Aquifer Solids Research Articles

Mobilization mechanisms and spatial distribution of arsenic in groundwater of western Bangladesh: Evaluating water quality and health risk using EWQI and Monte Carlo simulation

Arsenic (As) contamination in groundwater is emerging as a significant global concern, posing serious risks to the safety of drinking water and public health. To understand the release mechanisms, mobilization processes, spatial distribution, and probabilistic health risks of As in western Bangladesh, forty-seven samples were collected and analyzed using an atomic absorption spectrometer (AAS). The As concentrations in groundwater ranged from 1.97 to 697.4 μg L⁻1 (mean: 229.9), significantly exceeding recommended levels. The dominant hydrochemistry of As-enriched groundwater was Ca–Mg–HCO₃, with the primary sources of arsenic in groundwater being the dissolution of arsenic-bearing minerals in sediment and the recharge of aquifers from the Ganges River Basin. The assessment using the Entropy Water Quality Index revealed that the groundwater is unsuitable for drinking, with 89.36% (n = 42) of the samples surpassing the WHO's limit for arsenic. Rock-water interactions, including calcite dissolution and silicate weathering within the confined aquifer, predominantly influenced hydrochemical properties. The significant relationships among Fe, Mn, and As indicate that the reductive dissolution of FeOOH and/or MnOOH considerably contributes to the release of As from sediment into groundwater. Geochemical modeling analysis revealed that siderite and rhodochrosite precipitate into aquifer solids, suggesting a weak to moderate relationship among As, Fe, and Mn. The long residence time of groundwater, combined with the presence of a clayey aquitard, likely controls the mobilization of arsenic in the aquifer. For the first time, Monte Carlo simulations have been used in arsenic-prone areas to assess the severity of arsenic contamination in western Bangladesh. The analysis indicates that out of 100,000 people, 10 may develop cancer as a result of drinking arsenic-contaminated water, with children being more susceptible than adults.

Control of paleoclimate and paleoweathering on chromium contents in a non-ultramafic aquifer hosting high chromium groundwater.

Cr(VI) is a carcinogen with proven mutagenic and genotoxic effects. The effects of the depositional environment (e.g., paleoweathering, paleoclimate, and paleoredox condition) on Crenrichment in non-ultramafic aquifer solids are unclear. In this study, we presented the sedimentary characteristics of a borehole from a typical non-ultramafic aquifer with high Cr groundwater in Jingbian, central Ordos Basin, China. Chromium was enriched in the K1h sandstone aquifer, especially at depths of 400-500m, with the highest value of mass transport coefficient (τAl,Cr) up to 92.13% and τAl,Fe up to 33.5%. The provenance of aquifer Cr was predominantly intermediate and felsic igneous rocks with a mafic rock mixture. This mafic source was inferred from Cr-rich granodiorite and mafic/ultramafic rocks in the Yinshan (Daqingshan-Wulashan) Block, northern Ordos Basin. The Cr-rich aquifer in K1h was developed due to a moderate chemical index of alteration (CIA) (mean, 56.7) under relatively warm and humid paleoclimate, as evidenced by high CIA-temperature (CIA-Temp) (mean, 6.79°C) and paleoclimatic index values (mean, 0.40). Fe-Mn redox cycling in the oxic to suboxic environments contributed to aquifer Cr accumulation. Using path analysis, we identified that paleoclimate created favorable weathering conditions and enrichment of Fe contributed to the formation of high-Cr aquifers. The study reveals the formation of positive Cr anomalies in non-ultramafic aquifers, which is the potential source of groundwater Cr, and highlights the effects of depositional factors on Cr accumulation during aquifer deposition or early diagenesis. It can provide new insights into the natural processes of high-Cr sediments occurring in non-ultramafic aquifers.

