Adjacent Groundwater Research Articles

Utilize gadolinium as environmental tracer for surface water-groundwater interaction in Karst

The rare earth element (REE) group is widely used for geochemical prospection and the hydrochemical differentiation of waters. Most of the currently applied methods use normalized REE patterns to determine enrichments or depletions of certain REE in comparison to standard materials, which are caused by specific environmental conditions. Contrast agents containing Gadolinium (Gd), which are used for magnetic resonance imaging (MRI), have been emitted into surface waters since the 1980s. Patients excrete these contrast agents shortly after ambulant medication in hospitals or at home. Sewage treatment is currently unable to hold back Gd from this anthropogenic source. Therefore, the Gd concentration in the receiving channel increases significantly and creates a Gd peak in the REE pattern. This anthropogenic peak propagates into adjacent groundwater bodies. In a karst aquifer showing a connection between a river/ponor (input) and three springs (output), such an anthropogenic Gd anomaly has been traced, the local Gd background quantified, and surface water groundwater interaction evaluated. In two sampling campaigns, water samples were taken every day at the input and output side during one week in February and three weeks in May. Sampling of springs and brooks in the vicinity of the karst aquifer proved excessive Gd from anthropogenic sources. The evaluation of concentration, mass flow and total mass of Gd show that Gd can be an environmental tracer to monitor surface water-groundwater interaction as well as the anthropogenic influence on water bodies. Further anthropogenic pollutants - diclofenac, carbamazepine, galaxolide, caffeine, and acesulfame-K - representing different classes of common organic substances were tested as co-indicators to Gd. However, out of these only acesulfame-K was detected and is related with the Gd-anomaly. Our results indicate that Gd is a more powerful indicator of surface water- groundwater interaction than most organic pollutants.

Using stable isotopes to assess river water dynamics and groundwater input in the largest European Arctic river (Severnaya Dvina).

Rivers play a key role in the water cycle on the earth via integrating all hydrological channels to return terrestrial precipitations back to the oceans. In addition, rivers, together with groundwater, are powerful transformers of the surface lithosphere, responsible for chemical weathering of rocks and the removal of solute into the ocean. Tracing the dynamics of surface water and groundwater versus atmospheric feeding of rivers presents important issues in Arctic regions due to the ongoing change of the structure of hydrological runoff. In this study, stable water isotopes were used to reveal the temporal dynamics of water sources and to predict their possible change under the conditions of ongoing climate warming of the largest European Arctic river, the Severnaya Dvina, and adjacent groundwater. The isotopic composition of the river waters of the studied region is formed by the mixing of atmospheric precipitation with groundwater. The isotopic depletion in the springtime is mainly due to the recharge of thawed snow waters. A less pronounced effect in the autumn-winter period is provided by the discharge of groundwater into rivers, including the meltwater of the Last Glacial Period. This depletion is partially offset due to discharge of isotopically light thawed snow waters and is linked to evaporation in headwater streams, reservoirs, and wetlands. The isotopic composition of groundwater with low mineralization was formed throughout the Holocene and to a large extent depends on paleoclimatic conditions in the study area. In addition to fresh groundwater, brackish groundwater also takes part in the river's recharge. These brackish waters are associated with ancient and modern marine transgressions on the estuarine site and with the dissolution of Ca sulfate rocks in a karst region located in the middle reaches of the river. According to isotope data, the average annual input of the underground source to the total river flow is 25%. The results of this work will serve as the basis for continuing monitoring of the isotopic composition of river waters with an assessment of hydrological processes and observation of short as well as long-term climatic and anthropogenic impacts.

Municipal Solid Waste Landfills: An Underestimated Source of Pharmaceutical and Personal Care Products in the Water Environment.

