Uranium Concentrations In Groundwater Research Articles

Hydrogeochemical Characteristics of Uranium and Radon in Groundwater from the Goesan Area of the Ogcheon Metamorphic Belt (OMB), Korea

Uranium and radon concentrations in groundwater from the Goesan area of the Ogcheon Metamorphic Belt (OMB), central Korea, whose bedrock is known to contain the highest uranium levels in Korea, were analyzed from 200 wells. We also measured the uranium concentrations in the bedrock near the investigated wells to infer a relationship between the bedrock geology and the groundwater. The five geologic bedrock units in the Goesan area consist of Cretaceous granite (Kgr), Jurassic granite (Jgr) and three types of metasedimentary rocks (og1, og2, and og3). The percentages of the groundwater samples over 30 μg/L (maximum contaminant level, MCL of US EPA) were 2.0% of the 200 groundwater samples; 12% of Kgr and 1.8% of Jgr exceeded the MCL, respectively. Overall, 16.5% of the 200 groundwater samples exceeded 148 Bq/L (alternative maximum contaminant level, AMCL of US EPA); 60.0% of Kgr and 25.0% of Jgr exceeded the AMCL, but only 0% of og1, 7.9% of og2, and 2.6% of og3 exceeded the value, respectively. No direct correlation was found between uranium concentration and radon concentration in water samples. Radon has a slightly linear correlation with Na (0.31), Mg (−0.30), and F (0.36). However, uranium behavior in groundwater was independent of other components. Based on thermodynamic calculation, uranium chemical speciation was dominated by carbonate complexes, namely the Ca2UO2(CO3)3(aq) and CaUO2(CO3)32− species. Although uraniferous mineral phases designated as saturation indices were greatly undersaturated, uranium hydroxides such as schoepite, UO2(OH)2 and U(OH)3 became possible phases. Uranium-containing bedrock in OMB did not significantly affect radioactive levels in the groundwater, possibly due to adsorption effects related to organic matter and geochemical reduction. Nevertheless, oxidation prevention of uranium-containing bedrock needs to be systematically managed for monitoring the possible migration of uranium into groundwater.

Soil and Aquifer Properties Combine as Predictors of Groundwater Uranium Concentrations within the Central Valley, California.

With the increasing global need for groundwater resources to fulfill domestic, agricultural, and industrial demands, we face the threat of increasing concentrations of naturally occurring contaminants in water sources and a consequential need to improve our predictive capacity. Here, we combine machine learning and geochemical modeling to reveal the biogeochemical controls on regional groundwater uranium contamination within the Central Valley, California. We use 23 environmental parameters from a statewide groundwater geochemical database and publicly available maps of soil and aquifer physicochemical properties to predict groundwater uranium concentrations by random forest regression. We find that groundwater calcium, nitrate, and sulfate concentrations, soil pH, and clay content (weighted average between 0 and 2 m depths) are the most important predictors of groundwater uranium concentrations. By pairing multivariate partial dependence and accumulated local effect plots with modeled aqueous uranium speciation and surface complexation outputs, we show that regional groundwater uranium exceedances of drinking water standards, 30 μg L-1, are dependent on the formation of uranyl-calcium-carbonato species. The geochemical conditions leading to ternary uranyl complexes within the aquifer are, in part, created by infiltration through the vadose zone, illustrating the critical dependence of groundwater quality on recharge conditions.

Anomalous Concentration of Uranium in Groundwater in Parts of Salem District, Central Tamil Nadu, India

