Aquifer Minerals Research Articles

Natural background levels and driving factors of aluminum in shallow groundwater of an urbanized delta: Insight from eliminating anthropogenic-impacted groundwaters.

Knowledge on natural background levels (NBLs) of aluminum (Al) in groundwater can accurately assess groundwater Al contamination at a regional scale. However, it has received little attention. This study used a combination of preselection and statistic methods consisting of the oxidation capacity and the boxplot iteration methods to evaluate the NBL of shallow groundwater Al in four groundwater units of the Pearl River Delta (PRD) via eliminating anthropogenic-impacted groundwaters and to discuss driving factors controlling high NBLs of Al in groundwater in this area. A total of 280 water samples were collected, and 18 physico-chemical parameters including Redox potential, dissolved oxygen, pH, total dissolved solids, HCO3 -, NH4 +, NO3 -, SO4 2-, Cl-, NO2 -, F-, K+, Na+, Ca2+, Mg2+, Fe, Mn, and Al were analyzed. Results showed that groundwater Al NBLs in groundwater units A-D were 0.11, 0.16, 0.15, and 0.08 mg/L, respectively. The used method in this study is acceptable for the assessment of groundwater Al NBLs in the PRD, because groundwater Al concentrations in various groundwater units in residual datasets were independent of land-use types, but they were opposite in the original datasets. The dissolution of Al-rich minerals in sediments/rocks was the major source for groundwater Al NBLs in the PRD, and the interaction with Al-rich river water was secondary one. The high groundwater Al NBL in groundwater unit B was mainly attributed to the acid precipitation and the organic matter mineralization inducing the release of Al in Quaternary sediments. By contrast, the high groundwater Al NBL in groundwater unit C mainly was ascribed to the release of Al complexes such as fluoroaluminate from rocks/soils into groundwater induced by acid precipitation, but it was limited by the dissolution of Mg minerals (e.g., dolomite) in aquifers. This study provides not only useful groundwater Al NBLs for the evaluation of groundwater Al contamination but also a reference for understanding the natural geochemical factors controlling groundwater Al in urbanized deltas such as the PRD. PRACTITIONER POINTS: The natural background level (NBL) of groundwater aluminum in the Pearl River Delta (PRD) was evaluated. The dissolution of aluminum-rich minerals in sediments/rocks was the major source for groundwater aluminum NBLs in the PRD. The acid precipitation and organic matter mineralization contribute to high groundwater Al NBL in the groundwater unit B. The acid precipitation contributes to high groundwater Al NBL in the groundwater unit C, while dissolution of magnesium minerals limits it.

Sources of limestone dissolution from surface water-groundwater interaction in the carbonate critical zone

Dissolution of carbonate minerals in karst aquifers has long been recognized to result from recharge of surface water undersaturated with respect to calcite from carbonic acid produced by hydration of dissolved atmospheric and respired CO2. However, dissolution also results from additional acids produced by reactions of redox sensitive solutes in the subsurface, which may represent a source of CO2 to Earth's atmosphere. Because the magnitude of dissolution by these additional acids is poorly constrained, we compare here fractions of dissolution from initial surface water undersaturation and subsurface redox reactions. Estimates are based on chemical mixing and geochemical (PHREEQC) modeling of time series measurements of water compositions at a spring vent that receives surface water during stream flooding and a stream sink-rise system in north-central Florida. During a single spring reversal, 9.2 × 105 kg of limestone dissolved. At the stream sink-rise system, where subsurface residence times are shorter than during the spring reversal, both limestone dissolution (102–104 kg) and precipitation (102–105 kg) occur as water flows through the conduits with residence times ranging from 10 to 70 h. At both sites, maximum calcite dissolution rates of ∼10 μM hr−1 occurs at subsurface residence times between 30 and 50 h. For subsurface residence time > ∼20–60 h, the models indicate that production of additional acid in the subsurface is required for ∼53 ± 7% of dissolution. Oxidation of organic carbon, ammonium, pyrite, iron, and/or manganese produce sufficient acid for additional dissolution, but dissolved oxygen is insufficient for these reactions, indicating some acidity is generated under anerobic conditions. Dissolution caused by subsurface reactions in our samples represents mobilization of 20 × 104-30 × 104 kg of CO2 via remineralization of organic carbon or carbonate dissolution by nitric and sulfuric acids. Acid produced by subsurface redox reactions during surface water-groundwater interactions, including non‑carbonic acids, are important in conduit development and carbon cycling in the carbonate critical zone.

