Rock Aquifers Research Articles

Delineation of groundwater potential zone in hard rock terrain in Gangajalghati block, Bankura district, India using remote sensing and GIS techniques

This study employed with the integration of remote sensing (RS) and geographical information system (GIS) techniques to delineate ground water potential zones for ground water management of Gangajalghati block, Bankura district, West Bengal and is located on the eastern slope of Chotanagpur plateau and area belongs to predominantly Precambrian gneissic terrain, and small area belongs to Gondwana deposits and quaternary sediments. The groundwater in this region is confined within the weathered residuum and fracture zones in pediment region. Survey of India topographical maps and satellite imageries along with other data and field observation data have been utilized to prepare various thematic layers viz. drainage, slope, lineament, geology, hydrogeomorphic units, land-use/land cover, soil, and depth to water level map of this hard rock terrain. All the thematic map that influence ground water occurrences have been analyzed and integrated through GIS analysis based on weights assignment. The weighted index overlay method has been followed to delineate ground water potential zones. The result revealed that the study area can be categorized into four different ground water potential zones viz., very good, good, moderate, and poor zones. The bore well yield data reveals that medium yielding wells (50–100 L per min) are in and around the moderate to high lineament density zone and buried pediment medium region. Afterward validation with well yield data revealed a good correlation with respect to the observed ground water potential zonation. This study is useful for better planning and management of ground water resources as well as providing quick prospective guides for ground water exploration in hard rock aquifer system.

Evolutionary analysis of groundwater flow: Application of multivariate statistical analysis to hydrochemical data in the Densu Basin, Ghana

An evolutionary trend has been postulated through the analysis of hydrochemical data of a crystalline rock aquifer system in the Densu Basin, Southern Ghana. Hydrochemcial data from 63 groundwater samples, taken from two main groundwater outlets (Boreholes and hand dug wells) were used to postulate an evolutionary theory for the basin. Sequential factor and hierarchical cluster analysis were used to disintegrate the data into three factors and five clusters (spatial associations). These were used to characterize the controls on groundwater hydrochemistry and its evolution in the terrain. The dissolution of soluble salts and cation exchange processes are the dominant processes controlling groundwater hydrochemistry in the terrain. The trend of evolution of this set of processes follows the pattern of groundwater flow predicted by a calibrated transient groundwater model in the area. The data suggest that anthropogenic activities represent the second most important process in the hydrochemistry. Silicate mineral weathering is the third most important set of processes. Groundwater associations resulting from Q-mode hierarchical cluster analysis indicate an evolutionary pattern consistent with the general groundwater flow pattern in the basin. These key findings are at variance with results of previous investigations and indicate that when carefully done, groundwater hydrochemical data can be very useful for conceptualizing groundwater flow in basins.

Arid hypogene karst in a multi-aquifer system: hydrogeology and speleogenesis of Ashalim Cave, Negev Desert, Israel

Abstract Ashalim maze cave, and neighbouring caves in the NW Negev Desert, Israel demonstrate hypogene karst features. These features are shown to have developed as a result of the mixing of two types of groundwater flowing in opposite directions within two tiers of Cretaceous rock aquifers. The stable isotope composition indicates that the lower Kurnub sandstone aquifer was recharged over far-field Nubian Sandstone outcrops in the vicinity of the Precambrian basement outcrops of the Sinai Desert, which belongs to the Afro-Arabian dome. The water flows northward and rises into the Judea carbonate aquifer through deep faults. A similar hydrogeological system is inferred for the speleogenetic period of Ashalim Cave. Dewatering of the cave occurred in the Pliocene due to regional uplift. This is indicated by the first vadose speleothems, dated to the late Pliocene (3.1 Ma). This was followed by surface denudation, which breached the cave and formed the present entrance.

Carbon-13 in groundwater from English and Norwegian crystalline rock aquifers: a tool for deducing the origin of alkalinity?

