Estimate of shallow groundwater recharge in the Hadejia–Nguru Wetlands, semi-arid northeastern Nigeria

 The Hadejia–Nguru Wetlands are annually inundated flood plains in semi-arid northeastern Nigeria. The area has a unique ecosystem that forms a natural barrier against the encroachment of the Sahara desert. Both the rich wetland vegetation and local farmers using shallow tube wells depend on a groundwater mound (with a water table less than 6 m below the surface) that is present in the unconfined aquifer under the flood-plain area. Using well records (1991–97) and a hydrogeologic profile based on piezometers that were monitored for two years, it is shown that recharge through the annually inundated flood plains is the source of the groundwater mound. Maintenance of the groundwater-recharge function of the flood plains depends on wet-season releases from two large upstream dams. On the basis of a water-budget method, the mean (1991–97) wet-season unconfined groundwater recharge in the flood-plain area between Hadejia and Nguru and in the immediate vicinity (1250 km²) is estimated to be 132 mm (range, 73–197 mm). Outflow from the unconfined flood-plain aquifer to the unconfined upland aquifer is approximately 10% of the wet-season flood-plain recharge. The unconfined groundwater outflow from the flood-plain area can provide a significant contribution to the present-day rural water supply in the surrounding uplands, but it does not offer much potential for additional groundwater abstraction. In addition to outflow to the upland aquifer (∼14 mm), the distribution of the annually recharged water volume of the shallow flood-plain aquifer is (1) domestic uses (3 mm), (2) small-scale irrigation (∼15 mm), and (3) evapotranspiration ( 1 100 mm). Along the hydrogeologic profile, the recharge in the upland (i.e., outflow from the unconfined flood-plain aquifer and possibly diffuse rain-fed recharge) is in balance with the water uses (i.e., domestic uses, groundwater outflow, and evapotranspiration). The absence of a seasonal water-level trend in the two piezometers in the upland indicates that no rain-fed recharge occurs through preferential path-way (macropore) flow. Received, June 1998 / Revised, November 1998, January 1999 / Accepted, January 1999     

The influence of Zihe Stream on the groundwater resources of the Dawu well field and on the discharge at the Heiwang iron mine, Zibo City area, Shandong Province, China

 The Dawu well field, one of the largest in China, supplies most of the water for the Zibo City urban area in Shandong Province. The field yields 522,400–535,400 m³/d from an aquifer in fractured karstic Middle Ordovician carbonate rocks. Much of the recharge to the aquifer is leakage of surface water from Zihe Stream, the major drainage in the area. Installation of the Taihe Reservoir in 1972 severely reduced the downstream flow in Zihe Stream, resulting in a marked reduction in the water table in the Dawu field. Since 1994, following the installation of a recharge station on Zihe Stream upstream from the well field that injects water from the Taihe Reservoir into the stream, the groundwater resources of the field have recovered. An average of 61.2×10³ m³/d of groundwater, mostly from the Ordovician aquifer, is pumped from the Heiwang iron mine, an open pit in the bed of Zihe Stream below the Taihe Reservoir. A stepwise regression equation, used to evaluate the role of discharge from the reservoir into the stream, confirms that reservoir water is one of the major sources of groundwater in the mine. Received, May 1998 / Revised, May 1999 / Accepted, June 1999     

Groundwater circulation in the allochthonous limestone units between Lake Girdev and Kazanpınarı Spring, Antalya, southwestern Turkey