Anomalous concentration of Uranium in groundwater has been identified around Virakkal, Veerapanpalayam, Pakkanadu, Erithottam, Kammampatti, Kumarappalyam, Idappadiand Moolakkadu areas in parts of Salem district, Tamil Nadu. In this study, an area of 970 sq. km from Mettur in the north to Kumarapalayam in the south parallel to the Koratti shear zone has been examined for uranium content in groundwater. Systematic sampling of groundwater (n=78) from bore well, open well and hand pump have been collected. The samples were analysed for uranium concentration using LED Fluorimeter. Analysis resulted higher concentration of uranium along the southern extension of Koratti Shear Zone where the emplacement of younger granites, syenite and carbonatites has been reported. These lithounits might have played a vital role in the contribution of uranium to the groundwater. Based on the result, two areas have been identified such as North Block and South Block for detailed investigation.58 systematic samples from North block and 52 samples from South block have been collected and analysed. Uranium values assayed in these areas are many times higher than the prescribed limit of World Health organisation and Atomic Energy Regulatory Board of 30ppb and 60ppb respectively. In northern block, among 58 samples 18 samples were assayed higher than 30ppb in which the samples from Veerappanpalayam assayed upto 545.81 ppb. Apart from Veerappanpalayam, many areas such as Mosakumarapalayam (273.90), Arasiramani (250.49ppb), Vellarivalli (131.32ppb), Kodarapalayam (106.52ppb), Savuthanur (174.79ppb), Veerapanpalayam-2 (373.43ppb) and Kotamppalayam (100ppb) were assayed more than 100ppb. Similarly, in the southern block, 52 samples were assayed in which 15 samples were higher than the prescribed limit in which Kuppampatti analyzed 402.29ppb, Virakkal and Thannikuttampatti assayed more than 100ppb. Among the total samples (n=188), 28% of samples were falling under non-potable category. The Present study has spatially brought to light significant areas where groundwater enriched by uranium concentration. It is also provided indirect evidences for uranium exploration in the study area.

Radiological safety of groundwater around a uranium mine in Namibia

Uranium mining activities produce the main element used in nuclear energy production. However, it can also negatively affect the environment including groundwater by release of residues or effluent containing radioactive elements. The study investigated the concentration and radiological hazard of uranium in groundwater and seepage water from the tailings of a uranium mine in Namibia. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was used to assess the concentration of uranium in the groundwater and seepage water and the radiological hazards were determined. The radiological hazard indices Radium equivalent activity (Raeq), Absorbed dose (D), Annual Effective Dose equivalent (AEDE), External hazard index (Hex) and Internal hazard index (Hin) were determined and compared to limits recommended by United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). The calculated average value of D and Hin of groundwater is 108.11nGyh−1 and 1.26, respectively and are above the UNSCEAR values (55 nGyh−1 and 1). Further, the average values of Raeq, AEDE and Hex were below the recommended values. The isotopic ratio of uranium radionuclides in groundwater indicates that the uranium in the sampled groundwater is below 1 suggesting it is not natural uranium present but a possible contamination from the mine seepage. The radiological hazard parameters of the seepage water were above the recommended values and thus pose a radiation risk to human and environment.

Assessment of arsenic and uranium co-occurrences in groundwater of central Gangetic Plain, Uttar Pradesh, India

Arsenic and uranium in the aquatic environment are recognized as a major catastrophic problem worldwide and have natural as well as human-made sources such as mining, industry and agriculture. The severity of this problem is further accelerated by in-situ physio-chemical factors in the fluvial environment which enhances the concentration of arsenic and uranium in groundwater that feeds millions of people in Central Gangetic Plain in India. This study aims to establish a better understanding of the processes responsible for the co-occurrence of arsenic and uranium along with the factors controlling their solubility and mobility in the groundwater of central Gangetic plain. This study is an attempt to bring out the (a) the spatial distribution pattern of arsenic and uranium, (b) insight into the hydrogeochemical characteristics of aquifers that are controlling their co-occurrence and provides (c) information of their source which are validated by statistical tools. Silicate weathering controls U mobilization and distribution whereas carbonate dissolution and ion exchange process controls As in groundwater. The land use and land cover pattern of the North-eastern (NE) part of the study area is agriculture dominated and is composed of Holocene older alluvium. However, the South and South-western areas which are closer to the river are formed by the deposition of river born newer alluvial. Newer alluvium in the SW part has unoxidized organic-rich clay that enhances arsenic mobilization by reductive dissolution of Fe-oxyhydroxide. In the NE region, the abundance of fertilizers in the subsurface oxidizing environment augments the solubility and mobility of uranium.

