Cl HCO3 Research Articles

Hydrogeochemical evolution and assessment of groundwater quality in the Togo and Dahomeyan aquifers, Greater Accra Region, Ghana

Groundwater quality is generally better than surface water quality but this is not sacrosanct because during recharge and abstraction, groundwater may be subjected to variations due to influence from natural and anthropogenic processes. The Togo and Dahomeyan aquifers are threatened by several anthropogenic activities like dumping of domestic and industrial wastes in open landfill sites. These activities can be sources of groundwater constituents and can pose adverse health effects on humans and the ecosystem but little is known about the hydrogeochemical characteristics of groundwater and its quality in the area. Therefore, the present study is aimed at unravelling the hydrogeochemical characteristics and quality of groundwater in the Togo and Dahomeyan aquifers in the Greater Accra Region of Ghana. A total of 37 groundwater samples were collected and analysed for the concentrations of major ions, minor ions, and trace elements. The results were used to compute water quality parameters like electrical conductivity, sodium adsorption ratio, sodium percent, and magnesium ratio to assess the quality of the water for irrigation purposes. Groundwater shows acidic to slightly alkaline pH and evolved from Mg–Na–HCO3, Ca–Na–Mg–HCO3, Na–Ca–Mg–HCO3–Cl to Na–Mg–Ca–HCO3 with other mixed water types, which reflect the local geology. Geochemical modelling indicates that groundwater is supersaturated with respect to goethite and hematite and saturated with respect to calcite, aragonite, and dolomite in some samples. Hydrochemical graphing and multivariate statistical analysis indicate that the chemistry of groundwater in the area is primarily controlled by an interplay of chemical weathering, mineral dissolution, ion exchange reactions, agricultural activities, and sewage disposal. The groundwater is not entirely suitable for drinking purposes because of high concentrations of EC, TDS, Na+, Cl−, F−, Fe, Mn, Pb, Cr, and Ni, which exceed their maximum permissible limits provided by the World Health Organization. The computed parameters for assessing the quality of the water for irrigation reveal that 64.9% of the samples are suitable for irrigation purposes. However, 35.1% of the samples show very high salinity and sodium hazard and thus, are unsuitable for irrigation purposes. Therefore, it is recommended that mixing of the high salinity and sodium water with low salinity and sodium water can improve crop yields.

Integration of hydrochemical and isotopic characteristics for identifying groundwater recharge sources of the Eocene carbonate aquifer, Western Desert, Egypt

The Western Desert is considered as one of the most promising areas for groundwater resource and development in Egypt. The Eocene carbonate aquifer is one of the most exploited aquifers for development in the Egyptian Western Desert, especially in the area west of El-Minia in central Egypt. The present study aims to assess the hydrochemistry of the Eocene carbonate aquifer and the possible recharge sources to this aquifer in the western desert west of El-Minia district. Fifteen groundwater samples from the Eocene carbonate aquifer were analyzed for major ions, heavy metals, oxygen-18, and deuterium to assess the hydrochemistry and isotopic compositions in this area. TDS concentrations ranged from 510 to 1408 mg/l. However, the cluster analysis of the Eocene groundwater samples in the present work, reveals two main groups (A and B) with different chemical and isotopic characteristics. The chemical composition of the studied samples showed that the main chemical facies are Na–Cl, Na–Ca–HCO3, and Na–Cl–HCO3. Silicate weathering control the majority of groundwater samples of the Eocene aquifer, while carbonate dissolution governing the deep groundwater of Eocene carbonate aquifer. Isotope ratios of oxygen (18O) and hydrogen (2H) were used to identify the recharge sources, which showed relatively depleted 18O and 2H isotopic ratios and relative mixing of groundwater from the Eocene Limestone with paleowaters from the deep Nubian aquifer and water from the Nile River. However, the mixing ratio depends mainly on the distance from the Nile River, depth to groundwater, and local geologic structures also contribute to the mixing pattern. The present study indicates the need for a detailed structural study to detect the locations and properties of fractures as it plays a vital role in feeding the Eocene aquifer from the underlying aquifer. Integration of hydrogeochemical data and isotopic compositions provide a better understanding of the geochemical processes that control the groundwater hydrochemistry of the Eocene carbonate aquifer west of El-Minia, Egypt and in areas with similar conditions.

