Kinetics of gypsum nucleation and crystal growth from Dead Sea brine

The Dead Sea brine is supersaturated with respect to gypsum (Ω = 1.42). Laboratory experiments and evaluation of historical data show that gypsum nucleation and crystal growth kinetics from Dead Sea brine are both slower in comparison with solutions at a similar degree of supersaturation. The slow kinetics of gypsum precipitation in the Dead Sea brine is mainly attributed to the low solubility of gypsum which is due to the high Ca²⁺/SO₄²⁻ molar ratio (115), high salinity (∼280 g/kg) and to Na⁺ inhibition.Experiments with various clay minerals (montmorillonite, kaolinite) indicate that these minerals do not serve as crystallization seeds. In contrast, calcite and aragonite which contain traces of gypsum impurities do prompt precipitation of gypsum but at a considerable slower rate than with pure gypsum. This implies that transportation inflow of clay minerals, calcite and local crystallization of minerals in the Dead Sea does not prompt significant heterogeneous precipitation of gypsum. Based on historical analyses of the Dead Sea, it is shown that over the last decades, as inflows to the lake decreased and its salinity increased, gypsum continuously precipitated from the brine. The increasing salinity and Ca²⁺/SO₄²⁻ ratio, which results from the precipitation of gypsum, lead to even slower kinetics of nucleation and crystal growth, which resulted in an increasing degree of supersaturation with respect to gypsum. Therefore, we predict that as the salinity of the Dead Sea brine continues to increase (accompanied by Dead Sea water level decline), although gypsum will continuously precipitate, the degree of supersaturation will increase furthermore due to progressively slower kinetics.     

Preliminary investigations on the defluoridation of water using fired clay chips

The adsorption of fluoride ions on ground fired clay pot has been investigated. The maximum efficiency of the adsorbent for defluoridating 1–2 litres of water was found to be 200 mg fluoride kg⁻¹ adsorbent. The investigation showed that 5–20 mg l⁻¹ fluoride, from 1 litre of water, could be reduced to less than 1.5 mg l⁻¹ using 120–240 g of the adsorbing medium. The effects of the dose of the medium, the pH, the contact time and the initial fluoride content were studied in relation to defluoridation efficiency. Comparison of fluoride removal capacity of the adsorbent was also made with those of fired brick, clay soil and red ash. The latter exhibited practically no adsorption. A packed column of the same ground clay pot was saturated with 285 mg fluoride kg⁻¹ of adsorbent when 20 litres of water containing 10 mg l⁻¹ F was allowed to pass through it. This column defluoridated 6 litres of tap water containing 10 ppm F⁻ to below 1.5 mg l⁻¹.     

Mobilization and loss of elements from roofing tiles

Deposition, leaching and chemical transformation are processes that affect roofing tile and roof runoff water. Leaching experiments, with artificial rainwater in the laboratory, showed the presence of Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl⁻, NO₃ ⁻, SO₄ ²⁻, with a ratio of Ca²⁺ and SO₄ ²⁻ suggesting gypsum dissolution. X-ray fluorescence (XRF) of the exposed roof tile showed depletion such as Mg, Al, Si, P, Ti and K at the surface of the tile and an enrichment of Fe and Mn which hinted at a process akin to laterite formation. However, calcium appeared to be enriched at the surface as gypsum (confirmed by X-ray diffraction) and to a lesser extent calcite, which is characteristic of deposits on building surfaces in cities.     

