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1.
Dar es Salaam Quaternary coastal aquifer is a major source of water supply in Dar es Salaam City used for domestic, agricultural, and industrial uses. However, groundwater overdraft and contamination are the major problems affecting the aquifer system. This study aims to define the principal hydrogeochemical processes controlling groundwater quality in the coastal strip of Dar es Salaam and to investigate whether the threats of seawater intrusion and pollution are influencing groundwater quality. Major cations and anions analysed in 134 groundwater samples reveal that groundwater is mainly affected by four factors: dissolution of calcite and dolomite, weathering of silicate minerals, seawater intrusion due to aquifer overexploitation, and nitrate pollution mainly caused by the use of pit latrines and septic tanks. High enrichment of Na+ and Cl? near the coast gives an indication of seawater intrusion into the aquifer as also supported from the Na–Cl signature on the Piper diagram. The boreholes close to the coast have much higher Na/Cl molar ratios than the boreholes located further inland. The dissolution of calcite and dolomite in recharge areas results in Ca–HCO3 and Ca–Mg–HCO3 groundwater types. Further along flow paths, Ca2+ and Na+ ion exchange causes groundwater evolution to Na–HCO3 type. From the PHREEQC simulation model, it appears that groundwater is undersaturated to slightly oversaturated with respect to the calcite and dolomite minerals. The results of this study provide important information required for the protection of the aquifer system.  相似文献   

2.
Groundwater is a critical resource in Deoria district, as it is the main source of drinking water and irrigation. The aquifer has deteriorated to a high degree, during the last two to three decades, in quality and quantity due to high population growth and environmental pollution. More than 90% of the population get their drinking water from subsurface waters. Fifteen wells were sampled in June 2006 to probe the hydrogeochemical components that influence the water quality. The results show that groundwater have EC, TDS, Na+, Mg2+, HCO3− and TH higher than the WHO, 1997 maximum desirable limits. A hydrogeochemical numerical model for carbonate minerals was constructed using the PHREEQC package. The regression analysis shows that there are three groups of elements which are significantly and positively correlated. The main hydrochemical facies of the aquifer (Ca + Mg–HCO3) represents 33.33% of the total wells. The geochemical modeling demonstrated that the reactions responsible for the hydrochemical evolution in the area fall into three categories: (1) dissolution of salts, (2) precipitation of dolomite, (3) ion exchange. Solubility of dolomite, calcite, aragonite and gypsum were assessed in terms of the saturation index. The thermodynamic prerequisites for dolomite supersaturation reactions are satisfied by subsurface waters, since they are supersaturated with respect to dolomite, undersaturated (or in equilibrium) with respect to calcite, and undersaturated with respect to gypsum. The Ca2+ versus SO42− and Mg2+ versus SO42− trends are also compatible with homologous trends resulting from dolomite supersaturation.  相似文献   

3.
Geochemical processes that take place in the aquifer have played a major role in spatial and temporal variations of groundwater quality. This study was carried out with an objective of identifying the hydrogeochemical processes that controls the groundwater quality in a weathered hard rock aquifer in a part of Nalgonda district, Andhra Pradesh, India. Groundwater samples were collected from 45 wells once every 2 months from March 2008 to September 2009. Chemical parameters of groundwater such as groundwater level, EC and pH were measured insitu. The major ion concentrations such as Ca2+, Mg2+, Na+, K+, Cl−, and SO4 2− were analyzed using ion chromatograph. CO3 − and HCO3 − concentration was determined by acid–base titration. The abundance of major cation concentration in groundwater is as Na+ > Ca2+ > Mg2+ > K+ while that of anions is HCO3 − > SO4 2− > Cl− > CO3 −. Ca–HCO3, Na–Cl, Ca–Na–HCO3 and Ca–Mg–Cl are the dominant groundwater types in this area. Relation between temporal variation in groundwater level and saturation index of minerals reveals the evaporation process. The ion-exchange process controls the concentration of ions such as calcium, magnesium and sodium. The ionic ratio of Ca/Mg explains the contribution of calcite and dolomite to groundwater. In general, the geochemical processes and temporal variation of groundwater in this area are influenced by evaporation processes, ion exchange and dissolution of minerals.  相似文献   

