Aquifer Recharge Areas Research Articles

Investigating the hydrogeological properties of springs in a karstic aquifer in Dorfak region (Guilan Province, Iran)

Karstic aquifers are considered as the main sources of groundwater in the northeast of Rudbar, Iran. The present study was conducted to evaluate the hydrogeological properties of karstic springs in this region. For this purpose, saturation indices (SI values) were calculated using the geochemical PHREEQC model for a number of minerals in the groundwater in the karstic aquifer. Moreover, AqQA-RockWare software packages were used to prepare hydrogeochemical plots for the aquifer, using which the sources of the ions in the water were identified. The origin of bicarbonate, calcium, and magnesium ions in water was determined using chloro-alkaline indices. Moreover, through plotting a Piper diagram for spring water samples, it was discovered that water type of all springs is the Ca-HCO3 type, confirming the karstic characteristic of springs in the area. A Durov diagram also suggests that the water composition of the springs is of the bicarbonate type with the dominant Ca cation, suggesting the calcareous effects of the region on the quality of groundwater and exhibiting a single source for the springs. The calculated saturation indices show that most of the water samples are undersaturated with respect to calcite, dolomite, and CO2. The stable isotopes (δ18O and δ2H) and deuterium excess values were used to get information about transport pathways in groundwater, atmospheric moisture, and the degree of interaction between these reservoirs. The degree of karstification of the recharge area of the karst aquifer was determined to be 5.5 from an analysis of the hydrograph Sefidab Spring.

Evaluation of Geothermal Potential in the Vicinity of the Flooded Sierra Almagrera Mines (Almeria, SE Spain)

We evaluated the hydrogeochemical characteristics of water from the old flooded Sierra Almagrera mines to determine the possible origin of its geothermal fluids, to establish a geological–geochemical model of the geothermal system, and evaluate the site’s geothermal potential. The mine water contained high concentrations of chloride (59.6 g/L), Na (28 g/L), K (1.75 g/L), Ca (7.2 g/L), Mg (0.63 g/L), and Li (66 mg/L), especially in water from the old dewatering system. Metal concentrations were especially elevated in the old mine shafts, with high amounts of Fe (1990 mg/L), Mn (600 mg/L), Zn (460 mg/L), Pb (4 mg/L), and Ni (11.4 mg/L). The Cl/Br molar ratios of the water was high, which may indicate the possible leaching of natural halite from the evaporite deposits in the aquifer recharge area. The mine water had the most elevated temperatures and are, possibly, representative of the extent of equilibration in most of the reservoir. The estimated mean temperatures in the geothermal reservoir, based on the triangular (Giggenbach) Na–K–Mg diagram, was 190 °C for equilibrated waters, which may justify the development of this geothermal resource. The geothermal characteristics imply convection of groundwater to 2500–3000 m below sea level, in agreement with the hydrodynamic model proposed.

Groundwater level responses to precipitation variability in Mediterranean insular aquifers

Groundwater is one of the largest and most important sources of fresh water on many regions under Mediterranean climate conditions, which are exposed to large precipitation variability that includes frequent meteorological drought episodes, and present high evapotranspiration rates and water demand during the dry season. The dependence on groundwater increases in those areas with predominant permeable lithologies, contributing to aquifer recharge and the abundance of ephemeral streams. The increasing pressure of tourism on water resources in many Mediterranean coastal areas, and uncertainty related to future precipitation and water availability, make it urgent to understand the spatio-temporal response of groundwater bodies to precipitation variability, if sustainable use of the resource is to be achieved. We present an assessment of the response of aquifers to precipitation variability based on correlations between the Standardized Precipitation Index (SPI) at various time scales and the Standardized Groundwater Index (SGI) across a Mediterranean island. We detected three main responses of aquifers to accumulated precipitation anomalies: (i) at short time scales of the SPI (<6months); (ii) at medium time scales (6–24months); and at long time scales (>24months). The differing responses were mainly explained by differences in lithology and the percentage of highly permeable rock strata in the aquifer recharge areas. We also identified differences in the months and seasons when aquifer storages are more dependent on precipitation; these were related to climate seasonality and the degree of aquifer exploitation or underground water extraction. The recharge of some aquifers, especially in mountainous areas, is related to precipitation variability within a limited spatial extent, whereas for aquifers located in the plains, precipitation variability influence much larger areas; the topography and geological structure of the island explain these differences. Results indicate large spatial variability in the response of aquifers to precipitation in a very small area, highlighting the importance of having high spatial resolution hydro-climatic databases available to enable full understanding of the effects of climate variability on scarce water resources.