 The aim of the study is to investigate the interaction between waters of Lake Girdev and groundwater in the allochthonous limestone units exposed in the area between Lake Girdev and Kazanpınarı Spring, southwestern Turkey. The features analyzed include the flow direction and apparent groundwater velocity, their relationship with Lake Girdev, and the effect of lithological and structural features on the groundwater circulation. The results of a fluorescein tracer test indicate that groundwater flows east-northeast and the apparent flow velocity ranges from 26.2 to 35.6 m h^–1 between the injection site and various observation points. Tritium data suggest that the water of Lake Girdev and groundwater are probably similar in age, and oxygen-18 isotope data indicate that water derived from Lake Girdev is the main source of recharge to the aquifer. The aquifer is fed not only by Lake Girdev but also by rainfall percolating through allochthonous limestones; together, these provide the discharge of springs in Elmalı Polje. The permeability of the allochthonous limestone aquifer has been enhanced as a result of jointing and faulting. Received, June 1997 / Revised, June 1998, March 1999 / Accepted, July 1999     

Patterns in groundwater chemistry resulting from groundwater flow

 Groundwater flow influences hydrochemical patterns because flow reduces mixing by diffusion, carries the chemical imprints of biological and anthropogenic changes in the recharge area, and leaches the aquifer system. Global patterns are mainly dictated by differences in the flux of meteoric water passing through the subsoil. Within individual hydrosomes (water bodies with a specific origin), the following prograde evolution lines (facies sequence) normally develop in the direction of groundwater flow: from strong to no fluctuations in water quality, from polluted to unpolluted, from acidic to basic, from oxic to anoxic–methanogenic, from no to significant base exchange, and from fresh to brackish. This is demonstrated for fresh coastal-dune groundwater in the Netherlands. In this hydrosome, the leaching of calcium carbonate as much as 15 m and of adsorbed marine cations (Na⁺, K⁺, and Mg²⁺) as much as 2500 m in the flow direction is shown to correspond with about 5000 yr of flushing since the beach barrier with dunes developed. Recharge focus areas in the dunes are evidenced by groundwater displaying a lower prograde quality evolution than the surrounding dune groundwater. Artificially recharged Rhine River water in the dunes provides distinct hydrochemical patterns, which display groundwater flow, mixing, and groundwater ages. Received, May 1998 · Revised, August 1998 · Accepted, October 1998     

Origin and distribution of saline groundwaters in the upper Miocene aquifer system, coastal Rhodope area, northeastern Greece

 This paper describes the origins and distribution of saline groundwaters in the coastal area of Rhodope, Greece. The aquifer system includes two aquifers within coarse-grained alluvial sediments in the coastal part of the study area. Two major water-quality groups occur in the study area, namely Ca²⁺-rich saline groundwater and Ca²⁺-poor, almost fresh groundwater. The main process controlling the groundwater chemistry is the exchange of calcium and sodium between the aquifer matrix and intruding seawater. The natural salt water in the study area is probably residual water that infiltrated the aquifer system during repeated marine transgressions in late Pleistocene time. Seawater intrusion into the coastal aquifer system occurs as a result of overpumping in two seawater wedges separated vertically by a low-permeability layer. The rate of intrusion averages 0.8 m/d and is less than expected due to a decline of the aquifer's permeability at the interface with the seawater. The application of several hydrochemical techniques (Piper and Durov diagrams; Na⁺/Cl^–, Ca²⁺/Cl^–, Mg²⁺/Cl^–, and Br^–/Cl^– molar ratios; Ca²⁺/Mg²⁺ weight ratio; and chloride concentrations), combined with field observations, may lead to a better explanation of the origin of the saline groundwater. Received, May 1997 / Revised, May 1998, December 1998 / Accepted, February 1999     