Activation of iron oxide minerals in an aquifer by humic acid to promote adsorption of organic molecules

In aquifers, the sequestration and transformation of organic carbon are closely associated with soil iron oxides and can facilitate the release of iron ions from iron oxide minerals. There is a strong interaction between dissolved organic matter (DOM) and iron oxide minerals in aquifers, but the extent to which iron is activated by DOM exposure to active iron minerals in natural aquifers, the microscopic distribution of minerals on the surface, and the mechanisms involved in DOM molecular transformation are currently unclear. This study investigated the nonbiological reduction transformation and coupled adsorption of iron oxide minerals in aquifers containing DOM from both macro- and micro perspectives. The results of macroscopic dynamics experiments indicate that DOM can mediate soluble iron release during the reduction of iron oxide minerals, that pH strongly affects DOM removal, and that DOM is more efficiently degraded at low rather than high pH values, suggesting that a low pH is conducive to DOM adsorption and oxidation. Spherical aberration-corrected scanning transmission electron microscopy (SACTS) indicates that the reacted mineral surfaces are covered with large amounts of carbon and that dynamic agglomeration of iron, carbon, and oxygen occurs. At the nanoscale, three forms of DOM are found in the mineral surface agglomerates (on the surfaces, inside the surface agglomerates, and in the polymer pores). The microscopic organic carbon and iron mineral reaction patterns can form through oxidation reactions and selective adsorption effects. Fourier transform ion cyclotron resonance mass spectra indicate that both synergistic and antagonistic reactions occur between DOM and the minerals, that the release of iron is accompanied by DOM decomposition and humification, that large oxygen- and carbon-containing molecules are broken down into smaller oxygen- and carbon-containing compounds and that more molecules are produced through oxidation under acidic rather than alkaline conditions. These molecules provide adsorption sites for sediment, meaning that more iron can be released. Microscopic evidence for the release of iron was acquired. These results improve the understanding of the geochemical processes affecting iron in groundwater, the nonbiological transformation mechanisms that occur at the interfaces between natural iron minerals and organic matter, groundwater pollution control, and the environmental behavior of pollutants.

Using hydrogeochemical facies and signatures for groundwater characterization and evolution assessment in aquifers with contrasting climate and geology in Tanzania

This study aimed at characterizing groundwater evolution using hydrogeochemical facies and signatures in two basins with contrasting climate and geology, one in the central part and the other in the eastern coast of Tanzania. The Kimbiji (humid, unconsolidated) aquifer is covered by an unconfined layer in the upper parts and a confined layer in the lower parts, with strong artesian flow characteristics while groundwater in the Singida (semi-arid, consolidated) aquifer occurs in weathered shallow layers and in fractures of basement rocks. Fieldwork involved water sampling from precipitation, deep and shallow boreholes, springs and surface water from rivers and lakes in the two study areas. These were specifically conducted for hydrogeochemical analyses to unravel hydrogeochemical facies and signatures in the two aquifers. Physico-chemical water quality parameters [i.e., pH, electrical conductivity (EC) and total dissolved solids (TDS)] were measured in situ using HANNA HI 9829 Multiparameter Analyzer. Standard procedures for water sampling, preservation, transportation, and chemical analyses of major ions were conducted as documented in previous studies. Samples were carried and stored at 4 °C prior to their shipping and analyses at Water analysis and testing in environmental regions (WATER) laboratory in Iringa, Tanzania. The mechanism controlling groundwater geochemistry were revealed by assessing the reactions between groundwater and aquifer minerals. Chloro-Alkaline indices (CAIs) were used to study cation exchange processes between the groundwater and its host environment at stagnancy and/or during groundwater travel. The Gibbs ratio 1 values were found to range from 0.26 to 0.94 and Gibbs ratio 2 values ranged from 0.11 to 0.95. The majority of the samples irrespective of the contrast in climate and geology were observed to fall in the rock–water interaction zone. This is attributed to chemical weathering processes where the dissolution of rock forming minerals takes place. Some samples exhibited replacement of Na+ by Ca2+ or Mg2+ (S18), loss of Na+ through precipitation of evaporate rocks (S11, S13, S16, S19), and water flowing through crystalline rocks (S1, S2, S4, S6, S8, S10, S12, S13, S14, S21). The ratio Na+: Ca2+ > 1.0 (S1, S4, S8, S10, S12, S14, S17, S18, S19, S21) explains base ion exchange while the ratio < 1 implies a reverse ion exchange (S2, S6, S11, S13, S16).The Ca2+: SO42− + HCO3− ratio < 1.0 connotes groundwater flowing through a normal hydrological cycle (S1, S4, S8, S10, S12, S14, S17, S18, S2, S6, S11, S13, S21) and a ratio greater than 1 is an indication of Ca2+–Cl− brines (S16, S19). The HCO3−: Cl− hydrogeochemical signatures divided the Singida aquifer into upper water flow course, where groundwater recharge occurs (S52, S54, S56, S57, and S58) and the discharge zone, (S53, S59, S60, S61) which is a lower groundwater flow course. Interestingly, the Mg2+ + Ca2+: Na+ + K+ ratios as well confirmed that the Singida aquifer is a lower groundwater flow course (discharge zone). The greater than 1 Na+: Ca2+ ratios confirm the dominance of base ion exchange in the Singida aquifer as it has been explained by the CAIs and the Piper diagram. The Gibbs diagrams revealed that the hydrochemistry of groundwater in the Kimbiji and Singida aquifers are mainly in the rock weathering region, affirming that there is high dissolution with rock forming minerals. This is thus one of the main controls of groundwater mineralization in the two study areas. The similarity of hydrogeochemical signatures between a distant surface water body, Lake Inkhanoda and Mwankoko borehole in the Singida aquifer is an indication that there is a discernible interaction between groundwater and surface water, further revealing that the Singida aquifer is fed by sub-regional and regional groundwater flow systems.