Thermodynamic modeling of calcium carbonate scale precipitation: aqueous Na+-Ca2+-Cl–-HCO3–-CO32–-CO2 system

To allow for accurate calculations of calcium carbonate scaling in highly saline produced waters, we present a comprehensive thermodynamic model based on the electrolyte nonrandom two-liquid (eNRTL) activity coefficient equation for the aqueous Na+-Ca2+-Cl–-HCO3–-CO32–-CO2 system. The eNRTL binary interaction parameters for the H2O:(Na+-CO32–) pair, the H2O:(Na+-HCO3–) pair, the (Na+-Cl–):(Na+-CO32–) pair, and the (Na+-Cl–):(Na+-HCO3–) pair are identified in this work via the regression of thermodynamic, calorimetric, and phase equilibria experimental data. The binary interaction parameters associated with the H2O:(Na+-Cl–) pair, the CO2:(Na+-Cl–) pair, the H2O:(Ca2+-Cl–) pair, and the (Na+-Cl–):(Ca2+-Cl–) pair are retrieved from the literature. The remaining binary interaction parameters are retrieved from Aspen Plus or set to zero. In addition, the solubility product constants are identified for Na2CO3•10H2O(s), Na2CO3•7H2O(s), Na2CO3•H2O(s), Na2CO3•NaHCO3•2H2O(s), Na2CO3•3NaHCO3(s), and CaCO3(s) via regression of solubility data. The model is capable of accurately calculating all phase equilibria and calorimetric properties at temperatures up to 473.15 K and salt concentrations up to saturation.

Geochemical behavior of Mo and W in the CO2-rich mineral waters occurring in the East Elbrus area

Molybdenum and tungsten concentrations in cold CO2-rich mineral groundwaters of east Elbrus area lie in two ranges: 0.01-0.43 ppb and 0.01-410 ppb. The temperature of the water varies from 7.9 to 17.6 °C. Mo concentrations have irregular behaviour with temperature and do not demonstrate a significant correlation with any parameters. Tungsten concentrations are strongly and positively correlated only with As, indicating either common sources or common processes controlling their grades. The highest W concentrations are exclusively associated with Na–HCO3–Cl water types, with a circum-neutral condition (6<pH<7) and lower Eh (-60-+45 mV). The dominant species of Mo and W in mineral waters of eastern Elbrus are molybdate ion (MoO4), and [W7O24]6- polyanion. Based on the risk assessment results, for two potential contaminants (Mo and W), the concentration level of W exceeded the environmental quality standard, which suggests a severe to moderate ecological risk and, therefore, needs to be considered as the priority pollutant for the studied area.

Assessment of groundwater quality and the controlling factors in coastal aquifers of Ghana: An integrated statistical, geostatistical and hydrogeochemical approach

Coastal aquifers are complex groundwater bearing zones with multiple ways of interacting with seawater. Understanding of the main controls and evolution of such aquifers is essential for effective management of the groundwater. In this paper, a comprehensive study was conducted to characterize and identify the main factors and processes controlling the groundwater quality in some coastal aquifers through an integrated approach of Principal Component Analysis (PCA), Cluster Analysis (CA), geostatistical analysis and information entropy-based groundwater quality index coupled with detailed hydrogeochemical assessments. The PCA and CA yielded four clusters with distinct hydrogeochemical signatures (Cluster 1 and 2: freshwater influenced by rain, Cluster 3 transition zone and Cluster 4 marine influence/seawater intrusion or aerosol spray). Geostatistical analysis showed a wide variation in salinity from the coast to the inland while piper diagram revealed the evolution of the aquifers from Ca–HCO 3 , Ca–Cl which correspond to natural recharge zone in the north, to mixed Ca–Na–Mg–Cl–HCO 3 representing transition and Na–Cl towards the coast. The water suitability assessment for drinking using entropy-based groundwater quality index showed that about 59.4%, 20.3%, 7.8%, 2.6%, and 9.9% of the groundwater sample were estimated to be excellent, good, average/medium, poor, and extremely poor water quality. Ion exchange mechanism, dissolution of minerals from the rocks and marine influence are the dominant processes controlling the groundwater chemistry in the area. Recommendations for groundwater resource management and future research needs have also been discussed. • We examined the factors controlling the quality in a sparsely studied coastal aquifer. • Some areas of the aquifer have elevated levels of chloride, sulphate and sodium. • IEBGQI reveals areas that are not suitable for drinking. • Ca–HCO 3 , Ca–Cl, Ca–Na–Mg–Cl–HCO 3 and Na–Cl were delineated. • Water rock interaction, anthropogenic activities and marine influence control the groundwater chemistry.