The groundwater resources and sustainable yield of Cheju volcanic island, Korea

 Hydrogeologic data of 455 water wells comprising geologic logs, water qualities, and aquifer test results are analyzed to determine hydrogeological characteristics, water quality, and sustainable yield of the groundwater resources of Cheju volcanic island. The groundwater of the island occurs in unconsolidated pyroclastic deposits and clinkers interbedded in highly jointed basaltic and andesitic rocks as high-level, basal, and parabasal groundwater under unconfined conditions. The total storage of groundwater is estimated at about 44 billion m³. The average transmissivity and specific yield of the aquifer are at about 0.34 m² s^–1(29300 m² day^–1) and 0.12, respectively. The average annual precipitation is about 3.39 billion m³, of which 1.49 billion m³– equivalent to 44.0% of the total annual precipitation – is recharged into aquifers, with 0.638 billion m³ year^–1 of runoff and 1.26 billion m³ year^–1 of evapotranspiration. Based on a groundwater budget analysis, the sustainable yield is estimated at about 0.62 billion m³ year^–1, equivalent to 41.6% of annual recharge. A low-permeability marine sedimentary formation (Sehwari formation), composed of loosely cemented sandy silt, was recently found to be situated at 120±68 m below mean sea level. If the said marine sediment is distributed as a basal formation of the freshwater zone of the island, most of its groundwater will be of parabasal type. So the marine sediment is one of the most important hydrogeological boundaries and groundwater occurrences in the area. Received: 16 January 1997 / Accepted: 16 June 1997     

Natural arsenic in Triassic rocks: A source of drinking-water contamination in Bavaria, Germany

 The aquifer system of the Upper Triassic Keuper Sandstone, an important source of drinking water in northern Bavaria, is affected by elevated arsenic concentrations. Within the study area of 8000 km², no evidence exists for any artificial source of arsenic. Data from about 500 deep water wells show that in approximately 160 wells arsenic concentrations are 10–150 μg/L. The regional distribution of arsenic in the groundwater shows that elevated arsenic concentrations are probably related to specific lithofacies of the aquifers that contain more sediments of terrestrial origin. Geochemical measurements on samples from four selected well cores show that arsenic has accumulated in the rocks. This indigenous arsenic is the source of arsenic in the groundwater of certain facies of the middle unit of the Keuper Sandstone. Received, June 1998 / Revised, January 1999, May 1999 / Accepted, June 1999     

Seepage measurements from Long Lake,Indiana Dunes National Lakeshore

 Long Lake, located near Lake Michigan within the dune-complexes of Indiana Dunes National Lakeshore, USA, was formed some time during the Pleistocene and Holocene epochs. A surficial aquifer underlies Long Lake, which is either a source or sink for the later. The hydrologic processes in the lakeshore and surrounding environs have been significantly altered during the agricultural, municipal, and industrial development of the region. Limited data suggest that the organisms of Long Lake have elevated levels of several contaminants. This study attempts to quantify seepage within the lake to assess the potential threat to groundwater quality. Seepage measurements and minipiezometric tests were used to determine seepage within the lake. Seepage measurements and minipiezometric tests suggest that water seeps out of Long Lake, thus recharging the groundwater that flows southwest away from the lake. There is a great deal of variability in the seepage rate, with a mean of 11.5×10^–4±11.2×10^–4 m d^–1. The mean seepage rate of 0.3 m yr^–1 for Long Lake is greater than the 0.2 m yr^–1 recharge rate estimated for the drainage basin area. The Long Lake recharge volume of 2.5×10⁵ m³ yr^–1 is approximately 22% of the volume of the lake and is significant when compared to the total surface recharge volume of 4.8×10⁵ m³ yr^–1 to the upper aquifer of the drainage area. There is a potential for contamination of the groundwater system through seepage from the lake from contaminants derived from aerial depositions. Received: 16 August 1995 · Accepted: 18 September 1995     

The Ohlsbach Plume – Discharge of deep saline water from the crystalline basement of the Black Forest, Germany

