Groundwater Electrical Conductivity Research Articles

Using Water Temperature, Electrical Conductivity, and pH to Characterize Surface–Groundwater Relations in a Shallow Ponds System (Doñana National Park, SW Spain)

The physical limnology of a shallow pond system was characterized using field measurements of water temperature, pH, and electrical conductivity (EC). We determined the spatial variability in surface and groundwater temperature, pH, and EC along the pond’s shore and along the several pond-shore transects, analyzed the water column temperature gradient and estimated the groundwater discharge rate using a heat transfer model. The fieldwork was conducted in Santa Olalla and Dulce ponds located in Doñana National Park in southwestern Spain during different stages from 2016 to 2018. The results of this study have improved the understanding of the thermal structure and the surface–subsurface heat exchange in the ponds and highlighted the importance of groundwater discharge in the pond water balance. It also showed the heterogeneous nature of groundwater discharge through the bottom sediments of the Santa Olalla pond. These results are consistent with previous studies and strengthen the existing hydrological and limnological knowledge of these ponds located in the protected area which is receiving a great deal of public attention.

Quantifying Geophysical Inversion Uncertainty Using Airborne Frequency Domain Electromagnetic Data—Applied at the Province of Zeeland, the Netherlands

AbstractAn accurate understanding of the fresh‐saline distribution of groundwater is necessary for effective groundwater management. Airborne electromagnetic (AEM) surveys offer a rapid and cost‐effective method with which to map this, offering valuable additional information about the subsurface. To convert AEM data into electric conductivity and ultimately groundwater salinity, an inversion is undertaken. A number of algorithms are available for this purpose; however, these are affected by significant uncertainty, owing to inherent nonunique characteristics of this process. The most commonly used inversion codes in hydrogeophysical studies were quantitatively tested using frequency domain AEM and ground data from the province of Zeeland, the Netherlands. These include UBC1DFM code and quasi‐2D laterally constrained inversions. Following an investigation of inversion parameter settings, data were inverted for four inversion methods and interpolated into 3‐D volumes. Using geological data and empirical electrical conductivity and water salinity relationships, each inversion was converted into groundwater electrical conductivity and split into fresh‐brackish‐saline regions. For groundwater volume estimates out of a total volume of 2.8 billion m3, a fresh groundwater estimate could differ by as much as 178 million m3, depending on the inversion used. The primary factor here was the choice of model smoothness, which was shown to affect the thickness of the brackish interval. Fresh‐brackish‐saline interfaces were consistently mapped with an accuracy of ~3 m, the brackish being the most accurately resolved. The few layer method was less successful at resolving smoothly varying salinity distributions but more successful at mapping the brackish interface at greater depth.

Drivers, patterns and velocity of saltwater intrusion in a stressed aquifer of the East African coast: Joint analysis of groundwater and geophysical data in southern Kenya

Fresh groundwater resources in coastal East Africa are crucial for the region's socio-economic development but are under threat of salinization caused by changes in recharge patterns and increasing abstraction. With the aim of establishing the drivers behind saltwater intrusion and its current spatial extent, we studied the Kenyan South Coast aquifer, a representative, strategic aquifer under increased pressure. Investigations included electrical resistivity tomography (ERT) surveys and in-situ groundwater measurements (water table and basic quality) together with the analysis of available long-term climatic and borehole monitoring data. Over the last 40 years, groundwater electrical conductivity values at the well field increased by about three times and groundwater levels declined by 1–3 m over the last decade. When put in perspective with the long-term climate (rainfall, temperature) and abstraction records, these trends in groundwater appear to be primarily driven by increased borehole abstraction (+400 m3/day per year in average), whereas observed increasing temperature (+0.02 °C per year) and decreasing rainfall (−0.8 mm per year) could potentially act as a secondary control through reduced recharge. However the low statistical significance obtained for both rainfall and temperature trends over the observation period suggests that no clear conclusion can be made with regards to long-term climate impact on groundwater. Groundwater quality mapping showed that proximity to the ocean, presence of abstraction well-fields and regional geology control groundwater salinity patterns at regional scale. Locally, geophysical data showed that, saltwater intrusion spatial patterns are controlled by local aquifer lithology, groundwater abstraction and freshwater recharge in floodplains. Comparison with previous (1984) resistivity data showed that the saltwater front has advanced toward the well-field by up to 2 km and rose by up to 80 m over the last 30 years, which corresponds to a maximal velocity of about 60 m/y horizontally and 2 m/y vertically. Implementation of groundwater management strategies such as sustainable groundwater exploitation, sourced alternative water supply, and managed aquifer recharge are required to mitigate the effects of seawater intrusion along the East African coastal strip.