Studies on Uranium Hydrogeochemistry in Kamalavathi River Basin, Gulbarga and Yadgir Districts, Karnataka

Uranium is a radioactive element and its presence in ground water, used for human consumption, forms a serious societal issue. The present study, deals with the occurrence and geochemistry of uranium in the aquifers underlying parts of Gulbarga and Yadigir districts of Karnataka State. The study area is confined to Kamalavathi river basin, where groundwater is the major source for domestic use. High uranium (>30 ppb) is found in the north eastern part of the study area. The present study deals with the geochemistry of uranium in ground water of Kamalavathi river basin. The data was subjected to statistical analysis to understand the inter relationship between various elements. The 2D and 3D maps of groundwater flow directions and uranium concentrations were used to understand the variation of uranium concentration along the groundwater flow. Detailed uranium geochemistry and Eh-pH diagrams were used to understand the lithological controls on occurrence of uranium in groundwater.

Using Age Tracers and Decadal Sampling to Discern Trends in Nitrate, Arsenic, and Uranium in Groundwater Beneath Irrigated Cropland.

Repeat sampling and age tracers were used to examine trends in nitrate, arsenic, and uranium concentrations in groundwater beneath irrigated cropland. Much higher nitrate concentrations in shallow modern groundwater were observed at both the Columbia Plateau and High Plains sites (median values of 10.2 and 15.4 mg/L as N, respectively) than in groundwater that recharged prior to the onset of intensive irrigation (median values of <1 and <4 mg/L as N, respectively). Repeat sampling of these well networks indicates that high nitrate concentrations in modern, shallow groundwater have been sustained for decades, posing a future risk to older, deeper groundwater used for drinking water. In fact, nitrate concentrations in older modern water (30-60 years since recharge) at the High Plains site have increased in the past decade. Groundwater irrigated areas in the Columbia Plateau tend to have higher nitrate concentrations in groundwater than surface water irrigated areas,suggesting repeated dissolution of land applied fertilizer during recirculation may be an important factorcausing high nitrate concentrationsin groundwater. Mobilization of uranium and arsenic by land surface activities is suggested by the higher concentrations of these constituents in modern, shallow groundwater than in older, deeper groundwater at the Columbia Plateau site. Bicarbonate concentrations in modern groundwater are positively correlated with uranium (r = 0.72, p < 0.01), suggesting bicarbonate may mobilize uranium in this system. A positive correlation between arsenic and phosphorus concentrations in modern groundwater (r = 0.55, p < 0.01) suggests that phosphate from fertilizer outcompetes arsenate for sorption sites, mobilizing sorbed arsenic derived from past pesticide use or other sources.

Anthropogenic and geologic causes of anomalously high uranium concentrations in groundwater used for drinking water supply in the southeastern San Joaquin Valley, CA

Concentrations of uranium (U) >30 µg/L in groundwater are relatively uncommon in drinking water in the United States but can be of concern in those areas where complex interactions of aquifer materials and anthropogenic alterations of the natural flow regime mobilize U. High concentrations (>30 µg/L) of U in the southeastern San Joaquin Valley, California, USA, have been detected in 24 percent of 257 domestic, irrigation, and public-supply wells sampled across an approximately 110,000 km2 area. In this study we evaluated mechanisms for mobilization of U in the San Joaquin Valley proposed in previous studies, confirming mobilization by HCO3 and refuting mobilization by NO3 and we refined our understanding of the geologic sources of U to the scale of individual alluvial fans. The location of high concentrations depends on the interactions of geological U sources from fluvial fans that originate in the Sierra Nevada to the east and seepage of irrigation water that contains high concentrations of HCO3 that leaches U from the sediments. In addition, interactions with PO4 from fertilized irrigated fields may sequester U in the aquifer. Principal component analysis of the data demonstrates that HCO3 and ions associated with high total dissolved solids in the aquifer and the percentage of agriculture near the well sampled are associated with high U concentrations. Nitrate concentrations do not appear to control release of U to the aquifer. Age dating of the groundwater and generally increasing U concentrations of the past 25 years in resampled wells where irrigation is prevalent suggests that high U concentrations are associated with younger water, indicating that irrigation of fields over the past 100 years has significantly contributed to increasing concentrations and mobilizing U. In some places, the groundwater is supersaturated with uranyl-containing minerals, as would be expected in roll front deposits. In general, the interaction of natural geological sources high in U, the anthropogenically driven addition of HCO3 and possibly phosphate fertilizer, control the location and concentration of U in each individual fluvial fan, but the addition of nitrate in fertilizer does not appear control the location of high U. These geochemical interactions are complex but can be used to determine controls on anomalously high U in alluvial aquifers.

