Uranium In Groundwater Research Articles

Uranium Isotopic Fractionation Induced by U(VI) Adsorption onto Common Aquifer Minerals.

Uranium groundwater contamination due to U mining and processing affects numerous sites globally. Bioreduction of soluble, mobile U(VI) to U(IV)-bearing solids is potentially a very effective remediation strategy. Uranium isotopes (238U/235U) have been utilized to track the progress of microbial reduction, with laboratory and field studies finding a ∼1‰ isotopic fractionation, with the U(IV) product enriched in 238U. However, the isotopic fractionation produced by adsorption may complicate the use of 238U/235U to trace microbial reduction. A previous study found that adsorption of U(VI) onto Mn oxides produced a -0.2‰ fractionation with the adsorbed U(VI) depleted in 238U. In this study, adsorption to quartz, goethite, birnessite, illite, and aquifer sediments induced an average isotopic fractionation of -0.15‰ with the adsorbed U(VI) isotopically lighter than coexisting aqueous U(VI). In bicarbonate-bearing matrices, the fractionation depended little on the nature of the sorbent, with only birnessite producing an atypically large fractionation. In the case of solutions with ionic strengths much lower than those of typical groundwater, less isotopic fractionation was produced than U(VI) solutions with greater ionic strength. Studies using U isotope data to assess U(VI) reduction must consider adsorption as a lesser, but significant isotope fractionation process.

In Situ Bio-Reduction/Immobilization of Uranium at an In Situ Recovery Mining Site Utilizing Membrane Infused Gaseous Hydrogen

Abstract The most common technology currently used for restoring groundwater at In Situ Recovery (ISR) uranium mining sites is reverse osmosis (RO) and reinjection of the permeate. However, this practice does not restore the formation to its original reduced state, and in many cases groundwater uranium concentrations are not restored to premining baseline levels. Natural attenuation based methods are rarely field tested as a small number available sites and a lack of economic interest in the mining community have historically limited their usage. This study was performed to evaluate effectiveness of introducing dissolved hydrogen into a postmined formation at an ISR mining site to stimulate reduction and immobilization of residual soluble uranium to premining baseline levels. The main objectives of this research project were (1) to develop and optimize a system for minimizing air entrainment during water injection when employing a membrane gas-transfer device for down-hole hydrogen infusion; (2) to assess...

Distribution and potential health risk of groundwater uranium in Korea

Chronic exposure even to extremely low specific radioactivity of natural uranium in groundwater results in kidney problems and potential toxicity in bones. This study was conducted to assess the potential health risk via intake of the groundwater containing uranium, based on the determination of the uranium occurrence in groundwater. The groundwater was investigated from a total of 4140 wells in Korea. Most of the groundwater samples showed neutral pH and (sub-)oxic condition that was influenced by the mixing with shallow groundwater due to long-screened (open) wells. High uranium contents exceeding the WHO guideline level of 30 μg L−1 were observed in the 160 wells located mainly in the plutonic bedrock regions. The statistical analysis suggested that the uranium component was present in groundwater by desorption and re-dissolution processes. Predominant uranium phases were estimated to uranyl carbonates under the Korean groundwater circumstances. These mobile forms of uranium and oxic condition facilitate the increase of potential health risk downgradient. In particular, long-term intake of groundwater containing >200 μg U L−1 may induce internal exposure to radiation as well as the effects of chemical toxicity. These high uranium concentrations were found in twenty four sampling wells of rural areas in this study, and they were mainly used for drinking. Therefore, the high-level uranium wells and neighboring areas must be properly managed and monitored to reduce the exposure risk for the residents by drinking groundwater.

