Assessment of hydrogeochemistry and contamination of Varamin deep aquifer,Tehran Province,Iran

The present study investigates the hydrogeochemistry and contamination of Varamin deep aquifer located in the southeast of Tehran province, Iran. The study also evaluates groundwater suitability for irrigation uses. The hydrogeochemical study was conducted by collecting and analyzing 154 groundwater samples seasonally during 2014. Based on evolutionary sequence of Chebotarev, the aquifer is in the stage of SO₄ + HCO₃ in the north half of the plain and it has evolved into SO₄ + Cl in the south half. The unusual increase in TDS and Cl^? toward the western boundaries of the aquifer indicates some anomalies. These anomalies have originated from discharge of untreated wastewater of Tehran city in these areas. The studied aquifer contains four dominant groundwater types including Na–Ca–SO₄ (55%), Na–Ca–HCO₃ (22%), Na–Cl (13%) and Ca–Cl (10%). The spatial distributions of Na–Cl and Ca–Cl water types coincide with observed anomalies. Ionic relationships of SO₄ ^2? versus Cl^? and Na⁺ versus Cl^? confirm that water–rock interaction and anthropogenic contribution are main sources of these ions in the groundwater. The main processes governing the chemistry of the groundwater are the dissolution of calcite, dolomite and gypsum along the flow path, and direct ion exchange. Reverse ion exchange controls the groundwater chemistry in the areas contaminated with untreated wastewater. Based on Na% and SAR, 10.3 and 27% of water samples are unsuitable for irrigation purposes, respectively. Regarding residual sodium carbonate, there is no treat for crop yields. Only 6% of water samples represent magnesium adsorption ratios more than 50% which are harmful and unsuitable for irrigation.     

Impact of pit-toilet leachate on groundwater chemistry and role of vadose zone in removal of nitrate and E. coli pollutants in Kolar District, Karnataka, India

Assessment of chemistry of groundwater infiltrated by pit-toilet leachate and contaminant removal by vadose zone form the focus of this study. The study area is Mulbagal Town in Karnataka State, India. Groundwater level measurements and estimation of unsaturated permeability indicated that the leachate recharged the groundwater inside the town at the rate of 1 m/day. The average nitrate concentration of groundwater inside the town (148 mg/L) was three times larger than the permissible limit (45 mg/L), while the average nitrate concentration of groundwater outside the town (30 mg/L) was below the permissible limit. The groundwater inside the town exhibited E. coli contamination, while groundwater outside the town was free of pathogen contamination. Infiltration of alkalis (Na⁺, K⁺) and strong acids (Cl^?, SO₄ ^2?) caused the mixed Ca–Mg–Cl type (60 %) and Na–Cl type (28 %) facies to predominate groundwater inside the town, while, Ca–HCO₃ (35 %), mixed Ca–Mg–Cl type (35 %) and mixed Ca–Na–HCO₃ type (28 %) facies predominated groundwater outside/periphery of town. Reductions in E. coli and nitrate concentrations with vadose zone thickness indicated its participation in contaminant removal. A 4-m thickness of unsaturated sand + soft, disintegrated weathered rock deposit facilitates the removal of 1 log of E. coli pathogen. The anoxic conditions prevailing in the deeper layers of the vadose zone (>19 m thickness) favor denitrification resulting in lower nitrate concentrations (28–96 mg/L) in deeper water tables (located at depths of ?29 to ?39 m).     

Geochemical evaluation of nitrate and fluoride contamination in varied hydrogeological environs of Prakasam district,southern India