Spatial distribution and health risk assessment of As and Pb contamination in the groundwater of Rayong Province, Thailand

This study investigates the presence of arsenic (As) and lead (Pb) in groundwater and their spatial distribution in Ban Khai District, Rayong Province, Thailand. Forty groundwater samples were collected at different locations in the dry and wet seasons during March and August of 2019, respectively. The hydrochemical facies illustrate that the major groundwater types in both seasons mainly consisted of Ca–Na–HCO3, Ca–HCO3–Cl and Na–HCO3 types. The concentration of As ranged from <0.300 to 183.00 μg/L, accounting for 22% (18 of 80 samples), exceeding the WHO guidelines of 10 μg/L. The spatial distribution of As was distinctly predominant as a hot spot in some areas during the wet season. The wells may have been contaminated from human activity and thus constituted a point source in the adjacent area. For Pb, its concentration in all the wells were not exceeded 10 μg/L of the WHO guidelines, appearing as a background concentration in this area. Most of the wells were shown to be in an oxidation state, supporting AsV mobility. Moreover, the area also had a nearly neutral pH that promoted AsV desorption, while the presence of undissolved Pb in the aquifers tended to increase. Furthermore, chemical applications to agricultural processes could release the As composition into the groundwater. The health risk resulting from oral consumption was at a higher risk level than dermal contact. The non-carcinogenic risk affecting the adult population exceeded the threshold level by approximately 27.5% of the wells, while for the children group, the risk level was within the limit. Total cancer risk (TCR) of adult residents exceeded the acceptable risk level (1 × 10−6) in all wells, causing carcinogenic health effects. Therefore, health surveillance is important in monitoring the toxic effects on the local residents who use groundwater from these contaminated wells. Furthermore, a sanitation service and an alternative treatment of the water supply will be needed, especially in wells with high As levels.

Characterization of the Groundwater within Regional Aquifers and Suitability Assessment for Various Uses and Purposes-Western Iraq

Groundwater quality investigation has been carried out in the western part of Iraq (west longitude '40°40). The physicochemical analyses of 64 groundwater samples collected from seven aquifers were used in the determination of groundwater characterization and assessment. The concept of spatial hydrochemical bi-model was prepared for quantitative and qualitative interpretation. Hydrogeochemical data referred that the groundwater is of meteoric origin and has processes responsible for observed brackishness. The geochemical facies of the groundwater reveal that none of the anions and cations pairs exceed 50% and there are practically mixtures of multi-water types (such as Ca–Mg–Cl–HCO3 and Na+K–SO4–Cl water type) as dominant types. The hydrogeochemical evolution indicates that the groundwater is mainly controlled by the leaching and dissolution process of carbonate minerals. Increasing salt content is observed at different static water levels (groundwater flow) confirming mixing cases with multi water sources. Anthropogenic activities do not have a significant alteration in the geochemical nature of groundwater in aquifer systems. Most of the groundwater is classified within the category of C3S1 and C2S1 denoting admissible to good quality of water for irrigation in 67% of the total samples. On the other hand, 33% of samples are classified as bad to very bad. The groundwater of most aquifers has precedence for irrigation, agricultural purposes, animal drinking, and good to fair class for natural preserve activities. While the groundwater of Mullusi and Jeed-Rattga aquifers are suggested for human drinking purposes. Also, the groundwater within the hydrogeologic system can be used in low-pressure boilers, mining, construction industry, and unsafe in high-pressure boilers due to the relatively high total hardness (237 to 1456 mg/l). Corrosively ratio indicates that 83 % of exploited groundwater from boreholes is safe for long transport through metallic pipelines.