4.
Based on analysis of groundwater hydrogeochemical and isotopic data, this study aims to identify the recharge sources and understand geochemical evolution of groundwater along the downstream section of the Shule River, northwest China, including two sub-basins. Groundwater samples from the Tashi sub-basin show markedly depleted stable isotopes compared to those in the Guazhou sub-basin. This difference suggests that groundwater in the Tashi sub-basin mainly originates from meltwater in the Qilian Mountains, while the groundwater in the Guazhou sub-basin may be recharged by seepage of the Shule River water. During the groundwater flow process in the Tashi sub-basin, minerals within the aquifer material (e.g., halite, calcite, dolomite, gypsum) dissolve in groundwater. Mineral dissolution leads to strongly linear relationships between Na+ and Cl? and between Mg2++ Ca2+ and SO4 2??+?HCO3 ?, with stoichiometry ratios of approximately 1:1 in both cases. The ion-exchange reaction plays a dominant role in hydrogeochemical evolution of groundwater in the Guazhou sub-basin and causes a good linear relationship between (Mg2++ Ca2+)–(SO4 2??+?HCO3 ?) and (Na++ K+)–Cl? with a slope of ?0.89 and also results in positive chloroalkaline indices CAI 1 and CAI 2. The scientific results have implications for groundwater management in the downstream section of Shule River. As an important irrigation district in Hexi Corridor, groundwater in the Guazhou sub-basin should be used sustainably and rationally because its recharge source is not as abundant as expected. It is recommended that the surface water should be used efficiently and routinely, while groundwater exploitation should be limited as much as possible.  相似文献   

5.
Detailed hydrogeochemical investigation has provided new information concerning the major factors and mechanisms controlling the groundwater chemistry of Chougafiya basin. The hydrogeochemical characteristics of groundwaters comprise three main types: Cl–SO4–Ca, Cl–SO4–Na and Cl–Na. Hydrochemical characteristics based on the bivariate diagrams of major (Cl?, SO4 2?, NO3 ?, HCO3 ?, Na+, Mg2+, K+ and Ca2+) and some trace (Br? and Sr2+) ions, mineral saturation indices and hierarchical cluster analysis indicate different origins of groundwater mineralization. The water–rock interaction (dissolution of evaporitic minerals), followed by cation exchange reactions with clay minerals, constitute the main processes that control groundwater salinization. However, the chemical composition of brackish groundwater in the central and southern parts of the study area is influenced by a mixing process with Sabkhas salt groundwater. The mixing proportions inferred from chloride mass balance prove that the contribution of Sabkhas groundwater to Quaternary aquifer ranges between 2.7 and 9.1 %. These intrusion rates reflect the progress of the saltwater–freshwater interface, which is mainly controlled by the piezometric level variation and the distance to the Sabkhas.  相似文献   

6.
Located in semi-arid regions of northwestern China, Datong basin is a Quaternary sedimentary basin, where groundwater is the most important source for water supply. It is very important to study groundwater characteristics and hydrogeochemical processes for better management of the groundwater resource. We have identified five geochemical zones of shallow groundwater (between 5 and 80 m) at Datong: A. Leaching Zone (Zone I); B. Converging Zone (Zone II); C. Enriching Zone (Zone III); D. Reducing Zone (Zone IV); E. Oxidizing Zone (Zone V). In Zones I, II, and V and some parts of Zones III and IV, hydrolysis of albite/K-feldspar/chalcedony system and/or albite/K-feldspar/quartz system enhanced concentrations of Na+, K+, HCO3− and silicate. In Zone I, dissolution of carbonate and hydrolysis of feldspar generally controlled the groundwater chemistry. Infiltration of meteoric water promoted the formation of HCO3− in the water. In Zone II, the main geochemical processes influencing the groundwater chemistry were dissolutions of calcite and dolomite, ion exchange and evaporation. In Zones III and IV, in addition to ion exchange, evaporation and precipitation of calcite and dolomite, leaching of NaHCO3 in saline–alkaline soils dominated the water quality. Zone IV was under anoxic condition, and reduction reactions led to the decrease of SO42−, NO3− and occurrence of H2S, with the highest arsenic content (mean value of 366 μg/L), far exceeding Maximum Contaminant Level (MCL). Abnormal arsenic in the groundwater resulted in endemic disease of waterborne arsenic poisoning among local people. Zone V overlapped Zone I was intensively affected by coal mining activities. Sulfide minerals, such as pyrite, would have been oxidized when exposed to air due to coal mining, which directly added sulfate to groundwater and thus increased SO42− concentration. Oxidization of sulfide minerals also decreased pH and promoted dissolutions of calcite and dolomite.  相似文献   

