Shallow Aquifer System Research Articles

A comparison of helicopter-borne electromagnetic systems for hydrogeologic studies

The increased application of airborne electromagnetic surveys to hydrogeological studies is driving a demand for data that can consistently be inverted for accurate subsurface resistivity structure from the near surface to depths of several hundred metres. We present an evaluation of three commercial airborne electromagnetic systems over two test blocks in western Nebraska, USA. The selected test blocks are representative of shallow and deep alluvial aquifer systems with low groundwater salinity and an electrically conductive base of aquifer. The aquifer units show significant lithologic heterogeneity and include both modern and ancient river systems. We compared the various data sets to one another and inverted resistivity models to borehole lithology and to ground geophysical models. We find distinct differences among the airborne electromagnetic systems as regards the spatial resolution of models, the depth of investigation, and the ability to recover near-surface resistivity variations. We further identify systematic biases in some data sets, which we attribute to incomplete or inexact calibration or compensation procedures.

Correlation and spectral analyses to assess the response of a shallow aquifer to low and high frequency rainfall fluctuations

Summary With the predicted acceleration of drought and flood frequency worldwide, it is critical to build knowledge on how shallow groundwater systems respond to rainfall variability. In this study, we characterise the hydrodynamic response of an agricultural catchment located in southeast Queensland, Australia, to the low and high frequency fluctuations in precipitation that occurred in the past 25 years. Strong interannual variations in the precipitation input affected surface water flow more substantially than groundwater levels (GWLs). There was also a likely influence of groundwater abstraction on stream baseflow and GWLs, although it was difficult to quantify. Several low frequency oscillations were apparent in the GWL records, particularly in the upstream section of the aquifer, which were neither detectable in rainfall nor in discharge records. Statistically significant episodes of coherence were found at the 2–4-year band between the Nino3.4 index and GWLs for those upstream bores, especially during the 1995–2000 interval, which may be related to a strong La Nina event. In the downstream section of the catchment, higher groundwater persistence probably led to higher filtering of these low frequency oscillations. This paper also proposes a methodology for assessing the dynamic response time of GWLs in shallow aquifer systems to the precipitation input. Response time in a downstream borehole was highly variable temporally, ranging from 11 to 121 days. Rainfall amount was found to significantly affect the short-term dynamics of response time, with elevated rainfall leading to a decreased response time. Annually averaged response time was correlated with the annual number of days with rainfall >30 mm, which was interpreted as the potential for diffuse recharge. Higher recharge potential induced longer response times, probably because of the larger amplitude in GWL variations.

CO2 leakage in shallow aquifers: A benchmark modeling study of CO2 gas evolution in heterogeneous porous media

The physicochemical processes associated with CO2 leakage into shallow aquifer systems are complex and span multiple spatial and time scales. Continuum-scale numerical models that faithfully represent the underlying pore-scale physics are required to predict the long-term behavior and aid in risk analysis regarding regulatory and management decisions. This study focuses on benchmarking the numerical simulator, FEHM, with intermediate-scale column experiments of CO2 gas evolution in homogeneous and heterogeneous sand configurations. Inverse modeling was conducted to calibrate model parameters and determine model sensitivity to the observed steady-state saturation profiles. It is shown that FEHM is a powerful tool that is capable of capturing the experimentally observed outflow rates and saturation profiles. Moreover, FEHM captures the transition from single- to multi-phase flow and CO2 gas accumulation at interfaces separating sands. We also derive a simple expression, based on Darcy's law, for the pressure at which CO2 free phase gas is observed and show that it reliably predicts the location at which single-phase flow transitions to multi-phase flow.

Linking nitrogen management, seep chemistry, and stream water quality in two agricultural headwater watersheds.