Case study of ground penetration radar (GPR) to assess lead migration

This paper describes research to characterize subsurface contamination caused by leaching of lead (Pb) from batteries disposed of at the surface, which has spread with groundwater movement. The contaminated soils and aquifer are located in the Matano formation (Sulawesi, Indonesia). Ground Penetrating Radar (GPR) was used to detect and delineate Pb-contaminated soils (i.e., solid-phase Pb). Lead in the solid and aqueous phase have different characteristics and responses when subjected to electromagnetic (EM) waves. Many studies have used GPR to map solid-phase Pb contamination in the subsurface. GPR uses EM as the base medium to receive subsurface images and is useful for the detection of solid-phase Pb contamination but cannot detect aqueous-phase Pb. The first step in the remediation process was to delineate solid-phase Pb contamination in the subsurface using GPR, which required a geotechnical survey to support GPR. Samples of soil and aquifer solids were then taken to quantify lead concentrations using X-ray fluorescence (XRF). We collected 15 lines of GPR measurements and 11 soil samples to quantify Pb. Frequencies of 600 MHz and 900 MHz were used for the GPR antenna. The results identified a clay layer at a depth of between 3 m and 4 m, which appears to have served as barrier to downward migration of Pb-contaminated groundwater. A shadow zone and low reflectance in the GPR subsurface section images were used to identify as the Pb contamination, which has a distinct wavelength ranging between 0.36 m and 0.45 m. We conclude from the results of this study that GPR was an effective tool for the delineation of the vertical and horizontal spread of Pb contamination eastward from the source.

Hydrochemical and geological controls on dissolved radium and radon in northwestern Algeria hydrothermal groundwaters

This study presents the results of the first investigation on natural occurrence of radium and radon in Algerian thermal water systems. Activity concentrations of Rn and Ra isotopes were measured in sixteen hydrothermal springs of northwestern Algeria. Samples displayed high activities, especially for 222Rn, 224Ra and 226Ra (up to 377 × 103 Bq/m3, 730 Bq/m3 and 4470 Bq/m3, respectively). Approximately, 50% of the investigated springs displayed activities of combined long-lived Ra (226Ra + 228Ra) in excess of the maximum contaminant level (MCL) of the WHO and EPA for drinking water. Factors controlling the distribution of radionuclides in the aquifer system are investigated. The observed correlation between Ra isotope and TDS suggests that adsorption/desorption is not the dominant process controlling the distribution of Ra in waters. Our results indicate that the excess SO42− limits the concentration of dissolved Ba2+ and thereby, the elevated Ra activities in these hydrothermal systems are not simply limited by co-precipitation with BaSO4 (barite). The data shows that Ra activities are likely dominated by the recoil process of parent isotopes in the aquifer solids. The minimal abundance of clay minerals and oxides in the aquifer, in addition to thermal activities in northwestern Algeria, significantly enhances the mobilization of Ra into waters.

Distribution of legacy and novel per- and polyfluoroalkyl substances in surface and groundwater affected by irrigation in an arid region

Frequent exchange of surface water and groundwater occurs in arid/semi-arid areas due to high evaporation and intensive irrigation activities, affecting the migration and transformation of per- and polyfluoroalkyl substances (PFASs) and threatening drinking water safety. This study analyzed legacy PFASs and potential precursors in surface water, groundwater, soil, and aquifer solid samples collected from a typical arid area, the Hetao Irrigation District of Northern China, to explore PFASs distribution and transformation between surface and ground. Total PFASs (ΣPFASs) in surface water was 29–232 ng/L, higher than 2–77 ng/L in groundwater. ΣPFASs in soil were 0.29–0.59 ng/g, higher than 0.09–0.27 in the aquifer solids. Regarding horizontal distribution, the concentration of PFASs in groundwater increased in downtowns and the areas recharged with lake water. In terms of vertical distribution, ΣPFASs decreased with the increase of depth, and more PFASs adsorbed on clay particles in the aquifer. The total oxidable precursor analysis showed that 8:2 FT and 4:2 FT were the dominant precursors of PFASs, resulting in an increment of 0.1–4 ng/L PFASs. Hydrogen and oxygen stable isotope compositions suggest similar sources between surface water and groundwater in the study area, while principal component analysis and Bayesian inference also indicate that surface water is an important source of groundwater PFASs. The annual infiltration PFASs to groundwater from Ulansuhai was estimated by the water balance approach to be 9.39 kg. Results highlight the influence of agricultural irrigation activities and lake infiltration on groundwater PFASs in the arid region.

