Rock Aquifers Research Articles

Climate change effects on groundwater recharge and temperatures in Swiss alluvial aquifers

Climate change will have both quantitative and qualitative effects on groundwater resources. These impacts differ for aquifers in solid and unconsolidated rock, in urban or rural locations, and in the principal processes of groundwater recharge.Having knowledge about the intrinsic key parameters (aquifer geometries, storage properties, groundwater renewal rates, residence times, etc.), the principal groundwater recharge processes, and the temperature imprinting makes it possible to compare and forecast the sensitivity of individual aquifers to climate change.The sensitivity of future groundwater temperature development for selected climate projections was qualitatively investigated for representative Swiss unconsolidated rock groundwater resources in the Central Plateau as well as the Jura and Alpine region.For non-urban and rural areas, climate change is expected to have a strong overall impact on groundwater temperatures. In urban areas, however, direct anthropogenic influences are likely to dominate. Increased thermal subsurface use and waste heat from underground structures, as well as adaptation strategies to mitigate global warming, increase groundwater temperatures. Likewise, measurements for the city of Basel show that groundwater temperatures increased by an average of 3.0 ± 0.7 °C in the period from 1993 to 2016, and that they can exceed 18 °C, especially in densely urbanized areas. Similarly, regarding shallow aquifers with low groundwater saturated zone thicknesses, such as in Davos (Canton Grisons), groundwater temperatures will strongly be influenced by changes in groundwater recharge regimes. In contrast, groundwater temperature changes within deep aquifers with large groundwater saturated zone thicknesses, such as in Biel/Bienne (Canton Bern), or in some cases in aquifers with large distances from the land surface to the groundwater table and extended unsaturated zones, such as in Winterthur (Canton Zurich), are strongly attenuated and can only be expected over long time periods.In the context of the presented research we hypothesized that quantitative groundwater recharge and the associated temperature imprinting of aquifers is primarily determined by infiltrating surface waters (i.e. “river-fed aquifers”). We show that seasonal shifts in groundwater recharge processes could be an important factor affecting future groundwater temperatures. Moreover, the interaction with surface waters and increased groundwater recharge during high runoff periods are likely to strongly influence groundwater temperatures. Accordingly, for the “business as usual” climate change scenario and for the end of the century, a shift in precipitation and river flood events from summer to winter months could be accompanied by an increase in groundwater recharge in comparatively cool seasons, which would be accompanied by a tendency to “cool down” groundwater resources.

Modified Convergent Flow Tracing Method for Evaluating Advective Velocity and Effective Porosity in Fractured Rock Aquifers

This study presented the analysis of the modified convergent flow tracing method, which is a modified virtual solute transport approach to retrieve tracer masses from a pulse image (virtual) well to an extraction well. In the convergent flow tracer test, approximate analytical solutions were extended for the pulse image well using a single-well tracing method. This method transformed the drift-and-pumpback conditions of the single-well tracing method. The method requires a prior information of the effective porosity. Using sodium chloride as a tracer mass, the tracer data sampled through field-scale tests were used to obtain breakthrough curves. This modified method was different from the pre-existing single method because it considers both the ambient groundwater movement (the two classes of drifts) and the constant volumetric flow rate during the pumping phase. The method was applied to the tracer test at underground research tunnel for verifying the theory inductively derived from the single tracing method. Through field tests, the values of velocity and porosity were compared to the results of the drift-and-pumpback equations of the single-well test, and the several different equations related to breakthrough curves of the two-well tests conducted on a field scale.

Construction of lysimeters for researching the leaching of potentially toxic elements from building materials