Genetic and grade and tonnage models for sandstone-hosted roll-type uranium deposits, Texas Coastal Plain, USA

The coincidence of a number of geologic and climatic factors combined to create conditions favorable for the development of mineable concentrations of uranium hosted by Eocene through Pliocene sandstones in the Texas Coastal Plain. Here 254 uranium occurrences, including 169 deposits, 73 prospects, 6 showings and 4 anomalies, have been identified. About 80million pounds of U3O8 have been produced and about 60million pounds of identified producible U3O8 remain in place. The development of economic roll-type uranium deposits requires a source, large-scale transport of uranium in groundwater, and deposition in reducing zones within a sedimentary sequence. The weight of the evidence supports a source from thick sequences of volcanic ash and volcaniclastic sediment derived mostly from the Trans-Pecos volcanic field and Sierra Madre Occidental that lie west of the region. The thickest accumulations of source material were deposited and preserved south and west of the San Marcos arch in the Catahoula Formation. By the early Oligocene, a formerly uniformly subtropical climate along the Gulf Coast transitioned to a zoned climate in which the southwestern portion of Texas Coastal Plain was dry, and the eastern portion humid. The more arid climate in the southwestern area supported weathering of volcanic ash source rocks during pedogenesis and early diagenesis, concentration of uranium in groundwater and movement through host sediments. During the middle Tertiary Era, abundant clastic sediments were deposited in thick sequences by bed-load dominated fluvial systems in long-lived channel complexes that provided transmissive conduits favoring transport of uranium-rich groundwater. Groundwater transported uranium through permeable sandstones that were hydrologically connected with source rocks, commonly across formation boundaries driven by isostatic loading and eustatic sea level changes. Uranium roll fronts formed as a result of the interaction of uranium-rich groundwater with either (1) organic-rich debris adjacent to large long-lived fluvial channels and barrier–bar sequences or (2) extrinsic reductants entrained in formation water or discrete gas that migrated into host units via faults and along the flanks of salt domes and shale diapirs. The southwestern portion of the region, the Rio Grande embayment, contains all the necessary factors required for roll-type uranium deposits. However, the eastern portion of the region, the Houston embayment, is challenged by a humid environment and a lack of source rock and transmissive units, which may combine to preclude the deposition of economic deposits. A grade and tonnage model for the Texas Coastal Plain shows that the Texas deposits represent a lower tonnage subset of roll-type deposits that occur around the world, and required aggregation of production centers into deposits based on geologic interpretation for the purpose of conducting a quantitative mineral resource assessment.

Quantification and assessment of health risk due to ingestion of uranium in groundwater of Jammu district, Jammu & Kashmir, India

The uranium content in groundwater being used for drinking purposes in Jammu district, Jammu & Kashmir, India has been measured by using LED fluorimetric technique to determine associated carcinogenic and non-carcinogenic health risk for inhabitants of this area. Uranium concentration and age dependent ingestion dose varied from 0.18 to 20.81 µg l−1 and 0.16 to 42.46 µSv year−1, being well within the recommended limits suggested by different health agencies of the world. The physico-chemical properties (TDS, EC and pH) have also been measured and correlated with obtained uranium concentration. Hence, the groundwater can be considered to be safe for consumption by public.

용인 ○○마을 지하수내 우라늄 및 라돈-222의 산출특성

The occurrence of natural radioactive materials such as uranium and radon-222 in groundwater was examined with hydrogeochemistry and geology at ○○ village in the Yongin area. Two rounds of 19 groundwater and 5 surface water sampling were collected for analysis. The range of pH value in groundwaters was 5.81 to 7.79 and the geochemical types of the groundwater were mostly Ca(Na)-HCO3 and Ca(Na)-NO3(Cl)-HCO3. Uranium and radon-222 concentrations in the groundwater ranged from 0.06 to 411 μg/L and from 5.56 to 903 Bq/L, respectively. Two deep groundwaters used as common potable well-water sources exceeded the maximum contaminant levels of the uranium and radon-222 proposed by the United States Environmental Protection Agency (US EPA). Three groundwater samples from residential areas contained unsuitable levels of uranium, and 12 groundwater samples were unsuitable due to radon-222 concentrations. Radioactive materials in the unsuitable groundwater are naturally occurring in a Jurassic amphibole- and biotite-bearing granitic gneiss. High uranium and radon-222 groundwater concentrations were only observed in two common wells; the others showed no relationship between bedrock geology and groundwater geochemical constituents. With such high concentrations of naturally occurring radioactive materials in groundwater, the affected areas may extend tens of meters for uranium and even farther for radon-222. Therefore, we suggest the radon-222 and the uranium did not originate from the same source. Based on the distribution of radon-222 in the study area, zones of higher radon-222 concentrations may be the result of diffusion through cracks, joint, or faults. Surface radioactivity and uranium concentrations in the groundwater show a positive relationship, and the impact areas may extend for ~200m beyond the well in the case of wells containing high concentrations of uranium. The highest uranium and thorium concentrations in rock samples were detected in thorite and monazite.