Impact of nitrogen and sulfur fertilizers on leaching behavior of heavy metals from aquifer sediments to groundwater

BackgroundThe groundwater of the Bathinda district of Punjab is contaminated with heavy metals, nitrate (NO3), and sulfate (SO4) exceeding the BIS limits for drinking water in many areas. The article attempts to understand the role of fertilizers, nitrate and sulfate, in the mobilization of heavy metals from the aquifer minerals. MethodHeavy metal mobilization from aquifer sediments was studied through batch experiments using artificial groundwater (AGW) with varying concentrations of NO3 and SO4. For actual field conditions, column experiments were conducted with artificial groundwater containing 50 ppm NO3 as mobile phase and 1 ml/minute flow rate. The leached metal ions from the sediments were analyzed with ICP-MS. Significant findingsIt was found that compared to the AGW without NO3 and SO4, the heavy metal mobilization potential of AGW with NO3 and SO4 was significantly enhanced. The presence of nitrate significantly influenced the leaching of Cr, Co, Ni, Zn, and Hg, moderately affected the mobilization of As, and least impacted the mobilization of Fe, Mn, Cu, Cd, Pb, and U. An increase in leaching of Cr, Mn, Ni, Zn, As, and U was observed with the increase in SO4 concentration from 0 to 400 ppm, however, drastic reduction was observed with SO4 concentration of 500 ppm indicating high concentration of SO4 is posing an inhibitory action. The concentration of Cr, Fe, Co, Ni, Cu, Zn, Se, and Pb were significantly positively correlated indicating similar processes driving the mobilization of these metals. To reduce the mobilization of toxic heavy metals from the aquifer sediments, the NO3 and SO4 from the wastewater and agricultural run-off should be removed/reduced to the extent possible through optimized fertilizer usage, use of organic fertilizers, and treating the wastewater before discharging in the environment.

Impact of past mining activities on water quality in a karst area in the Cévennes region, Southern France

Sampling and analysis of groundwater and surface water were conducted to assess the potential impacts of abandoned mines on water quality in a karst area in Southern France. The results of multivariate statistical analysis and geochemical mapping revealed that water quality is affected by contaminated drainage from abandoned mine sites. Acid mine drainage with very high concentrations of Fe, Mn, Al, Pb and Zn was identified in a few samples collected from mine openings and near waste dumps. In general, neutral drainage with elevated concentrations of Fe, Mn, Zn, As, Ni and Cd was observed due to buffering by carbonate dissolution. The contamination is spatially limited around abandoned mine sites, suggesting that metal(oid)s are sequestered in secondary phases that form under near-neutral and oxidizing conditions. However, the analysis of seasonal variations in trace metal concentrations showed that the transport of metal contaminants in water is highly variable according to hydrological conditions. During low flow conditions, trace metals are likely to be rapidly sequestered in Fe-oxyhydroxides and carbonate minerals in the karst aquifer and the river sediments, while low or no surface runoff in intermittent rivers limits the transport of contaminants in the environment. On the other hand, significant amounts of metal(loid)s can be transported under high flow conditions, primarily in dissolved form. Dissolved metal(loid) concentrations in groundwater remained elevated despite dilution by uncontaminated water, likely as a result of the increased leaching of mine wastes and the flushing of contaminated waters from mine workings. This work shows that groundwater is the main source of contamination to the environment and highlights the need to better understand the fate of trace metals in karst water systems.