Hydrogeochemical controlling factors for high rate of groundwater contamination in stressed aquifer of fractured, consolidated rocks belonging to semi-arid watershed are examined. The groundwater in mid-eastern part of Prakasam district confining to Musi-Gundlakamma sub-basins is heavily contaminated with nitrate and fluoride. Distinct water chemistry is noticed among each group of samples segregated based on concentration of these contaminants. The nitrate is as high as 594 mg/l and 57 % of the samples have it in toxic level as per BIS drinking water standards, so also the fluoride which has reached a maximum of 8.96 mq/l and 43 % of samples are not fit for human consumption. Nitrate contamination is high in shallow aquifers and granitic terrains, whereas fluoride is in excess concentration in deeper zones and meta-sediments among the tested wells, and 25 % of samples suffer from both NO₃ ^? and F^? contamination. Na⁺ among cations and HCO₃ ^? among anions are the dominant species followed by Mg²⁺ and Cl^?. The NO₃ ^?-rich groundwater is of Ca²⁺–Mg²⁺–HCO₃ ^?, Ca²⁺–Mg²⁺–Cl^? and Na⁺–HCO₃ ^? type. The F^?-rich groundwater is dominantly of Na⁺–HCO₃ ^? type and few are of Na⁺–SO₄ ^2? type, whereas the safe waters (without any contaminants) are of Ca²⁺–Mg²⁺–HCO₃ ^?– and Na⁺–HCO₃ ^? types. High molecular percentage of Na⁺, Cl^?, SO₄ ^2? and K^? in NO₃ ^? rich groundwater indicates simultaneous contribution of many elements through domestic sewerage and agriculture activity. It is further confirmed by analogous ratios of commonly associated ions viz NO₃ ^?:Cl^?:SO₄ ^2? and NO₃ ^?:K⁺:Cl^? which are 22:56:22 and 42:10:48, respectively. The F^? rich groundwater is unique by having higher content of Na⁺ (183 %) and HCO₃ ^? (28 %) than safe waters. The K⁺:F^?:Ca²⁺ ratio of 10:5:85 and K⁺:F^?: SO₄ ^2? of 16:7:77 support lithological origin of F^? facilitated by precipitation of CaCO₃ which removes Ca²⁺ from solution. The high concentrations of Na⁺, CO₃ ^? and HCO₃ ^? in these waters act as catalyst allowing more fluorite to dissolve into the groundwater. The indices, ratios and scatter plots indicate that the NO₃ ^? rich groundwater has evolved through silicate weathering-anthropogenic activity-evapotranspiration processes, whereas F^? rich groundwater attained its unique chemistry from mineral dissolution-water–rock interaction-ion exchange. Both the waters are subjected to external infusion of certain elements such as Na⁺, Cl^?, NO₃ ^? which are further aggravated by evaporation processes leading to heavy accumulation of contaminants by raising the water density. Presence of NO₃ ^? rich samples within F^? rich groundwater Group and vice versa authenticates the proposed evolution processes.     

Groundwater appraisal of Dhekiajuli,Assam, India: an insight of agricultural suitability and arsenic enrichment

The present work is an effort to develop an appraisal of the hydrogeochemical regime for the aquifers of Dhekiajuli, Sonitpur district, Assam, which is imperative considering: (i) excessive use of groundwater for irrigation; (ii) reported high arsenic (As) contamination; (iii) application of fertilizer is an inevitable process undergoing in this region to achieve higher yield owing to deteriorating water quality; and (iv) study area being the location of many tea estates of Assam, that export tea in many foreign countries. The highest As concentration of 44.39 µg/L was detected in this study (Bachasimalu and Sitalmari region), implying high As-contaminated aquifers being used for drinking and irrigation purposes in the area. The relative abundance pattern of major cations and anions was in the order of Na⁺ > Mg²⁺ > Ca²⁺ > K⁺ and HCO₃ ^? > Cl^? > SO₄ ^2?, respectively. Majority of the samples belong to Na⁺–K⁺–Cl^?–HCO₃ ^? and mixed water type. Closer inspection of Piper plot reveals that a higher As value (>40 µg/L) was prevalent in HCO₃ ^? water type. Results of hydrogeochemical plots suggest silicate and carbonate weathering, ion exchange and anthropogenic activities to be the dominant processes governing groundwater contamination, including As which is further supported from PCA loadings. The Singri area to the east of the affected areas and adjacent to the Brahmaputra River has oxic aquifers owing to the absence of mass deposition of younger sediments, while reducing conditions prevails in the Bachasimalu and Sitalmari region. High positive correlation between As and Fe (r = 0.83**) and a negative correlation between ORP and Fe (r = ?0.68**) further add that Fe (hydr)oxides are the direct source of As release in the affected region, the mechanism being reductive hydrolysis of such (hydr)oxides. The study implies that although groundwater is suitable for irrigation use, there is a high probability of As getting into the food chain through tea and other edible plants irrigated with As-contaminated water; thus, the area has a maximum probability of facing health hazards caused by As-contaminated groundwater.     