Hydrogeochemical processes controlling fluoride enrichment within alluvial and hard rock aquifers in a part of a semi-arid region of Northern India

Rock–water interaction along with mineral dissolution/ precipitation plays a profound role in the control of fluoride ion concentration within the alluvial groundwater in a part of semi-arid northern India. In the premonsoon season, the alluvial region experiences evaporative processes leading to increase in Na⁺ ions which through reverse ion exchange processes are adsorbed onto suitable sites within the aquifer matrix in exchange for Ca²⁺ ion in solution. Increase in Ca²⁺ ions in solution inhibits fluorite mineral dissolution, thereby controlling premonsoon fluoride ion concentration within alluvial groundwaters (1.40?±?0.5 mg/l). In the postmonsoon season, however, higher average fluoride ion concentration within the alluvial aquifer samples (2.33?±?0.80 mg/l) is observed mainly due to increase in silicate weathering of fluoride-bearing rocks and direct ion exchange processes enabling Ca²⁺ ion uptake from solution accompanied with the release of fluoride ions. Combined effect of these processes results in average fluoride ion concentration falling above the WHO drinking water permissible limit (1.5 mg/l). Alternatively, the hard rock aquifer samples within the study area have an average fluoride ion concentration falling below the permissible limit in both the seasons.     

Hydrochemistry of groundwater (GW) and surface water (SW) for assessment of fluoride in Chinnaeru river basin,Nalgonda district, (AP) India

Hydrochemical studies were conducted in Chinnaeru river basin of Nalgonda district, Andhra Pradesh, India, to explore the causes of high fluorides in groundwater and surface water causing a widespread incidence of fluorosis in local population. The concentration of fluoride in groundwater ranges from 0.4 to 2.9 and 0.6 to 3.6 mg/l, stream water ranges from 0.9 to 3.5 and 1.4 to 3.2 mg/l, tank water ranges from 0.4 to 2.8 and 0.9 to 2.3 mg/l, for pre- and post-monsoon periods, respectively. The modified Piper diagram reflects that the water belongs to Ca²⁺–Mg²⁺–HCO₃ ^? to Na⁺–HCO₃ ^? facies. Negative chloroalkali indices in both the seasons prove that ion exchange between Na⁺ and K⁺ in aquatic solution took place with Ca²⁺ and Mg²⁺ of host rock. The interpretation of plots for different major ions and molar ratios suggest that weathering of silicate rocks and water–rock interaction is responsible for major ion chemistry of groundwater/surface water. High fluoride content in groundwater was attributed to continuous water–rock interaction during the process of percolation with fluorite bearing country rocks under arid, low precipitation, and high evaporation conditions. The low calcium content in rocks and soils, and the presence of high levels of sodium bicarbonate are important factors favouring high levels of fluoride in waters. The basement rocks provide abundant mineral sources of fluoride in the form of amphibole, biotite, fluorite, mica and apatite.     

Mechanism and numerical simulation of multicomponent solute transport in sodic soils reclaimed by calcium sulfate

The mechanism for reclaiming sodic soils using calcium sulfate (CaSO₄) could provide a theoretical basis for the field application of CaSO₄ substitutes, including the by-products of flue gas desulfurization (BFGD), fly ash, and phosphorus gypsum. In this study, Ca²⁺ application experiment was conducted to analyze the dynamic changes of the cations in the reclamation of sodic soils with CaSO₄. A multicomponent solute transport model (UNSATCHEM) that considers ion adsorption exchange and dynamic changes in the soil’s hydraulic conductivity was subsequently used to simulate and predict the movement of ions. The Ca²⁺ application experiment consisted of four treatments with four CaSO₄ concentrations (0.5, 1, 1.5, and 2 g L^?1). When the Ca²⁺ concentrations in the supplied water were 14.71, 22.06, and 29.41 mmol L^?1, Ca²⁺ achieved penetration, and this process was faster when the Ca²⁺ concentration in the supplied water was higher. Ca²⁺ did not achieve penetration when the Ca²⁺ concentration was 7.35 mmol L^?1. UNSATCHEM was able to simulate the transportation mechanism of Ca²⁺ and Na⁺ in the soil solution in the Ca²⁺ application experiment, the adsorption and exchange between the Na⁺ in the soil colloid and Ca²⁺ in the soil solution, and the precipitation and dissolution of CaSO₄ with a high degree of accuracy. Sodic soil reclamation with CaSO₄ was not a short-term process. Compared with applying CaSO₄ only once, applying CaSO₄ in batches decreased the accumulation of soil salts and promoted its dissolution.     