By using recycled waste in construction, natural materials are being replaced, thus establishing a circular economy at the local level. An important aspect is also the conservation of natural resources. This is especially important in case of earthworks (embankments, backfills), which are large consumers of materials. Compared to natural aggregates and earth, geotechnical composites based on recycled materials can contain a higher total content of potentially toxic elements (heavy metals, chloride, sulphate, fluoride, organic pollutants etc.). The prerequisite for beneficial use of such composites is that the potentially toxic elements are immobilized in the composites, meaning that they are chemically inert. Potential environmental impacts, especially those associated with transfer of potentially toxic elements from new geotechnical composites into soil (aquifer respectively), are usually evaluated on laboratory scale, while their behaviour in real environment is usually poorly investigated. For this reason, there is a demand for the development of sensitive, reliable, and cost and time efficient monitoring tools for determining mass flows of potentially toxic elements from building materials, for example geotechnical composites, which are under the influence of various environmental factors. This paper presents the construction of field laboratory, based on a system of pan lysimeters. The lysimeters are used to collect leachate from geotechnical composites based on recycled materials. They are constructed in a way to be relatively low cost and at the same time large enough to representatively reflect the processes in geotechnical fills. Obtained data on the amount and quality of leachate can be used as a basis for the study of immobilization processes and for water balance. Moreover, this data will be used as input in the geochemical numerical model for the simulation of transport of potentially toxic elements released from geotechnical fills in different types of aquifers (alluvial aquifer with intergranular porosity, aquifer in consolidated rocks with fissure porosity).

Using Carbon-14 of dissolved organic carbon to determine groundwater ages and travel times in aquifers with low organic carbon

This study used dissolved organic carbon (DOC) carbon-14 (14C) to determine groundwater ages that were then used to calculate groundwater travel times in southern Nevada aquifers that have low organic content. These travel times are compared with the more standard dissolved inorganic (DIC) 14C method for determining groundwater ages and travel times. Groundwater travel times for aquifers in southern Nevada using DOC 14C are thousands of years shorter than DIC 14C travel times for groundwater flow outside of recharge areas along four of the five flow paths evaluated for this study. The DOC 14C travel times range from 2,300 to 2,900 years (yrs) as compared to DIC 14C travel times that range from 8,200 to 22,000 yrs (uncorrected ages) and 4,700 to 19,000 yrs (corrected ages). The DOC 14C groundwater travel times in carbonate-rock and volcanic-rock aquifers of southern Nevada are similar to travel times determined from: (1) hydrogeologic data; (2) observations of rapid high-level tritium transport at the Nevada National Security Site; and (3) 550,000-yr δ18O and δ13C global climate records for calcite precipitated in Devils Hole, Nevada at the end of one of the flow paths. DOC 14C travel time calculations need to account for fewer processes than DIC 14C for aquifers that contain little organic matter and do not have redox reactions. DOC 14C travel-times can be calculated directly from the DOC 14C data in these aquifers without corrections if dissolution of organic carbon and sorption and matrix diffusion of DOC 14C onto or into the aquifer matrix is minimal. Laboratory experiments showed that little organic carbon was being leached from aquifer rocks, sorption of organic carbon ranged from 4.3% sorbed in carbonate rocks to 0.5% sorbed in volcanic rocks, and matrix diffusion coefficients were slower in lower porosity carbonate rocks (1.7 × 10−7 cm2/s) than in higher porosity volcanic rocks (2.9 × 10−7 cm2/s). The lack of dissolution of organic carbon in study area aquifers is also supported by the decrease in DOC along flow paths and the DOC composition of groundwater changing little as groundwater flows from recharge areas into the adjacent valleys. In contrast, DIC 14C groundwater travel-time calculations must be corrected for complex chemical reactions and physical processes, including mineral/gas dissolution, mineral/gas precipitation/exsolution, cation exchange, and carbon isotopic exchange that can significantly change the amount of DIC 14C in groundwater along flow paths by processes other than radioactive decay. DIC 14C can also be affected by sorption and matrix diffusion, but these processes may, or may not, be captured in geochemical modeling of precipitation/dissolution and carbon isotopic exchange reactions. Corrected DIC 14C ages, therefore, represent maximum ages.