7.
Hydogrochemical investigation of groundwater resources of Paragraph district has been carried out to assess the solute acquisition processes and water quality for domestic and irrigation uses. Fifty-five groundwater samples were collected and analyzed for pH, electrical conductivity, total dissolved solids, hardness, major anions (F?, Cl?, NO3, HCO3 ?, SO4 2?) and cations (Ca2+, Mg2+, Na+, K+). Study results reveal that groundwater of the area is alkaline in nature and HCO3 ?, Cl?, Mg2+, Na+ and Ca2+ are the major contributing ions to the dissolved solids. The hydrogeochemical data suggest that weathering of rock forming minerals along with secondary contributions from agricultural and anthropogenic sources are mainly controlling the groundwater composition of Pratapgarh district. Alkaline earth metals (Ca2++Mg2+) exceed alkalis (Na++K+) and weak acid (HCO3 ?) dominate over strong acids (Cl?+SO4 2?) in majority of the groundwater samples. Ca-Mg-HCO3 and Ca-Mg-Cl-HCO3 are the dominant hydrogeochemical facies in the groundwater of the area. The computed saturation indices demonstrate oversaturated condition with respect to dolomite and calcite and undersaturated with gypsum and fluorite. A comparison of groundwater quality parameters in relation to specified limits for drinking water shows that concentrations of TDS, F?, NO3 ? and total hardness exceed the desirable limits in many water samples. Quality assessment for irrigation uses reveal that the groundwater is good for irrigation. However, values of salinity, sodium adsorption ratio (SAR), residual sodium carbonate (RSC), %Na and Kelley index are exceeding the prescribed limit at some sites, demanding adequate drainage and water management plan for the area.  相似文献   

8.
Hydrogeochemical processes that accompany seawater intrusion in coastal aquifers can alter the resulting water quality and are important ingredients in coastal aquifer management. The presence of dissolution–precipitation reactions and ion exchange in the mixing zone of the Biscayne aquifer (FL, USA) are suggested based on changes in major ion concentrations and mineral saturation indices (SI). Major ion concentrations from 11 groundwater samples are compared with theoretical mixing between freshwater and seawater. PHREEQC code was used to calculate saturation indices of the samples with respect to common phases in the Biscayne aquifer. High Ca2+ and HCO3 ? content of the samples is typical of waters in contact with carbonate aquifers. Water quality of the samples is mainly attributed to mixing and precipitation–dissolution reactions with calcite and dolomite. The samples were saturated with calcite (SI ~ 0) and undersaturated for dolomite (SI < 0), while a few samples showed dolomite saturation. Because gypsum and halite SI could be predicted by theoretical mixing, reactions with those minerals, if present, are thought to be insignificant. In the active intrusion areas, cation exchange also appears to modify water quality leading to excess Ca2+, but depleted Na+, Mg2+ and K+ concentrations. On the other hand, samples from previous intrusion areas plotted very close to the theoretical mixing line and approached equilibrium with the seawater.  相似文献   

9.
A base line study involving analysis of groundwater samples from the Jhansi district were carried out to determine the major and trace element chemistry and to assess the hydrogeochemical processes and water quality for domestic and irrigation uses. Study results show that groundwater is mildly acidic to alkaline in nature and HCO3 ?, Cl?, Ca2+, Na+ and Mg2+ are the major contributing ions for the dissolved loads. The data plotted on the Gibbs and Piper diagrams reveal that the groundwater chemistry is mainly controlled by rock weathering with secondary contribution from anthropogenic sources. In a majority of the groundwater samples, alkaline earth metals exceed alkalies and weak acid dominate over strong acids. Ca–Mg–HCO3 is the dominant hydrogeochemical facies in the majority of the groundwater samples. The computed saturation indices demonstrate that groundwater is oversaturated with respect to dolomite and calcite. Kaolinite is the possible mineral that is in equilibrium with the water, implying that the groundwater chemistry favors kaolinite formation. A comparison of groundwater quality parameters in relation to specified limits for drinking water shows that the concentrations of TDS, F?, NO3 ?, total hardness and Fe are exceeding the desirable limits in many water samples. Quality assessment for irrigation uses reveal that the groundwater is of good to suitable category. Higher salinity and residual sodium carbonate values at some sites restrict the suitability of groundwater and need an adequate drainage and water management plan for the area.  相似文献   