Pharmaceutical and personal care products (PPCPs) have been the focus of increasing concern in recent decades due to their ubiquity in the environment and potential risks. Out-of-date PPCPs are usually discharged into municipal solid wastes (MSWs), enter the leachates in MSW landfills, and have serious adverse effects on the surrounding water environment. However, the occurrence and removal of PPCPs from landfill leachates have rarely been examined to date. This lack of knowledge makes the landfill an underestimated source of PPCPs in the environment. In this review, we collected the relevant publications of PPCPs in landfill leachates, systematically summarized the occurrence of PPCPs in landfill leachates globally, evaluated the removal performances for various PPCPs by different types of on-site full-scale leachate treatment processes, and assessed the impacts of landfill leachates on PPCPs in the adjacent groundwater. In particular, influencing factors for PPCPs in landfill leachates, including the physicochemical properties of PPCPs, climate conditions, and characteristics of landfill sites (i.e., landfill ages) as well as sociological factors (i.e., economic development), were extensively discussed to understand their occurrence patterns. Future perspectives were also proposed in light of the identified knowledge gaps. To the best of our knowledge, this is the first review regarding the occurrence and removal of PPCPs from landfill leachates worldwide.

Environmental impact assessment of inland purification and desalination plants: case study of Al Asyah plant, Qassim region, Central Saudi Arabia

The impact of reject brine chemical composition and disposal from Al Asyah inland desalination on soil and groundwater was evaluated. The reject brine is disposed directly into a surface impoundment in a permeable soil with low clay content. Samples were collected from four evaporation ponds and chemically analyzed. The total dissolved salts (TDS) and the concentration of radioactive constituents were quantified. The results indicate high concentrations of TDS in the evaporation ponds where it ranges from 9650 to 15,460 mg/l. The majority of TDS include sodium chlorides produced throughout the isolation process of fresh water from brine. Moreover, the radioactive isotopes of radium-226 and radium-228 have been identified with total concentrations of 78.89 and 198.77 (pCi/l), respectively. These concentrations may be increased over time due to increasing of radon accumulation in the filtration sands. These results indicate that these constituents are above the standards set by the Gulf Cooperation Council and the Saudi National standards for drinking water and effluents discharged into the desert. Hence, reducing of the environmental impact resulting from both the radioactive materials and the ratio of salinity in water is of utmost importance for Al Asyah plant. Furthermore, the continuous monitoring of the effects of radioisotopes on the validity of the adjacent groundwater is highly recommended.

Do high levels of PPCPs in landfill leachates influence the water environment in the vicinity of landfills? A case study of the largest landfill in China

Landfill leachates are identified as a significant source of pharmaceutical and personal care products (PPCPs), which might pose a threat to groundwater and surface water nearby the landfill. However, knowledge of PPCP contamination in the surrounding water environment of landfills is very limited. Here we investigated eighteen PPCPs in water environment near the largest landfill in China, focusing on their occurrences and spatial distribution, as well as the environmental risks. The results showed the concentration of target PPCPs was below the limit of quantification (<LOQ) to 53.6 ng/L in the adjacent groundwater samples, decreasing with the distance of sampling sites from landfill. The composition pattern of PPCPs in the groundwater was similar to that in raw landfill leachate. These observations indicated a considerable impact of raw landfill leachates on PPCP contamination in the nearby groundwater. In surface water samples, the occurrence of PPCPs was not consistent with that in raw or treated landfill leachates, but similar to that in the same watershed far away from landfill. Spatially, no obvious difference in the PPCPs concentrations was observed, indicating negligible contribution of landfill on PPCPs in surrounding surface water. The findings allowed the first insights into the impacts of well-constructed and managed landfills on PPCP contamination in the surrounding water environment.

Modelling and evaluation of groundwater filled boreholes subjected to natural convection

One of the challenges of designing ground source heat pumps systems is the calculation of the effective thermal borehole resistance which affects the heat extraction rate and thereby the required length of the borehole. Calculating effective borehole resistance is especially demanding when the boreholes are filled with groundwater. The natural convection in the groundwater affects the heat transport from the borehole heat exchanger to the borehole wall. The objective of this paper is to present the results of the modified Pygfunction software in which recently developed correlations for calculating influence of the natural convection in boreholes has been incorporated. The calculated results were validated by using results of thermal response test (TRT) from four adjacent groundwater filled borehole in the central parts of Sweden. The numerical results reveal that the original and unmodified Pygfunction can be used for accurate calculation of fluid temperatures in borehole heat exchangers by using an effective thermal conductivity of the filling material. However, that requires access to thermal response test data. The modified software calculates the effective borehole resistance with a deviation of about 15–30% compared to the effective borehole resistance from TRT. This deviation is an improvement compared with the standard assumption of neglecting natural convection in boreholes. However, for large installations with more than 4000 m of borehole heat exchangers a thermal response test is still recommended in order to ensure a more correct sizing of geothermal system.