Fluvial and Marine Depositional Environments Determined From Groundwater Chemistry and Calculated Clay‐Cation Compositions

AbstractCation mole precents (XCa, XMg, and XNa) on clay minerals in a siliciclastic coastal aquifer calculated from groundwater compositions, can aid in distinguishing fluvial from marine sediments and locate the fluvial/marine transition zone. The clay‐cation compositions of two clay‐rich siliciclastic coastal aquifers calculated from the composition of the groundwater were compared to the location of fluvial, fluvial‐marine transition and marine environments identified by traditional core, well log and paleontological analyses. The traditionally defined fluvial depositional environment is distinguished by clays with low XNa &lt; 8% (for 92% of the samples) and high XCa from 55% to 98% with the remainder XMg. In comparison, the traditionally defined marine depositional environment is distinguished by clays with higher XNa &gt; 8.0% (for 86% of the samples) and lower XCa ranging from 5% to 39% with the remainder XMg. The traditionally defined fluvial/marine transition zone has values overlapping the fluvial and marine end members, with 59% with XNa &lt; 8% (fluvial) and 41% with XNa &gt; 8% (marine), and XCa ranging from 45% to 98% with the remainder XMg. Calculations support that the excess Na (XNa &gt; 8%) on marine clays can be retained for 10s of millions of years despite flushing with meteoric water, because of the high clay content in marine sediments. The calculated cation composition of clays deposited from river water are XNa &lt; 8%. In contrast XNa 8%–54% is possible for seawater equilibrated clays supporting that the values found in the different depositional zones are possible. Calculated cation compositions might supplement traditional stratigraphic interpretations in distinguishing fluvial/marine depositional environments.

Evaluation of the groundwater quality index (GWQI) and the human health risk (HHR) on fluoride concentration in Namakkal district, South India

This research aims to determine the health consequences of fluoride contamination of groundwater in the Namakkal region in south India using the groundwater quality index (GWQI). Study area latitude and longitude: 11° 00' and 11° 30' in the north, and 77° 45' and 78° 15' in the east. Statewide, it is among the largest districts in the state. The study region occupies an area of 3406.37 km2. The geology of the studied area is mainly based on the Archaean crystalline and metamorphic complex. The district's major aquifer systems are composed of crystalline rocks that are weathered and fractured and of colluvial deposits. Alluvium and colluvium are examples of porous formations in the cross-section. Only the main river channels have alluvial deposits. The phreatic properties of groundwater Depending on the topography, these aquifers may reach 5 m saturation thickness. Groundwater samples were obtained from 58 bore well sites across the study area during the North-East Monsoon (NEM) of 2015. pH concentrations in suitable drinking water regions during the seasons assist in limiting the availability of groundwater for drinking purposes. TDS are an important factor in determining water suitability for various purposes. The groundwater sample in the study area shows cation domination in ascending order of Na+ &gt; Ca2+ &gt; Mg2+ &gt; K+ due to the dissolution of aquifer minerals in rainfall in the study area. In the NEM seasons, rock dominance and anthropogenic contributions to higher Na+ &gt; Mg2+ &gt; Ca2+ &gt; K+ values. Fluoride concentration differentiates into three groups such as &lt; 0.5 indicates low risk, 0.5 to 1.5 indicates moderate risk, and &gt; 1.5 means high risk. More than 2 fluoride implies very high risk, whereas fluoride in the range of 1.5 to 2.24 suggests a very high risk. The appraisal of non-carcinogenic risk was done to stress the health issues that succeed due to the intake and dermal contact of drinking water in the Namakkal district. The percentage of risk HQ &gt;1 shows that 48 men groundwater samples, followed by 46 groundwater samples women and 30 groundwater samples children, constitute possible health hazards. Overall, health risk estimation results showed that all the groundwater samples have surpassed the permissible limit of HQ &lt;1 for children.

Hydrogeochemical and Characteristics of Groundwater in Teluk Nilap Area, Rokan Hilir, Riau