10.
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11.
李状  苏晶文  董长春  叶永红  杨洋 《中国地质》2022,49(5):1509-1526
【研究目的】 了解长江中下游平原地区地下水流系统并深入分析其地下水水化学特征及其演化机制。【研究方法】 综合马鞍山市当涂地区的水文地质条件、水动力场等,基于研究区水化学基本特征,运用多元统计分析、水化学图件、离子比值和反向水文地球化学模拟等方法对该地区浅层地下水水化学演化进行分析。【研究结果】 结果表明：（1）研究区地下水主要为低矿化度偏碱性水,地下水组分中阳离子以Ca2+和Mg2+为主,阴离子以HCO3-和SO42-为主。（2）研究区地下水水化学类型主要可分为7类,其中松散岩类孔隙含水岩组和碎屑岩类孔隙裂隙含水岩组的水化学类型主要为HCO3-Ca型、HCO3-Ca·Na型、HCO3·Cl-Ca·Na型以及HCO3-Ca·Mg型;基岩类裂隙含水岩组的化学类型主要为HCO3·SO4-Ca·Mg型和SO4·HCO3-Ca·Mg型。（3）研究区浅层地下水水样超标率为46%,总体水质较差,超标率较高的组分依次为Mn、高锰酸盐指数（CODMn）、硝酸盐（以N计）、Fe、As、氨氮（以N计）等。（4）研究区地下水的化学组分主要受到岩石风化作用的控制;此外,还存在Na-Ca的正向阳离子交替吸附作用。反向水文地球化学模拟结果进一步定量论证了水岩相互作用对本区浅层地下水组分的形成和演化起着主导作用。【结论】 研究区地下水主要为低矿化度偏碱性,主要可分为松散岩类孔隙水、碎屑岩类孔隙裂隙水和基岩类裂隙水。主要离子比例和反向水文地球化学模拟揭示了本区浅层地下水化学组分主要是地下水溶滤方解石、白云石等碳酸盐矿物、石英、长石等硅酸盐矿物,高岭土等黏土矿物以及岩盐、石膏等达到过饱和之后形成的。  相似文献   

12.
This work addresses hydrogeochemical processes in shallow aquifers, represented by the Quaternary alluvial deposits, from a part of the semi-arid Mexican Highlands through the evaluations of physicochemical parameters as well as the δ18O and δ2H compositions of groundwater. Mifflin diagram separates the Na-bicarbonate, sulphate and mixed groundwater into one group showing interactions with volcanic lithology in the recharge zones and another group interacting with the evaporite rich sedimentary formation. In the Gibbs diagram, the samples with Cl?/(Cl? + HCO3?) < 0.4 showed higher influence of ion exchange and the samples with Cl?/(Cl? + HCO3?) > 0.4 showed higher effects of evaporation. All of them were oversaturated with carbonate minerals (i.e., calcite and dolomite) and unsaturated with evaporites (i.e., gypsum and halite). Evaporation (earlier stage) occurred before the water-rock interactions (later stage). Evolution occurs through three different routes such as up to 7.5‰ enrichment in δ18O caused by the infiltration with a certain delay and subsequently, the water-rock interaction became dominant. Ternary mixing models revealed dominant influence of local recharge (C1) on the water system, contributing 70.4%. Water-rock interaction (C3) with 18% and evaporation (C2) with 11.6% had comparatively less influences. The presence of nitrate (2–60 mg/L) in the groundwater indicated variable degrees of anthropogenic pollution.  相似文献   