The 13C signature is evaluated for various environmental compartments (vegetation, soils, soil gas, rock and groundwater) for three crystalline rock terrains in England and Norway. The data are used to evaluate the extent to which stable carbon isotopic data can be applied to deduce whether the alkalinity in crystalline bedrock groundwaters has its origin in hydrolysis of carbonate or silicate minerals by CO2. The resolution of this issue has profound implications for the role of weathering of crystalline rocks as a global sink for CO2. In the investigated English terrain (Isles of Scilly), groundwaters are hydrochemically immature and DIC is predominantly in the form of carbonic acid with a soil gas signature. In the Norwegian terrains, the evidence is not conclusive but is consistent with a significant fraction of the groundwater DIC being derived from silicate hydrolysis by CO2. A combined consideration of pH, alkalinity and carbon isotope data, plotted alongside theoretical evolutionary pathways on bivariate diagrams, strongly suggests real evolutionary pathways are likely to be hybrid, potentially involving both open and closed CO2 conditions.

Mechanisms of recharge in a fractured porous rock aquifer in a semi-arid region

Eleven porewater profiles in rock core from an upland exposed sandstone vadose zone in southern California, with thickness varying between 10 and 62 m, were analyzed for chloride (Cl) concentration to examine recharge mechanisms, estimate travel times in the vadose zone, assess spatial and temporal variability of recharge, and determine effects of land use changes on recharge. As a function of their location and the local terrain, the profiles were classified into four groups reflecting the range of site characteristics. Century- to millennium-average recharge varied from 4 to 23 mm y−1, corresponding to <1–5% of the average annual precipitation (451 mm over the 1878–2016 period). Based on the different average Cl concentrations in the vadose zone and in groundwater, the contribution of diffuse flow (estimated at 80%) and preferential flow (20%) to the total recharge was quantified. This model of dual porosity recharge was tested by simulating transient Cl transport along a physically based narrow column using a discrete fracture-matrix numerical model. Using a new approach based on partitioning both water and Cl between matrix and fracture flow, porewater was dated and vertical displacement rates estimated to range in the sandstone matrix from 3 to 19 cm y−1. Moreover, the temporal variability of recharge was estimated and, along each profile, past recharge rates calculated based on the sequence of Cl concentrations in the vadose zone. Recharge rates increased at specific times coincident with historical changes in land use. The consistency between the timing of land use modifications and changes in Cl concentration and the match between observed and simulated Cl concentration values in the vadose zone provide confidence in porewater age estimates, travel times, recharge estimates, and reconstruction of recharge histories. This study represents an advancement of the application of the chloride mass balance method to simultaneously determine recharge mechanisms and reconstruct location-specific recharge histories in fractured porous rock aquifers. The proposed approach can be applied worldwide at sites with similar climatic and geologic characteristics.

Thermodynamic Computations for Ion Exchange and Surface Protonation Reactions and the Implications for Acid Induced Contact Angle Evolution in Silica Rich Saline Aquifer Systems

To reduce current high concentrations of anthropogenic greenhouse gases in the atmosphere to levels stipulated by the Intergovernmental Panel on Climate Change, geological sequestration has been universally proposed. On the basis of cost analysis and global availability, deep saline aquifers are the prime targets for most proposed commercial and pilot scale projects.While the geological storage of anthropogenic carbon dioxide is expected to mitigate global warming, the technical aspects of the injection deserve to be considered for efficient injection projects. The water rock interaction phenomenon occurs due to carbonic acid generation which causes surface protonation reactions and has the potential to decrease water wettability of the system leading to enhanced water mobility and efficient gas injection. Therefore, for a saline aquifer rock with minerals capable of ion exchange reactions that consume solution protons, the wettability of such a system is likely to be preserved leading to reduced water mobility and poor gas injection. Generally, the extents to which surface protonation and ion exchange reactions occur depend on the free energy change of the reaction.In this paper, we have carried out thermodynamic computations for the free energies of surface protonation and ion exchange reactions. Based on the values of computed free energies, which show that ion exchange reactions have lower free energies, we have discussed the wettability implications for geological storage in silica rich saline aquifer systems.