Spatial distribution of stygobitic crustacean harpacticoids at the boundaries of groundwater habitat types in Europe

The distribution patterns of stygobitic crustacean harpacticoids at the boundaries of three different groundwater habitat types in Europe were analysed through a GIS proximity analysis and fitted to exponential models. The results showed that the highest frequency of occurrences was recorded in aquifers in consolidated rocks, followed by the aquifers in unconsolidated sediments and, finally, by the practically non-aquiferous rocks. The majority of the stygobitic harpacticoid species were not able to disperse across the boundaries between two adjacent habitats, with 66% of the species occurring in a single habitat type. The species were not evenly distributed, and 35–69% of them occurred from 2 to 6 km to the boundaries, depending on the adjacent habitat types. The distribution patterns were shaped by features extrinsic to the species, such as the hydrogeological properties of the aquifers, and by species’ intrinsic characteristics such as the preference for a given habitat type and dispersal abilities. Most boundaries between adjacent habitat types resulted to be “breaches”, that is transmissive borders for stygobitic harpacticoids, while others were “impermeable walls”, that is absorptive borders. Our results suggest that conservation measures of groundwater harpacticoids should consider how species are distributed within the different groundwater habitat types and at their boundaries to ensure the preservation of species metapopulations within habitat patches and beyond them.

Radium in groundwater hosted in porous aquifers: estimation of retardation factor and recoil rate constant by using NAPLs

A new method for estimating retardation factor and recoil constant of radium isotopes in groundwater hosted in porous aquifers is described. The method is based on the evidence that alpha-recoiled radium ions, supplied by thorium parent atoms which occur in phases immersed in NAPL (Non-Aqueous Phase Liquids), are not adsorbed on solid phases. Experimental evidence is given that manganese dioxide, zeolite 4A, natural clay, monazite and weathered volcanic rock, all phases normally adsorbing radium from aqueous solutions, when immersed in NAPL adsorb negligible amounts of radium. This allows using experimental data on rock samples, representative of porous aquifers, for estimating Ra retardation factor and its alpha recoil constant in groundwater, without using Rn data as a comparison term. Unlike estimation of retardation factor between the “NAPL method” and the method based on comparison with radon depends on the different process of entry from aquifer rock into groundwater for radon and radium. Precise estimates of retardation factor and recoil constants of radium allow to apply equations ruling the temporal evolution of radium isotopes in groundwater and to determine its age. Implications, useful for measuring the contamination age of soils by NAPL fluids, are described as well.

Groundwater–surface water interactions in an ephemeral savanna catchment, Kruger National Park

The semi-arid conditions in savanna landscapes ensure that ephemeral drainage dominates the hydrological network in these dryland systems. Quantification of their hydrological processes is important to inform ecosystem understanding and future conservation efforts under a changing climate, and to provide guidance for restoration. By combining in situ hydrometric observations, hydrochemistry, remote sensing and a soil water balance model, we characterise the groundwater–surface water interactions in ephemeral low-order catchments of the granitoid regions of the southern Kruger National Park (KNP). Streams at the lowest orders are augmented by lateral interflows from the catena, although the second- and third-order stream reaches are conduits for groundwater recharge to the fractured rock aquifer; the soils of the crests and foot-slopes also show preferential flow, and are truly recharge soils, whilst the duplex soils of the midslopes clearly show their responsive nature to a low soil moisture deficit in the shallow horizons. Actual evaporation (aET) differed between catena elements with surprisingly little variation at third-order hillslopes, with the greatest overall aET at the first order. Meanwhile, soil water balances demonstrated a significant variation in storage of the riparian zones as a result of interflow from upslope and aET losses. Furthermore, data support broader-scale observations that groundwater recharge through the vadose zone to the fractured rock aquifer is dependent upon threshold antecedent precipitation conditions. Moderate precipitation events (5 mm/day – 35 mm/day) over a 2–3 week period initiate groundwater responses with a 2–3 month lag, whilst intense precipitation events (100 mm/day) are expressed within 2–3 weeks.Conservation implications: Understanding the lateral connectivity of terrestrial ecosystems to the ephemeral drainage network expressed via hydrological processes in these savanna landscapes is important to infer potential impacts of climate variability on the continued conservation of these ecosystems, both within and external to protected areas.