Estimating the freshwater-lens reserve in the coastal plain of the middle Río de la Plata Estuary (Argentina)

Drinking-water supply is one of the main issues that populations face in many coastlands. Shallow coastal aquifers are often characterized by the presence of lens-shaped freshwater floating on the saline groundwater plume of marine origin. These groundwater lenses are commonly associated with landforms, such as littoral ridges and dunes and in many cases they represent the main source of water supply in remote coastal areas. At the right side of the middle Río de la Plata estuary (Argentina) the aquifer system is generally saline. Elongated and thin sandy beach ridge systems emerging from the general flat morphology of the marsh-flood plain are capable of storing precipitations forming freshwater lenses, which to date are the main freshwater supply for inhabitants. The aim of this study is to identify and delimitate the presence of such valuable freshwater reserves in order to provide the first necessary guidelines for the water management plan in this area, which has never been implemented since, to the Authors' knowledge, no specific investigation had been carried out before this study. To achieve this goal, Vertical Electrical Sounding, groundwater electrical conductivity measurements, water balances and groundwater chemical analyses were performed and interpreted together. The whole dataset was processed to define the electro-stratigraphic model of the study area and to produce the map of the electrical conductivity of the shallow aquifer. In addition, a three-dimensional model of the fresh water reservoir has been implemented for a better understanding of the relationship between geomorphology and groundwater. Results point out that a total freshwater volume of 78,259,700m3 is stored into a continuous lens and the annual average recharge from precipitation amounts to 6,303,500m3. Although preliminary, this work provides the basic knowledge on the potential fresh groundwater lenses and provides important information for addressing a sustainable use of the freshwater resource.

Using electrical resistivity tomography to assess the effectiveness of managed aquifer recharge in a salinized coastal aquifer.

Over 40years, the detrital aquifer of the Plana de Castellón (Spanish Mediterranean coast) has been subjected to seawater intrusion because of long dry periods combined with intensive groundwater exploitation. Against this backdrop, a managed artificial recharge (MAR) scheme was implemented to improve the groundwater quality. The large difference between the electrical conductivity (EC) of the ambient groundwater (brackish water due to marine intrusion) and the recharge water (freshwater) meant that there was a strong contrast between the resistivities of the brackish water saturated zone and the freshwater saturated zone. Electrical resistivity tomography (ERT) can be used for surveying similar settings to evaluate the effectiveness of artificial recharge schemes. By integrating geophysical data with lithological information, EC logs from boreholes, and hydrochemical data, we can interpret electrical resistivity (ER) with groundwater EC values and so identify freshwater saturated zones. Using this approach, ERT images provided a high-resolution spatial characterization and an accurate picture of the shape and extent of the recharge plume of the MAR site. After 5months of injection, a freshwater plume with an EC of 400-600μS/cm had formed that extended 400m in the W-E direction, 250m in the N-S direction, and to a depth of 40m below piezometric level. This study also provides correlations between ER values with different lithologies and groundwater EC values that can be used to support other studies.