Correction to Association of Radionuclide Isotopes with Aquifer Solids in the Midwestern Cambrian–Ordovician Aquifer System

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to Association of Radionuclide Isotopes with Aquifer Solids in the Midwestern Cambrian–Ordovician Aquifer SystemMadeleine MathewsMadeleine MathewsMore by Madeleine Mathews, Sean R. ScottSean R. ScottMore by Sean R. Scott, Madeline B. GotkowitzMadeline B. GotkowitzMore by Madeline B. Gotkowitz, and Matthew Ginder-Vogel*Matthew Ginder-VogelMore by Matthew Ginder-Vogelhttps://orcid.org/0000-0001-9183-1931Cite this: ACS Earth Space Chem. 2022, 6, 5, 1411–1412Publication Date (Web):April 13, 2022Publication History Received5 April 2022Published online13 April 2022Published inissue 19 May 2022https://doi.org/10.1021/acsearthspacechem.2c00037Copyright © 2022 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views122Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (501 KB) Get e-Alerts Get e-Alerts

Isotopic analysis of radium geochemistry at discrete intervals in the Midwestern Cambrian-Ordovician aquifer system

Radium (Ra) is a geogenic radioactive contaminant that frequently occurs at elevated levels in the Midwestern Cambrian-Ordovician aquifer system (MCOAS). Geochemical indicators (e.g., redox conditions or total dissolved solids) can broadly characterize conditions associated with elevated Ra levels in groundwater, but do not consistently correlate to elevated Ra within specific stratigraphic horizons. A coupled geochemical and isotopic study of groundwater and aquifer solids for major and trace elements, Ra, and uranium (U) at discrete intervals in the MCOAS was used to elucidate processes that may be responsible for this disconnect, via analysis of groundwater as well as extracted and digested solid aquifer samples. We find that the potential for Ra mobilization varies by stratigraphic unit, as observed by whole-rock 226Ra/238U (dis)equilibrium. Overall, the examined aqueous geochemical characteristics (e.g., redox conditions, total dissolved solids) do not explain Ra concentrations within the system, suggesting that alternative factors, like solid-phase associations or the extent of alpha recoil damage, may be more important. A relation between aqueous 87Sr/86Sr and 226Ra suggests that minerals with radiogenic 87Sr/86Sr are more likely to release 226Ra to the aqueous system. Overall, the release of U and Ra due to water-rock interaction varies with discrete stratigraphy, depending on aqueous geochemistry and available mineral associations. Due to complex Ra-rock interactions and the heterogeneous geology of the MCOAS, aqueous geochemistry does not fully predict the mobilization and concentration of Ra in groundwater. As sources and sinks of Ra within the MCOAS vary across stratigraphy, knowledge of aqueous geochemistry, available solid-phase associations, and nuclide leachability all are important to consider for understanding elevated Ra occurrence in aquifer systems.

Co-occurrence and correlations of PFASs and chlorinated volatile organic compounds (cVOCs) in subsurface in a fluorochemical industrial park: Laboratory and field investigations