Uranium in groundwater of the Al-Batin Alluvial Fan aquifer, south Iraq

This study focuses on identifying concentrations, species, spatial distribution and potential sources of uranium (U) in groundwater in Al-Batin area south of Iraq. Although few studies reported elevated concentration of U in groundwater in some parts of the Al-Batin Alluvial Fan, a comprehensive investigation of U in the groundwater of the entire fan is still missing so far. To achieve this goal, 43 groundwater samples are collected for major cations and anions, trace elements, total organic carbon and total inorganic carbon analyses. U concentrations range between 0.1 and 98 μg/L with an arithmetic average of 16 μg/L. The spatial distribution of U in groundwater shows an increase eastward and northeastward with some anomalies. UO2(CO3)22−, UO2(CO3)34− and UO2(HPO4)22− are the dominant U species according to PHREEQC simulations. Spearman correlation analysis (n = 43, p < 0.01) shows a positive correlation between U and K, HCO3−, Ca, Mg, Al, Si and rare earth elements (∑REE). Well depth, on the other hand, had a negative correlation (r = −0.65 at p < 0.01) with U, indicating that U is dominant in more shallow groundwater. This study assumes a geogenic source of U from the Arabian Shield in Saudi Arabia, derived by flood plain and trapped in the east and northeast of the study area under reduced conditions of the neighbor marshes. The release of uranium into the groundwater can be explained by three hypotheses: The first hypothesis is desorption of U sorbed onto ferric minerals (e.g., hematite, magnetite and goethite). The second hypothesis is desorption of U from clay minerals in mudstone lenses within the aquifer. The third hypothesis is the release of U from the carbonate lattice structure due to the replacement with Ca. The relatively high Eh and the elevated concentrations of SO42−, Ca2+ and Na+ in groundwater are appropriate conditions to release U load of the supposed sources into groundwater.

Dissolved radon and uranium in groundwater in a potential coal seam gas development region (Richmond River Catchment, Australia)

The extraction of unconventional gas resources such as shale and coal seam gas (CSG) is rapidly expanding globally and often prevents the opportunity for comprehensive baseline groundwater investigations prior to drilling. Unconventional gas extraction often targets geological layers with high naturally occurring radioactive materials (NORM) and extraction practices may possibly mobilise radionuclides into regional and local drinking water resources. Here, we establish baseline groundwater radon and uranium levels in shallow aquifers overlying a potential CSG target formation in the Richmond River Catchment, Australia. A total of 91 groundwater samples from six different geological units showed highly variable radon activities (0.14–20.33 Bq/L) and uranium levels (0.001–2.77 μg/L) which were well below the Australian Drinking Water Guideline values (radon; 100 Bq/L and uranium; 17 μg/L). Therefore, from a radon and uranium perspective, the regional groundwater does not pose health risks to consumers. Uranium could not explain the distribution of radon in groundwater. Relatively high radon activities (7.88 ± 0.83 Bq/L) in the fractured Lismore Basalt aquifer coincided with very low uranium concentrations (0.04 ± 0.02 μg/L). In the Quaternary Sediments aquifers, a positive correlation between U and HCO3− (r2 = 0.49, p < 0.01) implied the uranium was present as uranyl-carbonate complexes. Since NORM are often enriched in target geological formations containing unconventional gas, establishing radon and uranium concentrations in overlying aquifers comprises an important component of baseline groundwater investigations.