Quantification of groundwater storage heterogeneity in weathered/fractured basement rock aquifers using electrical resistivity tomography: Sensitivity and uncertainty associated with petrophysical modelling

Quantifying groundwater storage in weathered/fractured basement rock aquifers can be challenging owing to both their high degree of heterogeneity and their overall low storage capacity. Therefore, in these aquifers, the use of direct borehole hydraulic data is usually insufficient. Here we assessed the popular method of electrical resistivity tomography (ERT), combined with borehole data and including associated uncertainties, to resolve the spatial variability of groundwater storage properties at high resolution within a fractured mica schist aquifer in Ireland. Porosity distributions across both the saturated and unsaturated zones were calculated from two-dimensional (2D) ERT resistivities using two standard petrophysical models, Archie and Waxman & Smits (WS), the latter accounting for the influence of clay minerals on resistivity data. Our results demonstrated the importance of the hydrogeological conceptual constraints provided by ERT when parametrizing the 2D petrophysical models from borehole point data. They also confirmed the importance of accounting for clay minerals (the products of bedrock weathering processes) in the WS model, whereas predictions from Archie’s model produced unrealistically high porosity values of over an order of magnitude higher than the WS model. The WS model predicted porosities decreasing exponentially with depth, with values ranging from a few % in the shallowest, most-weathered part of the bedrock (upper 5 m on average) and deep fractured zones (to about 20 m deep), to <1% in the underlying fissured aquifer, and possibly down another order of magnitude in the deep massive bedrock. WS-derived porosities were in agreement with independent vertical water content profiles derived from magnetic resonance sounding (MRS), as well as point storativity values estimated from borehole hydraulic testing at the study site, with particularly good matches in the upper weathered/fractured bedrock and deeply weathered/fractured zones associated with regional faults. Detailed comparison suggested that WS provides an upper-bound estimate of groundwater storage in this environment. In the deep massive, un-weathered, and poorly fractured bedrock, however, discrepancies between groundwater storage estimate obtained from the three methods (ERT, MRS, and hydraulic) prevented reliable storage quantification, owing to the methods’ inherent technical limitations in such low porosity rocks. Our results demonstrated the suitability of resistivity tomography to quantify groundwater storage heterogeneity in weathered/fractured basement rock aquifers at high resolution and with reasonable overall uncertainty given the relative high uncertainties in petrophysical parameters at the kilometric scale. The results are promising for better characterization of groundwater storage variations in these hydrogeological systems, which are crucial to predict their response to climate variability and human exploitation.

Geogenic sources and chemical controls on fluoride release to groundwater in the Independence Basin, Mexico

High fluoride (F−) concentrations in groundwater are a recognized environmental health concern, and over 200 million people around the world routinely drink well water with F− concentrations that exceed safety guidelines. Groundwater in the Independence Basin of Central Mexico reaches F− concentrations of 15.5 mg L−1, which are over an order of magnitude greater than the World Health Organization limit of 1.5 mg L−1, but knowledge of sources and geochemical conditions responsible for releasing F− into solution is preliminary. The objectives of this work were to define F− hosts within a range of Independence Basin aquifer rock types and quantify chemical controls on F− release into solution. Solid-phase concentrations of F− in well-drill cuttings display no apparent depth dependence but are greatest within andesite, near-surface uncemented alluvium, and well-cemented Paleocene conglomerate samples, and they are least within volcanic glass, rhyolite, and ash matrix samples. Chemical extractions showed that large amounts of F− are bound with metal oxides/oxyhydroxides in all samples. Batch experiments examining F− release from aquifer materials under evolving groundwater conditions (i.e. increasing pH and specific conductance) revealed that F− may be released into solution with elevated pH but only slightly mobilized with increasing specific conductance. Therefore, declining aquifer water levels tapping into older, more mineralized groundwater (with high conductivity) in the Independence Basin may not have as great of an effect on F− release to solution than does evolving and increasing groundwater pH. Accordingly, the degree of rock weathering and pH of solution play the greatest roles in regulating the release of F− to groundwater, and results from this study may be used to better predict where F− groundwater contamination is most probable in aquifers around the world.