Fluorochemical industrial park (FIP) represents an important source of per- and polyfluoroalkyl substances (PFASs) and chlorinated volatile organic compounds (cVOCs). Exploring the co-occurrence and correlations of PFASs and cVOCs is a key step towards the understanding their distributions in the field. In this study, perfluorooctanoic acid (PFOA) was the dominant compound in groundwater and aquifer solids, and elevated concentrations of short-chain perfluoroalkyl carboxylic acids (PFCAs) and hexafluoropropylene oxide oligomers were also detected in the field, suggesting their wide applications as substitutes for PFOA. Correlation analyses between PFASs and cVOCs suggested that cVOCs had a significant influence on the distribution and composition of PFASs in the field. In addition, the presence of cVOCs in the form of dense non-aqueous-phase organic liquids (DNAPL) affected the distribution and migration of PFASs at various depths, as evidenced by the relatively high PFASs concentrations (204 μg/L) and PFOA abundance (85.4%) in the deep aquifer, likely due to DNAPL-water interfaces sorption or partition into bulk DNAPL. The log Kd values, determined in the laboratory, were found to increase in the presence of DNAPL, especially for PFOA, with more than one time higher than those of perfluorobutanoic acid (PFBA) and hexafluoropropylene oxide dimer acid (HFPO-DA). This conclusion further demonstrated that PFOA had a higher potential to participate into DNAPL, which can migrate with DNAPL to the deep aquifer, supporting the higher abundance of PFOA in the deep aquifer mentioned above. However, the log Kd-field values of PFBA and HFPO-DA in the field were higher than that of PFOA, and no significant correlations (p > 0.05) were found between log Kd-field values and the chain-length of PFCAs at various depths, suggesting that the phenomena observed in the field are a result of composite influencing factors.

Ubiquitous Production of Organosulfates During Treatment of Organic Contaminants with Sulfate Radicals.

Oxidation of organic contaminants by sulfate radical (SO4 •-) is becoming more popular for the treatment of hazardous waste sites by in situ chemical oxidation (ISCO) and industrial wastewater by advanced oxidation processes (AOPs). It is well documented that SO4 •- can produce similar oxygen-containing transformation products as hydroxyl radical-based treatment processes, but SO4 •- also has the potential to produce organosulfates by radical addition. Experiments conducted with a suite of 23 aromatic and 5 aliphatic compounds, including several contaminants typically detected at hazardous waste sites, demonstrated the formation of at least one stable sulfate-containing product for 25 of the compounds. These compounds likely exhibit higher mobility in the subsurface due to a lower affinity for surfaces (e.g., aquifer solids, activated carbon) than most other transformation products. Although the health risks associated with organosulfates are still uncertain, some aromatic organosulfates produced in this study (i.e. phenyl sulfate and p-cresyl sulfate) are known to be harmful uremic toxins. Further study of organosulfate formation, fate, and toxicity is needed before SO4 •--based treatment processes are more widely employed.

Association of Radionuclide Isotopes with Aquifer Solids in the Midwestern Cambrian–Ordovician Aquifer System

Groundwater, an important source of drinking water globally, is susceptible to contamination by naturally occurring metals and radionuclides. Regional trends in groundwater quality are useful in pr...

Molecular Evidence of Arsenic Mobility Linked to Biodegradable Organic Matter.

Molecular characteristics of natural organic matter (NOM) and their potential connections to arsenic enrichment processes remain poorly understood. Here, we examine dissolved organic matter (DOM) in groundwater and water-soluble organic matter (WSOM) in aquifer sediments being depth-matched with groundwater samples from a typical arid-semiarid basin (Hetao Basin, China) hosting high arsenic groundwater. We used Fourier transform ion cyclotron resonance mass spectrometry to determine molecular characteristics of DOM and WSOM and evaluate potential roles of biodegradable compounds in microbially mediated arsenic mobility at the molecular level. High-arsenic groundwater DOM was generally enriched in recalcitrant molecules (including lignins and aromatic structures). Although potential contribution of recalcitrant compounds to arsenic enrichment cannot be ruled out, preferential degradation of the labile molecules coupled with reduction of Fe(III) (oxyhydr)oxides seemed to dominate arsenic mobilization. Both the number and the intensity of biodegradable compounds (including aliphatic/proteins and carbohydrates) were higher in WSOM than those in DOM in depth-matched high-arsenic groundwater (arsenic >0.67 μmol/L or 50 μg/L). Groundwater arsenic concentration generally increased with the increase in the number and the intensity of unique biodegradable compounds (especially N-containing compounds) in WSOM at matched depths. Anoxic incubations of sediments and deionized water show that more arsenic and Fe(II) were released from aquifer sediments with greater numbers and intensities of consumed biodegradable compounds in WSOM (especially N-containing compounds), with a higher proportion of microbially derived compounds produced. These observations indicate that the biodegradation of aliphatic/proteins and carbohydrates (especially CHON formulas) in WSOM fueling the reductive dissolution of Fe(III) (oxyhydr)oxides predominantly promotes arsenic release from aquifer solids. Our unique data present a better understanding of arsenic mobilization shaped by microbial degradation of labile organic compounds in anoxic aquifers at the molecular level.