13.
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.  相似文献   

14.
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.  相似文献   

15.
This paper gives an account of the implementation of hydrochemical and isotopic techniques to identify and explain the processes that govern solute exchange in two groundwater-dependent shallow lakes in the Southeastern Pampa Plain of Argentina. Water samples (lakes, streams, spring water and groundwater) for hydrochemical and stable isotopic determination were collected and the main physical–chemical parameters were measured. The combination of stable isotope data with hydrogeochemical techniques was used for the identification of sources and preferential recharge areas to these aquatic ecosystems which allowed the explanation of the lake water origin. The hydrochemical processes which explain Los Padres Lake water chemistry are evaporation from groundwater, CO2 input, calcite dissolution, Na+ release by Ca2+ and Mg2+ exchange, and sulfate reduction. The model that best aligns with La Brava Lake hydrochemical constraints includes: mixing, CO2 and calcite dissolution, cationic exchange with Na+ release and Mg2+ adsorption, and to a lesser extent, Ca/Na exchange. This model suggests that the fractured aquifer contribution to this water body is greater than 50 %. An isotopic-specific fingerprint for each lake was identified, finding a higher evaporation rate for La Brava Lake compared to Los Padres Lake. Isotopic data demonstrate the importance of these shallow lakes as recharge areas to the regional aquifer, becoming areas of high groundwater vulnerability. The Tandilia Range System, considered in many hydrogeological studies as the impermeable bedrock of the Pampean aquifer, acts as a fissured aquifer in this area, contributing to low salinity waters and with a fingerprint similar to groundwater isotopic composition.  相似文献   

16.
The Panama coastal aquifer system is an important water resource in the southeast coast of Sri Lanka that provides adequate supplies of water for agriculture and domestic uses. One of the biggest threats to these fragile aquifers is the sea water intrusion. In this study, recharging mechanism and geochemical evaluation of groundwater in the coastal sandy aquifer of Panama were evaluated using chemical and stable isotope techniques. Thirty groundwater samples were collected and analyzed for their major ion concentrations and stable isotope ratios of oxygen (18O/16O) and hydrogen (D/H). All studied samples showed a ranking of major anions in the order Cl? > HCO 3 ?  > SO 4 2?  > N-NO3 ? while cations showed a decreasing order of abundance with Na+ > Ca2+ > Mg2+ > K+. Dominant groundwater hydrogeochemical types were Na–Cl and mixed Ca–Mg–Cl. Results of saturation index calculations indicate that the investigated groundwater body was mostly saturated with respect to calcite, dolomite and gypsum. In addition, stable isotope and geochemical data suggest that fresh groundwater in the aquifer is recharged mainly by local precipitation with slight modification from evaporation and saline water intrusions. Isotope data suggest that mixing of salt water with freshwater occurs in aquifers which are located towards the lagoon. Since the communities in the study area depend entirely on groundwater, an understanding of the hydrogeochemical characteristics of the aquifer system is extremely important for the better water resource management in the region.  相似文献   

17.
Presence of fluoride in groundwater is a public health problem in the so-called endemic fluorosis belt of the central Iran, where the groundwater is the major source of drinking water in most urban and rural areas. Therefore, an attempt has been made to determine the hydrogeochemical factors controlling fluoride enrichment in the groundwater resources at this belt. Fluoride concentrations ranged from 0.20 to 1.99 mg/L (1.02 ± 0.47) in groundwater samples. The presence of different F-bearing minerals and also clay minerals in the soils and aquifer materials was confirmed using XRD analysis. To identify probable sources of dissolved F? and investigate groundwater quality, multivariate statistical analyses were carried out. Geochemical modeling indicated that all samples were undersaturated with respect to fluorite, halite, gypsum and anhydrite and mostly oversaturated with respect to calcite and dolomite. Contrary to most high-fluoride regions in the World, the high F? content was dominated by Na–Cl- and Ca–SO4-type groundwater in the study area. Besides, fluoride showed negative relationship with pH and HCO3 ? in groundwater. In order to assess the bioavailability of fluoride in soils, a two-step chemical fractionation method was applied. The results showed that fluoride in soils mostly accompanied with the residual and water-soluble fractions and was poorly associated with soil’s bonding sites. Calculated aqueous migration coefficient demonstrated that fluoride in the studied soils was mobile to easily leachable to the groundwater. Finally, the results demonstrated that combination of water–rock interaction and influence of clay minerals is geochemical mechanism responsible for controlling fluoride enrichment in groundwater.  相似文献   