Groundwater plays important role as the main water resource for human needs. The vulnerability of groundwater to contaminants both naturally and by human activities can be not avoided as a trigger for groundwater quality degradation. Hydrogeochemical become important highlights in groundwater studies because groundwater conditions in quality and quantity influenced by the geological formation of rock minerals in aquifer. Naturally, the condition of the research area which consists of peat swamps can also affect the characteristics of groundwater. The aims of this research are to determine groundwater types and groundwater facies in study area with an analytical approach using stiff diagram and piper diagram. The method used was purposive sampling by collecting data from dug wells at the research site. 5 samples from dug wells were used as representatives in the groundwater facies analysis. The groundwater facies analysis was carried out by measuring the concentration of major ions such as Na, K, Ca, Mg, Cl, SO4, and HCO3. The highest groundwater level was in the northern part of study area (7,84 m) while the lowest groundwater level was in the southwest part of study area (2,05 m). The results showed three types of groundwater based on stiff diagram as sodium chloride (NaCl), sodium sulfate (NaSO4) and magnesium sulfate (MgSO4). The lithology conditions that composed the aquifer affected the facies or origin of groundwater. The alluvium layer in the research area which rich in sodium (Na+) minerals with chloride (Cl-) or sulfate (SO42-) anions forms chloride sulfate facies (Cl+SO4) which were located in the middle to the south of the study area and sodium (potassium) chloride (sulfate) facies (Na(K)Cl(SO4)) which were distributed in the northern part of study area.

Effect of Down-Hole Lithological Variation on Water Bearing Capacity of Some Boreholes in Ilorin, Nigeria

"Effect of Down-Hole Lithological Variation on Water Bearing Capacity of Some Boreholes in Ilorin, Nigeria. The paper attempts to explain the effect of downhole lithological variation on water bearing capacity of some boreholes in Ilorin Nigeria. Specifically, the study examined the lithological characteristics of the boreholes, assessed the variability in weathered overburden and analyzed the inter-relationships between lithology, hydrology and topography of the boreholes. Data used were extracted from twenty (20) borehole logs collected from the archive of Lower Niger Basin Development Authority in Ilorin. Information extracted from the borehole logs are: the number of lithological units intersected by each of the borehole and their depths, the nature of geological materials making up the lithological units and their moisture conditions. Information on coordinates and topographic heights of the boreholes are not given on the logs and those were collected from the field personally by the researcher using handheld GPS (Garmin GPS Channel 76 Model). The collected data were analyzed using descriptive statistics. Results reveal nine downhole lithological units with loamy and lateritic soil making up the first layer of lithology in 95% of the boreholes. Thickness of the top soil and the saprolite overlying the bedrock, has mean values of 4.2m and 11.3m respectively. Depth to water in the borehole ranged between 24.7 and 140m and with a mean value of 55.9m. Three (3) of the boreholes have two lenses of aquifer while the remaining seventeen (17) have one aquifer lens each. The three (3) boreholes with two aquifer lenses have their minor aquifers located within the saprolite. The main aquifer in most (65%) of the boreholes is located within the fractured basement while the remaining (35%) boreholes have their main aquifer located in the weathered basement. Correlation analysis revealed topographic elevation as one of the drivers of hydrology in the study area. Keywords: lithology, groundwater, saprolite, basement, topography. "

Formation of an up-flow hot spring of SO4-Ca type in the sandstone aquiclude near an anticline

The formation of springs is vital for understanding the subsurface transport of substances and energy in groundwater circulation. The Xiannvshan hot spring in the sandstone aquiclude near the Tongluoxia anticline in northeast Sichuan Basin of China is an up-flow spring discharging thermal groundwater from the underlying carbonate aquifer of the basin-anticline controlled type. This rarely-encountered up-flow spring neither issues directly from an aquifer, nor is controlled by a fault. The spring water is a very hard (hardness of 1050.069-1835.697 mg/L) and brackish hot spring water (TDS of 1650-2802 mg/L) of SO4-Ca type and low temperature (34-38°C) issuing from a neutral and reduction subsurface environment, and is characterized by high ratios of γNa/γCl (average 1.354) and low γCa/γSO4 (average 0.779), and high concentrations of Sr (7.62-17.183 mg/L) and F (1.87-8.15 mg/L). The ΣMREE of the hot water samples are greater than ΣLREE, and positive Eu and negative Ce anomalies exist. The dissolved constituents in the hot water are derived from the dissolution of calcite, dolomite, anhydrite, gypsum, polyhalite, halite, albite and K-feldspar and small amount of sylvite, epsomite, thenardite, langbeinite, celestite, barite, strontianite, magnesite, and fluorite in the carbonate aquifer, and the dissolution of sulphates prevails in the groundwater system. Hydrochemical similarity is found among the water samples from the two springs’ vents and the flowing borehole near the vents. Faster groundwater circulation caused by the flowing hot water borehole encourages the dissolution of minerals in the carbonate aquifer and slightly increases the TDS and temperature of the hot water from the flowing borehole.