Hydrogeochemical Simulation of Water—Rock Interaction Under Water Flood Recovery in Renqiu Oilfield,Hebei Province,China

Hydrogeochemical simulation is an effective method to study water-rock interaction. In this paper, PHREEQM was used for the simulation of water-rock interaction under water flooding in the Renqiu Oilfield. Calculated results revealed that when fresh water was injected into the reservoir, Cl⁻ and Na⁺ would decrease without involvement in water-rock interaction. Erosion to dolomite will lead to an increase in Ca²⁺, Mg²⁺ and CaHCO ₃ ⁺ . Saturation index of calcite and aragonite decreased first and then increased. With fresh water accounting for up to 70%, mixed water has the strongest erosion ability. Deoiled water has erosion ability under high temperature and high partial pressure of CO₂. Pyrite and gypsum were sensitive to deoiled water, which can cause the dissolution of pyrite and the precipitation of gypsum. Micrographs revealed a great deal of information about water-rock interaction. The project was granted by the National Natural Science Foundation of China (No. 49672159).     

Potassium leaching in undisturbed soil cores following surface applications of gypsum

Displacement studies on leaching of potassium (K⁺) were conducted under unsaturated steady state flow conditions in nine undisturbed soil columns (15.5 cm in diameter and 25 cm long). Pulses of K⁺ applied to columns of undisturbed soil were leached with distilled water or calcium chloride (CaCl₂) at a rate of 18 mm h⁻¹. The movement of K⁺ in gypsum treated soil leached with distilled water was at a similar rate to that of the untreated soil leached with 15 mM CaCl₂. The Ca²⁺ concentrations in the leachates were about 15 mM, the expected values for the dissolution of the gypsum. When applied K⁺ was displaced with the distilled water, K⁺ was retained in the top 10–12.5 cm depth of soil. In the undisturbed soil cores there is possibility of preferential flow and lack of K⁺ sorption. The application of gypsum and CaCl₂ in the reclamation of sodic soils would be expected to leach K⁺ from soils. It can also be concluded that the use of sources of water for irrigation which have a high Ca²⁺ concentration can also lead to leaching of K⁺ from soil. Average effluent concentration of K⁺ during leaching period was 30.2 and 28.6 mg l⁻¹ for the gypsum and CaCl₂ treated soils, respectively. These concentrations are greater than the recommended guideline of the World Health Organisation (12 mg K⁺ l⁻¹).     

Mechanism of fluoride enrichment in groundwater of hard rock aquifers in Medak,Telangana State,South India

A total of 194 groundwater samples were collected from wells in hard rock aquifers of the Medak district, South India, to assess the distribution of fluoride in groundwater and to determine whether this chemical constituent was likely to be causing adverse health effects on groundwater user in the region. The study revealed that the fluoride concentration in groundwater ranged between 0.2 and 7.4 mg/L with an average concentration of 2.7 mg/L. About 57% of groundwater tested has fluoride concentrations more than the maximum permissible limit of 1.5 mg/L. The highest concentrations of fluoride were measured in groundwater in the north-eastern part of the Medak region especially in the Siddipeta, Chinnakodur, Nanganoor and Dubhaka regions. The areas are underlain by granites which contain fluoride-bearing minerals like apatite and biotite. Due to water–rock interactions, the fluoride has become enriched in groundwater due to the weathering and leaching of fluoride-bearing minerals. The pH and bicarbonate concentrations of the groundwater are varied from 6.6 to 8.8 and 18 to 527 mg/L, respectively. High fluoride concentration in the groundwater of the study area is observed when pH and the bicarbonate concentration are high. Data plotted in Gibbs diagram show that all groundwater samples fall under rock weathering dominance group with a trend towards the evaporation dominance category. An assessment of the chemical composition of groundwater reveals that most of the groundwater samples have compositions of Ca²⁺–Mg²⁺–Cl^? > Ca²⁺–Na⁺–HCO₃ ^? > Ca²⁺–HCO₃ ^? > Na⁺–HCO₃ ^?. This suggests that the characteristics of the groundwater flow regime, long residence time and the extent of groundwater interaction with rocks are the major factors that influence the concentration of fluoride. It is advised not to utilize the groundwater for drinking purpose in the areas delineated, and they should depend on alternate safe source.     