Evaluation of changes in groundwater quality caused by a water inrush event in Taoyuan coal mine, China

The effects of a water inrush event on the chemical composition of groundwater in a coal measures sandstone aquifer that is important for water supply was investigated at the Taoyuan coal mine in the Huaibei region in China. Changes in groundwater quality caused by the inrush event were investigated using statistical techniques, a Piper trilinear diagram, saturation index, ion combination ratios and a fuzzy comprehensive evaluation method. These investigations indicated that Na+ + K+ and SO42− were the main cation and anion, and the average contents were 272 mg/L and 732 mg/L before water inrush, and 394 mg/L and 779 mg/L after water inrush, respectively. The concentrations of anions in groundwater before the inrush event were in the order SO42− > HCO3− > Cl− and the cation concentrations were in the order Na+ + K+ > Ca2+ > Mg2+. The chemical composition of groundwater was mainly SO4·Cl–Ca·Mg before water inrush event, and SO4·Cl–Na and Na–HCO3–Cl after this event. According to the saturation index method, gypsum, calcite, magnesite, and aragonite controlling the chemical composition of groundwater were reactive minerals in groundwater system. The oxidation of pyrite, dissolution of sulfate and carbonate minerals were main geochemical process before and after the event; while the oxidation of pyrite and cation exchange were enhanced after the water inrush event. The fuzzy comprehensive evaluation results showed that the type V water accounted for a large proportion of poor-quality groundwater. Groundwater quality in the aquifer near the mine generally deteriorated after the water inrush event.

Non-carcinogenic health risk assessment with source identification of nitrate and fluoride polluted groundwater of Wardha sub-basin, central India

In order to understand the pollution status of groundwater with geochemical evolution and appraisal of its probable public health risk due to nitrate (NO3–) and fluoride (F–), a total of 93 groundwater samples were collected during pre-monsoon (May) period from Wardha sub-basin, central India. By employing Piper plot, transition from Ca–HCO3 type water (recharge waters) to Na–Cl (saline water) type water through mixed Ca–Na–HCO3, mixed Ca–Mg–Cl (reverse ion exchange waters) and Ca–Cl types (leachate waters), were observed. The Geogenic processes such as silicate, dolomite, halite and carbonate weathering along with calcite precipitation and ion exchange process were identified as major controlling factors for evolution and alteration of groundwater chemistry. The Saturation index highlighted that the groundwater in the area is oversaturated with respect to the mineral calcite and dolomite, and under saturated with gypsum, fluorite and halite. The high NO3– and F– concentration overpassing the permissible limit were found in 54.8% and 18.5% of samples. The plot of F– with Na+/Ca2+, Na+/Mg2+ and F–/Cl– established fluoride bearing rock weathering is responsible for F– contamination. Based on the cluster analysis, the groundwater was grouped into Cluster-I Ca–Na–HCO3 type (61.3%) and Cluster-II Na–Ca–HCO3–Cl type (30.1%). The total hazard index (HI) based on human health risk assessment (HHRA) model for cumulative NO3– and F– toxicity through oral and dermal pathways were computed as 100%, 97.85% and 96.77% for children, female and male populations respectively. The HQ(nitrate) > 1 through ingestion pathway were in 84.95%, 68.82% and 62.37%, and HQ(fluoride) > 1 in 83.87%, 62.37% and 43.01% of the groundwater samples were recorded for children, female and male population respectively. The risk assessment study highlighted very high toxicity and severe health impact of ingestion of contaminated groundwater on public health.

Origin and hydrochemical characteristics of groundwater in the Northeastern Patagonia, Argentina: the relationship with geomorphology and soils