The Characteristics of Shallow Groundwater Resource in Cangkringan District Sleman Province Special Region of Yogyakarta

Cangkringan District (the research site) is one of the districts in Sleman Regency of which spatial function includeswater catchment area. Holding the predicate as a water catchment area, the research area serves as one of the groundwater supply areas for the community living in Sleman Regency. One aspect of integrated water resources management is the water resources information system aspect, in which the geohydrology information system (groundwater) is included. Based on the aspect of water resources management, the study on shallow groundwater characteristics as catchment area in the research site should be conducted. The characteristics of shallow groundwater resources being investigated in this study included the condition and the distribution of groundwater depth, groundwater flow direction, and groundwater electrical conductivity. The primary data were collected on excavation wells of which locationswere determined using systematic random sampling method, by means of making imaginary grids, measuring to 2 km x 2 km. the primary data collected included coordinate data, groundwater depth data, the site’s altitude, and the groundwater conductivity data. The samples of groundwater electrical conductivity were determined by cluster sampling method, based on the groundwater depth area. The data analysis results demonstrate that shallow groundwater resource in the research site has the following characteristics: the groundwater depth is mostly less than 5 meter, the groundwater flows to the south of the research site, the electric conductivity of the research area has various values, i.e. 187 microS/ cm of the lowest value, and 368 microS/ cm of the highest value. Keywords: Cangkringan District, shallow groundwater, groundwater depth, groundwater flow, groundwater electrical conductivity.

High frequency saltwater intrusion monitoring using borehole geophysical tools (SMD)

In February 2016, two remote controlled geophysical monitoring tools (SMD) have been installed for the first time in the Reunion Island. Settled into two piezometers drilled into a basaltic coastal aquifer, between the ocean and a production well, they allow the record of groundwater electrical conductivity (ECw) logs on a 30 min basis. Thanks to those two tools, water operator continuously knows the shape and the position of the SWI as data are available online on a secured web application designed especially for SWI data management. During the observation period a 5,15 m rise of SWI interface has been recorded. Knowing the average porosity, water table elevation and SWI interface position it is possible to estimate available fresh groundwater volume. Along a 1 km band between extraction well and the ocean, available fresh groundwater volume was found to be 1 259 000 m3 in June 2016. In June 2017, due to SWI progression this volume was found to be 777 000 m3, that to say a 480 000 m3 volume of freshwater replaced by brackish water. SMD network will now be spread in the Reunion Island to improve coastal extraction well management knowing SWI shape and position on a high frequency basis.

Study of the spatial distribution of groundwater quality using soft computing and geostatistical models

Groundwater quality monitoring and simulation is of great importance in arid and semi-arid regions due to water scarcity in such regions. Geostatistical methods are appropriate techniques for interpolating and spatial mapping of groundwater qualitative parameters. In the present study, geostatistic-based Kriging and Co-Kriging methods were used and compared with data-driven artificial neural network (ANN) and ANFIS models for predicting spatial distribution of groundwater electrical conductivity (EC), then the best model was selected for further sampling in the studied region. Data from 24 wells in the Keshit, Bam Normashir, and Rhmtabad plains (Kerman province, Iran) during the period of 2002–2011 were used for analysis. Root mean square error (RMSE), R2, and mean absolute error (MAE) statistical indices were used for assessing the applied models. Results showed that for both the models, i.e. triple input model (including longitude, latitude, and the number of months) and the quadruple-input model (including longitude, latitude, number of months, and Cl), ANN model presented the most accurate results with the lowest RMSE and MAE and the highest R2 values. Attending to the geostatistical methods, Co-Kriging method outperformed the Kriging method. Finally, using the tested geostatistical model, the EC data were produced for the regions without observational values.