Large deformation of tunnels in longwall coal mines

Large deformation of tunnels in longwall coal mines creates massive cracks in the surrounding rocks, which may cause groundwater loss and threaten the coal mine safety. Rock mechanical characterization is crucial for understanding the large deformation of underground openings. Based on the theoretical analysis and laboratory triaxial tests, this study aims to propose a strength degradation model of the rocks for a deep understanding on the large deformation of underground openings. The proposed model captures the non-linear post-peak rock strength degradation which is dependent on the plastic strains accumulated under the decreasing confining pressures. The stress-dependent elastic properties were not considered in this study. The proposed model was incorporated in a finite difference package (FLAC3D) for engineering application. The simulated surface convergence of the underground opening matches the in-mine measurements, which supports the proposed model. More importantly, the simulated crack zone after tunnel excavation agrees with the observations from borehole images. Therefore, the proposed model provides a helpful tool to evaluate the safe margin of an underground tunnel if it is close to a subsurface water-bearing formation. It also sheds lights on the underground tunnel design to prevent the adjacent groundwater from inrush.

CO2 evasion along streams driven by groundwater inputs and geomorphic controls

Headwaters are hotspots of carbon dioxide (CO2) evasion from rivers. While emerging evidence suggests that groundwater contributes disproportionately to CO2 in headwater streams, the processes of CO2 delivery to streams and subsequent evasion to the atmosphere remain largely unknown. Here we show the variability of CO2 input and evasion fluxes based on coupled measurements of dissolved CO2 along streams and in adjacent groundwater from two headwater catchments of the tropical and temperate zones. We find that the processes can be highly localized in both space and time. Spatially, they are significantly influenced by heterogeneities in the subsurface and stream landscape; temporally, they predominately occur during the transient activation of connected subsurface water flows. We highlight sharp increases and decreases in the stream CO2 flux, and suggest that current models fail to capture the true magnitude of CO2 evasion. The high spatial and temporal variability of CO2 input from groundwater and evasion to the atmosphere makes accurate assessment of CO2 evasion fluxes difficult, and will require a collaborative effort by catchment hydrologists and aquatic ecologists to fully understand the contribution of groundwater to stream CO2 emissions. Groundwater-derived CO2 inputs and emissions along streams are highly variable in both space and time, according to measurements of dissolved CO2 from two headwater catchments.

Geochemistry of El-Salam Canal and the adjacent groundwater in north Sinai, Egypt: an application to a water treatment process using magnetic zeolite nanoparticles

Water shortage is among the critical challenges facing many countries located in the arid zone of the southern the Mediterranean region. In the northern Sinai, El-Salam Canal and shallow groundwater in the Quaternary aquifer are considered the main irrigation sources for reclamation of 62,000 acres situated along the Mediterranean coast. The chemistry of surface water of El-Salam Canal varies greatly from the western to the eastern sides. Additionally, the groundwater chemistry is greatly influenced by dilution due to seepage of El-Salam Canal water. The historical and recent records of water chemistry show great variation of the concentrations of dissolved Al3+, Cu2+ and Zn2+ in both surface and groundwater, based on sampling time and locality. The concentrations of these heavy metals occasionally exceed the international recommended limits for drinking and short-term irrigation standards. The removal of dissolved heavy metals from water is crucial to fill the gap between the water supply and the growing demands using possible techniques of water treatment. Consequently, zeolite nanocomposites are one of the materials that have been used for water treatment. Magnetic zeolite nanocomposites (MZNCs) were prepared by the chemical co-precipitation of Fe2+ and Fe3+ in the presence of zeolite. The prepared magnetic nanocomposites were characterized by TEM, SEM, EDX, XRD, FTIR, TGA and VSM. The results show that MZNCs have a cubic crystal structure and good thermal stability. The MZNCs were used to remove Al(III), Zn(II) and Cu(II) from simulated water and then were easily separated from the medium by external permanent magnet. Batch adsorption experiments were conducted, and the effects of pH, initial ion concentration, adsorbent dose and contact time were studied. The selected pH range (pH = 5–6) and temperature (27 °C) in the batch adsorption experiments were close to the pH range of the surface and groundwater field data. Furthermore, the chosen initial concentrations and adsorbent doses were within the heavy metals concentration ranges in El-Salam Canal and the adjacent groundwater. The MZNCs show great removal capacity of heavy metals where 0.1 g is able to clean contaminated water with high concentrations (0.5–3 g/l) of Cu(II) and Zn(II) within 20 min and within 30 min for Al(III). The adsorption kinetics data of the system were well fitted to pseudo-second-order model, which indicates a faster kinetic sorption by the composites. Adsorption isotherms were studied using Langmuir and Freundlich isotherms. Although both of them fit the data, the Freundlich isotherm had the best fit for the selected metals.