Aerobic cometabolism of 1,4-dioxane by isobutane-utilizing microorganisms including Rhodococcus rhodochrous strain 21198 in aquifer microcosms: Experimental and modeling study

Aerobic cometabolism of the emerging contaminant 1,4-dioxane (1,4-D) by isobutane-utilizing microorganisms was assessed in pure culture and aquifer microcosm studies. The bacterium Rhodococcus rhodochrous strain ATCC 21198 transformed low, environmentally-relevant concentrations of 1,4-D when grown on isobutane. Microcosms were constructed with aquifer solids from Fort Carson, Colorado, a site contaminated with 1,4-D and trichloroethene (TCE). Multiple additions of isobutane and 1,4-D over 300 days were transformed in microcosms biostimulated with isobutane and microcosms bioaugmented with strain 21198. Results showed that, over time and with sufficient inorganic nutrients, biostimulation of native microorganisms with isobutane was just as effective as bioaugmentation with strain 21198 to achieve 1,4-D transformation in the microcosms. The presence of TCE at 0.2 mg/L did not inhibit 1,4-D transformation, though TCE itself was not readily transformed. An iterative process was used to determine kinetic parameter values to fit Michaelis-Menten/Monod models to experimental data for simultaneous isobutane utilization, biomass growth, and cometabolic transformation of 1,4-D. Parameter optimization resulted in good model fit to the data over multiple transformations of isobutane and 1,4-D in both short- and long-term experiments. Results suggest low concentrations of 1,4-D studied in the microcosms were cometabolically transformed according to a pseudo first-order rate of 0.37 L/mg TSS/day of 21198. Isobutane consumption was modeled with a maximum rate of 2.58 mg/mg TSS/day and a half saturation constant of 0.09 mg/L. 1,4-D transformation was competitively inhibited by the presence of isobutane and transformation rates were significantly reduced when inorganic nutrients were limiting. Simulations of the repeated additions found a first-order microbial endogenous decay coefficient of 0.03 day−1 fit the alternating periods of active transformation and stagnation between isobutane and 1,4-D additions over approximately one year. The model fitting process highlighted the importance of determining kinetic parameters from data representing low concentrations typically found in the environment.

Arsenic Release and Attenuation Processes in a Groundwater Aquifer During Anaerobic Remediation of TCE with Biostimulation

AbstractArsenic in groundwater in excess of the drinking water limit is usually from natural sources. The release of As, however, can be amplified by anthropogenic inputs of carbon, including those associated with the remediation of chlorinated solvents such as trichloroethylene (TCE). Large laboratory columns (15.2 cm diameter, 183 cm long) packed with aquifer solids from a TCE contaminated site near Hill Air Force Base (Utah) were fed with groundwater containing TCE and were biostimulated, bioaugmented, and monitored for TCE dechlorination over 7.5 years. This is a basin‐fill aquifer with As bearing geologic features. The objective of this study was to evaluate the biogeochemical changes that affect As solubilization that occurred after 7.5 years of feeding the columns with either whey or two formulations of Newman Zone® emulsified oil, and a no carbon addition control. The columns were analyzed in 10.16 cm sections for pore water and sediment quality parameters, parameters descriptive of redox conditions, and As geochemistry. The whey treatment resulted in 52.9% (±1.36%) (average ± standard deviation) of the total As in the solids leaching from the columns. The oil treatments promoted loss of 20.9% (±6.40%) of the total As. Arsenic solubility was associated with strongly reducing conditions developed with whey addition, leading to dissolution of crystalline Fe oxides and release of As. Arsenic was attenuated within the oil treated columns with As associated with carbonates in the lower layers. A consequence of adding whey, resulting in the desired full dechlorination of TCE in this aquifer, is the mobilization of As in groundwater.