Insights on pumping well interpretation from flow dimension analysis: The learnings of a multi-context field database

The flow dimension parameter n, derived from the Generalized Radial Flow model, is a valuable tool to investigate the actual flow regimes that really occur during a pumping test rather than suppose them to be radial, as postulated by the Theis-derived models. A numerical approach has shown that, when the flow dimension is not radial, using the derivative analysis rather than the conventional Theis and Cooper-Jacob methods helps to estimate much more accurately the hydraulic conductivity of the aquifer. Although n has been analysed in numerous studies including field-based studies, there is a striking lack of knowledge about its occurrence in nature and how it may be related to the hydrogeological setting. This study provides an overview of the occurrence of n in natural aquifers located in various geological contexts including crystalline rock, carbonate rock and granular aquifers. A comprehensive database is compiled from governmental and industrial sources, based on 69 constant-rate pumping tests. By means of a sequential analysis approach, we systematically performed a flow dimension analysis in which straight segments on drawdown-log derivative time series are interpreted as successive, specific and independent flow regimes. To reduce the uncertainties inherent in the identification of n sequences, we used the proprietary SIREN code to execute a dual simultaneous fit on both the drawdown and the drawdown-log derivative signals. Using the stated database, we investigate the frequency with which the radial and non-radial flow regimes occur in fractured rock and granular aquifers, and also provide outcomes that indicate the lack of applicability of Theis-derived models in representing nature. The results also emphasize the complexity of hydraulic signatures observed in nature by pointing out n sequential signals and non-integer n values that are frequently observed in the database.

Isotope and microbiome data provide complementary information to identify natural nitrate attenuation processes in groundwater

Natural attenuation processes alleviate the impact of fertilization practices on groundwater resources. Therefore, identifying the occurrence of denitrification has become a requirement for water quality management. Several approaches are useful for this purpose, such as isotopic and microbiological methods, each of them providing distinct but complementary information about denitrification reactions, attenuation rates and their occurrence in the aquifer. In this paper, we investigate the contribution of both approaches to describe denitrification in a consolidated rock aquifer (limestone and marls), with a porosity related to fracture networks located in the northeastern sector of the Osona basin (NE Spain).Isotopic methods indicated the origin of nitrate (fertilization using manure) and that denitrification occurred, reaching a reduction of near 25% of the nitrate mass in groundwater. The studied area could be divided in two zones with distinct agricultural pressures and, consequently, nitrate concentrations in groundwater. Denitrification occurred in both zones and at different levels, indicating that attenuation processes took place all along the whole hydrogeological unit, and that the observed levels could be attributed to a larger flow path or, in a minor extent, to mixing processes that mask the actual denitrification rates.Microbiological data showed a correlation between denitrifier genes and the isotopic composition. However, the groundwater microbiome and the distribution of denitrifying bacteria did not reveal a major influence on the denitrification level observed by isotopic methods. This focuses the interest of microbiological analysis to identify functional genes within the bacteria present in the aquifer.Results indicated that isotopic methods provide information of the overall denitrification ability of the hydrogeological unit, and that genomic data represent the processes actually acting nearby the well. A combination of both approaches is advised to support induced in situ attenuation actions in polluted sites.

Taking into Account the Role of the Weathering Profile in Determining Hydrodynamic Properties of Hard Rock Aquifers

The present study aims at understanding the role of the structure and the geometry of the weathering profile on the hydrodynamic behavior of hard rock aquifers. We first described 2D geophysical cross sections of weathering profiles realized and validated on an experimental site. Next, we implemented five long-term pumping tests in wells drilled at various locations of these cross sections. Finally, we chose the appropriate analytical solutions to determine the hydrodynamic parameters in consistence with the structure and the geometry of the weathering profile. Results reveal that land covers, weathering type and thickness, presence of no flow boundaries, etc. are all factors that explain the flow regime, which appears therefore much less unpredictable. In other words, the 2D geophysical data are enough to locate the best permeable areas, or the areas where the structure of the aquifer without impervious boundaries and with leakage favor a good long-term behavior of the well. The values of aquifer’s transmissivity vary between 5.10−3 and 4.10−5 m2/s. The storage varies between 0.06 and 7.10−7. The variability of these parameters from site to site reflects the high heterogeneity of hard rock aquifers.