Riparian seepage zones in headwater agricultural watersheds represent important sources of nitrate-nitrogen (NO-N) to surface waters, often connecting N-rich groundwater systems to streams. In this study, we examined how NO-N concentrations in seep and stream water were affected by NO-N processing along seep surface flow paths and by upslope applications of N from fertilizers and manures. The research was conducted in two headwater agricultural watersheds, FD36 (40 ha) and RS (45 ha), which are fed, in part, by a shallow fractured aquifer system possessing high (3-16 mg L) NO-N concentrations. Data from in-seep monitoring showed that NO-N concentrations generally decreased downseep (top to bottom), indicating that most seeps retained or removed a fraction of delivered NO-N (16% in FD36 and 1% in RS). Annual mean N applications in upslope fields (as determined by yearly farmer surveys) were highly correlated with seep NO-N concentrations in both watersheds (slope: 0.06; = 0.79; < 0.001). Strong positive relationships also existed between seep and stream NO-N concentrations in FD36 (slope: 1.01; = 0.79; < 0.001) and in RS (slope: 0.64; = 0.80; < 0.001), further indicating that N applications control NO-N concentrations at the watershed scale. Our findings clearly point to NO-N leaching from upslope agricultural fields as the primary driver of NO-N losses from seeps to streams in these watersheds and therefore suggest that appropriate management strategies (cover crops, limiting fall/winter nutrient applications, decision support tools) be targeted in these zones.

Assessment of shallow aquifer salinity in the Aqaba Coastal plain using ERT method: a case study of Maqnah region, northwestern Saudi Arabia

An electrical resistivity tomography survey has been conducted along the eastern coast of the Gulf of Aqaba in order to assess the salinity of the coastal shallow aquifer. The study area is extended from Ra’s Shikh Humayd to the town of Maqnah, northwest of Saudi Arabia. Eight electrical profiles were conducted using the Wenner–Schlumberger configuration. The total length of each profile was 360 m providing an expected maximum depth of penetration of about 50 m. All electrical profiles were conducted perpendicular to the coast and directed in the west–east direction. The inversion of the electrical data provided a clear two-dimensional image of the subsurface in the area that reflected the variations in the resistivity of the shallow aquifer system. The subsurface is composed of three layers: the upper layer corresponds to the dry alluvial and gravel deposits that have resistivity values in the range between 40 and 1400 Ω m. The second layer is the saturated zone of the alluvial sediments which represents the coastal aquifer in the study area. The resistivity value of the saturated zone is in the range of 0.15 to 25 Ω m. The lower layer in the subsurface stratification is the resistive bedrock which has resistivity values of more than 100 Ω m. It is composed of Pleistocene–Miocene sediments. The extension of saline water body has been mapped along all electrical profiles. The interpretation of the resistivity models shows that the salinity of the groundwater in the area is strongly related to three main factors: (1) the closeness to the coast; (2) closeness to wadis and low areas which allow saline surface water to infiltrate into the shallow aquifer and; (3) the abundance of gypsum outcrop in the vicinity. This last factor emphasizes the important effect of the local geological setting on the salinity of groundwater; the abundant supply of leached gypsum contributes to the salinity of the shallow aquifer.

Isotopic analysis, hydrogeochemistry and geothermometry of Tang-Bijar oilfield springs, Zagros region, Iran

This study is focused on warm and cold springs in Tang-Bijar oilfield of southern Iran. The springs emerge from fractures and faultlines within the carbonate and evaporitic rocks of Zagros Thrust Belt (ZTB) and vary in temperature between 20 and 44°C. Chemical analyses define three main chemical water associations reflecting different hydrochemical processes including: (1) Ca-HCO3,(2) Mg-SO4 and (3) Na-Cl. Based on isotope analysis, meteoric water is the origin of these spring waters. Two distinct hydrogeological systems are postulated: a deep moderate-temperature (40 to 45̊C) geothermal system recharged by meteoric waters mixed with oilfield brine and a shallow cold aquifer system related to local groundwater.

Evaluating Induced Fractures Between a Large Artificial Lake and an Aquifer-Coal Seam System: A Case Study in Tangshan Coal Mine, China

The hydrogeology of the Tangshan coal mine is extremely complicated. There are at least 20 major faults, with the offset exceeding 50 m. A large artificial lake was created where mining-induced subsidence occurred; it was filled with groundwater pumped from the adjacent aquifers near the coal seams. In addition, there are two nearby rivers that are also believed to have significant groundwater and surface water interactions. Both the river system and the large lake could be a potential threat to a new mining operation in the deep no. 5 coal seam. An in-situ hybrid packer system was designed to measure the thickness of the fracture zone and a 3-D hydrogeological model of the coal seam, associated aquifers, artificial lake, and surface water was established to simulate the groundwater flow field to evaluate the potential impact of induced fractures between the lake and the aquifers and coal seams. The results indicated that the lake has an insignificant impact on the aquifers and coal seams, though it does influence the shallow quaternary aquifer in the study area. Further study is suggested to monitor the groundwater and surface water interactions between the lake and the shallow aquifer system.