Fluoride Accumulation in Groundwater from Semi-arid Part of Deccan Volcanic Province, India: A Cause of Urolithiasis Outbreak

Groundwater fluoride and health problem was meticulously studied for dental and skeleton fluorosis except few studies on urolithiasis. Urolithiasis is multi-factorial disease and excess fluoride consumption is one of the causal factors. In view of this, increase of fluoride in groundwater is reported in semiarid Deccan Volcanic Province (DVP), India. To understand the fluoride and urolithiasis association, present study was carried out in Karha river basin of DVP region. Three stages of data generation were adopted for present study such as procuring of medical records of urolithiasis, previous groundwater chemistry data and geochemical investigation of 50 groundwater samples from representative villages. Further, these variables were used for correlation analysis, temporal and spatial distribution to find out their relationships. Result shows medical records of hospitals indicating the gradual increase in urolithiasis is reported during drought situations. In temporal variation, annual fluoride concentration of groundwater and hot days are positively correlated with annual urolith patients as well as spatial study supports the same. In conclusion, present study highlights the relationship of urolith formation with number of hot days, groundwater electrical conductivity and fluoride. However, detailed biomedical study may lead towards understanding of fluoride- urolithiasis relationship.

Experience in registration of variations caused by strong earthquakes in the level and physicochemical parameters of ground waters in the piezometric wells: the case of Kamchatka

The hardware complex that was produced by OOO Polynom, Khabarovsk, for registration of the level, temperature, and electrical conductivity of ground water in wells and meteorological parameters (atmospheric pressure, air temperature) at a measurement frequency from 5 min to 1 h is described. The equipment is installed in the wells of Kamchatka and has been used for several years to register variations caused by earthquakes in the parameters of ground waters. Different variations in measured parameters of ground waters due to strong earthquakes of February 28, 2013, M W = 6.8 and May 24, 2013, M W = 8.3 are registered with this equipment in wells YuZ-5 and E-1. The registered variations and their systematization are described taking into account the mechanisms of a seismic impact on the state of the well–water-saturated rock system.

Soluble ions dynamics in Mediterranean coastal pinewood forest soils interested by saline groundwater

The aim of the study was to evaluate the dynamics of soluble ions in the soils of a pinewood forest of the Mediterranean coastal area in the Province of Ravenna, Italy. A one year monitoring was carried out in four Entisols of the San Vitale pinewood forest, a vulnerable natural area due to subsidence and salt water intrusion. Ionic soluble forms were examined in saturated paste extracts (SPEs) and compared to groundwater soluble forms. Due to the local thermo-pluviometric conditions, both the water table depth and groundwater electrical conductivity (ECw) varied widely ranging respectively from 0 to −162cm in depth and from 2 to 28dS·m−1 in salinity content. As expected, this greatly influenced soluble ions concentrations in soil horizons, leading to variations in salt's speciation.In soils with a deep water table (Typic Ustipsamments), superficial horizons showed a prevalence of Ca2+ and HCO3– ion forms during the whole year, while in the deep horizons, Na+ and Cl− were the dominant ions. During summertime in soils with a shallow water table (Sodic Psammaquents), superficial ions enrichment was detected with Na+ and Cl− ions being prevalent. Autumn and winter rainfall provoked the leaching of both Na+ and especially of Cl− ions, leaving HCO3– as the main anion. In the soils with intermediate water table depth and moderate salinity (Aquic Ustipsamments), less relevant variations were observed. During winter the Ca2+ ion was the most present at the soil surface together with HCO3−. During summer Ca2+ and Cl− were the most present ions at the soil surface. At deeper horizons Na+ and Cl− ions always prevailed. The sodium adsorption ratio (SAR) reached the greatest values (>40) during summertime in Sodic Psammaquents superficial horizons and in Typic Ustipsamments deep horizons. On the basis of mixing curves, Na+ and Cl− displayed a conservative behavior and a likely sea origin. Both the Ca2+ and SO42− ions appeared to be partially released from the solid soil fraction, while the Mg2+ ion seemed to be partially absorbed by the solid matrix. On the basis of the hydrochemical characterization of both groundwater and soil SPEs, it was possible to identify different refreshing and salinization processes along the soil profiles. The one year monitoring of both the whole soil profile and groundwater, never performed before, allows a better understanding of the presence of distinct plant species and disease symptoms.