A diagnosis of groundwater quality from a semiarid region in Rajasthan,India

A diagnosis of the groundwater quality of 70 wells sampled during two climatic regimes (dry and raining seasons) from a semiarid area in Rajasthan, India, had been carried out using standard methods. Analysis of the results for various hydrochemical parameters wherein the geological units are alluvium, quartzite and granite gneisses showed that all the parameters did not fall within the World Health Organisation’s acceptable limits for irrigation and drinking water purposes. The order of major cations and anions obtained during the dry and raining seasons are Na⁺ ? Mg²⁺ ? Ca²⁺ ? K⁺ and Cl^?? HCO₃ ^? ? SO₄ ^2?? CO₃ ^?> F^? ? NO₃ ^?, respectively. A maximum value of nitrate of 491.6 mg/l has been examined and its contamination is due to discriminated highly impacted groundwater samples by agricultural activity and small-scale urbanization. Fluoride (F^?) concentration is 6.50 mg/l as a maximum value, whereas values in about 26 % of the samples are more than the permissible limit (1.5 mg/l) for drinking water. The cumulative probability distributions of the selected ions show two individual intersection points with three diverse segments, considered as regional threshold values and highly impacted threshold values for differentiating the samples with the effects of geogenic, anthropogenic and saline water mixing. The first threshold values indicate the background hydrochemical constituents in the study area. The second threshold value of 732 mg/l for bicarbonate indicates that sandy aquifer is being dissolved during wet period, whereas NO₃ ^? concentration of more than the initial threshold value (=75 mg/l) indicates discriminated highly impacted groundwater samples by agricultural activity and urbanization in dry season. Various parameters such as soluble sodium percentage (SSP), salinity (electrical conductivity (EC)), sodium adsorption ratio (SAR), residual sodium carbonate (RSC), Kelley’s ratio (KR), permeability index (PI), residual sodium bicarbonate (RSB) and magnesium absorption ratio (MAR) for the well samples show that, overall, 46 % of groundwater samples are not suitable for irrigation. Further, chloro-alkaline indices (CAIs) were used for distinguishing regional recharge and discharge zones whereas corrosivity ratio (CR) utilized for demarcating areas to use metallic pipes for groundwater supply. In general, groundwater quality is mainly controlled by the chemical weathering of rock-forming minerals. The information obtained represents a base for future work that will help to assess the groundwater condition for periodical monitoring and managing the groundwater from further degradation.     

Spatial variability of groundwater quality and its suitability for drinking and irrigation in the Amik Plain (South Turkey)

In this study, it is determined physicochemical properties of the groundwater and the spatial variability of physicochemical properties of the groundwater in the Amik plain and as well as assess its suitability for drinking and irrigation. A total 92 groundwater samples were collected from drilled well in June 2012. In addition, the 42 of 92 drilled wells were also sampled in September 2012 to evaluate the changes of groundwater properties. According to t test values, the mean Ca²⁺, SO₄ ^2?, Mg²⁺ and TH values in the June period were significantly lower than those of the September period. On the other hand, the mean (CO ₃ ^2?  + HCO₃ ^?) and RSC and MR values in the June period were significantly higher than those of the September period. The order of relative abundance of major cations in the groundwater (in mg L^?1) is in order Na⁺ > Mg²⁺ > Ca²⁺ > K⁺. The order of the anions abundance (mg L^?1) is SO₄ ^2? > Cl^? > HCO₃ ^? > CO₃ ^2? in this research. Log and square-root transformation were carried out for the most of the water properties before the calculation of semivariance. The nugget ratio showed all the variables were strongly spatial dependent except for K⁺ and Mg²⁺ and (CO₃ ^2? + HCO₃ ^?) which showed moderate spatial dependence (ratio ranging from 28 to 49.9 %). Spatial distribution analysis of groundwater quality indicated that The EC, TDS values and Na and Cl^? contents which is important water quality parameters increase from northern towards southern. The total hardness values increase also from northwestern towards southwestern.     

Hydrogeochemical assessment of groundwater quality along the coastal aquifers of southern Tamil Nadu,India

Hydrogeochemical investigation of groundwater has been carried out in the coastal aquifers of southern Tamil Nadu, India. Seventy-nine dug well samples were collected and analyzed for various physicochemical parameters. The result of the geochemical analysis indicates the groundwater in the study area is slightly alkaline with moderate saline water. The cation and anion concentrations confirm most of the groundwater samples belong to the order of Na⁺ > Mg²⁺ > Ca²⁺ > K⁺ and Cl^? > SO₄ ^2? > HCO₃ ^?. Thereby three major hydrochemical facies (Ca–Cl, mixed Ca–Mg–Cl and Na–Cl) were identified. Based on the US Salinity diagram, majority of the samples fall under medium to very high salinity with low to high sodium hazard. The cross plot of Ca²⁺ + Mg²⁺ versus chloride shows 61 % of the samples fall under saline water category. Higher EC, TDS and Cl concentrations were observed from Tiruchendur to Koodankulam coastal zone. It indicates that these regions are significantly affected by saltwater contamination due to seawater intrusion, saltpan deposits, and beach placer mining activities.     