The influence of water/rock − water/clay interactions and mixing in the salinization processes of groundwater

Study regionGroundwater from the Precambrian Shield rock and Pleistocene deposit aquifers in Saguenay-Lac-Saint-Jean region ( >13 000km2) in the province of Quebec, Canada. Study focusInterpretations are based on the combination of hierarchical cluster analysis (HCA) results, principal component analysis (PCA), binary plots investigations ([Na+, Ca2+, Br−] vs. Cl−; Ca2+vs. HCO3−; Ca2+vs. Na+) and Piper diagram investigations. The HCA and PCA was applied on 321 samples to specifically enable the identification of two very distinct salinization paths that produce the brackish groundwater in the study area. New hydrological insights for the regionThe results show that each of the two salinization paths exerts a major and different influence on the chemical signature of groundwater. Groundwater present in the crystalline bedrock naturally evolve from a recharge-type groundwater (Ca-HCO3-dominant) to a type of brackish groundwater (Ca-(Na)-Cl-dominant) due to water/rock interactions (plagioclase weathering and mixing with deep basement fluids). Groundwater evolution in confined aquifers is dominated by water/clay interactions. The term water/clay interactions was introduced in this paper to account for a combination of processes: ion exchange and/or leaching of salt water trapped in the regional aquitard. Mixing with fossil seawater might also increase the groundwater salinity. PCA revealed that Ca2+, Sr2+, Ba2+ are highly correlated with groundwater from bedrock aquifers, while Mg2+, SiO2, K+, SO42−and HCO3− are more representative of the regional confining conditions.

Hydrogeology of Hard Rock Aquifer System - A Case Study from Turinjahalli Watershed, Dharmapuri District, Tamilnadu, India

Hydrogeology of Hard Rock Aquifer System - A Case Study from Turinjahalli Watershed, Dharmapuri District, Tamilnadu, India

Multi-component transport of BTX in a discretely fractured aquifer with fracture–skin: numerical investigation and sensitivity analysis

Monitoring of BTX natural attenuation in a fractured rock aquifer is highly challenging due to lack of knowledge about the influence of interaction of heterogeneous domains on transport processes. Contaminant transport in a fractured rock is commonly investigated using dual continuum models by considering fracture and its surrounding rock–matrix as two different continuums. In this study, a numerical multi-component transport model based on a triple continuum modeling approach is developed to investigate the transport of dissolved BTX in a discretely fractured aquifer with fracture–skin. A residual BTX source zone is considered to be present at the fracture inlet. A multi-component dissolution model is coupled with the present numerical model to simulate the dissolution of benzene, toluene and xylene at the residual BTX source. Dissolved BTX components are considered to undergo sorption and biodegradation in addition to advection and dispersion within the fracture. Dissolved BTX components diffusing to fracture–skin and rock–matrix are considered to undergo sorption and biodegradation in fracture–skin and rock–matrix. A novel sensitivity analysis approach based on spatial moments is introduced in the manuscript to investigate the sensitivity of various flow and transport parameters of fracture–skin and rock–matrix on dissolved BTX mass retained in fracture and matrix. The presence of fracture–skin is found to significantly affect the concentration distribution and mass retention of dissolved BTX components in a fractured aquifer.

Groundwater Modeling of Hiranyakeshi Watershed of Ghataprabha Sub-basin

ABSTRACT Groundwater modeling is an effective tool for managing the groundwater resource and to predict for the future. There is a need for proper quantification of the scarce water resources that are under threat because of the population explosion, industrialization, urbanization and climate change. More than 60% of India is underlained by hard rock aquifers. The Hiranyakeshi watershed of Ghataprabha sub-basin, chosen for the study is also under hard rock aquifer and faces severe groundwater problems. This is due to majority of the agricultural and industrial activities in the watershed depend on the groundwater. A 3-D groundwater flow model, viz. Visual MODFLOW was used for the study with two conceptual layers. The first layer is a weathered zone which is about 20-30m from the top, followed by a second layerof fractured zone which is about 30-40m from the first. The model was simulated for a period of seven years (2008-2014), under transient case. The results from the modeling shows that for the next 10 years the water table is believed to decrease more than 50m in the study area. To overcome this critical stage, the present draft should be reduced by nearly 50%.