High-resolution vertical profiles of groundwater electrical conductivity (EC) and chloride from direct-push EC logs

Elevated groundwater salinity associated with produced water, leaching from landfills or secondary salinity can degrade arable soils and potable water resources. Direct-push electrical conductivity (EC) profiling enables rapid, relatively inexpensive, high-resolution in-situ measurements of subsurface salinity, without requiring core collection or installation of groundwater wells. However, because the direct-push tool measures the bulk EC of both solid and liquid phases (ECa), incorporation of ECa data into regional or historical groundwater data sets requires the prediction of pore water EC (ECw) or chloride (Cl−) concentrations from measured ECa. Statistical linear regression and physically based models for predicting ECw and Cl− from ECa profiles were tested on a brine plume in central Saskatchewan, Canada. A linear relationship between ECa/ECw and porosity was more accurate for predicting ECw and Cl− concentrations than a power-law relationship (Archie’s Law). Despite clay contents of up to 96%, the addition of terms to account for electrical conductance in the solid phase did not improve model predictions. In the absence of porosity data, statistical linear regression models adequately predicted ECw and Cl− concentrations from direct-push ECa profiles (ECw = 5.48 ECa + 0.78, R2 = 0.87; Cl− = 1,978 ECa – 1,398, R2 = 0.73). These statistical models can be used to predict ECw in the absence of lithologic data and will be particularly useful for initial site assessments. The more accurate linear physically based model can be used to predict ECw and Cl− as porosity data become available and the site-specific ECw–Cl− relationship is determined.

Ground water quality assessment for irrigation in Palwal block of Palwal district, Haryana, India

The present study examined the quality of groundwater for agriculture purpose in a 49785 ha region comprising Palwal block of Palwal district of Haryana state by focusing on spatial variability of electrical conductivity (EC), cationic and anionic composition of CO32-, HCO3-, Cl-, SO42-, Ca2+, Mg2+, Na+ and K+ of the ground water. It was found 75% of the samples showed EC values up to 4 dS/m and the maximum value of EC was found as 10.55 dS/m. Out of one hundred thirty three ground water samples 34.8 % were of good quality, 49.2 % saline and 16.0 % alkali in nature. Out of the saline water, 24.2, 1.5 and 23.5 % were marginally saline, saline and high SAR saline, respectively. In alkali group, 2.3, 2.3 and 11.4 % were marginally alkali, alkali and high alkali, respectively. Residual sodium carbonate (RSC) and sodium adsorption ratio (SAR) varied from nil to 5.50 me L-1 and 2.50 to 23.41 (m mol L-1)½, respectively. Counter map maps of EC, SAR, RSC and water quality of groundwater used for irrigation in the block were prepared through GIS to study spatial variability.

Groundwater quality evaluation by electrical resistivity method for optimized tubewell site selection in an ago-stressed Thal Doab Aquifer in Pakistan

Rapid and unchecked growths of private tubewells in poor water quality zones of Punjab province, Pakistan are the major sources of environmental degradation through the deployment of agricultural stresses on the underlying aquifer. There are broadly two environmental menaces associated with these agricultural stresses, increase of non-point source pollution loads at the surface and instigation of problem of secondary salinity (SS). The present study is applied vertical electrical soundings with Schlumberger electrode configuration having maximum current electrodes separation 300 m to assess the potential of freshwater layer lying over the saline groundwater. Primarily, the collected earth’s resistivities were converted to groundwater quality using groundwater electrical conductivity (EC) from exploratory wells drilled at regular interval in the entire Thal Doab. Secondly, based on these EC values, the study area is divided into three different tubewell suitability classes as high, moderate and low with interpreted EC values as less than 1.5 dS/m, between 1.5 and 2.5 dS/m and greater than 2.5 dS/m, respectively. The spatial distribution maps of these suitability classes are done at six depth zones (0–50, 50–100, 100–150, 150–200, 200–250, 250–300 m). Results indicate that there is an inverse relationship between the surface water recharge and SS which should be used for both tubewell depth as well as site optimization and a check on their future growth rates. In this way the eco-friendly agricultural growth rates can be established in Tehsil Kot Adhu, Thal Doab, Pakistan and the other areas having similar hydrogeological conditions.