Arsenic mobilization in an alluvial aquifer of the Terai region, Nepal

Abstract Study Region A shallow ( Study Focus We examine the hydrogeochemical characteristics of a shallow alluvial aquifer system in the Terai region (Nawalparasi district) to identify possible mechanisms and controls on geogenic As mobilization in groundwater. Groundwater and river water samples from a topo-gradient flow-path and floodplain of a minor river draining the Siwalik forehills were analyzed for physico-chemical parameters. New Hydrological Insights for the Region The aquifer is characterized by Ca-HCO3 type water and is multi-contaminated, with the WHO guideline values exceeded for As, Mn and F in 80%, 70% and 40% of cases respectively. The middle portion of the floodplain was heavily contaminated with As, predominantly as As(III). The river water displayed some evidence of reductive processes in the hyporheic zone contributing As, Fe and Mn to baseflow and also had elevated fluoride. The generally sub-oxic conditions, dominance of As(III) and Fe2+ species and positive correlation between As and both NH3 and UV-absorbance at 254 nm suggests that oxidation of organic matter coupled with microbial mediated reductive processes are important for mobilizing As in the aquifer. The apparent decoupling between As(III)(aq) and Fe2+(aq) may be explained by precipitation of siderite, but further work is required to resolve this unambiguously. Along with reductive processes, other geochemical mechanisms including silicate weathering and precipitation/dissolution of carbonate minerals, control the solute and major ion composition of groundwater.

Emerging Trends in Groundwater Pollution and Quality

Groundwater pollution due to anthropogenic activities may impact overall groundwater quality. Organic and inorganic pollutants have been routinely detected at unsafe levels in groundwater rendering this important drinking water resource practically unusable. Vulnerability of groundwater pollution and subsequent impact has been documented in various studies across the globe. Field studies as well as mathematical models have demonstrated increasing levels of pollutants in both shallow and deep aquifer systems. New emerging pollutants such as organic micro‐pollutants have also been detected in some industrialized as well as in developing countries. Increased vulnerability coupled with ever growing demand for groundwater may pose a greater threat of pollution due to induced recharge and lack of environmental safeguards to protect groundwater sources. In this review paper, comprehensive assessment of groundwater quality impact due to human activities such as improper management of organic and inorganic waste, and natural sources is documented. A detailed review of published reports and peer reviewed journal papers across the world clearly demonstrate that groundwater quality is declining over time. A proactive approach is needed to prevent human health and ecological consequences due to ingestion of contaminated groundwater.

Vulnerability assessment of coastal aquifer system for irrigation suitability — A classical approach from southern India

The vulnerability of the shallow aquifer system for saline water intrusion has been evaluated using the classical tools at a coastal area, southern India. Groundwater samples (N=144) from Quaternary aquifer system within 25 km2 area in pre- and post-monsoon seasons were analyzed for major ion chemistry including Electrical Conductivity (EC). The hydrochemical parameters are examined applying classical irrigation suitability tools. Based on their weight percentages (ratios in meq/l) the dominance of cations and anions was established as Na-Cl and Ca-SO4 type. Results show that high hydraulic conductivity (10−2 to 1 cm/s) of the sandy aquifer enhanced the vertical recharge leading to major spatial distribution suitable for irrigation use in post-monsoon. The overexploitation of groundwater resources has generated reversal of hydraulic gradient enhancing salinity intrusion from marine sources in pre-monsoon. Further, the Differential Global Positioning System (DGPS) survey and water level measurements are assessed to demarcate the study area into zones of water table ‘above mean sea level (amsl)’ and ‘below mean sea level (bmsl)’. It was deduced that, the industrial effluent and seawater were the prime sources of groundwater salinity of water table ‘amsl’ and ‘bmsl’ zones, respectively. The area up to 600 m from marine source is found vulnerable which is falling under ‘Unsuitable’ category of irrigation classifications. The remedial measures are also framed to protect further extension of aquifer vulnerability for sustainable agriculture.