Nitrate contamination of groundwater in an agroecosystem in Zhangye Oasis,Northwest China

In order to assess the extent of groundwater contamination by nitrate (NO₃ ⁻–N) and to provide information about the deterioration of the groundwater quality in Zhangye Oasis, Northwest China, a study was conducted in this area. The mean value of NO₃ ⁻–N concentrations in groundwater samples was 10.66 ± 0.19 mg l⁻¹. NO₃ ⁻–N concentrations exceeding 10 mg l⁻¹ (the threshold for drinking water set by the World Health Organization) were found in 32.4% of 71 wells, and were 13, 33.3, 52.4 and 50.0% in the groundwater samples from drinking wells, irrigation wells, hand-pumping wells and groundwater table observation wells, respectively. The result showed that the groundwater samples that had NO₃ ⁻–N concentrations exceeding the threshold for drinking water were mostly collected from a depth of less than 20 m. Groundwater NO₃ ⁻–N concentrations in areas used for the cultivation of vegetables, seed maize and intercropped maize were significantly higher than those in urban or paddy areas. NO₃ ⁻–N contamination of groundwater in areas with sandy soil was more severe than in those with loam soil.     

The impact of sewage-contaminated river water on groundwater ammonium and arsenic concentrations at a riverbank filtration site in central Delhi,India

The groundwater abstracted at a well field near the Yamuna River in Central Delhi, India, has elevated ammonium (NH₄ ⁺) concentrations up to 35 mg/L and arsenic (As) concentrations up to 0.146 mg/L, constituting a problem with the provision of safe drinking and irrigation water. Infiltrating sewage-contaminated river water is the primary source of the NH₄ ⁺ contamination in the aquifer, leading to reducing conditions which probably trigger the release of geogenic As. These conclusions are based on the evaluation of six 8–27-m deep drillings, and 13 surface-water and 69 groundwater samples collected during seven field campaigns (2012–2013). Results indicate that losing stream conditions prevail and the river water infiltrates into the shallow floodplain aquifer (up to 16 m thickness), which consists of a 1–2-m thick layer of calcareous nodules (locally known as kankar) overlain by medium sand. Because of its higher hydraulic conductivity (3.7 × 10^?3 m/s, as opposed to 3.5 × 10^?4 m/s in the sand), the kankar layer serves as the main pathway for the infiltrating water. However, the NH₄ ⁺ plume front advances more rapidly in the sand layer because of its significantly lower cation exchange capacity. Elevated As concentrations were only observed within the NH₄ ⁺ plume indicating a causal connection with the infiltrating reducing river water.     

Mapping groundwater quality for irrigation in Punjab, North-West India, using geographical information system

The state of Punjab—a part of the Indus basin of the Indian subcontinent has an excellent net work of irrigation facilities. However, due to intensive cultivation it is facing a major problem with respect to quality of groundwater for irrigation. In the present investigation, geo-referenced groundwater samples were analysed to map water quality using geographical information system. Electrical conductivity varied from 0.418 to 5.754 dS m^?1 with an average of 1.365 dS m^?1. The carbonate ranged between 0 and 120 mg L^?1, whereas bicarbonate ranged from 5 to 1,000 mg L^?1. Chloride varied from 7 to 2,347 mg L^?1. Calcium plus magnesium ranged from 12 to 1,216 mg L^?1 with a mean value of 169 mg L^?1. Sodium adsorption ratio ranged between 0.0 and 34.78 with an average of 2.66 meq L^?1/2. Residual sodium carbonate varied from 0 to 21.30 meq L^?1 with a standard deviation of 2.24. The Geographic Information System (GIS)-based mapping indicated that water in suitable category spatially covered 45.7 % of the state which is located mostly in the sub-mountain (Siwalik Hills), north-eastern undulating and piedmont and alluvial plain agro-eco-subregions. Marginally suitable groundwater spatially covered 46.1 % in the central alluvial plain and south-western alluvial plain agro-eco-subregions. Unsuitable groundwater covered 8.2 % of the state, mostly in the erstwhile sodic soils areas in the central alluvial plain and south-western alluvial plain agro-eco-subregions. GIS-based maps are effective in identifying hot spots which need immediate attention and call for strategic planning for sustainable management.     