The triple argon isotope composition of groundwater on ten-thousand-year timescales

Understanding the age and movement of groundwater is important for predicting the vulnerability of wells to contamination, constraining flow models that inform sustainable groundwater management, and interpreting geochemical signals that reflect past climate. Due to both the ubiquity of groundwater with order ten-thousand-year residence times and its importance for climate reconstruction of the last glacial period, there is a strong need for improving geochemical dating tools on this timescale. Whereas 14C of dissolved inorganic carbon and dissolved 4He are common age tracers for Late Pleistocene groundwater, each is limited by systematic uncertainties related to aquifer composition and lithology, and the extent of water-rock interaction. In principle, radiogenic 40Ar in groundwater acquired from decay of 40K in aquifer minerals should be insensitive to some processes that impact 14C and 4He and thus represent a useful, complementary age tracer. In practice, however, detection of significant radiogenic 40Ar signals in groundwater has been limited to a small number of studies of extremely old groundwater (>100 ka). Here we present the first high-precision (<1‰) measurements of triple Ar isotopes (40Ar, 38Ar, 36Ar) in groundwater. We introduce a model that distinguishes radiogenic 40Ar from atmospheric 40Ar by using the non-radiogenic Ar isotopes (36Ar, 38Ar) to correct for mass-dependent fractionation. Using this model, we investigate variability in radiogenic 40Ar excess (Δ40Ar) across 58 groundwater samples collected from 36 wells throughout California (USA). We find that Δ40Ar ranges from ~0‰ (the expected minimum value) to +4.2‰ across three study areas near Fresno, San Diego, and the western Mojave Desert. Based on measurements from a network of 23 scientific monitoring wells in San Diego, we find evidence for a strong dependence of Δ40Ar on aquifer lithology. We suggest that Δ40Ar is fundamentally controlled by the weathering of old K-bearing minerals and thus reflects both the degree of groundwater-rock interaction, which is related to groundwater age, and the integrated flow through different geological formations. Future studies of Late Pleistocene groundwater may benefit from high-precision triple Ar isotope measurements as a new tool to better interpret 14C- and 4He-based constraints on groundwater age and flow.

Geochemical modeling to infer genetic origin of groundwater and associated health risks in desertic aquifers

Lower rainfall coupled with higher evapotranspiration leads to enhanced salinity and inorganic contamination of groundwater in arid and semi-arid regions. In this study, 100 groundwater samples were collected from a part of the Thar Desert of India and analysed for various physico-chemical water quality parameters for quality assurance for potablewater supply. The electrical conductivity of the samples showed an ion-enriched aquifer environment with high alkalinity. The concentration of Na+, SO42−, Cl−, NO3− and F− ions in most of the samples were above the World Health Organization (WHO) guidelines for drinking water, posing a major public health concern. Saturation indices (SI) indicates that the dissolution of calcite bearing minerals and ion-exchange were major processes controlling the groundwater chemistry in the region. Most of the samples are oversaturated with aragonite, calcite, chalcedony, and dolomite while undersaturated with anhydrite, gypsum, halite. The results suggest that weathering of aquifer minerals and salinization due to high evaporation controls the quality and origin of major ions. The Na–Cl and Na–HCO3 water facies indicates the influence of evaporation and thus conducive condition for F− enrichment in groundwater while NO3− is mostly due to anthropogenic activities. The health index (HI) for risk assessment suggests both F− and NO3− contribute to the health risk of the residing population as the HI values were found to be > 1 in 97% and 93% for children and adults, respectively. The treatment technologies should be adopted to remove the multiple contaminants present in the groundwater of this region.

Regional hydrogeology of the Arab-D aquifer in Central and Eastern Saudi Arabia with highlighting its environmental and energy potential

The Jurassic Arab-D reservoir hosts major oil-producing zone in Eastern Saudi Arabia with production from individual wells exceeding 25000 B/D. From a water supply perspective, Saudi water authorities consider it a minor aquifer with small yields of relatively high salinity; hence, it did not receive much attention in previous studies of aquifers. The present paper describes regional hydrogeological characteristics of the Arab-D in terms of groundwater flow, salinity and temperature, and discusses geological factors controlling these characteristics. Although high groundwater salinity in the Arab-D precludes it from being a potential water supply resource, studying the hydrogeology of Arab-D provides a hydrodynamic tool to oil exploration and development project. It also sets the stage for detailed studies of Arab-D aquifer potential use for industrial effluent disposal and as new geothermal energy source. Most of groundwater flow in Arab-D occurs in the porous and permeable grainy-textured upper zones. The top limit of the groundwater flow domain in Arab-D is the overlying massive Arab-D anhydrite unit. Trends in Arab-D hydraulic head, water salinity and temperature show gravity-driven flow towards the coastal region of Eastern Arabia. Major anomalies in these trends exist near the Ghawar, Summan, Jauf and Yabrin north-south faults. These anomalies are results of fault zone architecture that consists of sealing fault core zones surrounded by conductive fault damage zones. Depth, salinity, and temperature of the Arab-D between north Ghawar and Berri fields show that it has potential uses for industrial effluent disposal and geothermal energy projects.