IMAGING SEAWATER INTRUSION IN COASTAL ZONE OF KAVALA (N. GREECE) WITH ELECTRICAL RESISTIVITY TOMOGRAPHY

The needs for water supply in the western coastal zone of Kavala (N. Greece) have been rapidly increased during the last decades because of the high tourist and agricultural development. This resulted to a number of wells that drilled along the coastline. During summer period, when human and irrigation consumptions are maximized, phenomena of groundwater salinization are observed. Although restrictions to new drillings have been taken, salinization in some aquatic systems of the area tends to become a major environmental and economical issue. The only available information till now was a timeseries of groundwater electrical conductivity measurements, in some of the wells of the area. This information is useful but not adequate for the study of the salt intrusion mechanism. Geophysical investigation was carried out and electrical resistivity tomography (ERT) was chosen as the most appropriate technique for the case. The geophysical survey was set in a site between the coastline and an existing borehole. The 2D ERT profiles gave a clear image of geoelectrical heterogeneities, associated with seawater intrusion in the coastal aquifers, contributing to future measures towards a rational management of ground water resources in the area.

Evaluation and mapping of Dead Sea coastal aquifers salinity using Transient Electromagnetic (TEM) resistivity measurements

Evaporite karst has intensively developed recently along the Dead Sea (DS) coastal area in Israel and Jordan. It takes place in very saline groundwater dissolving buried salt layers, causing collapse of the surface. In this paper, groundwater salinity throughout the DS coastal area is investigated using the Transient Electromagnetic (TEM) method. Twenty-eight TEM soundings along the DS coastal area were carried out close to observation boreholes to calibrate resistivity–salinity relationships. Groundwater electrical conductivity was measured in these boreholes, and its salinity was analyzed at the laboratory by the Geological Survey of Israel (GSI). Quantitative relationships between bulk resistivity (ρx), water resistivity (ρw) and chloride concentration (Ccl) were derived in the resistivity range less than 1.0 Ω·m that enabled to evaluate the salinity of the aquifer in in situ conditions. Average values of the effective porosity of sandy sediments, φe=0.32, and of silty ones, φe=0.44, were used to generate the corresponding Archie equations. The study has shown that a DS aquifer with bulk resistivity in the range of 0.55–1.0 Ω·m contains in pores brine with 50–110 gchloride/l of (22–50% of that in saturated conditions, respectively), i.e. it keeps the potential to dissolve up to 114–174g/l of salt.

Signals from groundwater in Gran Sasso underground laboratory during Amatrice earthquake of August 24th, 2016

<p><em>Since May 2015, hydraulic pressure, temperature and electrical conductivity of groundwater are in continuos recording near the deep underground laboratories of Gran Sasso of INFN. We used the S13 borehole that have pressure varying in the range of 24-28 bar during the year; these values mean that we have at least 300 m of water table above. The sampling of these parameters was brought until to 50 Hz using a 3 channels 24-bit ADC. During the period May 2015 – September 2016 (17 months) we detected hydraulic pressure signals from 12 earthquakes at different surface distances (from 12.000 to 30 km) and different magnitudes (from 8.3 to 4.3 Mw). For the Amatrice mainshock, we present, as first results, the hydroseismograph recorded at the S13 hydraulic pressure device compared to the time history recorded at GIGS station located both in the deep core of the Gran Sasso chain.</em></p><p><em> </em></p>

Geophysical characterization of saltwater intrusion in a coastal aquifer: The case of Martil-Alila plain (North Morocco)