An appraisal of groundwater quality for drinking and irrigation purposes in southern part of Bathinda district of Punjab, northwest India

Groundwater is being used for drinking and irrigation purposes in the agricultural dominated Indian state of Punjab. Fifty-six groundwater samples were collected from Bathinda, a south-western district of Punjab, during the pre-monsoon (March 2010) and post-monsoon (October 2011) seasons. These samples were tested for major cations, anions and contaminants. Various classification systems were used to study the groundwater quality with respect to drinking as well as irrigation purposes. Total dissolved solids (TDS) and total hardness (TH) are generally used to determine the suitability of groundwater for drinking purpose. Considering TDS as a parameter, 54 and 57 % groundwater samples were found to be unsuitable for use during the pre- and post-monsoon seasons. A wide range of TH values were observed in the pre-monsoon and post-monsoon waters samples (mean 250 and 270 mgL^?1). About 75 % of pre-monsoon and 79 % of post-monsoon samples exceeded the maximum permissible limit (MPL) of TH (150 mg L^?1) proposed by WHO. In terms of contaminant ions, 40 % and 55 % of the pre- and post-monsoon water samples were unfit for drinking purposes w.r.t. fluoride (MPL 1.5 mg F L^?1), 29 and 36 % were unfit w.r.t arsenic (MPL 10 μg L^?1) and 33 and 45 % were unfit w.r.t nitrate (MPL 45 mg NO₃ ^? L^?1), respectively. To determine the suitability of groundwater of Bathinda for irrigation purpose, three classification systems proposed by different research workers were used. The parameters electrical conductivity (EC), sodium adsorption ratio, and residual sodium carbonate (RSC) were calculated on the basis of chemical data. Considering EC and RSC together, 32 % samples collected during pre-monsoon season were fit, 19 % were marginal and 49 % were unfit for use. However, during post-monsoon, samples fit for irrigation decreased to 17 % and samples unfit for irrigation increased to 70 %. Increases in the percentage of unfit samples for irrigation after monsoon indicates addition of salts along with the rain water percolated into the groundwater. The other two classification systems, i.e. US Salinity diagram and Wilcox diagram also showed the similar results.     

Geochemistry and quality of groundwater of Gummanampadu sub-basin, Guntur District, Andhra Pradesh, India

Groundwater survey has been carried out in the area of Gummanampadu sub-basin located in Guntur District, Andhra Pradesh, India for assessing the factors that are responsible for changing of groundwater chemistry and consequent deterioration of groundwater quality, where the groundwater is a prime source for drinking and irrigation due to non-availability of surface water in time. The area is underlain by the Archaean Gneissic Complex, over which the Proterozoic Cumbhum rocks occur. The results of the plotting of Ca²⁺ + Mg²⁺ versus HCO₃ ^? + CO₃ ^2?, Ca²⁺ + Mg²⁺ versus total cations, Na⁺ + K⁺ versus total cations, Cl^? + SO₄ ^2? versus Na⁺ + K⁺, Na⁺ versus Cl^?, Na⁺ versus HCO₃ ^? + CO₃ ^2?, Na⁺ versus Ca²⁺ and Na⁺: Cl^? versus EC indicate that the rock–water interaction under alkaline condition is the main mechanism in activating mineral dissociation and dissolution, causing the release of Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃ ^?, CO₃ ^2?, SO₄ ^2? and F^? ions into the groundwater. The ionic relations also suggest that the higher concentrations of Na⁺ and Cl^? ions are the results of ion exchange and evaporation. The influences of anthropogenic sources are the other cause for increasing of Mg²⁺, Na⁺, Cl^?, SO₄ ^2? and NO₃ ^? ions. Further, the excess alkaline condition in water accelerates more effective dissolution of F^?-bearing minerals. Moreover, the chemical data plotted in the Piper’s, Gibbs’s and Langelier–Ludwig’s diagrams, computed for the chloro-alkaline and saturation indices, and analyzed in the principal component analysis, support the above hypothesis. The groundwater quality is, thus, characterized by Na⁺ > Ca²⁺ > Mg²⁺ > K⁺: HCO₃ ^? + CO₃ ^2? > Cl^? > SO₄ ^2? > NO₃ ^? > F^? facies. On the other hand, majority of groundwater samples are not suitable for drinking with reference to the concentrations of TDS, TH, Mg²⁺ and F^?, while those are not good for irrigation with respect to USSL’s and Wilcox’s diagrams, residual sodium carbonate, and magnesium hazard, but they are safe for irrigation with respect to permeability index. Thus, the study recommends suitable management measures to improve health conditions as well as to increase agricultural output.     