Sources and hydrogeological conditions that cause high iodine concentrations in deep groundwater in the Zhangwei watershed, North China Plain

The sources and primary mechanisms of high iodine concentration in deep groundwater are rarely reported, thereby restricting the development and utilization of the related groundwater resources. To address these issues, 194 deep groundwater samples were collected from the Zhangwei watershed in the North China Plain, China, to analyze their constituents including iodine. Statistics, principal component analysis and hydrological methods were employed to determine the distribution of iodine concentrations and their controlling hydrogeochemical processes. The results show that the iodine concentration ranged from 2 to 446 μg/L and generally increased along the groundwater flow direction. Three zones with high iodine concentration (> 20 μg/L) were delineated as the alluvial–proluvial plain (Zone A, average 70 μg/L), alluvial–lake plain (Zone B, average 83 μg/L) and coastal plain (Zone C, average 199 μg/L), respectively. In Zone A, aquifer minerals weathering probably releases iodate ions into groundwater. The iodate is reduced with nitrate as the electron acceptor of iodine and transported with the precipitation infiltrating through the vadose zone to recharge groundwater, resulting in increasing the groundwater iodine concentration. In Zone B, the iodine concentrations depend on the contents of the organic matter, clay minerals, and iron aluminum oxide in the alluvial–lake sediments, due to that the deeply buried organic matter is rich in iodine which is released into groundwater through the biodegradation of organic matter, In Zone C, the iodine is probably derived from the sediments which were deposited in Quaternary marine transgression events, and its enrichment was controlled by the strong reduction condition of the deep aquifers. In one word, the iodine sources and hydrogeological conditions determined the high iodine concentrations of deep groundwater in the studied watershed. These findings can provide foundation for further insight into the high iodine concentration of deep groundwater in other hydrogeological units of the North China Plain and other similar units over the world, thereby ensuring drinking groundwater safety.

A numerical model of groundwater flow in Karewa-Alluvium aquifers of NW Indian Himalayan Region

Process-based groundwater flow models are an important tool for gaining useful insights into the hydrogeological characteristics of a complex aquifer system. A conceptual model of a multilayer alluvial aquifer system at the base of Karewa mountain front is presented indicating the hydrogeological framework and the various flow processes affecting the groundwater flow system. Based on the conceptual model, a MODFLOW NWT-based numerical simulation model of groundwater flow was developed for the region. As interpreted from the hydrogeological framework, the simulation was carried out in the context of two aquifers, the top minor aquifer which is regarded as confined–unconfined and the lower major predominantly confined aquifer. Hydraulic heads measured in 104 wells during predevelopment period were used to calibrate hydraulic conductivity, natural recharge and evapotranspiration for the steady state model. For validation, observations from 38 wells corresponding to a recent steady state of aquifers were used. Performance statistic R2 = 0.83 and 0.79 for calibration and validation, respectively. Steady-state groundwater budgets including natural recharge were thus estimated. Calibrated horizontal hydraulic conductivity of aquifers is of the order of 0.0015–0.0031 m/s. Total natural recharge to the aquifers from precipitation and mountain subsurface flow corresponding to predevelopment and recent conditions was estimated as 96.39 and 64.21 Mm3/month, respectively. Steady-state simulations indicate an average decline of 2–5 m in groundwater heads over a period of about two decades, attributable to decreased recharge. Results of this model can help in sustainable development of groundwater in the region.

Potential for uranium release under geologic CO2 storage conditions: The impact of Fe(III)

Saline aquifers are considered ideal subsurface sinks for large amounts of CO2 storage. It is common to have trace levels of uranium-bearing minerals (naturally occurring radioactive material, NORM) in sandstone saline aquifers and CO2 injection may cause uranium mobilization due to the coupled chemical and physical interactions at mineral-water interfaces. In this study, we developed a TOUGHREACT model to assess the uranium mobilization potential from uraninite (UO2) dissolution induced by CO2 injection into a hypothetical CO2 storage reservoir with Fe(III)-bearing hematite in a time scale of 30 years CO2 injection and 100 years after CO2 injection. Numerical simulation results show that injection of CO2 reduced pH and induced small amounts of hematite dissolution, which released Fe3+ into aqueous phase. Fe3+ together with dissolved bicarbonate species caused oxidative dissolution of UO2 (Fe3+ serving as an oxidant), resulting in an increase of dissolved uranium concentrations in the CO2 storage reservoir. However, the released uranium was limited to a small region close to Fe3+ supply source and the maximum concentration of released uranium was only 9.00 × 10−10 mol/kg in the CO2 storage reservoir at t = 30 years. The availability of Fe3+ is the main factor that limits mineralized uranium release because the pH drop induced by CO2 injection is not low enough to cause significant Fe3+ release. For sorbed uranium, the main factor that influences sorbed uranium release is pH because uranium sorption is amphoteric. Based on our simulation results, the pH range in the CO2 storage reservoir does not cause a substantial release of sorbed uranium. Also, the potential for released uranium to migrate through a permeable zone in the caprock to the layer above the caprock and cause groundwater contamination is negligible. In summary, results from this study imply a very low risk of environmental contamination by bicarbonate and Fe(III)-induced uranium mobilization.