Radon and uranium concentration in ground water of nineveh plain region in iraq

The track registration technique with a CR-39 detector was used to measure radon concentrations, and uranium contents in ground water samples from the Nineveh plain region wells. Samples were selected from 20 locations for measurements. This research aimed to assess radiological risks from uranium ingestion, and measure annual effective dose AED resulting from the intake of radon in the ingested water. Radon concentrations in these water samples were found to vary from 0.362 to 1.485 BqL−1, which were below the safety recommended limits 4 to 40 BqL−1 based on the Scientific Committee of United Nations on Atomic Radiation Effects. AED was found to vary from 1.32 to 5.42 µSv/y. Uranium activity concentrations ranged from 0.356 to 1.488 BqL−1, and the corresponding uranium concentrations in water samples were found to vary from 28.76 to 120 μgL−1. Uranium concentrations were over the safety recommended limits when, compared with recommended limits of of 30 μgL−1 for drinking water based on the US environmental protection agency. The excess cancer risk varied from 0.398 to 1.666 x10-4 with a mean value of 0.9 x10-4, indicating that 9/100,000 people in these areas haves a cancer risk from the water.

Geochemical Behavior of Uranium and Radon in Groundwater of Jurassic Granite Area, Icheon, Middle Korea

Uranium concentrations (a total of 82 samples) in groundwater in Icheon, middle Korea, showed a wide range from 0.02 to 1640 μg/L with a mean of 56.77 μg/L, a median of 3.03 μg/L, and a standard deviation of 228.63 μg/L. Most groundwater samples had quite low concentrations: 32.9% were below 1 μg/L, while 15.9% exceeded 30 μg/L, the maximum contaminant level (MCL) of the US EPA (Environmental Protection Agency). Radon concentrations also ranged widely from 1.48 to 865.8 Bq/L. Although the standard deviation of radon was large (151.8 Bq/L), the mean was 211.29 Bq/L and the median was 176.86 Bq/L. Overall, 64.6% of the samples exceeded the alternative maximum contaminant level (AMCL) of the US EPA (148 Bq/L). According to statistical analyses, there was no close correlations between uranium and radon, but there were correlations between uranium and redox potential (Eh) (−0.54), dissolved oxygen (DO) (−0.50), HCO3− (0.45), Sr (0.65), and SiO2 (−0.44). Radon showed independent behavior with respect to most components in groundwater. Uranium concentrations in groundwater increased with increasing water–rock interactions. Anomalously high uranium and radon concentrations in groundwater are preferentially localized in granite areas and spatial distributions are remarkably heterogeneous.

Using spatial statistics to identify the uranium hotspot in groundwater in the mid-eastern Gangetic plain, India

The occurrence of uranium in groundwater is of particular interest due to its toxicological and radiological properties. It has been considered as a relevant contaminant for drinking water even at a low concentration. Uranium is a ubiquitously occurring radionuclide in the environment. Four hundred and fifty-six (456) groundwater samples from different locations of five districts of South Bihar (SB) were collected and concentrations of uranium (U) were analyzed using a light-emitting diode (LED) fluorimetric technique. Uranium concentrations in groundwater samples varied from 0.1 µg l−1 to 238.2 µg l−1 with an average value of 12.3 µg l−1 in five districts of Bihar in the mid-eastern Gangetic plain. This study used hot spot spatial statistics to identify the distribution of elevated uranium concentration in groundwater. The hypothesis whether spatial distribution of high value and low value of U is more likely spatially clustered due to random process near a uranium hotspot in groundwater was tested based on z score and Getis-Ord Gi* statistics. The method implemented in this study, can be utilized in the field of risk assessment and decision making to locate potential areas of contamination.