In arid zones, geomorphology and soils play a fundamental role in groundwater surveys as they condition the recharge phenomenon and some processes that modify water chemistry. The objective of this work was to identify the groundwater provenance and the relationship between its chemistry and isotope contents with the geomorphology and soil in the northeastern Patagonia, Argentina. Over an area of 10,600 km2, groundwater levels and major ionic and stable isotopic contents were measured. The main geomorphological units were mapped using satellite images and digital elevation models. In soils, pedogenetic carbonate contents (PC) and clay accumulation index (CAI) were measured. Different hydrochemical facies were identified in relation to geomorphological units, being the Cl–SO4–Na and Cl–Na ionic types dominant in fluvial terrace plains (terrace associations, TAs). The Cl–SO4–Na types are the most saline groundwaters and are coincident with the TA where Petrocalcids are the dominant soils. With less salinity contents, Cl–SO4–Na and Cl–Na types are the groundwaters associated with TA where the dominant soils are Natrargids and Haplocalcids. The only sector with Cl–HCO3–Na is those with fresh water coincident with the Aeolian field unit, where Psamments soils develop. Likewise, groundwater is isotopically differentiated in response to the origin being mostly allocthonus in the fluvial terrace plains and from local recharge in the Aeolian fields. The fluvial terraces are gravel deposits that would favor a local recharge, but this is prevented both by pedogenic carbonate and clay contents which developed in the upper part of the deposit. In this way, the measurement of pedogenetic carbonates and clays becomes soil properties of utmost importance to be considered in groundwater prospecting in arid regions worldwide.

Impact of urbanization on hydrogeochemistry and trace metal distribution on five major ponds in the holy city of Gaya, India

Gaya, a prominent city of Bihar (India) with rich cultural and religious significance has been susceptible to massive urbanization, population growth and pollution which have huge impact on its surface water bodies. The study was conducted on five major ponds of Gaya namely Bisar, Dighi, Vaitarni, Ramsagar and Suryakund. This paper attempts to evaluate their drinking and irrigational water quality status, trace metal contamination in water and sediments (except Suryakund), hydrogeochemical characterization and evolutionary trends and processes involved in the water chemistry. The WQI values (>130) revealed that the ponds are facing heavy pollution load and the water is not fit for drinking purposes; however, irrigational indices indicates that the water of these ponds is suitable for irrigational purposes. The ponds' water and sediments are heavily contaminated with trace metals particularly cobalt (CF and PI >17) and lead (CF>1.4 and PI>5) in sediments. The PCA and HCA were also performed to find the relevant sources, trends and groups in trace metal contamination in their water. The hydrogeochemical profile of surface water (Piper's plot, Durov's diagram, Gibbs diagram and IBE) indicated that they are of mixed water type with most abundant facies being Na–Ca–Mg–Cl, Ca–Na–Mg–Cl and Ca–Na–Mg–Cl–HCO3. SI values showed ponds to be oversaturated with Ca–Mg based minerals and dissolution of halite, magnesite and anhydrite indicating high degree of rock water interaction and reverse cation exchange process dominating the water chemistry. However extensive mixing of pollutants and dissolution has caused the overall geochemical character of water to change. The overall study shows that urbanization may further increase the rate of anthropogenic activities overtime which could enhance trace metal accumulation in the ponds and pose a serious health risk.

Major ion, trace metal and environmental isotope characterization of groundwater in selected parts of Uddanam coastal region, Andhra Pradesh, India

This paper elaborates the hydrochemical and environmental isotope (δ2H and δ18O) inferences obtained from Uddanam region, Andhra Pradesh, India. Groundwater samples collected during pre-monsoon (June 2019) showed that the quality is fresh (EC < 1539 µS/cm) and contaminants like fluoride (<1.6 mg/L) and nitrate (<49 mg/L) are present within permissible limits. The composite water quality indices for drinking (DWQI: 14.1–92.5) and irrigation (IWQI: 2.8–20.2) are found to be satisfactory. The major water types are found to be Ca–Na–HCO3, Na–Ca–HCO3, Na–Mg–HCO3–Cl, Ca–Mg–HCO3–Cl and Na–HCO3. Three geochemical pathways are found signifying evaporite dissolution, contribution of silicate mineral weathering and base-exchange process, which is supported by estimated chloro-alkaline indices (CAI-1: −4.3 to −0.2, CAI-2: −1.03 to −0.08). Trace metal data clearly suggest that groundwater is free from any metal pollution. Dissolved silica (SiO2) levels range from 34 to 131 mg/L and do not show any particular spatial trend. Isotope data infer that groundwater is recharged by rainwater after undergoing evaporation (δ18O: −6.0‰), which matches with that of the combined isotope signature (δ18O: −5.5‰) of SW and NE monsoon rainfall. δ18O–TDS correlations and hydrochemical facies evolution (HFE) diagram do not infer any seawater intrusion into these coastal aquifers.