Distribution of natural uranium in groundwater around Kudankulam

A systematic study was carried out to estimate the uranium concentration in the ground water around Kudankulam in Southern Tamil Nadu. The uranium concentration in ground water varies from 0.2 to 6.6 μg/l, with a mean value of 2.0 μg/l. The Quantalase uranium analyzer was used to measure the uranium concentration. These groundwater samples were analyzed for the water quality parameters such as pH, conductance, total dissolved solids (TDS), salinity, chloride, and sulfate. An attempt has been made to correlate the uranium concentration with the water quality parameters. It is observed that conductance, TDS, salinity, chloride, and sulfate show positive correlation with uranium concentration.

Spatial distribution of uranium and metalloids in groundwater near sandstone-type uranium deposits, Southern Mongolia

Spatial distribution of uranium and metalloids in groundwater near sandstone-type uranium deposits, Southern Mongolia

Physico-Chemical Heterogeneity of Organic-Rich Sediments in the Rifle Aquifer, CO: Impact on Uranium Biogeochemistry.

The Rifle alluvial aquifer along the Colorado River in west central Colorado contains fine-grained, diffusion-limited sediment lenses that are substantially enriched in organic carbon and sulfides, as well as uranium, from previous milling operations. These naturally reduced zones (NRZs) coincide spatially with a persistent uranium groundwater plume. There is concern that uranium release from NRZs is contributing to plume persistence or will do so in the future. To better define the physical extent, heterogeneity and biogeochemistry of these NRZs, we investigated sediment cores from five neighboring wells. The main NRZ body exhibited uranium concentrations up to 100 mg/kg U as U(IV) and contains ca. 286 g of U in total. Uranium accumulated only in areas where organic carbon and reduced sulfur (as iron sulfides) were present, emphasizing the importance of sulfate-reducing conditions to uranium retention and the essential role of organic matter. NRZs further exhibited centimeter-scale variations in both redox status and particle size. Mackinawite, greigite, pyrite and sulfate coexist in the sediments, indicating that dynamic redox cycling occurs within NRZs and that their internal portions can be seasonally oxidized. We show that oxidative U(VI) release to the aquifer has the potential to sustain a groundwater contaminant plume for centuries. NRZs, known to exist in other uranium-contaminated aquifers, may be regionally important to uranium persistence.

Distribution and sources of 226Ra in groundwater of arid region

As a part of characterizing radioactivity in groundwater of the eastern Arabian Peninsula, a first systematic evaluation of 226Ra activity in groundwater indicates a wide range (0.65–203.66 mBq L−1) with average of 17.56 mBq L−1. Adsorption/desorption process, groundwater residence time and uranium concentration are the main controlling factors of 226Ra distribution in groundwater of the different aquifers. Estimation of 226Ra effective dose from water ingestion suggests potential risk of drinking water from the carbonate aquifer.

Occurrence of high uranium and radon in hard rock aquifers of South India – Evaluating the temporal and spatial trends

Total uranium concentration and radon activity in groundwater were measured in the hard rock aquifer of South India to understand the spatial and temporal distribution of these radioactive elements and their implication on human health. A detailed study was conducted by collecting a total of 124 samples representing four different seasons in various lithologies of Madurai district of Tamil Nadu. The study focuses on identifying the sources of uranium and radon with the help of stable isotopes, statistical analysis and pCO2 values. The higher concentration of uranium and radon is observed in Granitic terrains. 13% of samples in uranium exceed the permissible limit of WHO (world health organization) standard in all seasons while radon shows that 19% of samples during southwest monsoon and 13% of samples during north east monsoon exceed the permissible limit for drinking (USEPA limit of 11.1Bq/l). Speciation of uranium shows that among different species of uranium in aqueous media, carbonate complexes [UO2(CO3)22−] are found to be dominant. High uranium coupled with high pCO2 values of groundwater indicates that bicarbonate enhances the weathering process and thus mobilizes uranium in groundwater and especially around the granitic terrain, which is confirmed by correlation between uranium and bicarbonate ion. The carbonates were compared to that of the uranium concentrations and its relationship to other ions was established by adopting statistical analysis. The stable isotope signatures of δ18O and δD indicate that most of the uranium rich groundwaters are rainwater recharged and the samples of fissile hornblende biotite gneiss region show evaporative enrichment. However the isotope trends observed in groundwaters of different formations indicate that the recharge mechanism is not same throughout the study area. This study also demonstrates the fact that lithology controls uranium distribution in groundwater.