 Salt-water discharges from a fault system in the crystalline basement of the Black Forest into the gravel aquifer of the Kinzig River valley near Ohlsbach, upper Rhine River valley, southwestern Germany. The salt water (TDS, 16 g/kg) ascends from a reservoir at  1 3 km depth. Once discharged into the gravel aquifer, the saline deep water mixes with fresh groundwater and is carried along the groundwater flow path to the middle of the Rhine River valley. There, the natural geogene salt-water plume merges with a man-made chloride-rich infiltration zone along the Rhine River. The plume was mapped using (1) chloride data from groundwater observation wells, and (2) resistivity data from geoelectric sounding. Background chloride is about 7 mg/kg. In the central region of the plume, chloride concentration exceeds 200 mg/kg. A continuous area of Cl  1 50 mg/kg is distinguished from the discharge fault to the Rhine River over a distance of 12 km. Resistivities range from  1 50 Ω in uncontaminated regions to <7 Ω in the 700 m-long central region of the plume. A low resistivity plume (7–10 Ω) stretches for  1 7 km into the Rhine River valley. The two plume maps are in good agreement. Received, April 1998 / Revised, November 1998, January 1999 / Accepted, January 1999     

Groundwater resources of the middle and upper Odra River basin, southwestern Poland

 The total amount of groundwater resources in the middle and upper Odra River basin is 5200×10³ m³/d, or about 7.7% of the disposable groundwater resources of Poland. The average modulus of groundwater resources is about 1.4 L/s/km². Of the 180 'Major Groundwater Basins' (MGWB) in Poland, 43 are partly or totally located within the study area. The MGWB in southwestern Poland have an average modulus of groundwater resources about 2.28 L/s/km² and thus have abundant water resources in comparison to MGWB from other parts of the country. Several types of mineral waters occur in the middle and upper Odra River basin. These waters are concentrated especially in the Sudety Mountains. Carbon-dioxide waters, with yields of 414 m³/h, are the most widespread of Sudetic mineral waters. The fresh waters of the crystalline basement have a low mineralization, commonly less than 100 mg/L; they are a HCO₃–Ca–Mg or SO₄–Ca–Mg type of water. Various hydrochemical compositions characterize the groundwater in sedimentary rocks. The shallow aquifers are under risk of atmospheric pollution and anthropogenic effects. To prevent the degradation of groundwater resources in the middle and upper Odra River basin, Critical Protection Areas have been designated within the MGWB. Received, January 1995 Revised, May 1996, August 1997 Accepted, August 1997     

Groundwater recharge and flow in the Lower Cretaceous Nubian Sandstone aquifer in the Sinai Peninsula, using isotopic techniques and hydrochemistry

The present work was conducted in the Sinai Peninsula (1) to identify the recharge and flow characteristics and to evaluate the continuity of the Lower Cretaceous Nubian Sandstone aquifer; and (2) to provide information for the aquifer's rational appraisal. Isotopic and hydrochemical compositions combined with the geological and hydrogeological settings were used for this purpose. A considerable depletion in isotopic content (oxygen-18 and deuterium) and low d-excess values exist in the studied groundwater, reflecting the contribution of old meteoric water that recharged the aquifer in pluvial times. Modern recharge also occurs from precipitation that falls on the aquifer outcrops. The wide scatter of the data points around the two meteoric lines, the global meteoric water line (GMWL) and Mediterranean meteoric water line (MMWL), in the δ¹⁸O–δD diagram indicates considerable variation in recharge conditions (amount, altitude, temperature, air masses, distances from catchment, overland flow, etc.). The isotopic composition in the El-Bruk area is minimum (¹⁸O=–9.53‰), very close to the average value of the Western Desert Nubian Sandstone (¹⁸O=–10‰), where the local structural and lithologic conditions retard groundwater flow and the main bulk of water becomes noncyclic. The continuity of the aquifer in northern and central Sinai is evidenced by the isotopic similarity between samples taken from above and below the central Sinai Ragabet El-Naam fault, the distribution of potentiometric head, and hydrogeological cross sections. The combination of isotopic composition in terms of ¹⁸O and chemical composition in terms of TDS and salt contents is the basis for separating the studied groundwater into groups that reflect the recharge sources and isotopic and chemical modifications during flow. Electronic Publication     

Hydrochemical evidence for mixing of river water and groundwater during high-flow conditions, lower Suwannee River basin, Florida, USA