High Radionuclides in Groundwater of an Inland Basin from Northwest China: Origin and Fate

Inland basins show various redox conditions in the groundwater system, which control the distribution and transportation of redox-sensitive radionuclides. However, the origin and fate of groundwater radionuclides in those basins are still unclear. High levels of naturally occurring uranium (U) and radon (Rn) have been observed in low total dissolved solid and oxic groundwater in the recharge area of the Hetao basin, a typical inland basin. Around 80% of investigated groundwater had U concentrations above the international drinking water standards (30 μg/L), and 97% exceeded the United States Environmental Protection Agency (U.S. EPA) guideline of 11.1 Bq/L Rn. Groundwater U was mobilized by oxic weathering and complexation with carbonate, while Rn-222 was mainly provided by α recoil of adsorbed Ra on the aquifer solids. Relatively high radium (Ra) activities were frequently found in reducing groundwater of the transition area and the flat plain, although combined Ra-226 and Ra-228 did not exceed the inter...

Effect of geochemical conditions on radium mobility in discrete intervals within the Midwestern Cambrian-Ordovician aquifer system

Radium (Ra) commonly occurs in groundwater obtained from the Midwestern Cambrian-Ordovician aquifer system (C-O-AS) at activities approaching and exceeding the United States Environmental Protection Agency's Maximum Contaminant Level (MCL) of 5 pCi/L for combined 226Ra and 228Ra. The occurrence of Ra(II) in groundwater is dependent on a number of factors, including the prevalence of parent radionuclides within hydrogeological strata, as well as aquifer geochemical conditions. Interbedded aquifer and aquitard sequences within the Midwestern C-O-AS are stratified with respect to Ra(II) activity and geochemical conditions, and thus the formations that serve as Ra(II) sources to groundwater remain poorly constrained. This study analyzes aqueous samples collected from short-screened wells at various depths within the Midwestern C-O-AS near Madison, WI, USA, to determine geochemical parameters including dissolved oxygen; pH; major and minor ions; and metals, including 226Ra, 228Ra, and parent isotopes 238U and 232Th. Additionally, the elemental composition of aquifer solids is determined as a function of depth. Within solid phases, 238U and 232Th occur in both fine-grained facies and as coatings on sandstone minerals. Most groundwater samples contain dissolved combined Ra(II) lower than 2.5 pCi/L; however, one well completed in the unconfined and one well completed in the confined portion of the groundwater system exceed 3.5 pCi/L. In the confined system, anoxic conditions are associated with elevated Ra(II) concentrations, while in the upper, oxic aquifer, elevated total dissolved solids are positively related to Ra(II). These results demonstrate that multiple factors impact Ra(II) sources and mobility in the regionally unconfined portion of the Midwestern C-O-AS.