The Mt Conero limestone ridge: the contribution of stable isotopes to the identification of the recharge area of aquifers

The recharge settings of aquifers (as those of the carbonate ridges in central Apennines) is strongly dependent on hydrogeological and geo-structural complexity; in fact, geochemical data, hydrographs interpretation, hydrogeological and geo-structural surveys, tracer and isotope data are usually not so developed and quite difficult to put into relation each other. In this paper, the importance of relating isotope techniques to hydrogeological survey on the recharge area evaluation is demonstrated by studying the system of the Mt Conero limestone ridge, located in central Italy close to the Adriatic sea. A closed system, at a pilot scale, with sufficiently well defined outcropping areas of aquifer, which is offering a contribution to the aquifer recharge area evaluation. In this study a hydrogeological investigation was performed to identify the infiltration areas in the aquifer, analysing the entire geological formation divided into several members, each of them showing different hydrogeological behaviour. In addition, periodic sampling of groundwater and of precipitation at different elevations were carried out to study the isotopic composition over a period of about 4 years. Weighted mean and arithmetic mean of isotopes were used in the gradient calculation and compared giving actually different results. The mean recharge altitude of the aquifer, as evaluated by weighted mean of isotopes, is about 100 m higher than the average elevation of the aquifer outcrop; moreover, it was proven that the vast majority of the recharge is due to the more permeable members of the aquifer (about 20% of the outcropping rocks, located at higher elevation). The recharge mechanism of the aquifer is therefore depending both on the isotope values of the local precipitation and on the distinct infiltration conditions existing in the lithotypes.

Earthquake-Related Changes in Species Spatial Niche Overlaps in Spring Communities

Species interactions between stygobites (obligate groundwater organisms) are poorly known, reflecting the difficulty in studying such organisms in their natural environments. Some insight can be gained from the study of the spatial variability in microcrustacean communities in groundwater-fed springs. Earthquakes can increase hydraulic conductivity in the recharge area of karstic aquifers and flow rates in discharge zones, thus dislodging stygobites from their original habitats to the spring outlets. Earthquakes are expected to alter species spatial niche overlap at the spring outlets, where stygobites coexist with non-stygobites living in benthic and subsurface habitats. We compared the abundance of stygobiotic and non-stygobiotic microcrustaceans in groundwater-fed springs before and after the 6.3-Mw earthquake that hit the karstic Gran Sasso Aquifer (Italy) in 2009. Pre-seismic (1997, 2005) overall niche overlaps were not different from null expectations, while post-seismic (2012) species mean niche overlaps were higher, following the redistribution of animals caused by the earthquake-triggered discharge. The reduced abundance of stygobites following their dislodgement from the aquifer and the concomitant displacement of non-stygobites led to a higher post-seismic co-occurrence of stygobites and non-stygobites. Changes in aquifer structure destroyed pre-seismic species segregation patterns by creating new or strengthening already existing interactions.

Hydrochemical assessment of Hydrological Environmental Services in the recharge area in the Southwest of Mexico City

The aquifer recharge area that supplies water to Mexico City is being protected with the implementation of land use restrictions and with the use of payment schemes for maintaining environmental services (PES). In order to assess the effects of PES in the conservation soil area, the chemical and isotopic compositions of water from springs were characterized and the water baseline chemistry was established to provide a useful standard to monitor the water resources and to support the decision-making under current water management policies. A total of 32 water samples taken in four field surveys, during the dry and rainy season, and background chemical data from different information sources, were studied. The water salinity increases from southwest to northeast towards the urbanized area. The chemical composition of water is due to the occurrence of natural chemical interactions between water and rocks in aquifers and to the presence of effluents generated by human activities. In the forest area, water chemistry has not changed significantly over the past three decades and there are no major discernible trends in the compiled water chemistry data, suggesting that PES has contributed in part to maintain the initial condition in the aquifer recharge area. The natural reference levels proposed have allowed the current chemical conditions in the system to be understood and can be implemented to monitor water resources in the area of conservation soil in the Sierra de Las Cruces with an acceptable degree of reliability.