 Karstic aquifers are highly susceptible to rapid infiltration of river water, particularly during periods of high flow. Following a period of sustained rainfall in the Suwannee River basin, Florida, USA, the stage of the Suwannee River rose from 3.0 to 5.88 m above mean sea level in April 1996 and discharge peaked at 360 m³/s. During these high-flow conditions, water from the Suwannee River migrated directly into the karstic Upper Floridan aquifer, the main source of water supply for the area. Changes in the chemical composition of groundwater were quantified using naturally occurring geochemical tracers and mass-balance modeling techniques. Mixing of river water with groundwater was indicated by a decrease in the concentrations of calcium, silica, and ²²²Rn; and by an increase in dissolved organic carbon (DOC), tannic acid, and chloride, compared to low-flow conditions in water from a nearby monitoring well, Wingate Sink, and Little River Springs. The proportion (fraction) of river water in groundwater ranged from 0.13 to 0.65 at Wingate Sink and from 0.5 to 0.99 at well W-17258, based on binary mixing models using various tracers. The effectiveness of a natural tracer in quantifying mixing of river water and groundwater was related to differences in tracer concentration of the two end members and how conservatively the tracer reacted in the mixed water. Solutes with similar concentrations in the two end-member waters (Na, Mg, K, Cl, SO₄, SiO₂) were not as effective tracers for quantifying mixing of river water and groundwater as those with larger differences in end-member concentrations (Ca, tannic acid, DOC, ²²²Rn, HCO₃). Received, March 1999 / Revised, July 1999 / Accepted, July 1999     

Exploration of an alluvial aquifer in Oman by time-domain electromagnetic sounding

 One-third of the population of Oman depends upon groundwater extracted from the alluvium of the Batinah Plain, on the coast of the Gulf of Oman. Deep geophysical exploration techniques were used to determine the depth and nature of the alluvium and the boundaries of the aquifer. The base and structural controls of the alluvial basin at its contact with Tertiary marine sediments and Cretaceous ophiolite were mapped with seismic reflection data, recorded originally for oil exploration. The base of the alluvium dips northward from the foothills of the Northern Oman Mountains, reaching a maximum depth of 2000 m at the coast. The varying facies of the alluvium are grossly characterised by different, overlapping ranges of electrical resistivity, depending largely on the clay content and degree of cementation. Resistivities near the coast are reduced by saline intrusion. These variations of resistivity were mapped with time-domain electromagnetic sounding along 400 km of profile, to distinguish among the three zones of the alluvial aquifer. The wedge of saline intrusion was also delineated, up to 10 km from the coast. The thickness of the saturated gravel aquifer ranges from 20–160 m in an area greater than 600 km². Received, April 1997 · Revised, January 1998 · Accepted, April 1998     

Modeling of groundwater flow for Mujib aquifer, Jordan

Jordan is an arid country with very limited water resources. Groundwater is the main source for its water supply. Mujib aquifer is located in the central part of Jordan and is a major source of drinking water for Amman, Madaba and Karak cities. High abstraction rates from Mujib aquifer during the previous years lead to a major decline in water levels and deterioration in groundwater quality. Therefore, proper groundwater management of Mujib aquifer is necessary; and groundwater flow modeling is essential for proper management. For this purpose, Modflow was used to build a groundwater flow model to simulate the behavior of the flow system under different stresses. The model was calibrated for steady state condition by matching observed and simulated initial head counter lines. Drawdown data for the period 1985–1995 were used to calibrate the transient model by matching simulated drawdown with the observed one. Then, the transient model was validated by using drawdown data for the period 1996–2002. The results of the calibrated model showed that the horizontal hydraulic conductivity of the B2/A7 aquifer ranges between 0.001 and 40m/d. Calibrated specific yield ranges from 0.0001 to 0.15. The water balance for the steady state condition of Mujib aquifer indicated that the total annual direct recharge is 20.4 × 10⁶m³, the total annual inflow is 13.0 × 10⁶ m³, springs discharge is 15.3 × 10⁶ m³, and total annual outflow is 18.7 × 10⁶ m³. Different scenarios were considered to predict aquifer system response under different conditions. The results of the sensitivity analysis show that the model is highly sensitive to horizontal hydraulic conductivity and anisotropy and with lower level to the recharge rates. Also the model is sensitive to specific yield     