Evapotranspiration and energy balance dynamics of a semi-arid mountainous steppe and shrubland site in Northern Mongolia

The semi-arid forest-steppe ecotone in the Khentii Mountains in Northern Mongolia is characterized by southerly exposed steppe slopes, shrublands in the floodplain of river valleys and northerly exposed taiga slopes. Here, the freshwater for the downstreaming agricultural, rural and mining sectors is generated. To gain insight into the main water-generating sources in mountainous river basins, we studied the actual evapotranspiration (ET) and its main influencing eco-hydrometeorological parameters at a steppe and a shrubland site during the growing season 2012. Latent (LE) and sensible (H) heat fluxes were measured using the Bowen ratio energy balance method, and the surface soil heat flux (G 0) was determined with the PlateCal and GradCal approach. During water-stressed soil conditions at the steppe site, volumetric water content (VWC) values of 0.05 m3 m−3 (−10 cm) resulted in significant limitations of the mean actual ET rates to 0.4 mm day−1. In contrast, high VWC with maxima of >0.4 m3 m−3 and high mean actual ET rates >6.0 mm day−1 were observed during water-unstressed soil conditions. As precipitation and change of stored soil moisture were approximately equal to actual ET, the contribution of freshwater from mountainous steppe within the forest-steppe ecotone can be neglected. At the shrubland site, which is underlain by a shallow aquifer system, VWC remained relatively constant with mean values of 0.4 m3 m−3 (−10 cm). A multiple regression analysis indicated that actual ET, with mean rates of 2.3 mm day−1, was not significantly limited by precipitation and VWC, but by net radiation (R n) and air temperature. As precipitation exceeded total actual ET, shrub covered river floodplains can contribute to freshwater generation.

A geochemical context for stray gas investigations in the northern Appalachian Basin: Implications of analyses of natural gases from Neogene-through Devonian-age strata

As the pace of drilling activity in the Marcellus Formation in the northern Appalachian Basin has increased, so has the number of alleged incidents of stray natural gas migration to shallow aquifer systems. For this study, more than 2300 gas and water samples were analyzed for molecular composition and stable isotope compositions of methane and ethane. The samples are from Neogene- to Middle Devonian-age strata in a five-county study area in northeastern Pennsylvania. Samples were collected from the vertical and lateral sections of 234 gas wells during mud gas logging (MGL) programs and 67 private groundwater-supply wells during baseline groundwater-quality testing programs. Evaluation of this geochemical database reveals that microbial, mixed microbial and thermogenic, and thermogenic gases of different thermal maturities occur in some shallow aquifer systems and throughout the stratigraphy above the Marcellus Formation. The gas occurrences predate Marcellus Formation drilling activity. Isotope data reveal that thermogenic gases are predominant in the regional Neogene and Upper Devonian rocks that comprise the potable aquifer system in the upper 305 m (1000 ft) (average 13C1 = 43.53; average 13C2 = 40.95; average DC1 = 232.50) and typically are distinct from gases in the Middle Devonian Marcellus Formation (average 13C1 = 32.37; average 13C2 = 38.48; average DC1 = 162.34 ). Additionally, isotope geochemistry at the site-specific level reveals a complex thermal and migration history with gas mixtures and partial isotope reversals (13C1 13C2) in the units overlying the Marcellus Formation. Identifying a source for stray natural gas requires the synthesis of multiple data types at the site-specific level. Molecular and isotope geochemistry provide evidence of gas origin and secondary processes that may have affected the gases during migration. Such data provide focus for investigations where the potential sources for stray gas include multiple, naturally occurring, and anthropogenic gases.

Structure and hydrogeochemical functioning of a sparkling natural mineral water system determined using a multidisciplinary approach: a case study from southern France

Natural mineral waters (NMW), often used to produce bottled water, are of high socio-economic interest and need appropriate management to ensure the sustainability of the resource. A complex sparkling NMW system at La Salvetat, southern France, was investigated using a multidisciplinary approach. Geological and geophysical investigations, pumping test analyses, time-series signal processing, hydrogeochemical and isotopic data (both stable and radiogenic), and numerical modelling provided complementary information on the geometry, hydrodynamic characteristics and functioning of this mineral system. The conceptual model consists of a compartmentalized reservoir characterized by two subvertical, parallel deeply rooted hydraulically independent permeable structures that are fed by deep CO2-rich crustal fluids. The non-mineralized shallow aquifer system corresponds to a fissured layer within the weathered zone that is recharged by leakage from the overlying saprolite. This surficial aquifer responds rapidly to recharge (40–80 days), whereas the deep system’s response to recharge is much longer (up to 120 days). This research demonstrates the need for multidisciplinary approaches and modelling (quantity, hydrochemistry) for understanding complex NMW systems. This knowledge is already being applied by the bottling company that manages the resource at La Salvetat, and would be useful for conceptualising other NMW sites.