Relationship of groundwater geochemistry and flow to volcanic stratigraphy in basaltic aquifers affected by magmatic CO2, Jeju Island, Korea

Groundwater from pristine volcanic rock aquifers on dormant Jeju Island, Korea, was investigated to identify sources and geochemical processes of dissolved inorganic carbon (DIC) and related solutes along with characteristics of groundwater flow using a multi-isotope approach. δ18O, δ2H, and 3H of groundwater indicated the water is of meteoric origin, and is mainly derived from recent recharge, except Na-rich mineral water which has a significant contribution of 3H-free old water. 87Sr/86Sr of dissolved Sr suggests that solutes in groundwater were mainly derived from old alkali basalt in the lower part of lava flows. δ13CCO2(g) calculated using δ13CDIC and measured hydrogeochemical parameters indicated that (1) biogenic soil CO2 is a dominant source of DIC in low mineralized water, (2) CO2-rich water had mostly mantle-derived magmatic CO2, and (3) mineral water contained both biogenic and magmatic CO2. δ13CCO2(g) in mineral water was affected by precipitation of calcite, which complicated the estimation of the contribution of CO2 sources to DIC. Concentrations of mobile elements were mainly controlled by the amount of magmatic CO2 and groundwater residence time. δ13CCO2(g) and 3H content were used to distinguish four types of groundwater with different spatial patterns of occurrence in relation to the volcanic stratigraphy of Jeju Island. Groundwater types I and II are low mineralized water with lower levels of DIC from biogenic CO2, composed of either recent recharge (<40years, type I) or older water with negligible 3H (>60years, type II). Type III is Mg-rich mineral water with significant recent recharge while type IV is Na-rich mineral water with older residence time. Types III and IV had somewhat elevated levels of DIC (up to 7.6mM) with mixed signatures of magmatic and biogenic CO2, while CO2-rich water (a subset of type III) had DIC up to 100mM with signatures of mantle-derived magmatic CO2. Groundwater in the eastern area of Jeju Island is mostly type I, which can be attributed to a lack of both low-permeability rocks and recent volcanic rocks in that area. Types III and IV were found in the western area where the latest volcanic rocks are distributed. In the southwestern area, type III is associated with permeable basaltic aquifers with a contribution of magmatic CO2 and type IV is from the younger lava flows dissected by older massive trachytic rocks and shallower hydrovolcanic tuffs, which led to the higher degree of mineralization. A conceptual model is proposed to integrate the chemical and isotopic constraints of groundwater with volcanic stratigraphy and suggest the processes that generated groundwater types with different residence times and chemical compositions. This study may contribute to understanding the processes of groundwater flow and mineralization in volcanic aquifers affected by deep-source CO2 and variable residence time of groundwater in both dormant and active volcanic areas.