Evaluation of scraping treatments to restore initial infiltration capacity of three artificial recharge projects in central Iran

 A limiting factor in developing artificial recharge of groundwater is clogging of the soil surface and consequent reduction of infiltration rates. In order to evaluate the degree of improving infiltration rates by scraping away various amounts of the upper soil materials, a study was conducted at three artificial recharge sites (Kohrouyeh, Bagh-Sorkh, and Kachak) in Isfahan Province, central Iran. Five treatments (T1–T5) were considered. Infiltration was measured: T1, on deposited sediment layer; T2, after removing the sediments; T3, scraping of sediments and 5 cm of soil; T4, scraping of sediments and 10 cm of soil; and T5, removing sediments and 15 cm of soil. Initial soil-moisture content of the sites ranged from 1.0–2.87% for Kohrouyeh, 1.18–3.47% for Bagh-Sorkh, and 1.89–3.93% for Kachak. The main texture of the soils was sandy loam. Clay particles have penetrated to a depth of more than 40 cm in some of the recharge basins. A significant increase in final infiltration rate of T5 as compared to T1 treatment was observed for all recharge sites. The final infiltration rates of T1 and T5 treatments for Kohrouyeh, Bagh-Sorkh, and Kachak sites were 0.35, 7.9; 1.22, 12.3; and 0.93, 6.2 cm/h, respectively. The differences between infiltration rates of T2, T3, and T4 treatments were not statistically significant. It is concluded that on average, the infiltration capacity of the untreated recharge facilities have reached 20.3% of the original values, and that scraping the top sediment layer and 15 cm of topsoil could restore 68.3% of the initial infiltration capacity. Received, July 1998 / Revised, April 1999, May 1999 / Accepted, June 1999     

Mass transport modelling for assessement of groundwater contamination around Mathura oil refinery, Mathura, Uttar Pradesh, India

Mathura oil refinery was commissioned during 1977 and effluent storage ponds were constructed at the same time. These storage ponds receive wastewater from the refinery at a rate of 10000 m³/day. After treatment, waste water is discharged through a 3-km pipeline to a stream leading to the Yamuna river. The groundwater-monitoring as well as water-quality monitoring was carried at 24 observation wells in the refinery site during 1997. The water quality measurements indicated total dissolved chloride and sulphate concentration of native groundwater as 400 mg/l, whereas elevated levels up to 600 mg/l were found at the wells close to polishing ponds. Thus combined transport of chloride and sulphate was simulated in the mass transport model. A three-dimensional flow, pathlines and mass transport model of the aquifer system were constructed to analyze the impact of seepage from polishing ponds contaminating the groundwater regime. The permeability of aquifer varies between 1.5–2.5 m/day. The porosity of formation was assumed as 0.2. The constant head and constant concentration boundaries were assigned to the nodes representing effluent storage ponds. Longitudinal dispersivity of 100 m, horizontal transverse dispersivity of 10 m and vertical transverse dispersivity of 0.01 m were assumed. The mass transport model was calibrated for 20 years by comparing total dissolved chloride and sulphate concentrations from 1997. The model predictions indicate further migration of contaminants on the east of effluent ponds in future. Received: 4 January 1999 · Accepted: 12 July 1999     

Depth of the base of the Jackson aquifer, based on geophysical exploration, southern Jackson Hole, Wyoming, USA