Main formation conditions of soda-type groundwater: A case study from south-eastern Transbaikal region (Russia)

Chemical and isotopic groundwater composition analyses in the south-eastern Transbaikal case study region allowed three geochemical types of waters and fifteen subtypes to be identified: bisiallite (Ca–HCO3), soda (Na–HCO3) and salt (Na–HCO3–Cl–SO4). All three types differed significantly with respect to TDS content, pH, composition of chemical elements and heavy water isotopes. The transition from the first to the subsequent types was accompanied by CO32−, HCO3−, SO42−, Cl− and Na+ accumulation, whereas a weaker dependence was exhibited for Mg2+ and K+, and no relationship with Ca2+ was found. Water was found to be gradually enriched in heavy isotopes and some trace elements (e.g. F, Mo, Br, B and Li). Findings showed that the groundwater–rock system is one of an equilibrium-disequilibrium. From the extent of the deeper horizons to the surface water, groundwater in the study region continuously dissolves minerals that are in disequilibrium with the groundwater and simultaneously forms new minerals. Moreover, over time, not only does the composition of the solution change, but the type of secondary minerals and the ratio between chemical elements also changes because some elements precipitate out of solution, while others continue to accumulate. The stage of soda-type groundwater formation was found to be at an intermediate level between the formation of fresh bisiallite (Ca–HCO3) water of different cationic composition and salt (Na–HCO3–Cl–SO4) water with mixed anionic composition.

Hydrogeochemical characteristics, temporal, and spatial variations for evaluation of groundwater quality of Hamedan–Bahar Plain as a major agricultural region, West of Iran

This study was conducted to assess the suitability of groundwater resources for drinking and irrigating purposes in Hamedan–Bahar Plain, west of Iran as a major agricultural district, in the spring and summer of 2018. In so doing, a total of 60 water specimens were collected from the semi-deep water wells of the study area with an average depth of 50–75 m and then the hydrogeochemical characteristics of groundwater samples and their suitability were investigated. The evaluation of the groundwater quality was carried out by assessing the physicochemical variables notably temperature (T), pH, electrical conductivity (EC), total dissolved solids (TDS), total hardness (TH), and by measuring the rates of major ions including Ca2+, Cl−, HCO3−, K+, Mg2+, Na+, NO3−, PO43−, and SO42− and trace elements, such as arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn). The results indicated that the groundwater specimens were somewhat alkaline and brackish. The cationic trend of the specimens in the spring season was found to be Ca > Mg > Na > K > Pb > As > Cu > Zn > Ni > Fe > Cr > Mn > Cd, while, in the summer season it manifested itself as Ca > Mg > Na > As > K > Pb > Cu > Zn > Fe > Ni > Cr > Mn > Cd. However, the trend of anionic contents in both seasons was HCO3 > NO3 > SO4 > Cl > PO4. The analysis of the data showed that Na–Cl–HCO3 was the dominant groundwater type in both seasons. The studied specimens were also described in terms of some indices, including the total hardness (TH), Kelley’s ratio (KR), magnesium hazard (MH), permeability index (PI), the residual sodium carbonate (RSC), sodium adsorption ratio (SAR), soluble sodium percentage (SSP), and maximum permissible limit (MPL). The results indicated that groundwater samples have suitable quality for the main uses. Based on the values obtained for chloro-alkaline indices (CAI-1 and CAI-2), chemical weathering was suggested as the main hydrogeochemical process controlling calcium, magnesium, sulfate, and carbonate distribution in the groundwater supplies.

The hydrochemistry of Tigris River in Baghdad city, Iraq

The primary objective of this study was to investigate the current status of water-quality conditions and assessment it in the Tigris River, Baghdad, Iraq, and to determine how those conditions are changing over time of pollution if any. A series of Hydrochemical tests were carried out to ascertain the influence of major Cations and Anions, Total Dissolved Solids (TDS), Electrical Conductivity (EC) and Potential of hydrogen (pH) on the quality of water. To assess the environmental pollution of the study area: 34 water samples were collected along Tigris River from north to south Baghdad City; 17 on January 2019 and 17 on April 2019. Result of the test were compared with the World Health Organization standards, and showed that all the ions in addition of EC and TDS are within their acceptable limits, except for samples number 7 and 16where Sulfate concertation was above the acceptable limits. Therefor the Tigris River water in most of the study area is acceptable for all kinds of consumption. The most common water type in the area was Ca Na Mg- SO4 Cl HCO3 in January 2019 and Na Ca Mg- SO4 Cl in April 2019.