Finding of Groundwater Recharge, Transit and Discharge Areas

Groundwater recharge, transit and discharge areas for aquifers must be found. Their location depends on the influence of ground surface and hydrographical network (rivers, lakes, sea). It is commonly agreed that the recharge areas are located at hilly places where maximums of infiltration flows and piezometric groundwater levels coincide. Such method was applied for the hydrogeological model of Latvia LAMO . The model provides results for a complex spatial hydrogeological system where conditions even within one aquifer may differ considerably. For this reason, the common method of finding recharge, transit and discharge areas fails to provide accurate results. The new method has been developed. It is based on appliance of the ratio for velocities of vertical to horizontal groundwater flows. The resulting velocity of the vertical flow is found as the difference of velocities of flows on the top and bottom surfaces of the aquifer. The ratio r is the non-dimensional function. Its values r = 1 and r = 0 determine the locations of boundaries for the recharge and discharge areas, accordingly. For the transit area 0 1 and r < 1, correspondingly. The new method provides accurate results even for discontinuous aquifers where the zones of zero thickness appear. Within such zones r = 0. The method will be applied as a tool for investigating complex groundwater processes that are modelled by LAMO . The method was used for extra calibration of LAMO in order to improve its results. The research was supported by the Latvian State Research Program EVIDEnT.

Impact assessment of climate change on a coastal groundwater system, Central Vietnam

Coastal plains in Central Vietnam are characterized by strong seasonal precipitation. As predicted by the A1B gas emission scenario, higher precipitation with more extremes is expected by 2050 for Central Vietnam. To assess impact of these changes on the groundwater resources of the coastal aquifers, a statistical downscaling method with the weather generator LARS-WG coupled with the physically distributed rainfall–runoff model WetSpa and the variable-density groundwater flow model SEAWAT is employed. Results show that contrary to expectation the increase in precipitation by 2050 for the wet months of October and December leads to a sharp decrease in groundwater recharge and groundwater head and consequently a decrease in groundwater resources for the study area. It is concluded that in the assessment of impact of climate change on groundwater resources of coastal sloping plains controlling factors like precipitation intensity in combination with terrain characteristics of the recharge area of aquifers play a major role.

Hazard and risk assessment of pollution on the groundwater resources and residents’ health of Salfit District, Palestine

Abstract Study region The study area is the Salfit District which is located in the northern part of the West Bank of Palestine. This district is located on the outcrops and recharge areas of the karstified dolomitic limestone aquifers of the study area. Study focus As these aquifers are the main sources of drinking water for the residents of the district, this paper aims at evaluating groundwater pollution and assessing the vulnerability, hazards and risks of pollution on groundwater resources and on the residents’ health. New hydrological insights for the region There are many pollutants in the Salfit's aquifer recharge area and thus percolating and polluting the groundwater aquifers. Using a Durov diagram, the sources of water proved to be polluted and, therefore, the health of the residents of Salfit District is directly threatened. A hazard map was developed to classify all polluting activities in the district. Microbiological analysis of the drinking water revealed higher levels of total and fecal Coliforms. The high incidence rate of water related diseases is an indication of the drinking water pollution. This paper contains research findings and policy recommendations to help Salfit District alleviate health and pollution problems associated with this vital resource of groundwater. In addition, Salfit governorate is encouraged to begin addressing the institutional issues and improving public awareness.

Vegetation coverage in hydrographic basins in the central region of the State of São Paulo, Brazil

Vegetation coverage can be inappropriately used, especially in the absence of proper planning, and can result in a reduction of the occupied area. Demographic and economic alterations are factors that contribute to the degradation of vegetation coverage in landscape units. In addition, because vegetation is essential for protection of recharge areas in aquifers, the fragmentation of habitats in hydrographic basins causes changes in climate temperature, soil erosion, eutrophication, and siltation of watercourses. This study analyzed the vegetation coverage from the municipality of São Carlos, State of São Paulo (SP) to assess the environmental quality of water resources in the hydrographic basins and sub-basins, in the Guarani Aquifer System. The vegetation coverage was analyzed in three scales: municipality, Hydric Resource Management Units (UGRHIs), and hydrographic sub-basins based on map overlapping from the LAPA/UFSCar Digital Cartographic Collection and visual interpretation of LANDSAT 5, TM sensor, Path 220, row 075 on satellite images. The municipality of São Carlos has vegetation coverage of 31,776.4 hectares, in which 57% is classified as preserved vegetation typology, and 58% is over the Guarani aquifer recharge area. The vegetation coverage with savannas, riparian forests, and mesophyll forests represented 28% of the total studied area and is located over 28.3% of the Guarani aquifer recharge area extension. The Permanent preservation areas (PPAs) represent 21.6% of the total vegetation coverage with 51% of it being vegetated. The municipality has a total of 686 springs (Topographic maps of IBGE, escale 1:50,000) distributed on an average of 60 springs per km2; 40% of these are protected by vegetation.