Assessment of groundwater salinity using GIS and multivariate statistics in a coastal Mediterranean aquifer

The integration of the statistical approaches and GIS tools with the hydrogeological and geological contexts allowed the assessment of the processes that cause groundwater quality deterioration in the great important deltaic aquifer in the northeastern Tunisia (Medjerda Lower Valley Aquifer). The spatial variation of the groundwater parameters and the molar ratio (Cl^?/Br^?) were also used to determine the possible impacts from seawater intrusion and from the septic tank leachate. Sixty shallow groundwater samples were collected in 2014 and analyzed for major and trace ions over an area of about 1090 km² to determine the suitability for drinking or agricultural purposes. The total dissolved solids (TDS) content ranges from 1005 to 19,254 mgl^?1 with a mean value of 3477.18 mgl^?1. The chemistry is dominated by the sodium–chloride waters (55%). Mapping of TDS, Cl^?, Na⁺, SO₄^2? and NO₃^? using kriging method shows a clear increase in salinity toward the coastline accompanied by Na⁺ and Cl^? increase which may be related to seawater intrusion and halite dissolution. Locally, higher nitrate concentration is related to the agricultural activities inducing contribution of chemical fertilizers and irrigation with treated wastewater. The saturation indices indicate that all carbonate minerals tend to reach saturation equilibrium confirming water–rock interactions, while evaporitic minerals are still in sub-saturation state and may increase the salinity of the groundwater. The principal component analysis proves the occurrence of groundwater contamination principally by seawater intrusion in the factor I (74.15%) and secondary by an anthropogenic source in the factor II (10.35%).     

Hydrochemical characteristics and quality assessment of regolith aquifers in Enugu metropolis, southeastern Nigeria

Twenty groundwater samples were collected from Enugu metropolis over two seasonal periods in order to characterize the groundwater and to determine its quality for domestic and irrigation purposes. The results show that groundwater of the area is strongly acidic to slightly alkaline in nature and varied from “soft water” to “moderately hard” water type. The major ionic trend is in the order Cl^? > Na⁺ > HCO₃ ^? > K⁺ > Mg²⁺ > Ca²⁺ > SO₄ ^2?and Mg²⁺ > Cl^? > Na⁺ > K⁺ > Ca²⁺ > HCO ₃ ^?  > SO₄ ^2? in abundance for dry and rainy seasons, respectively. The results also reveal that there is an increase in trend of the ionic concentrations during the dry season, which arises from weathering of the host rocks and anthropogenic activities. Two hydrochemical facies were identified, namely, Na⁺ –K⁺ –Cl^? –SO₄ ^2?and Ca²⁺ –Mg²⁺ –Cl^? –SO₄ ^2? _, with Na⁺ –K⁺ –Cl^? –SO₄ ^2? as the dominant facies for the two seasons. Groundwater quality ranges from “very poor water” to “good water” and “water unsuitable for drinking purposes” to “good water” for the dry season and rainy season investigations, respectively. The groundwater is suitable for irrigation purposes for the two seasons.     

Anthropogenic contamination of groundwater with nitrate in arid region: case study of southern Hodna (Algeria)