Modeling groundwater flow and salinity evolution near TSF Żelazny Most. Part I – groundwater flow

Tailings which are by-product of the extraction of various metals (copper, gold, silver, molybdenum, etc.) are often stored in so called Tailings Storage Facilities (TSF), where they are deposited as a soil-water mixture by spigotting. In many cases the water discharged together with tailings to the TSF is rich in salts and other chemical compounds imposing negative pressure to the groundwater environment. Even in the case of total or partial lining of such facilities and well-developed drainage systems to control leaching, some portion of contaminated water often seeps either through the surrounding dams or the bed into adjacent groundwater bodies. Numerical models can be very helpful tools to assess the extent of the contamination and particularly to predict its potential development in the future. This paper and the companion one describe such a numerical model developed for Żelazny Most Tailings Storage Facility (south-west Poland), one of the world’s largest tailings sites. In the first part general information about the facility is provided and a 3D hydrogeological numerical model of the structure is described. Groundwater flow pattern near the facility obtained from numerical simulations is confronted with the measurements from a comprehensively developed monitoring system. Part II will be focused on the modelling of chloride transport in groundwater.

Evaluation of geogenic and anthropogenic impacts on spatio-temporal variation in quality of surface water and groundwater along Cauvery River, India

Assessment of groundwater and surface water quality along a river is important as it directly affects the agricultural, industrial activities and population. The objective of the study is to assess the quality of the Cauvery river water and adjacent groundwater for drinking and irrigational purposes and to identify the infuence of geogenic and anthropogenic sources. Groundwater and surface water samples were collected along the course of the river at approximate intervals of 25 km. The samples were analysed for electrical conductivity, pH, sodium, calcium, magnesium, potassium, bicarbonate, chloride and sulphate. Sodium was identified as the dominant cation and bicarbonate was the dominant anion for both river water and groundwater. These values were compared with limits recommended by the Bureau of Indian Standards for drinking purposes. The total dissolved solids were found to exceed the permissible limits for drinking water in most of the groundwater samples, and it was below the permissible limits in river water samples. Most of the river water samples were found to be suitable as per the drinking water quality standards, but most of the groundwater samples were unsuitable based on the concentration of major ions. Irrigation water quality was also assessed based on magnesium hazard, residual sodium carbonate, sodium percentage, sodium adsorption ratio, permeability index and salinity hazard. Most of the river water samples collected were suitable for irrigation, whereas most of the groundwater samples collected were doubtful for irrigation based on residual sodium carbonate and sodium percentage. Drinking water and irrigation water quality indices were also computed to assess the characteristics of water. Groundwater quality in locations nearer to the confluence of tributaries and industrial areas was of poor quality, while both river water and groundwater near the coast were poor, both for drinking and irrigation purposes. Comparison of the dissolved load with other rivers of the world was also made, which reveals that the Cauvery River yields comparatively higher dissolved load per area than most of the rivers. The chemical load in the river is due to natural and anthropogenic sources. Therefore, it is necessary to enforce the existing norms for the discharge of treated effluents by industries and townships along the river so as to reduce the chemicals contributed by anthropogenic sources.