Charakterystyka hydrologiczna Kosarzewki

&lt;p&gt;W oparciu o materiały hydrograficzne zbierane w Zakładzie Hydrologii od lat 50. XX wieku przedstawiono warunki występowania wód podziemnych i ich rolę w zasilaniu Kosarzewki. Jest to zlewnia o powierzchni 209,3 km&lt;sup&gt;2&lt;/sup&gt;, położona 12 km na południe od Lublina, w dorzeczu górnej Bystrzycy. Zasoby wodne tego terenu, ich ilość i jakość, decydują o zaopatrzeniu Lublina w wodę. &lt;/p&gt;&lt;p&gt;Wody podziemne w zlewni Kosarzewki występują w szczelinowo-porowych, węglanowych skałach górnej kredy oraz paleocenu. O warunkach hydrogeologicznych decyduje tektonika górotworu oraz naprzemianległe występowanie w stropowych partiach skał górnej kredy zróżnicowanych litologicznie warstw decydujących o utrzymywaniu się kilku poziomów wodonośnych Czynniki te zadecydowały o braku ciągłości pierwszego zwierciadła wody, o istnieniu skokowo zmiennych rzędnych zwierciadła wody oraz o istnieniu źródeł w różnym położeniu hipsometrycznym, zarówno w dolinach rzecznych jak też na wysoko wyniesionych równinach denudacyjnych obszaru zlewni.&lt;/p&gt;&lt;p&gt;Przepływ wód podziemnych następuje z południowego wschodu na północny zachód, zgodnie z układem głównych dolin. W regionalnym drenażu wód podziemnych stwierdza się możliwość podziemnego przepływu wody z lewej części zlewni Kosarzewki do Bystrzycy, która jest głębiej wcięta w podłoże skalne.&lt;/p&gt;W strukturze odpływu Kosarzewki dominuje zasilanie podziemne, z którego pochodzi 87% wody rzecznej. Woda podziemna dociera do rzek poprzez bezpośredni drenaż korytowy oraz przez źródła zasilane z głównego poziomu występującego w skałach górnej kredy. W okresie badań stwierdzono synchroniczne zmiany stanów wody podziemnej, wydajności źródeł i przepływu Kosarzewki. Rzeka słabo reaguje na zasilania atmosferyczne, wody opadowe są retencjonowane w podłożu skalnym. Spływ powierzchniowy pojawia się sporadycznie, częściej w okresie przemarznięcia gruntu niż w okresie letnim.

Modeling fracturing pressure parameters in predicting injector performance and permeability damage in subsea well completion multi-reservoir system

The significance of fracturing parameters which are aquifer integrity, rock properties, thermal stress, fracturing pressure and produced water quality to alter permeability damage, cake formation and injectivity performance was highlighted in a robust improved internal filtration—hydraulic model and permeability reduction model incorporating a R_{text{AT}} (c) function. The studied system is an injection well multi-reservoir formations. Field data obtained from the log and field reports and improved model were used to simulate injector, fracturing and permeability damage performance. Thus, data requirements in the R_{text{AT}} (c) function which are rock properties, water quality, aquifer integrity, fractures rates and pressures parameters were assessed for its impact on injector performance and permeability damage simulated in MATHLAB and COMSOL multi physics environment. The profile of injector performance and damage reservoir permeability to changes in rock properties and aquifer integrity were demonstrated to have a profound influence on both fracturing phenomena. Thus, sustainable re-injection scheme was shown as a direct consequence of rock mechanics parameters, well hydraulics aquifer integrity that largely depends on the initial concentration of active constituents of the produced water as well as physic-chemical properties of the host aquifer.

The Application of Radon for Mapping Open Fracture Networks in a Thin Vadose Zone

Core Ideas Locating preferential pathways for infiltration is critical for contaminated fractured rock aquifers. Mapping open fractures in buried bedrock formations has been marginally successful and costly. Mapping at greater resolution and lower cost can be valuable for many fractured‐rock sites. We used CR‐39 particle track 222Rn detector technology in a simple passive sampling design. Our methodology is characterized by low cost and ease of deployment. The use of naturally occurring tracers to elucidate subsurface flow and transport of water and gases through fractured vadose zones represents a powerful and inexpensive methodology for understanding geologic systems. Our study was conducted at Shepley's Hill, a highly fractured granite highland at the former Fort Devens military base. This study evaluated the applicability of using inexpensive, readily available passive Rn detectors to identify conductive structures (e.g., fractures and fracture networks) in fracture‐dominated vadose zones. Results from the Shepley's Hill study show a clear spatial correlation of elevated 222Rn concentrations emanating from fracture zones previously identified by independent geologic studies. At Shepley's Hill, the 222Rn concentrations measured from detector locations directly above bedrock fractures located within the Disc Golf Fracture Zone were almost exclusively the highest values measured in the study. Conversely, probes located above areas of less‐fractured bedrock and the Nona–Shep Fracture Zone showed relatively low 222Rn concentrations. These two observations provide strong supporting evidence that not all fractures are equal when it comes to their ability to transmit gas and, by inference, water into and out of the subsurface. Based on the results of this study, 222Rn is an environmental tracer capable of efficiently detecting major bedrock fracture sets in the vadose zone that readily transport gas and may be responsible for focusing water infiltration into contaminated aquifers.