Uranium and thorium behavior in groundwater of the natural spa area “Choygan mineral water” (East Tuva)

The natural spa area “Choygan mineral waters”, a unique deposit of natural carbon dioxide mineral waters in Siberia, is located in the Eastern Sayan Mountains. There are 33 spring discharges in this area. Spring waters are mainly of HCO3-Na-Ca type. TDS varies from 300 mg/L to 2600 mg/L, the temperature ranges from 7 °C (in spring 33) to 39 °C (in spring 12), pH varies from 5.9 to 8.3, and the value of the oxidation-reduction potential is from -170 mV to 236 mV. All studied waters were divided into two groups according to their temperature and geochemical conditions: cold fresh water in oxidizing environment and warm slightly brackish water in reducing environment. The uranium concentration varies from 0.7 to 14 μg/l and the thorium concentration varies from 0.001 to 0.33 μg/l in the studied waters. The predominant uranium complexes are (UO2(CO3)3)4-, (UO2(CO3)2)2-, UO2CO3, (UO2(PO4)2)4- in the waters in oxidizing and reducing environments. It was found that acid-alkaline and oxidizing-reducing conditions were the determining factors for uranium behavior and speciation in the studied waters. The pH conditions are determining factors for thorium behavior and speciation in the studied waters. In slightly acidic water the predominant thorium species is negatively charge complex (ThCO3(OH)3)- (more than 95%).

Fertilizing water contamination

Enviromental Science Excess nutrients such as nitrogen and phosphorus can negatively affect aquatic ecosystems. Nutrient-rich fertilizer runoff stimulates productivity, which can lead to harmful algal blooms or fish kills. Nolan and Weber show that such pollution has another wide-ranging consequence: increasing the mobility of uranium in groundwater. Geochemical data for two major aquifers in the United States, which in combination provide drinking water to millions and irrigation for one-sixth of U.S. agriculture, show that increased nitrate levels correlate strongly with the presence of uranium. Nitrate can oxidatively dissolve naturally occurring uranium minerals, which in turn can lead to potentially harmful levels of soluble uranium in groundwater, especially in shallow aquifers. Environ. Sci. Technol. Lett. 10.1021/acs.estlett.5b00174(2015).

Biostimulation by Glycerol Phosphate to Precipitate Recalcitrant Uranium(IV) Phosphate.

Stimulating the microbial reduction of aqueous uranium(VI) to insoluble U(IV) via electron donor addition has been proposed as a strategy to remediate uranium-contaminated groundwater in situ. However, concerns have been raised regarding the longevity of microbially precipitated U(IV) in the subsurface, particularly given that it may become remobilized if the conditions change to become oxidizing. An alternative mechanism is to stimulate the precipitation of poorly soluble uranium phosphates via the addition of an organophosphate and promote the development of reducing conditions. Here, we selected a sediment sample from a U.K. nuclear site and stimulated the microbial community with glycerol phosphate under anaerobic conditions to assess whether uranium phosphate precipitation was a viable bioremediation strategy. Results showed that U(VI) was rapidly removed from solution and precipitated as a reduced crystalline U(IV) phosphate mineral similar to ningyoite. This mineral was considerably more recalcitrant to oxidative remobilization than the products of microbial U(VI) reduction. Bacteria closely related to Pelosinus species may have played a key role in uranium removal in these experiments. This work has implications for the stewardship of uranium-contaminated groundwater, with the formation of U(IV) phosphates potentially offering a more effective strategy for maintaining low concentrations of uranium in groundwater over long time periods.