Discrete fracture network characterization using multiple, high-resolution borehole methods in a crystalline rock aquifer in tropical Sao Paulo city, Brazil

The geological scenario of thick weathering materials over a fresh bedrock is characteristic of tropical climate regions. The application of the Discrete Fracture Network (DFN) methodology relying on multiple, high resolution measurements methods on continuous cores and/or boreholes in such geological conditions, particularly in a contaminated area, is unprecedent. A total of 977 structures were described, between rock cores, geophysical profiling and outcrops, with emphasis on brittle structures due to their importance for groundwater flow. Five fracture sets were characterized, related to lithology. The correlation of these fracture sets with large structures from regional studies indicated the representativeness of this detailed survey. Finally, it is expected that the model presented here can be applied in the management of other contaminated areas of similar geological contexts, particularly in Brazil, where the discussions regarding contaminated fractured aquifers are still quite recent.

Characterisation of groundwater dissolved organic matter using LC[sbnd]OCD: Implications for water treatment

The polarity and molecular weight of dissolved organic matter (DOM) is an important factor determining the treatability of water for domestic supply. DOM in surface water and groundwater is comprised of a mixture of carbon with varying molecular weight ranges, with its composition driven by DOM sources and processing. Here, we present the largest dataset of chromatographic DOM in surface and groundwater samples (n = 246) using liquid chromatography organic carbon detection (LCOCD). Our data represents four categories (surface water, hyporheic zone water, local groundwater, and regional groundwater) from five different sites across Australia. In all environments, high molecular weight hydrophilic DOM such as biopolymers (BP) and humic substances (HS) are present in surface waters and are processed out of groundwater as it moves from surface water and hyporheic zones into shallow local groundwater and deeper regional groundwaters. This results in a higher percentage of low molecular weight neutrals (LMWN) and hydrophobic organic carbon (HOC) in deeper regional groundwaters. Our findings indicate that the presence of sedimentary organic matter strongly influence the character of surface and groundwater DOM, resulting in groundwater with higher HS aromaticity and molecular weight, and reduced percentage of LMWNs. We also observe highly variable hydrophilic / HOC ratios in groundwater at all sites, with 9.60% and 25.64% of samples at sites containing sedimentary peat layers and non-sedimentary peat sites respectively containing only hydrophilic dissolved organic carbon (DOC). We identify average hydrophilic / HOC ratios of 4.35 ± 3.76 and 7.53 ± 5.32 at sites containing sedimentary peat layers and non-sedimentary peat sites respectively where both hydrophilic DOC and HOC are present. Overall our results suggest that fractured rock and alluvial aquifers in sedimentary organic carbon poor environments may contain DOC which is better suited to ozonation, biologically activated carbon filtration powdered activated carbon, suspended ion exchange treatment or magnetic ion exchange resin since DOC is more hydrophilic and of lower molecular weight and lower aromaticity. Aquifers located near sedimentary organic matter layers may benefit from pre-treatment by coagulation/flocculation, sedimentation and sand filtration which have high removal efficiency for high molecular weight and polar compounds.

Distinguishing Groundwater Flow Paths in Fractured Rock Aquifers Formed Under Tectonic Stress Using Geophysical Techniques: Cankurtaran Basin, Denizli, Turkey

Gokpinar spring is one of the most important drinking water resources of Denizli city (Turkey), covering more than one third of the water need of the municipality. In this paper, we present a combination of geophysical methods in order to define the groundwater flow paths in Gokpinar spring region. The spring of Gokpinar is a result of the Fault-fracture network formed during the tectonic events which took place in the study area. This fault and fracture system present in the Gokpinar spring zone are characterized by the Cankurtaran fault in the east and Babadag fault in the south. To highlight the main directions of the groundwater flows feeding Gokpinar spring, an electrical resistivity tomography (ERT) survey was carried out in the study area. The results obtained from this survey have been confirmed by a frequency domain electromagnetic (FEM) survey carried out along four profiles in addition to four ground penetrating radar profiles (GPR) profiles. The comparison of the two auxiliary methods with the ERT profiles allowed a better understanding of the groundwater movements. The ERT data was collected along six profiles corresponding to Wenner–Schlumberger array and located predominantly in the southern and eastern parts of the spring surrounding area. In order to confirm the hypothesis from the interpretation of the ERT profiles, two simplified different scenarios were numerically and experimentally considered. The results of the combined methods have ultimately led to define the main direction of groundwater flows feeding the Gokpinar spring, which is related to four factors: The Fault-Fracture network, karstic features, the topography, and deep groundwater.