Chlorofluorocarbon apparent ages of groundwaters from west Hawaii, USA

Summary The volcanic coastal aquifers of west Hawaii supply drinking water to the area’s residents and nutrient-rich groundwater discharge to the nearby oligotrophic coastal waters. Despite the societal and ecological importance of the water in these aquifers, very little is known about the ages and recharge areas of the groundwater. We therefore determined aquifer recharge areas and groundwater residence times by sampling 18 locations for the oxygen and hydrogen isotopic composition of groundwater and chlorofluorocarbon (CFC) apparent groundwater ages. We sampled water supply wells, coastal wells, and coastal ponds. We applied a δ 18 O/altitude gradient and well-established lapse rates to find that groundwater recharge predominantly occurs in the area’s maximum rainfall zone. Furthermore, the isotopic data suggest that fog drip contributes to aquifer recharge. A single-water source model yielded recharge years ranging from the mid-1960s to mid-1980s for ten samples (56% of samples). Alternatively, a simple binary mixing model, with one water source recharging before1940 and the other after 1940, indicated that 14 samples (78% of samples) contained young water that recharged the aquifer between the mid-1970s and mid-1980s. We also find that CFCs can be used to distinguish between water originating from different aquifers in the area.

Groundwater flow and geochemical modeling of the Acque Albule thermal basin (Central Italy): a conceptual model for evaluating influences of human exploitation on flowpath and thermal resource availability

Although the Acque Albule Basin has been studied since the middle of the 19th century, a comprehensive geologic conceptual model of the area has not yet been developed. The natural setting has been heavily modified by anthropic activities. Rapid evolution during the last 25 years has caused many interferences, which have led to a drastic increase of the hazards and linked risks, mainly related to water resource overexploitation and subsidence. The implementation of an exhaustive framework has become mandatory for environmental and management purposes. Starting from a critical review of previous studies, hydrogeologic and hydrogeochemical surveys and related numerical modeling have been carried out in order to achieve a quantitative understanding of the active phenomena and processes. Several hydrogeologic issues have been addressed concerning aquifer recharge areas and the different flowpaths of groundwater in respect to their division into a shallow and a deep circuit. Account has been taken of the groun...

Impact of an agricultural chronosequence in recharge areas of aquifers in the Brazilian savannah

Current study was conducted, in 2010, on the Boa Vista Farm at the Rio Claro watershed of the southwestern region of Goias, state, Brazil. The region features micro-reliefs with marshy fields and predominantly Haplic Plinthosols. Most areas were incorporated into the agricultural production systems without evaluating the impact on their hydro-physical characteristics. Current analysis evaluates the transformation impact of marshy lands into agricultural areas through an investigation of empirical methods of water infiltration into the soil. Three chronosequenced areas for agricultural use and a preservation area were selected. Water infiltration in the soil was analyzed by field data and by calculations following Kostiakov, Horton and Lewis-Kostiakov. Models overestimated infiltration rates at the beginning of the process and compared to those from field data. The model proposed by Horton was highly similar to rate of basic infiltration speed harvested from field data. Structural quality was reduced through infiltration velocity in the area with human interference with grown under no-tillage system. Key words: Haplic plinthosol, mounds, hillocks, cylinder infiltrometers, no-tillage system.