Adsorption studies of 1,2,4-Trichlorobenzene onto shallow aquifer media at the Luhuagang landfill site in Kaifeng, China

The Luhuagang landfill site (LLS) in Kaifeng, China, lacks liner and leachate collection systems. Thus, leachate generated from the waste dump has contaminated the surrounding subsoil and shallow aquifer with various chemicals, including 1,2,4-Trichlorobenzene (1,2,4-TCB). This paper is a part of a series of studies on adsorption, transport and biodegradation and fate of 1,2,4-TCB in the shallow aquifer beneath LLS. Here, adsorption of 1,2,4-TCB onto silt, fine sand and medium sand aquifer deposits collected at LLS was conducted by performing batch experiments involving four common adsorption kinetic models. The results of the analyses showed that the pseudo-second-order adsorption kinetic model provided the best fit for the equilibrium data with a coefficient of determination (R 2) greater than 0.99. Least squares analysis of Henry, Freundlich and Langmuir linearly transformed isotherm models was used to establish the best isotherm for 1,2,4-TCB adsorption onto the three aquifer materials. The Freundlich isotherm provided the best fit for experimental data with R 2 > 0.99. The results further suggested that the highest adsorption rate of 1,2,4-TCB (27.55 μg/g) was onto silt deposit, followed by fine sand (21.65 μg/g) and medium sand (14.88 μg/g). This showed that silt layer beneath the LLS was critical for retarding the downward percolation and migration of 1,2,4-TCB into the shallow aquifer systems under the landfill. The findings of the study were adopted as basis for designing the slated transport and biodegradation study of 1,2,4-TCB in aquifer system at LLS.

Electrical resistivity tomography monitoring studies at Balçova (Turkey) geothermal site

ABSTRACTThis investigation examines the electrical resistivity tomography (ERT) monitoring performed at geothermal sites. It includes two phases of time‐lapse ERT studies of the shallow geothermal liquid transportation that results from the circulation of injected and re‐injected liquids: synthetic modelling and field surveys. The synthetic modelling stage indicated that the injection process in the horizontal layered environment could cause temporal variations. The field investigation was performed between March 2010 and February 2011 at the Balçova geothermal site, Izmir‐Turkey, which has supplied in‐house heating since the 1990s. The time‐lapse ERT investigations were performed on a shallow aquifer system near two boreholes used as injection and re‐injection. In this study, the percentage changes in the synthetic models were determined and compared to the observed inverted time‐lapse monitoring data. We propose that time‐lapse inversion results are more reliable than the standard inversion approximation. However, the resistivity artefacts were significant, and were dependent on the selection of the comparison model and the inversion parameters. Also the selection of the initial model was shown to be the most important step in constraining the later temporal datasets. During the monitoring period, we observed very substantial decreases in the resistivity of time‐lapse results. We conclude that these observed decreases are a result of subsurface temperature or salinity changes associated with the hydrothermal system and fault zone. As a result, this study indicates that time‐lapse studies could be important in the characterisation of the subsurface changes that are connected with geothermal operations and climatic fluctuations.

Dynamic numerical modeling of the usage of groundwater for cooling in north east Jordan – A geothermal case study

Geothermal energy has the potential to significantly contribute to the cooling of buildings. A shallow aquifer system in north east Jordan was proven as a geothermal resource for its efficiency for cooling utilization. A numerical 3D model was developed in order to predict the future performance of the geothermal cooling reservoir. Different possible geothermal installations were studied, using various approaches. The study shows that a geothermal utilization of the respective basaltic reservoir is feasible. It features sufficient hydraulic and thermal properties to be utilized for cooling purposes. The developed model has proven to be robust and flexible. It can be easily extended for analyzing other sites.