Factors controlling the distribution of radon (222Rn) in groundwater of a tropical mountainous river basin in southwest India

Studies on occurrence of radon in the environment are receiving growing attention worldwide due to its adverse impact on human health. Despite that, the dissolved radon in water is found to be a useful tracer in many hydrogeological studies. Although, several studies focused on the occurrence of high 222Rn in groundwater, the processes responsible for its variation is still not well understood. Hence, an attempt has been made in the present study to elucidate the underlying factors influencing the abundance 222Rn in hard rock (gneissic) aquifers of Karamana River Basin, southwest India. 222Rn in groundwater was analyzed in 71 dug wells during the pre-monsoon period of 2017.A large variability in 222Rn activities (170–68,350 Bq/m3) was noticed in groundwater and high activities were mainly seen in the khondalite formation. No significant dependencies between 222Rn activity and depth to water table, groundwater temperature and electrical conductivity were observed. However, majority of the presence of high 222Rn activity in groundwater matches with the location of lineaments. Furthermore, radium content in the host rock, degree of weathering and fracturing and the emanation coefficient of the rock were found to have an important bearing on the occurrence of radon in groundwater. The underlying factors influencing the abundance of radon in hard rock aquifers were also conceptualized. Thus, the study highlights the usefulness of 222Rn as a potential tool in delineating the macro-structural features like fractures/lineaments that are significant repositories of groundwater, which could be explored for groundwater development in hard rock terrains.

Groundwater oxygen anomaly related to the 2016 Kumamoto earthquake in Southwest Japan.

Here, we report the groundwater oxygen isotope anomalies caused by the 2016 Kumamoto earthquake (MJMA7.3) that occurred in Southwest Japan on April 16, 2016. One hundred and seventeen groundwater samples were collected from a deep well located 3 km to the southeast of the epicenter in Mifune Town, Kumamoto Prefecture; they were drinking water packed in PET bottles and distributed in the area between April 2015 and March 2018. Further, the oxygen and hydrogen isotopes were evaluated via cavity ring-down spectroscopy without performing any pretreatment. An anomalous increase was observed with respect to the δ18O value (up to 0.51‰) soon after the earthquake along with a precursory increase of 0.38‰ in January 2016 before the earthquake. During these periods, there was no noticeable change in the hydrogen isotopic ratios. Rapid crustal deformation related to the earthquake may have enhanced the microfracturing of the aquifer rocks and the production of new surfaces, inducing δ18O enrichment via oxygen isotopic exchange between rock and porewater without changing δ2H.

Conservation of oxygen and hydrogen seasonal isotopic signals in meteoric precipitation in groundwater: An experimental tank study of the effects of land cover in a summer monsoon climate

δ18O and δD values in meteoric groundwaters reflect those in their source precipitation, which normally displays seasonal ranges of several to many permil. Normally there are substantial reductions in the groundwater isotopic ranges due to mixing in any vegetation, soil cover and the aquifer itself, plus the distortions that can be introduced by evaporation. Nevertheless, in carbonate karst regions (and others) many spring waters are found to preserve significant proportions of these seasonal signals. They are of current interest because they may also be detected in calcite speleothems precipitated from groundwater in caves, in calcretes and calcareous nodules in soils, etc. thus permitting detailed paleoclimate reconstructions.This paper presents some baseline data on reduction of isotope seasonal signals in groundwater that are pertinent to such speleothem studies. They are from artificial tank experiments at Shawan Karst Test Site, Guizhou, China. The climate is humid subtropical with mean annual precipitation of 1340 mm, >80% falling between May and October. The concrete tanks measure 20 × 5 m, 3 m deep each, point-drained at one end to simulate a spring. They are filled with 2.5 m of local limestone quarry gravel, creating carbonate aquifers with primary porosities ∼ 50%. A first tank is left bare, simulating the rocky desertification found in parts of the region. The other tanks are topped with 0.5 m of local, clay-rich residual soil, one left bare, the other three sown with rainy season corn, permanent grass and permanent shrubs respectively. Measurements cover the three climatic years, November 2015-November 2018. > 90% of the rainfall events were sampled, and the drains every ten days.δ18O and δD in the rainfall displayed strong and regular sinusoidal oscillations with the successive seasons. In the bare rock tank these were reduced (damped) by 56~74% in the different years, with phase (time) lags of 127~134 days at the drain. In the soil-topped tanks damping ranged from 61% to 93% and the time lags from 164 to 202 days: differences between them are not statistically significant but all do differ significantly from the bare rock. In all cases, the responses of the two isotopes were similar in direction and magnitude. The 0.5 m soil cover had the most important effect. The bare rock aquifer conserved the most information. Losses were similar in the four soil-topped tanks, responding to stronger evaporation and obstruction of flow in the soil. These findings are briefly compared to seasonal isotope variations reported in speleothem drip waters in limestone caves in China and elsewhere in the world.