Multi-tracer investigation of groundwater in El Eulma Basin (northwestern Algeria), North Africa

The hydrogeochemical and isotopic compositions of groundwaters of the Mio-Plio-Quaternary (MPQ) aquifer of the El Eulma area, Northeast Algeria were examined to determine the main factors controlling groundwater chemistry and salinity as well as its hydrogeochemical evolution. Groundwater occurs in different water-bearing formations belonging to Quaternary, Neogene, Upper Cretaceous and Jurassic age. Different geochemical interpretation methods were used to identify the geochemical characteristics. Groundwater of the MPQ aquifer has the highest salinity values (564.5 ≤ total dissolved solids ≤ 2,333 mg/L) in the study area due to the impact of saltwater of Chotts and/or Sebkha “Bazar” and agricultural activities. Plotting data in a Piper diagram showed that Cl and SO4 are the dominant anions, whereas Na is the most dominant cation, although sometimes replaced by Ca and/or Mg in the groundwaters. Dissolution of carbonate and sulphate minerals in the aquifer matrices and recharge areas as well as cation exchange is shown to modify the concentration of ions in groundwater. Groundwater-mineral equilibria showed the prevailing dissolution-precipitation reactions in the groundwater. The groundwaters are depleted in 2H and 18O and display an isotopic signature close to that of meteoric water with d-excess values indicating present-day precipitation over the region and reflect the contribution of vapour masses from Mediterranean Sea and Atlantic origin. The isotopic features suggest that most of the groundwaters at the study area result from mixing between recent recharge and an older component recharged under climatic conditions cooler than at present.

Groundwater storage in adaptation to climate change

The Trust project, funded by the European Commission's Life+ programme and the Italian Ministry of Environment, aims to identify adaptation and mitigation measures to counteract the impacts of climate change on the groundwater of the upper plain in the Veneto and Friuli regions in northeastern Italy. Intensive groundwater abstraction over recent decades has resulted in declining water table levels; this problem, common to many other places in the world, will be exacerbated by future temperature increases unless appropriate solutions are adopted. Trust aims to implement a water balance modelling tool to support institutions in formulating sustainable water management planning policies and best practices. This paper reviews the development and application of the water balance model that simulates water deficit affecting summer crops using agronomic and climatic data at small spatial and temporal resolution. Remote sensing identification methods were employed to map irrigated crops. Projections on the water deficit as a function of climate change have used future precipitation and evapotranspiration patterns derived from climate simulations (SRES-IPCC scenarios A1B and A2) of the Mediterranean region for the twentieth and twenty-first centuries. Model outputs showed that, due to climate change, water deficits for summer crops could be of the order of 400 mm, while the balance model showed that climate change can lead to a reduction of average groundwater resource of about 5–10%, especially in the apical areas of the high plain. However, a significant part of the future water deficit might be recovered through rationalisation of water withdrawal and managed aquifer recharge areas.

Risk assesment of an urban aquifer based on environmental tracers

Groundwater from a Pleistocene sandy-gravel aquifer is a drinking water resource for the Union brewery, located near the centre of Ljubljana (Slovenia). A large part of the aquifer recharge area is highly urbanized, which represents a great risk for the groundwater quality assurance. The groundwater dating techniques were used to study the contamination risk of this drinking-water resource. The application of chlorofluorocarbons (CFCs), sulphur hexafiuoride (SF6) and tritium-helium-3 (3H-3He) age indicator was tested, as they haven't been used in Slovene urban areas so far. The results reflect that the 3H-3He dating technique is the most suitable for a groundwater age determination in the study urban aquifer, since SF6 and particularly CFCs concentrations could be affected by the local contaminations. They indicated that average groundwater residence times range from 10 to 30 years. Boreholes that are more distant from the Šišenski hrib hill are more vulnerable to contamination due to flow of young groundwater from a direction of the main aquifer, which is exposed to the urban pollution. The presented results were supplemented with chemical investigations of groundwater organic pollutants. An unknown trace organic pollutant with a base ion mass-to-charge ratio 147 was put into focus. Its identification based on chromatographic separation and a mass spectrometric detection with GC-MS, LC-MS and LC-TOF MS techniques. The newly detected trace organic pollutant in sampled groundwater represents together with the 3H and 3He data a new technique to study the flow paths and contaminant transport in the urban aquifer in both, the lateral and vertical directions.

Methodology for rapid assessment of aquifer recharge areas

The environmental tools of local appliance, such as surveillance and permits of deforestations and water use, environmental impact assessments of local scale, and delimitation of preservation areas, demand customized methodologies to deal with hydrogeological issues. In this study, a structured one for rapid environmental assessment aiming at recharge of aquifers safety was presented. This comprises qualitative and quantitative evaluations by means of textual and cartographical descriptions, complemented by weighted spreadsheets for rapid assessment. Applications in case studies took place in sites selected in the Paracatu River Basin. The results showed a positive potential for knowledge and protection of aquifers in micro-watersheds.