Radium isotope response to aquifer storage and recovery in a sandstone aquifer

Radium isotopes and water-rock interaction were evaluated in an aquifer storage and recovery (ASR) pilot study conducted in 2010–2011 in Minnesota (USA) in order to identify mechanisms governing Ra activities when low-Ra water is recharged into a sandstone aquifer. Groundwater in the aquifer selected for the study, the Cambrian Mt. Simon Sandstone, contains naturally occurring radium that in many areas exceeds United States drinking water standards (185 mBq/L or 5 pCi/L combined 226Ra+228Ra), highlighting the need to identify the rates and mechanisms by which stored water acquires Ra isotopes. Major element concentrations of recovered water largely resembled recharged water, while Ra activities exceeded the Ra activities of the recharged water. 224Ra reached ∼100 mBq/L during the first 8 h of recovery (overall range 15.5–133 mBq/L). 226Ra and 228Ra also increased during the 47-day recovery period (23.7–82.5 mBq/L and 33.7–85.5 mBq/L, respectively). Ra isotope ratios indicate the relative contribution of alpha recoil vs. chemical processes (e.g. adsorption/desorption). During recovery, the 224Ra/228Ra and 228Ra/226Ra ratios declined, approaching their expected limiting values near unity. Collectively, the rates of Ra activity change with time, trends in Ra isotope ratios, barium concentrations, and manganese concentrations suggest that Ra was governed by chemical processes and alpha recoil, in which the half-lives of each Ra isotope determined the primary mechanism(s) controlling radionuclide mobilization from the aquifer solids. Radium-mobilizing processes during storage may include: (1) recharge of low-Ra water into an aquifer containing high-Ra groundwater induced adsorption/desorption disequilibrium and caused net Ra desorption; (2) chemical conditions during storage (e.g. the Ba content of the recharge water or the reducing conditions in the aquifer) could have further released Ra from the aquifer solids or reduced the effectiveness of Ra adsorption; and/or (3) mobilization from radioactive decay of solid-phase thorium parents (alpha recoil) contributed Ra isotopes into the low-Ra recharge water. The short-lived 224Ra was released dominantly by alpha recoil while the longer-lived 226Ra was dominantly released by chemical mechanisms such as desorption. Radium-228, of intermediate half-life, also appears to have been released predominantly by alpha recoil, although significant chemical release of 228Ra cannot be ruled out. Accordingly, at near-neutral pH, groundwater geochemical conditions (such as redox state and/or shifts in Ra activities or Ba concentrations) can influence observed Ra activities in recovered water, which in proportional terms impart the largest effect on the longer-lived 226Ra. Given the roles for both alpha recoil and chemical reactions, the duration of storage could influence radium activities in recovered water from ASR wells.

Groundwater co-contaminant behavior of arsenic and selenium at a lead and zinc smelting facility

Co-contaminant behavior of arsenic (As) and selenium (Se) in groundwater is examined in this study at a former lead and zinc smelting facility. We collected water quality data, including concentrations of trace metals, major ions, and metalloid speciation, over a 15-year period to document long-term trends and relationships between As, Se, geochemical parameters, and other redox-sensitive trace metals. Concentrations of dissolved As and Se were negatively correlated (Kendall's Tau B correlation coefficient, r = −0.72) and showed a distinctive L-shaped relationship. High-concentration arsenic wells (>5 mg L−1) were characterized by intermediate oxidation-reduction conditions (75 < Eh < 275 mV), near-neutral pH (6.1–7.9), low Ca/Na ratios, elevated Fe and Mn concentrations, and high proportions of As(III) relative to total dissolved As. High-concentration Se wells (>500 μg L−1) were characterized by more positive Eh (305–500 mV), low Fe concentrations, and high proportions of As(V). Batch micocosm experiments showed that aquifer solids contain mineral surfaces and/or microbial communities capable of removing selenate from groundwater. Electron microprobe and Se K-edge X-ray absorption near-edge spectroscopic analyses demonstrated that Se was predominantly associated with elemental Se in the reduced aquifer solids. Factor analysis revealed three discernible groupings of trace metals. Group I includes U, Se, and nitrate-N, all of which are mobile under oxygenated to moderately oxygenated conditions. Group II includes elements that are mobile under Fe(III)-reducing conditions: Fe, total dissolved As, As(III), and ammonium-N. Group III elements (Mo, Sb, and V) showed mobility across the entire range of redox conditions encountered in site groundwater; As(V) clustered with this group of elements. Geochemical modeling suggests that As and Se species were in a state of disequilibrium with respect to measured parameters indicative of redox conditions, although predicted patterns of redox-controlled mobility and attenuation were confirmed. This analysis is important to better understand groundwater contaminant behavior in response to redox conditions ranging from oxic/suboxic to Fe(III)-reducing, but excluding sulfate-reducing conditions.