Monsoon impact on groundwater chemistry and geochemical processes in the shallow hard rock aquifer

Impact of monsoon recharge on groundwater chemistry and geochemical processes was evaluated using geochemical methods in the shallow hard-rock aquifer, southern India. Groundwater samples were collected from Salem city and its outskirts during pre-monsoon (PRM) and post-monsoon (PM) seasons and analysed for major and minor ions. Results suggest that during PRM, the average concentration of TDS, major ions and electrical conductivity (EC) in groundwater are higher than the PM season except for Na+ and HCO3–. The major water types also varied with seasons (PRM: NaCl > CaMgCl > CaHCO3; PM: CaHCO3 = NaHCO3 = NaCl). Pearson correlation analysis indicates that Cl− and SO42− show a strong positive correlation with EC, TDS, TH and major cations during PRM season whereas HCO3– and NO3– have a strong positive correlation with most of the ions during PM season. Before monsoon, the water chemistry is governed by the weathering of carbonate and silicate minerals, reverse ion exchange and evaporation processes, which resulted in high EC, TDS, TH and major ions in the groundwater. After the monsoon, the water chemistry is regulated by the mineral weathering, cation exchange and dilution processes. Geochemical modelling studies indicate that groundwater is saturated and oversaturated with carbonate minerals and undersaturated with sulphate and chloride minerals. During monsoon, the recharging water flushed the weathered layer and dissolved the soil CO2 in the vadose zone, which subsequently enhanced the concentration of Na+ and HCO3– in the aquifer. Further, the high concentrations of Cl−, SO42- and NO3– imply that the aquifer is polluted by surface contamination sources. After the monsoon, NO3– implies that monsoon recharge facilitated the pollutant movement from surface to the aquifer. Hence, a proper aquifer management plan is required to protect this aquifer and to provide clean and safe drinking water to the local community.

Radon Concentrations in Raw Water and Treated Water Used for Bottled Water in South Korea

Radon concentrations in the raw water and treated water used for 59 brands of bottled water produced in South Korea were analysed. The radon levels in 59 raw water samples ranged from 3.7 to 476.8 Bq/L, with a geometric mean of 49.0 Bq/L. The mean radon levels in raw water samples were high in Jurassic granite aquifers and low in volcanic rock aquifers. However, the maximum radon levels were observed in metamorphic rock aquifers. The concentrations in 55 treated water samples ranged from 0.1 to 239.4 Bq/L, with a geometric mean of 7.7 Bq/L. In treated water, radon levels decreased by 16.0–98.9% (average, 74.9%) due mainly to storage in water tanks and treatment with granular activated carbon (GAC) filters. The radon levels in raw water and treated water samples exceeded the US EPA alternative maximum contaminant level (AMCL) of 148 Bq/L by 16.9% and 1.8%, respectively. Considering the radon reduction rate, it is anticipated that the radon concentrations in bottled water in stores will not exceed 148 Bq/L because it takes about 1–2 weeks for treated water to reach the customer as bottled water.

