The Li Valdeflorez deposit is located in the Cáceres Syncline (Spain). Its northern flank forms a narrow valley between two quartzitic ridges, in the middle of which the Li mineralization is located in an Ordovician psammopelitic sequence (Valhondo unit) with 111.3 Mt @ 0.61 wt% of Li2O, one of the largest Li deposits in Europe.
Underground mining works will be located in the low permeability Valhondo Unit, while the Tailing Mills Facility (TMF), refining plant and auxiliary facilities will be located 1.5km to the southwest on top of El Calerizo Unit, a carbo-dolomitic Carboniferous sequence. Both units are isolated from each other by levels of slates and vulcanites with very low permeability that guarantee the individualization of their hydrogeological behavior.
Underground facilities have been projected using a responsible design, optimized through geotechnical modeling, which includes a crown pillar, in order to avoid mining collapses and protect the Valhondo creek, which drains the area. Will be accessed via two ramps. Auxiliary infrastructures and TMF will be isolated from the substrate using multi-barrier systems. Mine development has been planned to reduce the surrounding rock disturbance and hence to minimize effects on its permeability. Mine water collection and management, and the monitoring program, will prevent waters mixing and infiltration of water from the mine to the aquifers.
The carbo-dolomitic aquifer substrate has been characterized through various geophysics campaigns: SEVs, Electrical Tomography, Magneto-Telluric Tomography, in order to determine the geometry of its superficial zone (0-20 m), and deep zone (up to 300 m). 11 infiltration tests were carried out on the decalcification clays that cover the carbonate outcrops that will constitute the substrate for the auxiliary facilities and the TMF. They show permeability values in the range of K = 10-7 / 10-6 m/s. The deep substrate has been characterized through 4 pumping test, obtaining transmissivities of less than 1 m2 /day. Two additional tests, somewhat further south, indicated higher transmissivities: 16 to 100 m2 /day.
This information, and the results of piezometric and chemical quality campaigns define a conceptual model that shows the heterogeneity of El Calerizo aquifer, where areas with different hydrogeological characteristics coexist, and confirms the marked anisotropy of the medium and a blocks-structure with different hydrogeological conditions. This information is relevant for the location of Surface facilities and the observation boreholes of the Underground Water Control Network, which will allow the performance assessment and evolution of the El Calerizo aquifer.

The presence of water invariably causes a loss of performance of the pit slopes. The water pressure acting within any discontinuities and pore spaces in the rock mass reduces the effective stress, with a consequent reduction in shear strength of the rock mass. Either the slope must be depressurized, designed with a lower factor of safety, or flattened to compensate for the reduced rock mass strength. Where excess water pressures occur below the pit floor, heave may result groundwater pressure is the only geotechnical parameter in pit slope engineering that can readily be modified. It is for this reason that it is necessary to know which sectors of the pit may present stability problems triggered or unleashed by groundwater, that is, where hydrogeology may be a risk to the stability of the open pit slopes.

This paper presents a methodology to estimate the hydrogeological risks associated with slope stability in open-pit operations. The proposed approach integrates geotechnical and hydrogeological data, emphasizing the influence of groundwater flow, pore pressure, and water table fluctuations on slope performance. By combining field measurements, hydrogeological numerical modeling (developed in MINEDW software) and hydrogeological uncertainty analysis and stability analysis (simulated by FLAC3D Software), this methodology provides a comprehensive tool to assess potential risks and inform mitigation strategies. The results aim to enhance slope management practices, minimize failures, and improve safety in open-pit mining environments. The methodology combines different maps that account for (1) Density of existing hydrogeological data in the mine, (2) Deviation between monitored and modelled heads and pore pressures, (3) compliance of pore pressures targets to maintain FoS above defined thresholds, and (4) the sensitivity of FoS to fluctuations in the pore pressures. A hydrogeological risk contour map is generated from these maps for several predictive stages of the mine.

These maps provide a quick and simple way to assess the implications of hydrogeology on slope stability, identifying areas where depressurization processes are necessary, zones where improved hydrogeological characterization and monitoring is needed, and even sectors where the mine planning design needs to be reviewed.

We present an approach to get the most information from static tests. The geochemical characteristics of mining waste and ore are a key factor for the technical and environmental viability of a mine. In this regard, the static geochemical tests usually used are focused in acid-base accounting (ABA) based mainly on carbonates as neutralizer and pyrite as the sulphide. However, this is a partial view. In many cases, the environmental risk of a mining project must also consider other mineral species such as silicates, as they can also provide neutralization capacity and also release metals. Furthermore, metal leaching is sometimes not fully considered in the static tests suite, and is left for long-duration humidity cell or column tests. However, the risk of metal leaching can also be assessed by combining on-site water samples and static leaching tests on drill-cores and old waste dumps.

Mineralogical analysis (XRD) can be used as an initial approximation to calculate a mineralogical neutralization potential (NP) in the sample and check whether the ABA test (EN 15875) may not consider all the available NP, for example, from silicates. Regarding metal leaching, in Spain, the Spanish Geological Mining Institute (IGME) recommends the UNE12457 standard as a leaching test for existing old dumps. This could also be applied to drill-core samples to test for immediate leaching. In addition, the assay of the NAG (Net Acid Generation) test eluates can be used to assess the risk of metal leaching if sulphides are oxidised. Instead of using the Geochemical Abundance Index - GAI (Gard Guide) as an approximation to environmental risk based on rock analysis, we assess the risk based on leaching tests. The reason is that an enrichment in the rock – what the GAI assesses- is not directly related to a risk in metal mobility. Instead, we compare the results of the leaching tests with European or national standards for surface waters, inspired by the IGME methodology.

Our procedure has allowed us to identify whether NP from silicates is likely underestimated in the ABA test and also, based on short-term tests, the metals that pose an environmental risk if the future mine waste is not managed properly.

The results are compared with the existing mine-influenced waters at the site and specific management measures are proposed to the different lithologies of the future mine.