Uranium Groundwater Monitoring and Seismic Analysis: A Case Study of the Gran Sasso Hydrogeological Basin, Italy

Uranium groundwater anomalies, observed before the L’Aquila earthquake (April 6th, 2009) and before the seismic swarm, which occurred in the second half of 2010, represent a key geochemical signal of a progressive increase of deep fluids fluxes at middle–lower crustal levels associated with the geodynamics of the earthquake. In this paper, temporal variations of uranium groundwater are studied in association with the seismic pattern around Gran Sasso National Laboratory (LNGS-INFN). The normalized seismic energy release and the number of earthquakes are analyzed in detail by means of monthly sliding time windows. They are compared with uranium anomalies to highlight any possible correlation.

Natural Uranium Contamination in Major U.S. Aquifers Linked to Nitrate

Groundwater geochemical data collected from two major U.S. aquifers, High Plains (HP) and Central Valley (CV), revealed naturally occurring groundwater uranium (U) exceeding the U.S. Environmental Protection Agency maximum contaminant level (MCL = 30 μg/L) across 22375 km2 where 1.9 million people live. Analysis of geochemical parameters revealed a moderately strong correlation between U and nitrate, a common groundwater contaminant, as well as alkalinity and calcium [Spearman’s rho (ρ) ≥ 0.30; p < 0.001]. Nitrate is recognized to alter U solubility by oxidative dissolution of reduced U(IV) minerals. Approximately 78% of areas where U concentrations were interpolated above the MCL were correlated to the presence of nitrate (Pearson’s r ≥ 0.5; p < 0.05). Shallow groundwater was determined to be the most susceptible to co-contamination (HP, ρ = 0.46; CV, ρ = 0.52). Together, these results indicate that nitrate, a primary contaminant, should be considered as a factor leading to secondary groundwater U contam...

Uranium in groundwater — Fertilizers versus geogenic sources

Due to its radiological and toxicological properties even at low concentration levels, uranium is increasingly recognized as relevant contaminant in drinking water from aquifers. Uranium originates from different sources, including natural or geogenic, mining and industrial activities, and fertilizers in agriculture. The goal of this study was to obtain insights into the origin of uranium in groundwater while differentiating between geogenic sources and fertilizers. A literature review concerning the sources and geochemical processes affecting the occurrence and distribution of uranium in the lithosphere, pedosphere and hydrosphere provided the background for the evaluation of data on uranium in groundwater at regional scale. The state of Baden-Württemberg, Germany, was selected for this study, because of its hydrogeological and land-use diversity, and for reasons of data availability. Uranium and other parameters from N=1935 groundwater monitoring sites were analyzed statistically and geospatially. Results show that (i) 1.6% of all water samples exceed the German legal limit for drinking water (10μg/L); (ii) The range and spatial distribution of uranium and occasional peak values seem to be related to geogenic sources; (iii) There is a clear relation between agricultural land-use and low-level uranium concentrations, indicating that fertilizers generate a measurable but low background of uranium in groundwater.

Lithological and hydrochemical controls on distribution and speciation of uranium in groundwaters of hard-rock granitic aquifers of Madurai District, Tamil Nadu (India)

Uranium is a radioactive element normally present in hexavalent form as U(VI) in solution and elevated levels in drinking water cause health hazards. Representative groundwater samples were collected from different litho-units in this region and were analyzed for total U and major and minor ions. Results indicate that the highest U concentration (113 µg l(-1)) was found in granitic terrains of this region and about 10 % of the samples exceed the permissible limit for drinking water. Among different species of U in aqueous media, carbonate complexes [UO2(CO3)(2)(2-)] are found to be dominant. Groundwater with higher U has higher pCO2 values, indicating weathering by bicarbonate ions resulting in preferential mobilization of U in groundwater. The major minerals uraninite and coffinite were found to be supersaturated and are likely to control the distribution of U in the study area. Nature of U in groundwater, the effects of lithology on hydrochemistry and factors controlling its distribution in hard rock aquifers of Madurai district are highlighted in this paper.