Prediction of Oil and Gas Occurrence in the Jurassic Reservoirs of the Zone of Junction of the Yenisei–Khatanga and West Siberian Basins

Abstract —Based on a comprehensive analysis of the geologic structure, hydrogeology, and hydrogeochemistry, we predict oil and gas occurrence in the Jurassic reservoirs of the zone of junction of the Yenisei–Khatanga and West Siberian basins. We have established the regularities of formation of sandstones of the Sigovaya, Malyshevka, Vym, Nadoyakha, Sharapovka, and Zima reservoirs and examined their poroperm properties. The studied Lower and Middle Jurassic deposits, beginning from the Malyshevka reservoir, are characterized by abnormally high formation pressures with an anomaly ratio of up to 1.92. The Jurassic reservoirs bear weakly alkaline, moderately brackish to slightly saline groundwater of Cl Na, Cl–HCO3 Na, and HCO3–Cl Na compositions with TDS = 3.0–23.3 g/dm3. The low-mineralization connate waters determine an inverse vertical hydrogeochemical zoning in the sedimentary cover of the study region. The research data show favorable conditions for the generation and accumulation of hydrocarbon pools. It is shown that the main criteria for oil and gas occurrence are hydrogeochemical (contents of organic compounds, NH4, B, I, Br, naphthenic acids, and benzene; B/Br and HCO3/Cl coefficients), gas (total gas saturation of formation waters, degree of their gas saturation (Kg), and composition of water-dissolved gases), and hydrodynamic (formation pressures and their anomaly ratio (Ka)) indicators. Also, complex anomalies have been revealed in the Jurassic deposits, which trace the gas fields and revealed oil and gas occurrences. The Jurassic reservoirs are most promising for structure-lithologic traps in the peripheral zones of the basin and on the slopes of large positive structures. The Middle Jurassic deposits in the interior of the Yenisei–Khatanga Basin, poorly studied by deep drilling, might also be of interest as potential hydrocarbon pools.

Constraints on the hydrogeochemistry and origin of the CO2-rich mineral waters from the Eastern Carpathians – Transylvanian Basin boundary (Romania)

The Eastern Carpathians, along the Neogene to Quaternary volcanic chain, host important natural resources of mineral waters. Most of these are in the form of CO2-rich natural springs of different types, associated with CO2 gas emissions. In order to understand the origin of these waters, the natural processes responsible for the observed physical–chemical features and to check the exposure and vulnerability of the hydrogeological system to potential contamination and environmental changes, 121 mineral water springs and wells were investigated. The investigations performed, offered an insight on the processes affecting the waters after their infiltration that led to a wide range of chemical and isotopic compositions. The diversity in the geological structure of the area, alteration processes and interaction with CO2, all explain the variety of the hydrogeochemical facies of the investigated waters. Three major hydrogeochemical types that are the result of the geological variety of the study area and water–rock interaction were identified: Ca–Na–Mg–HCO3, Ca–Na–Mg/Na–Ca ± Mg–HCO3–Cl ± SO4, and Na–Cl waters. Further changes in the geochemical features are attributable to mixing between different water types during their ascent, enhanced by the tectonic setting of the area. Considering the isotopic composition (δ18O, δD) of the waters, most of them proved to be of meteoric origin. Extreme isotopic shifts towards enriched δ18O and δD values of +8.59 and −12.2‰ (V-SMOW) respectively were observed in the case of 11 springs. These shifts were attributed to the interaction of water with clay minerals and diagenesis. As most of these waters are of meteoric origin, their discharge may be influenced by meteorological factors. Moreover, the mixing of aquifers with very shallow waters most likely facilitates their exposure to external contamination.

