas, such as new industrial areas, generally follow the classic methodology, which corresponds to the presentation of Geotechnical Units Map (GUM) in association with extensive tables with the characteristics of the various Geotechnical Units (GUs). The GUs are defined based on the different lithological and/or lithogenetic types. The tables associated with the GUMs present the characteristics of the various UGs, namely identification properties, in-situ physical parameters, strength parameters, and deformability parameters. In addition to these parameters, it is common to find geological, geomorphological, geodynamic, and hydrogeological elements, with the development of certain specificities depending on each region. In the present case study, in addition to the GUM, in association with some tables with a vast set of parameters, a Geotechnical Zoning Map (GZM) is presented, which is the result of a final document based on a methodology that the authors understand that it should always be used and standardized for this type of situation, i.e. the final map should be the result of overlaying three partial maps, according to the following: 1st Level – Topographic Map, with perfect reading not only of what is common in this type of map but also an adequate reading of the urban fabric, road network, and others.; 2nd Level - Classic GUM; this level must be presented in classic symbology for the different lithologies, so that, when overlapping the previous level, it is possible to read both levels; 3rd Level – GZM, which corresponds to a colour map, with relatively transparent colours, so that when overlaying the previous levels, it is always possible to collect information from the three levels; this last level will have several colours, the main ones being red, green and yellow, which correspond respectively to Very Poor, Excellent and Intermediate Suitability, concerning Suitability for Urban/Industrial Occupation; other intermediate colours may be used, depending on the classification of each area under study. Note that each colour corresponds to a Geotechnical Zone (GZ), representing the suitability for urban-industrial occupation of an area of the territory, as defined in the legend of this map. Therefore, the main objective of this paper is to present a case study with the above situations, but with the advance of applying a methodology that can be implemented with Geographic Information Systems (GIS) to obtain colour zoning, which will be a consequence of overlaying 3 new maps: i) Bearing capacity map for foundations; ii) Settlement susceptibility map, and iii) Slope stability map. Each of these analytical maps is the result of massive calculations using the parameters of each GU for the different places of the territory under study. It should be noted, for example, that different GUs, one made up of clays and the other of sands, which are completely different, can fall under the same GZ. The important point is to define a zoning in which the territory of each zone has the same reaction to any similar action, following what is commonly used for the dimensioning and implementation of urban buildings and/or other similar ones: bearing capacity, settlements, and stability of the natural slope. Finally, the GZM of the area under study is presented, with some conclusions.