Geological and hydrogeochemical controls on radium isotopes in groundwater of the Sinai Peninsula, Egypt

Radium isotopes (226Ra and 228Ra) were analyzed in 18 groundwater samples from the Nubian Sandstone Aquifer System (NSAS) and the shallow alluvial aquifers overlying the basement complex of the Sinai Peninsula, Egypt. Groundwater samples from deep Nubian aquifer wells (total depths 747 to 1250m) have 226Ra and 228Ra activities ranging from 0.168 to 0.802 and 0.056 to 1.032Bq/L, respectively. The shallower Nubian aquifer wells (63 to 366m) have 226Ra and 228Ra activities ranging from 0.033 to 0.191 and 0.029 to 0.312Bq/L, respectively. The basement shallow alluvial aquifers have 226Ra and 228Ra activities ranging from 0.014 to 0.038 and 0.007 to 0.051Bq/L, respectively. Combined Ra activities in most wells were generally in excess of the US Environmental Protection Agency (EPA), the European Union (EU), and the World Health Organization (WHO) maximum contaminant levels (MCL) for drinking water. Radium in groundwater is produced mainly by decay of parent nuclides in the aquifer solids, and observed activities of dissolved Ra isotopes result from a combination of alpha-recoil, adsorption/desorption, co-precipitation/dissolution processes. The observed correlation between Ra activities and salinity indicates that adsorption/desorption processes may be the dominant factor controlling Ra mobility in Sinai groundwater. Radium activities in central and northern Sinai are generally higher than those in southern Sinai, consistent with a gradual increase in salinity and water-rock interaction with increasing groundwater age. Barite is approximately saturated in the groundwater and may limit maximum dissolved Ra concentration. The results of this study indicate that Sinai groundwater should be used with caution, possibly requiring Ra removal from water produced for domestic and agricultural consumption.

Enhanced adsorption of arsenic through the oxidative treatment of reduced aquifer solids

Arsenic (As) contamination in drinking water is an epidemic in many areas of the world, especially Eastern Asian countries. Developing affordable and efficient procedures to remove arsenic from drinking water is critical to protect human health. In this study, the oxidation of aquifer solids through the use of sodium permanganate (NaMnO4), hydrogen peroxide (H2O2), and exposure to air, enhanced the adsorption of arsenic to the aquifer material resulting in treatment of the water. NaMnO4 was more effective than H2O2. NaMnO4 was tested at different loading rates (0.5, 1.5, 2.4, 3.4, and 4.9 g NaMnO4/kg aquifer material), and after 30 days contact time, arsenic removal ([As+3]INITIAL = 610 μg/L) was 77%, 88%, 93%, 95%, 97%, respectively, relative to un-oxidized aquifer material. Arsenic removal increased with increasing contact time (30, 60, 90 days) suggesting removal was not reversible under the conditions of these experiments. Oxidative treatment by exposing the aquifer solids to air for 68 days resulted in >99% removal of Arsenic ([As+3]INITIAL = 550 μg/L). Less arsenic removal (38.2%) was measured in the un-oxidized aquifer material. In-situ oxidation of aquifer materials using NaMnO4, or ex-situ oxidation of aquifer materials through exposure to air could be effective in the removal of arsenic in ground water and a potential treatment method to protect human health.

Field‐scale observations of a transient geobattery resulting from natural attenuation of a crude oil spill

AbstractWe present evidence of a geobattery associated with microbial degradation of a mature crude oil spill. Self‐potential measurements were collected using a vertical array of nonpolarizing electrodes, starting at the land surface and passing through the smear zone where seasonal water table fluctuations have resulted in the coating of hydrocarbons on the aquifer solids. These passive electrical potential measurements exhibit a dipolar pattern associated with a current source. The anodic and cathodic reactions of this natural battery occur below and above the smear zone, respectively. The smear zone is characterized by high magnetic susceptibility values associated with the precipitation of semiconductive magnetic iron phase minerals as a by‐product of biodegradation, facilitating electron transfer between the anode and the cathode. This geobattery response appears to have a transient nature, changing on a monthly scale, probably resulting from chemical and physical changes in subsurface conditions such as water table fluctuations.