Large-Scale Uranium Contamination of Groundwater Resources in India

Groundwater overexploitation has caused massive groundwater depletion and raised concerns for water and food security in India. Groundwater in India also suffers from multiple water quality issues such as arsenic and fluoride contamination that pose human health risks. Here we report new data showing that the occurrence in uranium in Indian groundwater is an emerging and widespread phenomenon. We present compiled data on groundwater uranium from 16 Indian states and new data from 324 wells in the states of Rajasthan and Gujarat that show a high prevalence of uranium concentrations above the World Health Organization provisional guideline value of 30 μg/L across India. Using geochemical and uranium isotope data, we suggest factors that may drive high uranium concentrations in groundwater, including uranium content in aquifer rocks, oxidation state, and groundwater chemistry that promotes the formation of soluble uranyl carbonate complexes. While the primary source of uranium is geogenic, anthropogenic fact...

Concentration of uranium in groundwater and its correlation with the gamma activity of primordial radionuclides in the bedrock samples: A study from northeastern part of Bengaluru city, India

The present investigation aims to study the incorporation of uranium from the bedrock to groundwater through leaching. In view of this, rock powder samples were collected in the form of slurry from the bedrock of freshly drilled borewells of the study area. The rock powder and the supernatant were separated. The gamma activity concentrations of primordial radionuclides-238U (226Ra), 232Th, and 40K in the rock powder samples were measured using HP-Ge gamma-ray spectrometer. The supernatant was analyzed for the concentration of Unatusing laser-induced fluorimeter. A strong positive correlation was observed between the concentration of uranium in the rock powder and the corresponding concentration in the water samples indicating the possible leaching of uranium from the bedrock to groundwater under favorable conditions.

Occurrence of Uranium in Groundwater Along the Lithological Contacts in Central Tamilnadu, India: An Isotope Hydrogeochemical Perspective

Groundwater contributes to the highest exposure level of naturally occurring uranium (U) to biosphere, and hence, the source and concentration of uranium in groundwater needs to be monitored periodically. In the present study, groundwaters from different lithologic locations were collected and measured for uranium concentration and major ions in order to establish any possible link with the lithology on the uranium distribution in central parts of Tamil Nadu, South India. About 11% of the samples contain U in excess of the permissible limit of WHO (Guidelines for drinking-water quality, WHO, Geneva, 2011), and the contamination was limited to mostly hard rock terrain, which is granitic in nature. The correlations among U, major ions, and environmental isotopes were studied to understand the mechanism governing uranium dissolution and transport in groundwater of this region. Observations lead us to infer that the older water with near-neutral pH and oxidizing condition contains higher dissolved U compared with relatively young groundwater. The results also reflect the possible health risk to the local population through long-term consumption of uranium-containing groundwater without any pretreatment.

Weathering and evaporation controls on dissolved uranium concentrations in groundwater – A case study from northern Burundi

The potential use of groundwater for potable water supply can be severely compromised by natural contaminants such as uranium. The environmental mobility of uranium depends on a suite of factors including aquifer lithology, redox conditions, complexing agents, and hydrological processes. Uranium concentrations of up to 734μg/L are found in groundwater in northern Burundi, and the objective of the present study was to identify the causes for these elevated concentrations. Based on a comprehensive data set of groundwater chemistry, geology, and hydrological measurements, it was found that the highest dissolved uranium concentrations in groundwater occur near the shores of Lake Tshohoha South and other smaller lakes nearby. A model is proposed in which weathering and evapotranspiration during groundwater recharge, flow and discharge exert the dominant controls on the groundwater chemical composition. Results of PHREEQC simulations quantitatively confirm this conceptual model and show that uranium mobilization followed by evapo-concentration is the most likely explanation for the high dissolved uranium concentrations observed. The uranium source is the granitic sand, which was found to have a mean elemental uranium content of 14ppm, but the exact mobilization process could not be established. Uranium concentrations may further be controlled by adsorption, especially where calcium-uranyl‑carbonate complexes are present. Water and uranium mass balance calculations for Lake Tshohoha South are consistent with the inferred fluxes and show that high‑uranium groundwater represents only a minor fraction of the overall water input to the lake. These findings highlight that the evaporation effects that cause radionuclide concentrations to rise to harmful levels in groundwater discharge areas are not only confined to arid regions, and that this should be considered when selecting suitable locations for water supply wells.