The hydraulic conductivity field and groundwater flow in the unconfined aquifer system of the Keta Strip, Ghana

This study investigates the hydraulic conductivity field and the groundwater flow pattern as predicted by a calibrated steady state groundwater flow model for the Keta Strip, southeastern Ghana. The hydraulic conductivity field is an important parameter in evaluating aquifer properties in space, and in general basin-wide groundwater resources evaluation and management. This study finds that the general hydraulic conductivity of the unconsolidated unconfined aquifer system of the Keta Strip ranges between 2m/d and 20m/d, with an average of 15m/d. The spatial variation in horizontal hydraulic conductivity appears to take the trend in the variations in the nature of the material in space. Calibrated groundwater recharge suggests that 6.9–34% of annual precipitation recharges the shallow aquifer system. This amount of recharge is significant and suggests high fortunes in terms of groundwater resources development for agriculture and industrial activities in the area. A spatial distribution of groundwater recharge from precipitation is presented in this study. The spatial pattern appears to take the form of the distribution in horizontal hydraulic conductivity, and suggests that the vertical hydraulic conductivity takes the same pattern of spatial variation as the horizontal hydraulic conductivity. This is consistent with observations in other areas. The resulting groundwater flow is dominated by local flow systems as the unconfined system is quite shallow. A general northeast – southwest flow pattern has been observed in the study area.

Noble gas composition in rainwater and associated weather patterns

[1] This work represents the first comprehensive noble gas study in rainwater. It was carried out in southeast Michigan. Results show that all rainwater samples are in disequilibrium with surface conditions. Two noble gas patterns are identified. The first one, associated with low-pressure systems, presence of fog and light rainfall, displays a relative Ar enrichment together with Ne, Kr, and Xe depletion. The second one, associated with the passage of frontal systems, displays a mass-dependent depletion pattern. Precipitation is characterized by thunderstorms, heavy rainfall, and high cloud ceiling heights. A diffusion mass-transfer model suggests that noble gas patterns originate from ice. Complete re-equilibration with surface conditions should occur within hours. For the first time, this study establishes a direct correlation between the noble gas composition in rainwater and weather patterns and highlights their potential to identify timing and location of recharge in shallow aquifer systems where infiltration is rapid.

Evaluation of changes in post-fire recharge under native woodland using hydrological measurements, modelling and remote sensing

Summary This paper examines the use of a controlled fuel reduction burn in native woodland to increase recharge to a shallow aquifer system for water supply in south-western Australia. Soil moisture trends from neutron probe measurements and watertable dynamics from piezometers under adjacent burned and unburned plots were compared to determine the difference in recharge resulting from the fire. Remotely sensed evapotranspiration (ET) subtracted from rainfall was used to independently estimate groundwater and soil moisture recharge and compare against a physically based model of soil–water fluxes. The use of naturally occurring chemicals ( n -alkanes and cycloalkanes) produced in the fire as tracers of the recharge pulse in the winter following the fire was tested. It was found that in the winter following the fire (annual rainfall 701 mm), water storage in the 9 m thick unsaturated zone increased by about 300 mm but recharge to the watertable was only about 60 mm. In the subsequent year (rainfall 630 mm), leaf area index in the burned woodland recovered to be about 10% less than the unburned plot, remotely sensed ET rose above that in the unburned plot and recharge was lower in the burned than unburned plot. This trend continued and, after 3 years, increased ET negated any early recharge gains, and there was a net decrease in recharge resulting from the fire. The combination of water balance measurements, modelling and remote sensing provides a robust method to gain hydrological understanding of recharge mechanisms. Further work is required to refine the use of burn residue chemicals as soil water tracers, particularly in improving instrument design for groundwater sample collection in fine textured soils. As climate continues to change and regions with growing water shortages seek innovative solutions, approaches such as controlled burning may be needed; however, in this example, the approach was unproductive and further the environmental consequences need to be evaluated to make an appropriate assessment of trade-offs and viability of this approach.

Hydrochemical Processes in the Alluvial Aquifer of the Gwydir River (Northern New South Wales, Australia)

The hydrochemistry of the Narrabri Formation, the shallow aquifer system of the alluvial fan of the Gwydir River (NSW, Australia), is analyzed to better understand the hydrogeological processes involved in aquifer recharge, and to set up future management options that preserve the quantity and quality of water resources. Results show that groundwater hydrochemistry in this alluvial aquifer is mainly controlled by silicate weathering and cation exchange. However, salt remobilization in specific sedimentary layers within this alluvial fan deposit may locally increase groundwater salinity. Mixing between stream leakage and aquifer groundwater controls the hydrochemistry of water resources and produces a decrease in its salinity, which is beneficial for human uses.