The European regulations concerning the water protection and management (Directive 2000/60/EC) and the quality of water for human consumption (Directive 98/83/EC) pose a great challenge for water supply in dispersed rural communities such as those of Galicia in the northwestern corner of the Iberian Peninsula (Fig. 1) (Naves et al. 2019; 2021). The technical and economic feasibility of centralized infrastructures in these regions is severely limited by the distance to highly populated areas and the large required investments to undertaken them. Local people have developed spontaneously autonomous water supply systems based on spring catchments, shallow dug wells and deep drilled wells. More than 650,000 people rely on groundwater supply from hard-rock aquifers through this kind of solutions in the rural areas of Galicia.
Improving the knowledge of the hydrogeology of hard-rock aquifers in the area is essential for the proper groundwater protection and management. Hard rocks generally show a large spatial heterogeneity in both vertical and horizontal directions, which causes large differences in the values of hydrogeologic parameters. Hard rock aquifers usually present: 1) A shallow regolith layer with clay-rich material derived from the in situ weathering of the bedrock; 2) A fractured rock layer, which often presents a dense horizontal network of fractures in the first few meters and a depth-decreasing density of subhorizontal and subvertical fractures (Taylor and Howard 2000); and 3) The fresh rock basement which is permeable only when tectonic fracture zones are present (Krasny 2002; Lubczynski and Gurwin 2005; Dewandel et al. 2006). The proposed conceptualizations of groundwater flow in hard rocks include (Selroos et al. 2002): double porosity models (Barenblatt et al. 1960), discrete fracture models (Lee and Farmer 1993; Long et al. 1982; Molinero and Samper, 2004; Molinero et al., 2004; Dong et al. 2019), parallel plate models (Bear 1993; Lee and Farmer 1993) and equivalent porous media models (Lubczynski and Gurwin 2005; Dewandel et al. 2006).
The main challenges for the sustainable groundwater supply in the rural area of Galicia include: (1) Low guarantee of water supply in dry periods, (2) Groundwater quality deterioration and (3) Deficiencies in the governance of groundwater use and waste treatment and disposal (Naves et al., 2019; Life Rural Supplies, 2020).
Previous hydrological research and water resource assessment have been performed in a small pilot watershed in Abegondo, the Abelar watershed (Fig. 1). The basin has an area of approximately 10.7 ha. It was equipped in 1997 with two meteorological stations, two piezometers and a streamflow gauging station to monitor the effects of eucalyptus plantations on surface water and groundwater resources (Soto et al. 2005; Rodríguez-Suárez et al. 2011; 2014). The results reported by Rodríguez-Suárez et al. (2011; 2014) show that fast-growing trees may reduce the availability of the water resources in dry periods, leading to a decline of the water table and the drying up of springs and small creeks.
Climate change could aggravate the current problems of water supply guarantee in the region during drought periods. Raposo et al. (2013) evaluated the impacts of climate change on groundwater resources in Galicia by using a hydrological model and the meteorological series of the PRUDENCE climate project (Christensen et al. 2007). Raposo et al. (2013) reported that groundwater recharge could concentrate in the winter and decrease dramatically in the summer and the autumn.
There is a concern about the chemical and microbiological quality of groundwater supply in rural areas due to the lack of proper control of the water quality by well owners. Agricultural contamination is often a pressure on the groundwater chemical status where nitrate is the main concern for groundwater quality (EC, 2010). Other risks for groundwater contamination are the poor management of the manure in the fields, the discharge of slurry from farms and the inadequate planning of land use, which does not account for groundwater protection.
Here we address the sustainability of groundwater resources of weathered and fractured schists in the rural areas of Abegondo (Galicia, Spain). The available topographic, meteorological, geological, electric resistivity tomography (ERT), piezometric, streamflow and hydrochemical data are integrated into a conceptual hydrogeological model of the study area. The impact of climate change on groundwater resources is quantified with a hydrological water balance model. The study includes also the assessment of groundwater chemistry and pollution and the recommendations for groundwater management and protection to prevent groundwater pollution and achieve a sustainable groundwater supply.