Geochemical controls on a calcite precipitating spring

A small spring fed stream was found to precipitate calcite by mainly inorganic processes and in a nonuniform manner. The spring water originated by rainwater falling in a 0.8 km² basin, infiltrating, and dissolving calcite and dolomite followed by dissolution of gypsum or anhydrite. The Ca²⁺/Mg²⁺ indicates that calcite is probably precipitated in the subsurface from a supersaturated solution. This water emerges from the spring still about 5 times supersaturated with respect to calcite and continues calcite precipitation. When 10 times supersaturation is reached, due to CO₂ degassing the precipitation is more rapid. The calcite accumulation from the stream with a flow of 5 l/s is calculated to be 12600 kg/yr with the highest rates in areas where CO₂ degassing is the greatest. The non-equilibrium, as shown by the high calcite supersaturation, is also reflected in a variable partitioning pattern for Sr²⁺ between the water and calcite.     

The coprecipitation of strontium,magnesium, sodium,potassium and chloride ions with gypsum. An experimental study

The coprecipitation of Sr²⁺, Mg²⁺, Na⁺, K⁺ and Cl^? into gypsum was studied as a function of temperature, brine concentration and growth rate. The concentrations of the studied cations in the gypsum increase with growth rate (kinetic effect), with a tendency to reach a limiting value at high growth rates. The partition coefficients of Sr tend to increase with brine concentration and decrease with temperature. The partition coefficients of the other cations also decrease with temperature but depend only very slightly on brine concentration. The concentrations of coprecipitated chloride are negligibly small.The coprecipitation behavior is explained in terms of the relation between the rate of desorption of the coprecipitating ions from the surface of the growing crystal, and the rate of growth. The studied cations may substitute for Ca²⁺ in its normal lattice sites and/or reside in interstitial positions among the structural water molecules. The relative amount of foreign cations occupying interstitial positions increases with increasing growth rate.The elucidation of the behavior of coprecipitated ions in gypsum given here forms a basis for the utilization of these ions as geochemical indicators for the environment of deposition of gypsum. These indicators may help in reconstructing important parameters such as temperature, brine concentration and growth rate.     

A study on the high fluoride concentration in the magnesium-rich waters of hard rock aquifer in Krishnagiri district, Tamilnadu, India

Excess fluoride in groundwater affects the human health and results in dental and skeletal fluorosis. Higher concentration of fluoride was noted in hard rock terrain of the south India, in the Krishnagiri district of Tamilnadu. The region has a complex geology ranging from ultra basic to acid igneous rocks, charnockite and gneissic rocks. Thirty-four groundwater samples were collected from this study area and analysed for major cations and anions along with fluoride. The order of dominance of cations is Na⁺?>?Mg²⁺?>?Ca²⁺?>?K⁺ and the anions in the following order HCO₃ ^??>?Cl^??>?NO₃ ^??>?SO₄ ^2?. It is found that nearly 58 % of the samples have more fluoride ranging from 1 to 3 mg/L. It is also noted that high fluoride waters correspond to magnesium water types. This is due to the release of fluoride from the magnesium-bearing minerals like, biotite, hornblende, etc., or weathering of apatite/hydroxyapatites found in charnockites.     