Uraniferous dolomite: a natural source of high groundwater uranium concentrations in northern Bavaria, Germany?

Naturally high uranium (U) concentrations occur in the groundwater of northern Bavaria (southeastern Germany) although the source(s) and geochemical processes controlling its occurrence are poorly understood. An earlier study identified the weathering of uraniferous apatite as responsible for elevated groundwater U in a part of the region. This present study focuses on a uraniferous dolomite facies in the Triassic sandstone aquifer of northern Bavaria as a potential source of dissolved uranium in the regional groundwater. Hydrogeochemical and mineralogical analytical methods (INAA, ICP-OES, SEP, XRD, C/S measurements), in conjunction with existing hydro- and geochemical datasets, as well as hydrogeochemical modeling approaches indicate a strong connection between groundwater U and the dolomitic facies. Highest groundwater concentrations (max 58.3 µg L−1) occur under slightly alkaline and oxic to slightly reducing conditions. Uranium speciation is dominated by mobile U(VI), predominantly in the form of uranyl-carbonate complexes. Groundwater is undersaturated with respect to U mineral phases. In addition, high values in the dolomite extraction step (SEP) and a positive correlation of dolomite (XRD) and Ca with U (INAA) support the assumption of mobilization from the uraniferous dolomite as a potential source for elevated U concentrations, and hence one of the causes for the geogenic groundwater U problem in this region.

Radionuclides in groundwater, rocks and stream sediments in Austria – results from a recent survey

Abstract In 2014, the Geological Survey of Austria (GBA) published – in cooperation with further national institutions – an overview map on radionuclides in groundwater, rocks and stream sediments at a scale of 1:500 000 with explanatory notes. In the frame of this activity, the uranium, 228 Ra, 226 Ra, 222 Rn, 210 Pb and 210 Po analyses in groundwater studies made by the Austrian Agency for Health and Food Safety (AGES) and Environment Agency of Austria (Umweltbundesamt), as well as the uranium and thorium analyses of stream sediments of the GBA and whole-rock analyses from different sources, were evaluated statistically. Furthermore, the GBA's comprehensive airborne radiometric data were exploited. The aim of this study was to work out typical spectra of the radionuclide content in the groundwater and aquifers of different geological settings. It appeared that the concentration of 222 Rn in groundwater depends significantly on the uranium content of the aquifer. In contrast to this, the other radionuclides in groundwater did not show a clear correlation with uranium and thorium in the subsurface geology. Concerning 228 Ra, 226 Ra, 210 Pb and 210 Po, the lack of relationship to the subsurface composition seems to be a result of the low concentrations in groundwater. With respect to uranium in groundwater, there is a mixed situation: on the one hand, high uranium concentrations in groundwater can be observed in the Alps in regions with uranium bearing orthogneisses. On the other hand, in sediment basins of NE Austria where the underlying geology contains little uranium. Whether this is caused by special geological features combined with the given low precipitation or by the extensive agriculture (uranium from phosphate fertilizer) is under examination. Concerning the threshold values of the radionuclides in groundwater (radiation), no exceedance could be observed. In spite of this, the concentration of the heavy metal uranium sometimes exceeded the threshold value of 15 µg l −1 : this is especially true for the regions mentioned above. In addition, an attempt was made to compare the Austrian values with data from neighbouring countries. It became clear that only a few published datasets exist that are comparable. Radon analyses of soil gas in the Czech Republic and Bavaria show the same geological patterns as the Austrian radon analyses of the groundwater. In addition, to enable the reader to compare the Austrian data with datasets from other countries, additional tables are included here for all types of data. They show the statistic distributions of different geological classes in a coordinated way.