Assessment of the cytotoxic and mutagenic potential of the Jialu River and adjacent groundwater using human-hamster hybrid cells

The Jialu River in China has been seriously polluted by the direct discharge of industrial and domestic wastewater. The predominant contaminants of the Jialu River and its adjacent groundwater were recently investigated. However, the potential genotoxic impact of polluted water on human health remains to be clarified. Here, we used human–hamster hybrid (AL) cells, which are sensitive for detecting environmental mutagens. We found that the cytotoxicity and mutagenicity of the groundwater in the Jialu River basin were influenced by the infiltration of the Jialu River. Hydrological periods significantly affected the cytotoxicity, but not the mutagenic potential, of surface and groundwater. Further, the mutagenic potential of groundwater samples located <1km from the Jialu River (SM-2 water samples) was detected earlier than that of groundwater samples located approximately 20km from the Jialu River (SN water samples). Because of high cytotoxicity, the mutagenic potential of water samples from the Jialu River (SM-1 water samples) was not significantly enhanced compared with that of untreated controls. To further assess the mutagenic dispersion potential, an artificial neural network model was adopted. The results showed that the highest mutagenic potential of groundwater was observed approximately 10km from the Jialu River. Although further investigation of mutagenic spatial dispersion is required, our data are significant for advancing our understanding of the origin, dispersion, and biological effects of water samples from polluted areas.

Assessing net-uptake of nitrate and natural dissolved organic matter fractions in a revitalized lowland stream reach

Lowland streams are often revitalized by hydrologically reconnecting their surrounding terrestrial environment, which likely alters central ecosystem functions such as autotrophic and heterotrophic carbon and nutrient metabolism. However, such central ecosystem functions of stream reaches following revitalization have rarely been investigated. Here, we measured net-uptake of nitrate and of various dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) fractions (using size-exclusion chromatography, SEC), as well as fluorescence components (established by parallel factor analysis, PARAFAC) repeatedly along a revitalized 1.4km reach of a Danish lowland stream during base flow conditions. Samples were taken at six stations every three hours for one day. We measured discharge at five of the six stations to calculate whole-stream net-uptake. Moreover, we continuously measured oxygen at the start and at the end of the reach to assess stream metabolism, and took piezometer samples from ten shallow groundwater sites to assess potential determinants of organic matter and nitrate metabolism. We found high metabolic activity within the stream reach with a gross-primary production of 4.8 and 3.6g O2 m−2day−1 and a production to respiration ratio of 0.8 and 0.9 at the start and end of the reach, respectively. Nitrate exhibited relatively constant high net-uptake rates of 0.41–0.52gNm−2 d−1, which varied little and were not related to the time of the day. Therefore, autotrophic nitrate uptake for was likely of minor importance, despite the apparently high primary production. In contrast, SEC DON and DOC fractions, as well as PARAFAC components did not suggest net-uptake or release. Instead, DOC and DON concentration were highly variable among the six stations and sampling times, a pattern that was not explainable by measurement errors but was likely related to the high variability of DOC and DON concentrations in the hyporheic zone and adjacent groundwater bodies. This pointed to a potentially high interaction with the hyporheic and riparian zone, underlining the strong linkage of DOM-related processes across the terrestrial-aquatic boundary. The high nitrate uptake points to the high retention potential of revitalized stream reaches, which, however, would need to be corroborated by further studies with reference reaches.

Relative linkages of stream water quality and environmental health with the land use and hydrologic drivers in the coastal-urban watersheds of southeast Florida.

A systematic data analytics was employed to determine the relative linkages of stream water quality and environmental health with the land use and hydrologic drivers in the coastal‐urban watersheds of southeast Florida. Power law‐based partial least squares regression models were developed to reliably estimate the linkages by appropriately resolving multicollinearity (Nash‐Sutcliffe efficiency = 0.72–0.95). The analytics indicated Everglades as the external and the largest source of total nitrogen (TN) in the coastal‐urban streams for both wet (June–October) and dry (November–May) seasons. The “external driver” exhibited 1.5–2 times stronger control on stream TN than that of the watershed “land use,” “hydrology,” and the “upstream reach” contributions. In contrast, Everglades appeared to be a minor source of in‐stream total phosphorus (TP), which was predominantly controlled by the internal watershed processes. TP was most strongly linked with the upstream reach concentrations and watershed land uses in the wet and dry seasons, respectively. Despite the predominantly built‐up fraction (74%) of the study area, agricultural land was the most substantial watershed source of in‐stream nutrients. The linkages of algal biomass (Chl a) with the drivers indicated TP as the limiting nutrient. Stream dissolved oxygen was most strongly influenced by the adjacent groundwater depth and watershed land uses, respectively, in the wet and dry seasons. The estimated relative linkages and insights would be useful to identify the management targets and priorities to achieve healthy coastal‐urban stream ecosystems in southeast Florida and around the world.