Joint use of singular value decomposition and Monte-Carlo simulation for estimating uncertainty in surface NMR inversion

We propose a simple and robust approach for investigating uncertainty in the results of inversion in geophysics. We apply this approach to inversion of Surface Nuclear Magnetic Resonance (SNMR) data, which is also known as Magnetic Resonance Sounding (MRS). Solution of this inverse problem is known to be non-unique. We inverse MRS data using the well-known Tikhonov regularization method, which provides an optimal solution as a trade-off between the stability and accuracy. Then, we perturb this model by random values and compute the fitting error for the perturbed models. The magnitude of these perturbations is limited by the uncertainty estimated with the singular value decomposition (SVD) and taking into account experimental errors. We use 106 perturbed models and show that the large majority of these models, which have all the water content within the variations given by the SVD estimate, do not fit data with an acceptable accuracy. Thus, we may limit the solution space by only the equivalent inverse models that fit data with the accuracy close to that of the initial inverse model. For representing inversion results, we use three equivalent solutions instead of the only one: the “best” solution given by the regularization or other inversion technic and the extreme variations of this solution corresponding to the equivalent models with the minimum and the maximum volume of water. For demonstrating our approach, we use synthetic data sets and experimental data acquired in the framework of investigation of a hard rock aquifer in the Ireland (County Donegal).

Lithological and structural controls on the development of aquifer in basement rock dominated Tsalit- Ira River Basin, Tigray, Northern Ethiopia

Lithological and structural controls on the development of aquifers in low-grade Neoproterozoic rocks in Tsalit–Ira River Basin, northern Ethiopia are discussed in this paper. Metavolcanic and metasedimentary rocks represent the low grade basement rocks and are overlain by younger sedimentary and volcanic rocks. Fractures, joints, foliations, faults and shear zones are prominent and dominate secondary structures. Four areas, potential for groundwater are identified using structure and borehole data. They are moderate (Alluvial sediments), moderate to low (volcanics), low (sedimentary rocks) and low to weak potentiality aquifers (basement rocks). Based on borehole and structure data presence of multilayer aquifers, their thickness and productivity are suggested.Keywords: Groundwater, Aquifer, Structures, Basement, Tsalit-Ira Basin, Tigray, Ethiopia

Radium isotopes, radon and 210Pb in karstic waters: Example of the Lez system (South of France)

We present in this study the first data on Ra isotopes, 222Rn, and 210Pb in waters from the Lez karst system, one of the main ground-water resources in the South of France. The low Ra isotope activities of the Lez system waters (from 0.35 to 3.45mBq/L of 226Ra) were measured by gamma spectrometry using the method developed in our previous work. Our data reveal the coherent behavior of 226Ra in Lez spring waters, well correlated to other major and trace elements, like Cl, Na, K, Mg, Li, Rb and Ba. The (228Ra/226Ra) ratios are distinct between the Lez spring (0.60 to 0.72) and two neighboring springs (0.52 to 0.65), showing the spatial variability in karst systems. In spite of their small variations in the Lez spring, it was possible to trace different water components and mixing processes from Lower-Cretaceous, Upper-Jurassic and Middle Jurassic end-members, in agreement with previous studies based on major and trace elements. Data obtained on waters derived from the Upper-Jurassic karst reveal that their (228Ra/226Ra) ratios are not related to the Th/U ratio of the Jurassic limestone, but are rather influenced by the soil and alterite cover of the recharge area.222Rn activities in the Lez spring are relatively low (0.5 to 3.7Bq/L) compared to other karst regions. The highest 222Rn activities are found in diluted waters following heavy rainfall episodes, suggesting a subsurface origin of Rn. Soil and alterite samples that have much higher 226Ra activities (from 51 to 130Bq/kg), compared to those from the main aquifer rocks (from 2.9 to 16Bq/kg), are probably the main source of Rn, rather than the rocks of the karst itself. The study of several flood episodes reveals the correlation between Rn peak-values or total activity discharged at the spring with cumulative rainfall. Finally, 222Rn dissolved in water decays to 210Pb, and our data show that constraints on transfer times of underground waters can potentially be obtained from their coupled measurement.