Assessing the impact on groundwater chemistry of an environmental restoration performed using industrial solid waste from TiO2 production

A hydrogeochemical study was performed to assess the impact on groundwater chemistry of industrial solid waste (ISW) used for environmental restoration of a site degraded by past quarry activities in southern Tuscany (Italy). Water samples were collected from springs, piezometers and drains around and within this site where solid waste generated by industrial processes for the production of titanium dioxide (TiO2) has been disposed. Water samples were analysed for the physico-chemical parameters (temperature, pH, electrical conductivity, redox potential), major ions (Na, K, Ca, Mg, Cl, HCO3, SO4), trace elements (Fe, Mn, Ti, B) and isotopes (δ18O, δ2H, δ13C, 3H). The study area is characterised by a complex hydrogeological system consisting of groundwater belonging to four hydrochemical facies. The leachate of the stored ISW had high salinity and concentrations of major ions (mainly SO4, Cl, Na, Mg) and trace elements (Fe, Mn). The chemical features of leachate in the stored ISW are similar to those of water found in the ISW before disposal, primarily due by the reactions between the raw material (ilmenite slags) and reagents (e.g. sulphuric acid, seawater and limestone) during production of TiO2. The hydrochemical and hydrogeological findings suggested that: i) no change of chemistry due to leakage of the ISW leachate occurred in groundwater around the ISW disposal site; ii) dilution of the ISW leachate by meteoric waters was found in the landslide zone of the ISW disposal site; iii) mixing between the ISW leachate and groundwater [Na–HCO3(Cl) waters] probably took place under the ISW disposal site in the period immediately following a landslide event.

Authigenic Carbonates in the Water–Biota–Bottom Sediments’ System of Small Lakes (South of Western Siberia)

We studied 46 small, drainless lakes in various landscape types: The sub-taiga (Vasyugan plain), forest–steppe (Baraba lowland), and steppe and subzone of ribbon forests (Kulunda plain). Sampling of lake components (sediments, water, and biota) was performed. The materials were analyzed via a combination of modern analytical methods (atomic absorption spectroscopy, X-ray fluorescence, scanning electron microscopy and X-ray diffractometry). It was found that in the south of Western Siberia, lakes with a bicarbonate-sodium water composition are widespread against the background of general landscape zoning. This composition contributes to the abundant growth of biota in the lakes, which leads to the processes of authigenic carbonate formation from calcite–dolomite series and aragonite on geochemical barriers, i.e., drifting biota–water, submerged biota–water, and water–bottom sediments against a background of terrigenous demolition and organic matter accumulation. The article shows the differences in the composition and structure of low-temperature carbonate minerals formed on various geochemical barriers. It was found that low-magnesium calcite and aragonite are the most common authigenic carbonates in small lakes in the south of Western Siberia and are formed on all three geochemical barriers in lakes. High-magnesium calcites and Ca-excess dolomites are formed only at the water–bottom sediment barrier in lakes with HCO3–Na and Cl–HCO3–Na water composition at pH &gt; 9 and with a total dissolved solids &gt; 3 g·L−1 (in some lakes of HCO3-Na composition with a TDS &lt; 3 g·L−1 and pH &gt; 9).

Geochemical and health risk evaluation of fluoride rich groundwater in Sattenapalle Region, Guntur district, Andhra Pradesh, India

To assess the geochemical mechanisms of fluoride occurrence in the groundwater and its impact on human health, groundwater samples collected from the Sattenapalle Region, Guntur district, Andhra Pradesh, India were analyzed for various chemical parameters. Results show that the groundwater quality is of alkaline in nature, which is mainly characterized by Na-HCO3 facies. According to the groundwater quality index, 75% and 25% of the groundwater sampling points come under the poor and very poor groundwater quality categories for drinking purpose, respectively. The fluoride content varies from 1.3 to 12.9 mg/L, with 75% of the groundwater sampling points exceeding the drinking water quality limit of 1.5 mg/L. The study on Ca2++Mg2+ vs. HCO+SO Na++K+ vs. TC, Na+ vs. Cl HCO vs. TC, trilinear diagrams and CA indices specifies the soil-water-rock interactions together with dissolution, ion exchange and evaporation as the dominant controlling processes that affect the groundwater chemistry. The non-carcinogenic risk is from 0.83 to 9.77, exceeding its acceptable limit of one in 75%, 90% and 100% of the groundwater samples with respect to men, women and children, respectively, depending upon their body weights. Remedial measures are suggested to reduce the health risk in the study region.