18.
Continual expansion of population density, urbanization, agriculture, and industry in most parts of the world has increased the generation of pollution, which contributes to the deterioration of surface water quality. This causes the dependence on groundwater sources for their daily needs to accumulate day by day, which raises concerns about their quality and hydrogeochemistry. This study was carried out to increase understanding of the geological setup and assess the groundwater hydrogeochemical characteristics of the multilayered aquifers in Lower Kelantan Basin. Based on lithological data correlation of exploration wells, the study area can be divided into three main aquifers: shallow, intermediate and deep aquifers. From these three aquifers, 101 groundwater samples were collected and analyzed for various parameters. The results showed that pH values in the shallow, intermediate and deep aquifers were generally acidic to slightly alkaline. The sequences of major cations and anions were Na+ > Ca2+ > Mg2+ > K+ and HCO3? > Cl? > SO42? > CO32?, respectively. In the intermediate aquifer, the influence of ancient seawater was the primary factor that contributed to the elevated values of electrical conductivity (EC), Cl? and total dissolved solids (TDS). The main facies in the shallow aquifer were Ca–HCO3 and Na–HCO3 water types. The water types were dominated by Na–Cl and Na–HCO3 in the intermediate aquifer and by Na–HCO3 in the deep aquifer. The Gibbs diagram reveals that the majority of groundwater samples belonged to the deep aquifer and fell in the rock dominance zone. Shallow aquifer samples mostly fell in the rainfall zone, suggesting that this aquifer is affected by anthropogenic activities. In contrast, the results suggest that the deep aquifer is heavily influenced by natural processes.  相似文献   

19.
The hydrogeochemistry and isotope geochemistry of groundwater from 85 wells in fractured dolomite aquifers of Central Slovenia were investigated. This groundwater represents waters strongly influenced by chemical weathering of dolomite with an average of δ13CCARB value of +2.2 ‰. The major groundwater geochemical composition is HCO3 ? > Ca2+ > Mg2+. Several differences in hydrogeochemical properties among the classes of dolomites were observed when they were divided based on their age and sedimentological properties, with a clear distinction of pure dolomites exhibiting high Mg2+/Ca2+ ratios and low Na+, K+ and Si values. Trace element and nutrient concentrations (SO4 2?, NO3 ?) were low, implying that karstic and fractured dolomite aquifers are of good quality to be used as tap water. Groundwater was generally slightly oversaturated with respect to calcite and dolomite, and dissolved CO2 was up to 46 times supersaturated relative to the atmosphere. The isotopic composition of oxygen (δ18OH2O), hydrogen (δDH2O) and tritium ranged from ?10.3 to ?8.4 ‰, from ?68.5 to ?52.7 ‰ and from 3.5 TU to 10.5 TU, respectively. δ18O and δD values fell between the GMWL (Global Meteoric Water Line) and the MMWL (Mediterranean Meteoric Water Line) and indicate recharge from precipitation with little evaporation. The tritium activity in groundwater suggests that groundwater is generally younger than 50 years. δ13CDIC values ranged from ?14.6 to ?9.3 ‰ and indicated groundwater with a contribution of degraded organic matter/dissolved inorganic carbon in the aquifer. The mass balances for groundwater interacting with carbonate rocks suggested that carbonate dissolution contributes from 43.7 to 65.4 % and degradation of organic matter from 34.6 to 56.3 %.  相似文献   

20.
Rock water interactions play an important role in the flow of groundwater. Groundwater samples were collected from deep production wells with depths ranging from 120 to 230 m. Complete chemical analysis of 40 groundwater samples was collected from the fractured limestone aquifer including major cations (Na+, K+, Ca2+, Mg2+) and major anions (Cl?, SO4 2?, HCO3 ?, CO3 2?). A geochemical modeling (NETPATH Software) was applied for environmental simulate net geochemical mass-balance reactions between initial and final waters along a hydrologic flow path. This program simulates selected evolutionary waters for every possible combination of the plausible phases that account for the composition of a selected set of chemical constraints in the system. The groundwater of the Eocene aquifer mainly belongs to fairly fresh water with salinity contents ranging from 228 to 3595 ppm. The measured groundwater levels range between 8 and 25 m near the river Nile to the limestone plateau (eastwards). Consequently, groundwater flows from east to westward toward the river Nile. Groundwater aquifer in the study area is mainly composed of fractured limestone; the saturated states of the PCO2, calcite, aragonite, dolomite, siderite, gypsum, anhydrite, hematite, and goethite in addition to H2 gas were estimated. The undersaturated state of carbon dioxide reflects closed conditions and very low probability of recent recharge, and it reveals also the high tendency of water to precipitates carbonate species. Undersaturation by carbonate minerals is only restricted to some pockets distributed on the different places of the aquifer in the study area. The majority of groundwater samples of Eocene aquifer in the study area indicated that groundwater is not suitable for irrigation with treatment and requires good drainage.  相似文献   

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