IMPORTÂNCIA DAS ÁREAS COM VEGETAÇÃO NA ÁREA DE CONSERVAÇÃO NATURAL DO AQUÍFERO ARENITO BASAL SANTA MARIA, SANTA MARIA, RS

Protected Areas are spaces of resources preservation and/or conservation associated to them and, areestablished by law or by public authorities. Because of this characteristic, they are also areas that protectwater resources in terms of quality and quantity. In the town of Santa Maria there are some protected areasthat are considered essential for the occurrence of water infiltration with quality and quantity, as it is SantaMaria Basal Sandstone Aquifer recharge area case. This and other existent protected areas in the town performenvironmental services that manage the local and regional hydrological cycle. Thus, this research aims todiscuss the necessity of maintenance of existent native vegetation areas and the institution of protected areas inSanta Maria that hold the environmental function of setting the local and regional hydrological flow. The resultsshow that in the aquifer recharge area, defined in the town Law of Land Use and Occupancy, there are still areaswith native vegetation; however, these areas are exposed to urban expansion. Therefore, it is important that thetown maintains these vegetated areas in this natural water recharge area.

Hydro-geochemical and isotopic composition of groundwater, with emphasis on sources of salinity, in the aquifer system in Northwestern Tunisia

The hydro-geochemical and isotopic data of groundwater of the aquifer of the El Kef area, North-Western Tunisia, were examined to determine the main factors controlling the groundwater chemistry and salinity as well as its hydro-geochemical evolution. This study area has a complex geological structure which is mainly controlled by halokinesis movements and inherited structures. Groundwater occurs in different water bearing formations belonging to Upper Cretaceous, Paleogene (Eocene) and Mio-Plio-Quaternary (MPQ). Different geochemical interpretation methods were used to identify the geochemical characteristics. Groundwater of the MPQ aquifer has the highest salinity values (0.3–7.0gl−1) in the study area due to the impact of agricultural activities. Piper diagram showed that Cl− and SO42- are the dominant anions, where as Na+ is the most dominant cation, where it is sometimes replaced by Ca2+ and/or Mg2+ in the hydro-chemical facies of the groundwater. Dissolution of carbonate and sulfate minerals in the aquifer matrices and recharge areas as well as cation exchange are shown to modify the concentration of ions in groundwater. The groundwaters are depleted in 2H and 18O and displayed an isotopic signature close to that of meteoric water with d-excess values indicating present-day precipitation over the region and reflect the contribution of vapor masses from Mediterranean and Atlantic origins. The isotopic features suggest that most of the groundwater at the study area result from mixing between recent recharge and an older component recharged under climatic conditions cooler than at present.

Multi-tracer investigation of groundwater in El Eulma basin, Northwestern Algeria

The hydrogeochemical and isotopic data of groundwaters of the Mio-Plio-Quaternary (MPQ) aquifer of the El Eulma area, Northeast Algeria were examined to determine the main factors controlling the groundwater chemistry and salinity as well as its hydrogeochemical evolution. Groundwater occurs in different water bearing formations of Quaternary, Neogene, Late Cretaceous, and Jurassic age. Different geochemical interpretation methods were used to identify the geochemical characteristics. Groundwater of the MPQ aquifer has the highest salinity values (564.5 ≤ TDS≤2333 mg/L) in the study area due to the impact of saltwater of Chotts and/Sebkha “Bazer” and agricultural activities. A Piper diagram showed that Cl and SO4 are the dominant anions, whereas Na is the most dominant cation, sometimes replaced by Ca and/or Mg in the hydrochemical facies of the groundwaters. Dissolution of carbonate and sulfate minerals in the aquifer matrices and recharge areas as well as cation exchange are shown to modify the concentration of ions in groundwater. Groundwater-mineral equilibria showed the prevailing dissolution–precipitation reactions in the groundwater. The groundwaters are depleted in 2H and 18O and displayed an isotopic signature close to that of meteoric water with d-excess values, indicating present-day precipitation over the region and reflect the contribution of vapour masses from Mediterranean Sea and Atlantic origin. The isotopic features suggest that most of the groundwaters result from mixing between recent recharge and an older component recharged under climatic conditions cooler than at present.