 A geophysical survey was conducted to determine the depth of the base of the water-table aquifer in the southern part of Jackson Hole, Wyoming, USA. Audio-magnetotellurics (AMT) measurements at 77 sites in the study area yielded electrical-resistivity logs of the subsurface, and these were used to infer lithologic changes with depth. A 100–600 ohm-m geoelectric layer, designated the Jackson aquifer, was used to represent surficial saturated, unconsolidated deposits of Quaternary age. The median depth of the base of the Jackson aquifer is estimated to be 200 ft (61 m), based on 62 sites that had sufficient resistivity data. AMT-measured values were kriged to predict the depth to the base of the aquifer throughout the southern part of Jackson Hole. Contour maps of the kriging predictions indicate that the depth of the base of the Jackson aquifer is shallow in the central part of the study area near the East and West Gros Ventre Buttes, deeper in the west near the Teton fault system, and shallow at the southern edge of Jackson Hole. Predicted, contoured depths range from 100 ft (30 m) in the south, near the confluences of Spring Creek and Flat Creek with the Snake River, to 700 ft (210 m) in the west, near the town of Wilson, Wyoming. Received, May 1997 · Revised, February 1998 · Accepted, April 1998     

Recharge rate estimation in the Mountain karst aquifer system of Figeh spring, Syria

Figeh watershed spring is one of the important groundwater aquifer, which is considered a major source for drinking waters of Damascus city and countryside. The origin identification and recharge estimates of groundwater are significant components of sustainable groundwater development in this Mountain karst aquifer of Figeh spring. During the period 2001–2009, monthly groundwater and precipitation samples were taken and the isotopic compositions of δ¹⁸O, δ²H, and chloride contents were analyzed to identify groundwater origins and to estimate recharge rates. The δ¹⁸O, δ²H of the groundwater show that the groundwater recharge is of meteoric origin. The chloride mass balance (CMB) method was used to quantify recharge rates of groundwater in the Mountain karst aquifer of Figeh spring. The recharge rate varies from 192 to 826 mm/year, which corresponds to 43 and 67% of the total annual rainfall. Recharge rates estimated by CMB were compared with values obtained from other methods and were found to be in good agreement. This study can be used to develop effective programs for groundwater management and development.     

Recharge source and hydrogeochemical evolution of shallow groundwater in a complex alluvial fan system,southwest of North China Plain

Many cities around the world are developed at alluvial fans. With economic and industrial development and increase in population, quality and quantity of groundwater are often damaged by over-exploitation in these areas. In order to realistically assess these groundwater resources and their sustainability, it is vital to understand the recharge sources and hydrogeochemical evolution of groundwater in alluvial fans. In March 2006, groundwater and surface water were sampled for major element analysis and stable isotope (oxygen-18 and deuterium) compositions in Xinxiang, which is located at a complex alluvial fan system composed of a mountainous area, Taihang Mt. alluvial fan and Yellow River alluvial fan. In the Taihang mountainous area, the groundwater was recharged by precipitation and was characterized by Ca–HCO₃ type water with depleted δ¹⁸O and δD (mean value of −8.8‰ δ¹⁸O). Along the flow path from the mountainous area to Taihang Mt. alluvial fan, the groundwater became geochemically complex (Ca–Na–Mg–HCO₃–Cl–SO₄ type), and heavier δ¹⁸O and δD were observed (around −8‰ δ¹⁸O). Before the surface water with mean δ¹⁸O of −8.7‰ recharged to groundwater, it underwent isotopic enrichment in Taihang Mt. alluvial fan. Chemical mixture and ion exchange are expected to be responsible for the chemical evolution of groundwater in Yellow River alluvial fan. Transferred water from the Yellow River is the main source of the groundwater in the Yellow River alluvial fan in the south of the study area, and stable isotopic compositions of the groundwater (mean value of −8.8‰ δ¹⁸O) were similar to those of transferred water (−8.9‰), increasing from the southern boundary of the study area to the distal end of the fan. The groundwater underwent chemical evolution from Ca–HCO₃, Na–HCO₃, to Na–SO₄. A conceptual model, integrating stiff diagrams, is used to describe the spatial variation of recharge sources, chemical evolution, and groundwater flow paths in the complex alluvial fan aquifer system.