Regional appraisal of the fluoride occurrence in groundwaters of Andhra Pradesh

Fluoride (F^?) is essential for normal bone growth, but higher concentration in the drinking water causes health problems which are reported in many states of India. Andhra Pradesh is one of the states which suffer from excess fluoride in groundwater particularly in the hard rock terrain. In this context, a study was conducted in Andhra Pradesh based on chemical analysis of water samples from hydrograph net work stations (dug wells) and exploratory bore wells. The concentration of fluoride in groundwaters ranges from traces to 9.75 mg/l. The occurrence of fluoride is mostly sporadic, uneven and varies with depth. The highly affected districts include Nalgonda and Warangal in Telangana region, Prakasam in coastal region, Anantapur and Kurnool in Rayalaseema region. In certain areas of Nalgonda district, 85% of wells have fluoride more than permissible limit (> 1.5 mg/l) for drinking water. High F^? is present in all the geological formations, predominantly in granitic aquifers, compared to the other formations. The average value of fluoride is high in the deeper zone (1.10 mg/L), compared to the shallow zone (0.69 mg/L). The fluoride-rich minerals present are the main sources for fluoride concentrations in groundwater. Residence time, evapotranspiration and weathering processes are some of the other supplementary factors for high fluoride concentrations in groundwater. Long-term data of hydrograph net work stations (dug wells) reveal that fluoride concentrations do not show any marked change of trend with respect to time. The concentration of fluoride is found to increase with increase of Na⁺and HCO ₃ ^? , and decrease with increase of Ca²⁺. Sodium bicarbonate waters are more effective in releasing fluoride from minerals into groundwater. High fluoride waters are of Na⁺ type. The paper presents a brief account of the study and its results.     

Regional groundwater flow and geochemical evolution in the Amacuzac River Basin,Mexico

An approach is presented to investigate the regional evolution of groundwater in the basin of the Amacuzac River in Central Mexico. The approach is based on groundwater flow cross-sectional modeling in combination with major ion chemistry and geochemical modeling, complemented with principal component and cluster analyses. The hydrogeologic units composing the basin, which combine aquifers and aquitards both in granular, fractured and karstic rocks, were represented in sections parallel to the regional groundwater flow. Steady-state cross-section numerical simulations aided in the conceptualization of the groundwater flow system through the basin and permitted estimation of bulk hydraulic conductivity values, recharge rates and residence times. Forty-five water locations (springs, groundwater wells and rivers) were sampled throughout the basin for chemical analysis of major ions. The modeled gravity-driven groundwater flow system satisfactorily reproduced field observations, whereas the main geochemical processes of groundwater in the basin are associated to the order and reactions in which the igneous and sedimentary rocks are encountered along the groundwater flow. Recharge water in the volcanic and volcano-sedimentary aquifers increases the concentration of HCO₃ ^–, Mg²⁺ and Ca²⁺ from dissolution of plagioclase and olivine. Deeper groundwater flow encounters carbonate rocks, under closed CO₂ conditions, and dissolves calcite and dolomite. When groundwater encounters gypsum lenses in the shallow Balsas Group or the deeper Huitzuco anhydrite, gypsum dissolution produces proportional increased concentration of Ca²⁺ and SO₄ ^2–; two samples reflected the influence of hydrothermal fluids and probably halite dissolution. These geochemical trends are consistent with the principal component and cluster analyses.     

Fluoride levels in the groundwater of the south-eastern part of Ranga Reddy district,Andhra Pradesh,India

The fluoride level in groundwater is controlled by the distribution of Ca²⁺ and SO₄^2?, ionic strength and the presence of complex ions in its composition. In the study area, situated in the Ranga Reddy district, Andhra Pradesh, India, the concentrations of fluoride in the groundwater vary from 0.7 to 4.80 mg/l and from 0.4 to 4.20 mg/l during the pre- and post-monsoon seasons respectively. From the correlation coefficient studies, it is observed that fluoride is inversely related with Ca²⁺ and positively related with HCO₃^?, whereas the correlation coefficient between fluoride and other ions is very poor during both seasons. The difference in F^? concentrations between pre- and post-monsoon seasons could be because the ionic concentrations in the groundwater during the post-monsoon period were generally less than their counterparts during the pre-monsoon period, because of dilution by rainwater. By contrast, the fluoride concentration in many places was relatively high during the post-monsoon period. This indicates contamination of groundwater from surface pollutants.     