Study on the Flow of Groundwater between Adjacent Groundwater Basins

Study on the Flow of Groundwater between Adjacent Groundwater Basins

Estimate of the Aquifer Temperature of Assammaqieh Well in Akkar by Geothermometric Equations

This research aims at estimating the temperature of the aquifer that supplies Assammaqieh well at the depth of 550 m, on the basis of chemical analyses and geothermometric techniques which are one of the methods used for searching for the renewable geothermal energy and conserving the environment. In this study, about twenty-two geothermometric indicators have been used. For verifying the results, these results have been compared with data and estimates of temperature of fluids of deep typical wells in New Zealand, and it has been noticed that the theoretical and actual results approach the limits of 95% in many indicators. The study has been restricted to the relations of Cations because they are the most reliable, and the least affected by dissolution and evaporation. Most of the indicators that are based on the four chemical elements: Calcium (Ca), Potassium (K), Sodium (Na), Magnesium (Mg), have been adopted. The laboratory analysis data of Assammaqieh well confirmed that it was hot sulphurous water that acquired its chemical properties from complicated geochemical conditions, underground thermal conditions and volcanic rock nature. It also turned out that the underground heating process was basically due to thermal conductivity and rock adjacency, and that Assammaqieh well was supplied with water from adjacent groundwater tables whose source was the penetration of surface water. It also appeared that most of the equations used in the search for geothermal energy revealed the presence of an aquifer of hot and very hot water, and they were compatible with the high thermal gradient in volcanic rocks. It also tuned out that 86% of the used geothermometric equations estimated the aquifer temperature of Assammaqieh well as being hot and very hot with around 135.5 Celsius (±20). The study concluded with the hypothesis that Akkar possessed a huge geothermal energy, and benefiting from this energy might put an end to the chronic problem of electricity in Lebanon, and opened up many prospects and uses that could participate in a sustainable and comprehensive development of Akkar and Lebanon as a whole.

TerraSAR-X Data for High-Precision Land Subsidence Monitoring: A Case Study in the Historical Centre of Hanoi, Vietnam

In this study, subsidence patterns in the Historical Centre of Hanoi, Vietnam are mapped using the Interferometric Synthetic Aperture Radar (InSAR) technique, with particular emphasis on the stability of ancient monuments, historical buildings and archaeological sectors. Due to the small and scattered characteristics of these structures, not only is a comprehensive coverage of radar targets needed, but also the details of a single building or monument. We took advantage of the high-resolution TerraSAR-X imagery with the aid of oversampling implementation on the Small Baseline (SB) InSAR approach to reveal the subsidence patterns. A total of 6.29 million radar targets were obtained, maintaining the average density of 217,012 points/km2. Our results suggest that image oversampling not only increased the number of measurement points 4.4 times more than the standard processing chain, but also removed some of the noisiest points. The observed subsidence patterns are mostly related to adjacent groundwater extraction and construction activities, with maximum subsiding rate reaching −18.1 mm/year for the study period April 2012 to November 2013. Generally, heritage assets and monuments in the Citadel, the Old Quarter and French Quarter remain in a steady state, whereas those located along the Red River and in southern Hanoi are subject to subsidence.