Characterization of weathering profile and quality of groundwater over hard rock terrain

In this study, we present a detailed characterization of weathering profile and groundwater over a hard rock terrain showing the formation of kaolinite, groundwater quality assessment, and hydrogeochemistry. The crystal structure, chemical composition, and spectral characteristics of a weathering profile collected from Thiruvananthapuram district, the southern part of Kerala, India, were studied using XRD, ED-XRF, TG-DTA, UV-Vis-NIR, XPS, and FTIR spectroscopy. The physicochemical parameters of the groundwater were determined and evaluated for the groundwater suitability for drinking, irrigation, and industrial purposes based on the values of total hardness, TDS, corrosivity ratio, RSC, SAR, USSL classification, saturation index, and Schoeller and Stuyfzand classification derived using “HYCH” program. Interpretation of the results shows that the groundwater is suitable for drinking, irrigation, and industrial purposes. The characterization of the profile samples reveals that the aquifer is a weathered profile with the formation of kaolinite mineral at the bottom. The results show that the hydrogeochemical processes that exist in the present study area are controlled by precipitation, not by rock–water interaction or evaporation, which suggests that the groundwater chemistry is not influenced by the aquifer minerals.

Elevated radium levels in Nubian Aquifer groundwater of Northeastern Africa

The Nubian Sandstone Aquifer System in Northeast Africa and the Middle East is a huge water resource of inestimable value to the population. However, natural radioactivity impairs groundwater quality throughout the aquifer posing a radiological health risk to millions of people. Here we present measurements of radium isotopes in Nubian Aquifer groundwater from population centers in the Western Desert of Egypt. Groundwater has 226Ra and 228Ra activities ranging from 0.01 to 2.11 and 0.03 to 2.31 Bq/L, respectively. Most activities (combined 226Ra + 228Ra) exceed U.S. EPA drinking water standards. The estimated annual radiation doses associated with ingestion of water having the highest measured Ra activities are up to 138 and 14 times the WHO-recommended maxima for infants and adults, respectively. Dissolved Ra activities are positively correlated with barium and negatively correlated with sulfate, while barite is approximately saturated. In contrast, Ra is uncorrelated with salinity. These observations indicate the dominant geochemical mechanisms controlling dissolved Ra activity may be barite precipitation and sulfate reduction, along with input from alpha-recoil and dissolution of aquifer minerals and loss by radioactive decay. Radium mitigation measures should be adopted for water quality management where Nubian Aquifer groundwater is produced for agricultural and domestic consumption.

Evaluation of natural background levels of high mountain karst aquifers in complex hydrogeological settings. A Gaussian mixture model approach in the Port del Comte (SE, Pyrenees) case study

The hydrogeological processes driving the hydrochemical composition of groundwater in the alpine pristine aquifer system of the Port del Comte Massif (PCM) are characterized through the multivariate statistical techniques Principal Component Analysis (PCA) and Gaussian Mixture Models (GMM) in the framework of Compositional Data (CoDa) analysis. Also, the groundwater Natural Background Levels (NBLs) for NO3 and SO4 and Cl are evaluated, which are specially important for indicating the occurrence of groundwater contamination derived from the anthropic activities conducted in the PCM.The different hydrogeochemical facies found in the aquifer system of the PCM comprises low mineralized Ca-HCO3 water for the main Eocene karst aquifer, and Ca-SO4 and highly mineralized NaCl water types in the minor aquifers discharging from the PCM. The NBL values of SO4, Cl and NO3 obtained for the main karst aquifer are 14.33, 4.06 and 6.55 mg/L, respectively. These values are 35, 3 and 1.2 times lower than the respective official NBLs values that were determined by the water administration to be compared with in the case of conducting a pollution assessment characterization in the main karst aquifer. Official overestimation of NBLs can put important groundwater resources in the PCM at risk.