Geochemical and qualitative assessment of groundwater of the High Mekerra watershed,NW Algeria

Groundwater constitutes the main source of water supply in the High Mekerra watershed of northwestern Algeria. This resource is currently under heavy pressures to meet the growing needs of drinking water and irrigation. This study assesses the geochemical characteristics of groundwater of the High Mekerra watershed at 21 points distributed across the two main aquifers (Ras El Ma and Mouley Slissen) in the region. Hydrochemical facies of Ras El Ma groundwater are dominantly MgCl and CaCl type, while those of Mouley Slissen groundwater are of CaHCO₃ type. Principal component analysis shows a strong correlation between groundwater mineralization and Ca²⁺, Na⁺, Cl^? and SO₄ ^2? ions stemming from the dissolution of carbonates, gypsum and anhydrite. Groundwater mineralization evolves from south to north. Geochemical modeling shows that the High Mekerra groundwater is saturated with respect to calcite and dolomite and undersaturated with respect to gypsum and anhydrite. Nitrate concentrations that exceed the WHO standard (50 mg L^?1) at several points are linked to the agro-pastoral activities in this region.     

室温条件下青海湖水中镁离子浓度对沉淀碳酸钙同质多像类型的调控

青海湖是我国唯一报道过的现代湖底沉积物中白云石、方解石和文石等多种碳酸盐矿物共存的高原内陆咸水湖泊.以青海湖水和除菌青海湖水作为载体,以CaCl2和MgCl2·6 H2O作为反应原料,在实验室常温条件下采取控制变量法制备出不同浓度Mg2+参与下的钙质沉淀物,探讨Mg2+浓度对沉淀物类型的影响.仅添加CaCl2时,青海湖...     

Groundwater solute chemistry,hydrogeochemical processes and fluoride contamination in phreatic aquifer of Odisha,India

The work investigates the major solute chemistry of groundwater and fluoride enrichment(F~-) in the shallow phreatic aquifer of Odisha.The study also interprets the hydrogeochemical processes of solute acquisition and the genetic behavior of groundwater F~-contamination.A total of 1105 groundwater samples collected from across the state from different hydro-geomorphic settings have been analyzed for the major solutes and F~-content.Groundwater is alkaline in nature(range of pH: 6.6–8.7; ave.: 7.9) predominated by moderately hard to very hard types.Average cation and anion chemistry stand in the orders of Ca~(2+) Na~+ Mg~(2+) K~+and HCO_3~- Cl~- SO_4~(2-) CO_3~(2-)respectively.The average mineralization is low(319 mg/L).The primary water types are Ca-Mg-HCO_3 and Ca-Mg-Cl~-HCO_3, followed by Na-Cl, Ca-Mg-Cl, and Na-Ca-Mg-HCO_3~-Cl.Silicate-halite dissolution and reverse ion exchange are the significant processes of solute acquisition.Both the geogenic as well as the anthropogenic sources contribute to the groundwater fluoride contamination,etc.The ratio of Na~+/Ca~(2+) 1.0 comprises Na-HCO_3(Cl) water types with F~- 1.0 mg/L(range 1.0–3.5 mg/L)where the F~-bears geogenic source.Positive relations exist between F~-and pH, Na~+, TDS, and HCO_3~-.It also reflects a perfect Na-TDS correlation(0.85).The ratio of Na~+/Ca~(2+) 1.0 segregates the sample population(F~- range: 1.0–4.0 mg/L) with the F derived from anthropogenic sources.Such water types include Ca-Mg-HCO_3(Cl) varieties which are recently recharged meteoritic water types.The F~-levels exhibit poor and negative correlations with the solutes in groundwater.The Na-TDS relation remains poor(0.12).In contrast, the TDS levels show strong correlations with Ca~(2+)(0.91), Mg~(2+)(0.80) and even Cl~-(0.91).The majority of the monitoring points with the anthropogenic sources of groundwater F~-are clustered in the Hirakud Canal Command area in the western parts of the state, indicating the role of irrigation return flow in the F~-contamination.     