Several factors can affect the quantity and the quality of groundwater resources, but in coastal aquifers seawater intrusion is often the most significant issue regarding freshwater supply. Further, saltwater intrusion is a worldwide issue because about seventy percent of the world's population lives in coastal regions.Generally, fresh groundwater not affected by saltwater intrusion is characterized by low salinity and therefore low electrical conductivity (EC) values. Consequently, high values of EC in groundwater along the coastline are usually associated to seawater intrusion. This effect is amplified if the coastal aquifer is overexploited with a subsequent gradual displacement of the freshwater-saltwater interface towards the continent.Delineation of marine intrusion in coastal aquifers has traditionally relied upon observation wells and collection of water samples. This approach may miss important hydrologic features related to saltwater intrusion in areas where access is difficult and where wells are widely spaced. Consequently, the scarcity of sampling points and sometimes their total absence makes the number of data available limited and most of the time not representative for mapping the spatial and temporal variability of groundwater salinity.In this study, we use a series of geophysical methods for characterizing the aquifer geometry and the extension of saltwater intrusion in the Martil-Alila coastal region (Morocco) as a complement to geological and hydrogeochemical data. For this reason, we carried out three geophysical surveys: Gravity, Electrical Resistivity and Frequency Domain Electromagnetic. The geometry of the basin has been determined from the interpretation of a detailed gravity survey. Electrical resistivity models derived from vertical electrical soundings allowed to characterize the vertical and the lateral extensions of aquifer formations. Finally, frequency domain electromagnetic methods allowed delineating the extension of the saltwater intrusion.

Spatial variation modelling of groundwater electrical conductivity using geostatistics and GIS

Optimized management of water resources, conservation and their quality increase is needful with data existence in basis of situation, amount and distribution of water chemical factors for example; electrical conductivity (EC) in determined geographical region. Accuracy of interpolation appropriate methods and variation map preparation of groundwater quality variables is independent to region conditions and existence of enough data. That is true selection of interpolation methods is basic and important step in management of groundwater resources. EC is one of the important indicators for groundwater quality evaluation. The objective of this research was to determine the most suitable interpolation method and their accuracy for analysis and checking spatial variation of groundwater EC amount in central regions of Guilan province, northern Iran. This investigation evaluated the inverse distance weighting (IDW), global polynomial interpolation (GPI), local polynomial interpolation (LPI), radial basis function (RBF) and ordinary kriging (OK) methods for estimation of groundwater EC in paddy fields. In IDW method, for variable estimation used power value 1–5 that power value equal 1 was exact. Gaussian model was the best one fitted on empirical semivariogram of variable data in OK method. Standard statistical performance evaluation criteria include root mean square error (RMSE), correlation coefficient (R) and mean absolute error (MAE) were used to control the accuracy of the prediction capability of the developed methods. Results showed that the best estimator was OK method which was the most exact with regard to other methods for estimation groundwater electrical conductivity.

Identifications of aquifer group classification by using environmental isotope and hydrogeochemistry method: a case study of Huabei plain, China

Aquifer group classification is a prerequisite for groundwater resources evaluation as well as groundwater utilization, which making an important effect on human being living and production activities. So far, lithology is the primary criteria in aquifer group classification, but the available and specific supporting ideas are still insufficient. Supposing that two aquifers separated by clay had hydraulic connection in multilayer aquifer systems, groundwater flow from top to bottom of aquifer would be impacted by the clay in chemistry and isotope characteristic and presents some kind of regulations. According to these regulations, aquifer group classification would be more reasonability, and groundwater resources assessment and pollution management would be more purposeful. This research analyzed the hydraulic connection of groundwater in different aquifer and salt movement in clay soil by using isotopic and chemical data. The results showed that electrical conductivity of groundwater in clay soil is influenced by the source of the groundwater, having a continuous trend with depth, and clay soil in certain depth presented the feature of impeding salt migration. Because of the semipermeable feature of clay soil, stable isotope composition of groundwater in different depth is affected by clay’s distribution. This pattern of isotope and hydrogeochemical composition would be a valuable reference for groundwater evaluation and aquifer group classification.