Modeling for Inter-Basin Groundwater Transfer Identification: The Case of Upper Rift Valley Lakes and Awash River Basins of Ethiopia

Groundwater movement beneath watershed divide is one component of the hydrological cycle that is typically ignored due to difficulty in analysis. Numerical ground-water models, like TAGSAC, have been used extensively for predicting aquifer responses to external stresses. In this paper TAGSAC code was developed to identify the inter-basin groundwater transfer (IBGWT) between upper Awash River basin (UARB) and upper rift valley lakes basin (URVLB) of Ethiopia. For the identification three steady state groundwater models (for UARB, URVLB and for the two combined basins) were first created and calibrated for the 926 inventoried wells. The first two models are conceptualized by considering the watershed divide between the two basins as no-flow. The third model avoids the surface water divide which justifies IBGWT. The calibration of these three models was made by changing the recharge and hydrogeologic parameters of the basins. The goodness of fit indicators (GoFIs) obtained was better for the combined model than the model that describes the URVLB. Furthermore, the hydraulic head distribution obtained from the combined model clearly indicates that there is a groundwater flow that doesn’t respect the surface water divide. The most obvious effect of IBGWT observed in these two basins is that it diminishes surface water discharge from URVLB, and enhances discharge in the UARB. Moreover, the result of this study indicates potential for internal and cross contamination of the two adjacent groundwater.

Self‐accelerated development of salt karst during flash floods along the Dead Sea Coast, Israel

AbstractWe document and analyze the rapid development of a real‐time karst system within the subsurface salt layers of the Ze'elim Fan, Dead Sea, Israel by a multidisciplinary study that combines interferometric synthetic aperture radar and light detection and ranging measurements, sinkhole mapping, time‐lapse camera monitoring, groundwater level measurements and chemical and isotopic analyses of surface runoff and groundwater. The &gt;1 m/yr drop of Dead Sea water level and the subsequent change in the adjacent groundwater system since the 1960s resulted in flushing of the coastal aquifer by fresh groundwater, subsurface salt dissolution, gradual land subsidence and formation of sinkholes. Since 2010 this process accelerated dramatically as flash floods at the Ze'elim Fan were drained by newly formed sinkholes. During and immediately after these flood events the dissolution rates of the subsurface salt layer increased dramatically, the overlying ground surface subsided, a large number of sinkholes developed over short time periods (hours to days), and salt‐saturated water resurged downstream. Groundwater flow velocities increased by more than 2 orders of magnitudes compared to previously measured velocities along the Dead Sea. The process is self‐accelerating as salt dissolution enhances subsidence and sinkhole formation, which in turn increase the ponding areas of flood water and generate additional draining conduits to the subsurface. The rapid terrain response is predominantly due to the highly soluble salt. It is enhanced by the shallow depth of the salt layer, the low competence of the newly exposed unconsolidated overburden and the moderate topographic gradients of the Ze'elim Fan.

Biogeochemical gradients above a coal tar DNAPL

Naturally occurring distribution and attenuation processes can keep hydrocarbon emissions from dense non aqueous phase liquids (DNAPL) into the adjacent groundwater at a minimum. In a historically coal tar DNAPL-impacted site, the de facto absence of a plume sparked investigations regarding the character of natural attenuation and DNAPL resolubilization processes at the site. Steep vertical gradients of polycyclic aromatic hydrocarbons, microbial community composition, secondary water quality and redox-parameters were found to occur between the DNAPL-proximal and shallow waters. While methanogenic and mixed-electron acceptor conditions prevailed close to the DNAPL, aerobic conditions and very low dissolved contaminant concentrations were identified in three meters vertical distance from the phase. Comprehensive two-dimensional gas chromatography–mass spectrometry (GC×GC–MS) proved to be an efficient tool to characterize the behavior of the present complex contaminant mixture. Medium to low bioavailability of ferric iron and manganese oxides of aquifer samples was detected via incubation with Shewanella alga and evidence for iron and manganese reduction was collected. In contrast, 16S rDNA phylogenetic analysis revealed the absence of common iron reducing bacteria. Aerobic hydrocarbon degraders were abundant in shallow horizons, while nitrate reducers were dominating in deeper aquifer regions, in addition to a low relative abundance of methanogenic archaea. Partial Least Squares – Canonical Correspondence Analysis (PLS-CCA) suggested that nitrate and oxygen concentrations had the greatest impact on aquifer community structure in on- and offsite wells, which had a similarly high biodiversity (H’ and Chao1). Overall, slow hydrocarbon dissolution from the DNAPL appears to dominate natural attenuation processes. This site may serve as a model for developing legal and technical strategies for the treatment of DNAPL-impacted sites where contaminant plumes are absent or shrinking.