Hydrogeology and hydrogeochemistry at a site of strategic importance: the Pareja Limno-reservoir drainage basin (Guadalajara,central Spain)

A small calcareous basin in central Spain was studied to establish the role of groundwater in the Pareja Limno-reservoir. Limno-reservoirs aim to preserve a constant water level in the riverine zone of large reservoirs to mitigate the impacts arising from their construction. Groundwater flow contribution (mean 60 %) was derived by recharge estimation. In situ measurements (spring discharge, electrical conductivity and sulfate) were undertaken and spring discharge was compared with a drought index. Twenty-eight springs were monitored and three hydrogeological units (HGUs) were defined: a carbonate plateau (HGU1), the underlying aquitard (HGU2), and the gypsum-enriched HGU3. HGU1 is the main aquifer and may play a role in the preservation of the limno-reservoir water level. Hydrogeochemical sampling was conducted and the code PHREEQC used to describe the main geochemical processes. Weathering and dissolution of calcite and gypsum seem to control the hydrogeochemical processes in the basin. Water progresses from Ca²⁺–HCO₃ ^– in the upper basin to Ca²⁺–SO₄ ^2– in the lower basin, where HGU3 outcrops. A clear temporal pattern was observed in the limno-reservoir, with salinity decreasing in winter and increasing in summer. This variation was wider at the river outlet, but the mixing of the river discharge with limno-reservoir water buffered it.     

Geochemistry and assessment of hydrogeochemical processes in groundwater in the southern part of Bathinda district of Punjab, northwest India

Hydrogeochemistry of groundwater is important for sustainable development and effective management of the groundwater resource. Fifty-six groundwater samples were collected from shallow tube wells of the intensively cultivated southern part of district Bathinda of Punjab, India, during pre- and post-monsoon seasons. Conventional graphical plots were used to define the geochemical evaluation of aquifer system based on the ionic constituents, water types, hydrochemical facies and factors controlling groundwater quality. Negative values of chloroalkaline indices suggest the prevalence of reverse ion exchange process irrespective of the seasons. A significant effect of monsoon is observed in terms chemical facies as a considerable amount of area with temporary hardness of Ca²⁺–Mg²⁺–HCO₃ ^? type in the pre-monsoon switched to Ca²⁺–Mg²⁺–Cl^? type (18%) followed by Na⁺–HCO₃ ^? type (14%) in the post-monsoon. Evaporation is the major geochemical process controlling the chemistry of groundwater process in pre-monsoon; however, in post-monsoon ion exchange reaction dominates over evaporation. Carbonate weathering is the major hydrogeochemical process operating in this part of the district, irrespective of the season. The abundance of Ca²⁺ + Mg²⁺ in groundwater of Bathinda can be attributed mainly to gypsum and carbonate weathering. Silicate weathering also occurs in a few samples in the post-monsoon in addition to the carbonate dissolution. Water chemistry is deteriorated by land-use activities, especially irrigation return flow and synthetic fertilisers (urea, gypsum, etc.) as indicted by concentrations of nitrate, sulphate and chlorides. Overall, results indicate that different natural hydrogeochemical processes such as simple dissolution, mixing, weathering of carbonate minerals locally known as ‘‘kankar’’ and silicate weathering are the key factors in both seasons.