Ex situ groundwater treatment triggering the mobilization of geogenic uranium from aquifer sediments

Uranium (U) concentrations in groundwater extracted for drinking water usage from a Quaternary fluvial aquifer partly exceed the German drinking water guideline of 10μgL−1. Responsible sources and mobilization processes were unknown and gave rise to this study. Land use of the watershed is mainly agricultural leading to groundwater nitrate concentrations >50mgL−1 and a need for water treatment prior to utilization as drinking water. This is successfully accomplished by addition of nutrients triggering bacterial nitrate reduction, followed by the addition of NaOH for water softening and CO2 for pH adjustment, with subsequent reinfiltration into the aquifer. Three boreholes were drilled to obtain a total of 127 solid samples from Quaternary and underlying Tertiary sediments. Geochemistry and mineralogy were assessed using elemental analysis (CS, ICP-MS), X-ray diffraction and scanning electron microscopy to complement hydrochemical data and unravel U occurrence in the subsurface. Solid phase U fractionation was characterized by a sequential extraction procedure, U remobilization potential by a 137days column experiment. Shallow Quaternary sediments yielded low U contents <1μgg−1, higher values were found in depths of more than 20m below ground surface. Here, strata of elevated Corg and Cinorg contain up to 14μgg−1 U, mainly bound in organic and carbonate fractions. Groundwater U concentrations >10μgL−1 almost exclusively appear in this same depth range, and only in wells influenced by water treatment runoff. Results suggest that the applied water treatment approach triggers U remobilization from geogenic sources in the aquifer. The most probable mechanism is dissolution of U bearing calcite induced by CO2 application; redox reactions and pH-driven desorption appear to play a minor role in mobilization. We conclude that groundwater treatment should carefully account for unwanted hydrogeochemical side effects triggering the mobilization of geogenic trace elements such as uranium.

Large decadal-scale changes in uranium and bicarbonate in groundwater of the irrigated western U.S.

Samples collected about one decade apart from 1105 wells from across the U.S. were compiled to assess whether uranium concentrations in the arid climate are linked to changing bicarbonate concentrations in the irrigated western U.S. Uranium concentrations in groundwater were high in the arid climate in the western U.S, where uranium sources are abundant. Sixty-four wells (6%) were above the U.S. EPA MCL of 30μg/L; all but one are in the arid west. Concentrations were low to non-detectable in the humid climate. Large uranium and bicarbonate increases (differences are greater than the uncertainty in concentrations) occur in 109 wells between decade 1 and decade 2. Similarly, large uranium and bicarbonate decreases occur in 76 wells between the two decades. Significantly more wells are concordant (uranium and bicarbonate are both going the same direction) than discordant (uranium and bicarbonate are going opposite directions) (p<0.001; Chi-square test). The largest percent difference in uranium concentrations occur in wells where uranium is increasing and bicarbonate is also increasing. These large differences occur mostly in the arid climate. Results are consistent with the hypothesis that changing uranium concentrations are linked to changes in bicarbonate in irrigated areas of the western U.S.

High Uranium Concentrations in Groundwater in Burundi

Uranium occurs naturally in groundwater and frequently exceeds maximum admissible concentration levels. Here we present the results of a study from Burundi where dissolved uranium concentrations can exceed 700 μg/L. A conceptual model is proposed that relates these high levels to strong evapotranspiration of groundwater where uranium appears by dissolution of minerals from the granitic host rock. The proposed model is consistent with water balance considerations and corroborated by simulations using the geochemical code PHREEQC. Varying degrees of evapotranspiration, mineral dissolution and uranium concentrations of the source rock account for the large variation of the chemical composition of groundwater observed in the study area. These findings highlight the need for caution when developing water supply systems in the vicinity of groundwater discharge zones characterized by strong evapo-concentration.