Assessment of groundwater quality using water quality index (WQI): A case study of a hard rock terrain in Sri Lanka

Chronic Kidney Disease of uncertain etiology (CKDu) is a widespread health issue in rural dry zone regions in Sri Lanka. Monaragala region, located in eastern Sri Lanka is one of the hardest hit areas with CKDu. In order to investigate the possible relationship between the incidence of CKDu and drinking water quality, 99 groundwater samples from deep boreholes and shallow wells in hard rock aquifers in the Monaragala region, were collected and analysed for major cations and anions, and some selected trace element contents. The results revealed that over 65% of the groundwater samples from Monaragala area were alkaline. The anions in groundwater varied as HCO3− > Cl− > SO42− > F− while cations varied in the order of Na > Ca > Mg > K. The Majority of the samples (75%) belong to the Ca2+-Mg2+- HCO3− type. Among the studied parameters, electrical conductivity, chloride, sulphate, hardness, fluoride exceeded the WHO recommended values for drinking water in most cases. For instance, 76% of wells in the study area showed fluoride levels higher than the recommended levels (0.5 mg/L) for Sri Lanka. The higher ion contents in groundwater were mainly due to dissolution of aquifer minerals and a higher rate of evaporation. The calculation of Water Quality Index (WQI) indicated that over 50% of groundwater samples of the study area are poor in quality. The higher values of WQI also overlap with high prevalence areas of CKDu. This work revealed that groundwater quality has a direct effect on the etiology of CKDu in the region.

Análise de Favorabilidade para Exploração de Água Subterrânea em Aquífero Costeiro, Estado do Maranhão

Esta pesquisa aplica a análise de favorabilidade para a exploração de águas subterrâneas, visando à diminuição do risco exploratório em função, principalmente, das características da rocha reservatório em região costeira. O estudo foi elaborado com dados de litologia, vazão, nível estático e nível dinâmico de poços instalados próximos à cidade de São Luís / MA em área portuária / industrial. A área alvo foi escolhida devido à complexidade geológica e a proximidade com o mar, que acarretam baixa previsibilidade no comportamento hidrodinâmico antes dos projetos de perfuração, além de ser demandante de altas vazões de água subterrânea. As áreas com valores de capacidade específica superiores a 1,0 m3/h/m foram consideradas produtivas. Os resultados encontrados limitaram três principais áreas (norte, centro-leste e sudoeste) com maiores potenciais de exploração em função dos dados disponíveis de descrição litológica e vazão. Além disso, o maior valor de contraste encontrado na pesquisa (4,98) esteve associado à variável porcentagem de arenitos, o que demonstra ser esta variável um fator importante para o potencial exploratório do aquífero nesta área.

Hydrogeological framework of the volcanic aquifers and groundwater quality in Dangila Town and the surrounding area, Northwest Ethiopia

Volcanic aquifers are sources of groundwater for both urban and rural areas. Their occurrence in geological formations and water quality are the main issues for sustainable utilisation. Dangila town and its surrounding area, northwest Ethiopia, is assessed for hydrogeological framework and groundwater quality based on well and hydrochemical data. The study showed that the area has a multi-aquifer system: an unconfined perched aquifer at shallow depth and; semi-confined and confined aquifers at greater depth in Quaternary basalts.The aquifer has five groundwater facies: Ca-HCO3, Ca-Mg-HCO3, Ca-Na-HCO3, Na- Ca-HCO3 and Na-HCO3. The Ca-HCO3 groundwater types are dominant in the shallow unconfined aquifer system, and the Na- Ca-HCO3 and Na-HCO3 types are dominant in deep aquifer systems. Mixing of waters from shallow and deep aquifer systems is minimal and possible only through interconnected fractures. Groundwater storage and flow is controlled by intensity and interconnection of fractures. Hydraulic conductivity is higher for fracture dominant aquifers than weathered rock aquifers. The groundwater chemistry is mainly controlled by rock weathering and cation exchange. Groundwater quality assessment shows that water from both aquifer sources is potable. Based on sodium adsorption ratio (SAR) and residual sodium carbonate (RSC) values, all groundwater schemes are in the excellent quality class and can be used for irrigation without any problem. However, high Na+ in borehole samples restrict the deep groundwater suitability for irrigation use without adjustment. The combined results of the study are used to construct a hydrogeological conceptual model of volcanic aquifers, which can be used to manage the groundwater resource for sustainable development. This study would be helpful for water resources management in other similar geological settings.