In southern Hodna, an arid region of Algeria, the extension of irrigated agriculture and overexploitation of groundwaters have led to a rupture with traditional land use by pastoralism. Due to the arid conditions, groundwaters are the only water resources for man and irrigation. This study focuses on nitrate contamination of groundwaters and its increase since the last 40 years, on the basis of two archives and recent analyses. The chemical facies of waters is sulphate-chloride, the risk of salinity is moderate to large. The sodicity risk, as estimated by the SAR, is low due to the large salinity and the sandy soil texture. Nitrate contamination of deep groundwater is a clear evidence when recent data are compared to the historical data. From 1996 to 2008, the proportion of samples with NO ₃ ^? concentrations larger than 50 mg/L increases from 24 to 61 %, the proportion of samples with NO ₃ ^? concentrations larger than 100 mg/L increases from 12 to 27 %. The study points at a general contamination of aquifers from anthropic origin: phreatic water was already contaminated when pastoralism was dominant (1967); as population increased and irrigation agriculture developed with large use of N-fertilizers and organic amendments, contamination extended spatially and vertically to deep aquifer. To remediate this contamination, fertilizers should be fractionated and limited to plant requirements on the basis of soil and plant analyses. Excess of irrigation should be avoided. Soil surface should be continuously covered to prevent nitrate leaching. Secondly, more efficient irrigation techniques, such as localized irrigation, should be implemented, with adaptation of crop systems and fertilizer inputs to arid conditions. Farmers should then be trained; simultaneously, local agronomic references that are presently lacking should be acquired.     

Hydrogeochemical characterization and quality assessment of groundwater around Umrer coal mine area Nagpur District,Maharashtra, India

Quality assessment as well as hydrogeochemical characterization of 45 representative groundwater samples around Umrer coal mine area was undertaken. The pH of the water lies in the normal range i.e. from 7.5 to 8.5, the electrical conductivity varies from 826 to 1,741, the total hardness varies from 289 to 1,302 and the TDS values range from 528.6 to 1,114.2 mg/l which reflects variation in lithology and thus, the distinction in hydrogeological regime. The cation chemistry is dominated by Ca²⁺ and Mg²⁺ while anion chemistry is dominated by Cl^? and HCO₃ ^?. Out of total ten hydrochemical facies, the two dominant facies are Mg–Ca–HCO₃ (37.7 %) and Ca–Mg–SO₄–HCO₃ (17.7 %). The groundwater in the study area, in general, is useful for drinking and domestic use; however, it has marginal utility for irrigation purpose. Standard US Salinity Laboratory classification shows that water of the study area belongs to C2–S1 and C3–S1 classes. The concentration of 9 trace elements analysed from 18 samples did not exceed the desirable limit.     

Using chemical analysis and modeling to enhance the understanding of soil solution of some calcareous soils

The chemistry of soil solutions can be altered by human activities, due to the intense agricultural and husbandry, leading to leaching of nutrients and subsequently elevating ground water levels. Multivariate statistical and inverse geochemical modeling techniques were used to determine the main factors controlling soil solution chemistry of calcareous soils. In this research, a total of 21 calcareous soils was characterized and assessed for soil solution using soil column. The major cations in the studied soil solutions were in the decreasing order as Ca²⁺ > Mg²⁺ > Na⁺ > K⁺. The anions were also arranged in decreasing order as HCO $ _{3}^{ - } $  > Cl $ ^{ - } $  > SO $ _{4}^{2 - } $  > NO $ _{3}^{ - } $ . Concentrations of NO $ _{3}^{ - } $ , P, and K⁺ in soil solutions were in the range of 6.8–307.5 mg l^?1 (mean 63.2 mg l^?1), 5.0–10.4 mg l^?1 (mean 5.9 mg l^?1), and 2.8–54.6 mg l^?1 (mean 11.3 mg l^?1), respectively. Results suggest that the concentration of P in the soil solutions could be primarily controlled by the solubility of dicalcium phosphate dihydrate and dicalcium phosphate. Interactions between soil properties and observed solubility of nutrients were described, and put into empirical multivariate formulations. Obtained equations contained electrical conductivity (EC) as a key factor in determining nutrients solubility. Inverse geochemical modeling of soil solution using PHREEQC indicates the dissolution of calcite, anhydrite, halite, CO₂ (g), N₂ (g), and hydroxyapatite, and precipitation of sulfur. Cation exchange between Ca²⁺, Mg²⁺, K⁺ and Na⁺ occurred with Mg²⁺ and K⁺ into the solution, and Ca²⁺ and Na⁺ out of the solution. Determination of soil solution will improve soil management in the area, and preventing groundwater deterioration.     

Impact of agricultural activity and lithology on groundwater quality in the Merdja area, Tebessa, Algeria

This work presents results of the hydrogeological and hydrochemical studies on groundwater samples from the alluvial aquifer of Merdja in Tébessa, located in the Western part of this town. Its groundwater resources are used mainly for crop irrigation in an agriculture dominated area. Hydrochemical and water quality data obtained through a sampling period (December 2008) and analysis program indicate that nitrate pollution can be a serious problem affecting groundwater due to the use of nitrogen (N) fertilizers in agriculture. The concentration of nitrate in groundwater ranged from 19 to 281 mg/l. Considerable seasonal fluctuations in groundwater quality were observed as a consequence of agricultural practices and other factors such as annual rainfall distribution and the wadi El Kebir flow regime. The chemical composition of the water is not only influenced by agricultural practices, but also by interaction with the alluvial sediments. The dissolution of evaporites accounts for part of the Na⁺, K⁺, Cl^?, SO ₄ ^2? , Mg²⁺, and Ca²⁺, but other processes, such as calcite precipitation and dedolomitization, also contribute to groundwater chemistry.     

Hydrogeochemistry and microbial contamination of groundwater from Lower Ponnaiyar Basin, Cuddalore District, Tamil Nadu, India

Groundwater is the major source of fresh water in regions where there is inadequate surface water resources. Forty-seven groundwater samples were collected from Lower Ponnaiyar basin, Cuddalore District, south India, during the premonsoon (PRM) and postmonsoon (POM) seasons of 2005. Out of 47 groundwater samples, 15 samples showing higher nitrate concentration were those collected during PRM 2005. Microbial analysis of these samples was carried out by employing 16S rRNA gene sequence tool. Detailed analysis was conducted to determine the hydrogeochemical processes and microbial contamination responsible for deterioration of quality. The abundance of the ions during PRM and POM are in the following order: Na?>?Ca?>?Mg?>?K?=?Cl?>?HCO₃?>?SO₄?>?CO₃. The dominant water types in PRM are in the order of NaCl?>?CaMgCl?>?mixed CaNaHCO₃, whereas during POM NaCl?>?CaMgCl?>?mixed CaNaHCO₃, and CaHCO₃. However, NaCl and CaMgCl are major water types in the study area. The quality of groundwater in the study area is mainly impaired by surface contamination sources, mineral dissolution, ion exchange and evaporation. Groundwater chemistry was used to assess quality to ensure its suitability for drinking and irrigation, based on BIS and WHO standards. Suitability for irrigation was determined on the basis of the diagram of US Salinity Laboratory (USSL), sodium absorption ratio (SAR), residual sodium carbonate (RSC), and Na%. According to SAR and USSL classification, 27.66% (PRM) and 40.43% (POM) of samples fall under C3S2 category, indicating high salinity and medium sodium hazard, which restrict its suitability for irrigation. Microbiological analysis and its effects on the water quality were also addressed. The 16S rRNA gene sequences of 11 bacterial contaminants exhibited five groups with 11 operational taxonomic units with aerobic and facultatively anaerobic organisms. The presence of aerobic organisms in the groundwater samples reflects the active conversion of ammonia to nitrite by Nitrosomonas sp. which is further converted to nitrates by other organisms. Further the presence of nitrate reducers could also play a role in the process of conversion of nitrate to ammonia and nitrate to molecular nitrogen.     

Spatial assessment of groundwater quality in the Jangseong region,South Korea

A total of 129 groundwater samples were collected in the Jangseong region of South Korea to characterize and evaluate groundwater quality and its suitability for irrigation and domestic uses. Samples were chemically analyzed for major ions, pH, electrical conductivity, and total dissolved solids following standard methods. The AquaChem 2014.2 model linked with PHREEQC was used for the statistical analysis and characterization of the hydrochemistry of the groundwater. The analysis showed that in all samples Ca–HCO₃ was the leading water type and that the abundance of major cations was in the order Ca > Na > Mg > K, and of anions in the order HCO₃ > Cl > SO₄ > F. According to the correlation analysis, Ca showed strong interdependence with HCO₃, suggesting that these parameters may have originated from common sources. Saturation index calculations indicated that all samples were undersaturated with respect to aragonite, calcite, dolomite, fluorite, gypsum, halite, and siderite, and oversaturated with respect to goethite and hematite. The irrigation suitability analysis revealed that groundwater in the Jangseong area can be used for irrigation without any restrictions based on EC, sodium adsorption ratio, percent sodium, residual sodium carbonate, Kelley ratio, permeability index, and the US Salinity Laboratory diagram analysis. The drinking water suitability analysis made for major parameters by comparison with the WHO guidelines indicates that the groundwater in the area is suitable for drinking except in some samples with high nitrate–N concentrations. The elevated nitrate concentrations in the groundwater are likely an indicator of agricultural pollution.