Shallow Alluvial Aquifer Research Articles

Paired RNA Radiocarbon and Sequencing Analyses Indicate the Importance of Autotrophy in a Shallow Alluvial Aquifer

Determining the carbon sources for active microbial populations in the subsurface is a challenging but highly informative component of subsurface microbial ecology. This work developed a method to provide ecological insights into groundwater microbial communities by characterizing community RNA through its radiocarbon and ribosomal RNA (rRNA) signatures. RNA was chosen as the biomolecule of interest because rRNA constitutes the majority of RNA in prokaryotes, represents recently active organisms, and yields detailed taxonomic information. The method was applied to a groundwater filter collected from a shallow alluvial aquifer in Colorado. RNA was extracted, radiometrically dated, and the 16S rRNA was analyzed by RNA-Seq. The RNA had a radiocarbon signature (Δ14C) of −193.4 ± 5.6‰. Comparison of the RNA radiocarbon signature to those of potential carbon pools in the aquifer indicated that at least 51% of the RNA was derived from autotrophy, in close agreement with the RNA-Seq data, which documented the prevalence of autotrophic taxa, such as Thiobacillus and Gallionellaceae. Overall, this hybrid method for RNA analysis provided cultivation-independent information on the in-situ carbon sources of active subsurface microbes and reinforced the importance of autotrophy and the preferential utilization of dissolved over sedimentary organic matter in alluvial aquifers.

Assessment of short-term aquifer thermal energy storage for demand-side management perspectives: Experimental and numerical developments

In the context of demand-side management and geothermal energy production, our proposal is to store thermal energy in shallow alluvial aquifers at shorter frequencies than classical seasonal aquifer thermal energy storage. We first conducted a one-week experiment in a shallow alluvial aquifer, which is characterized by a slow ambient groundwater flow, to assess its potential for thermal energy storage and recovery. This experiment has shown that up to 90% of the stored thermal energy can be recovered and would therefore suggest that aquifer thermal energy storage could be considered for demand-side management applications. We then conceptualized, developed, and calibrated a deterministic 3D groundwater flow and heat transport numerical model representing our study site, and we simulated 77 different scenarios to further assess this potential. This has allowed us to demonstrate that low-temperature aquifer thermal energy storage (temperature differences of −4 K for precooling and 3, 6, and 11 K for preheating) is efficient with energy recovery rates ranging from 78 to 87%, in a single aquifer thermal energy storage cycle. High-temperature aquifer thermal energy storage (temperature differences between 35 and 65 K) presents lower energy recovery rates, from 53 to 71%, with all other parameters remaining equals. Energy recovery rates decrease with increasing storage duration and this decrease is faster for higher temperatures. Retrieving directly useful heat (without upgrading with a groundwater heat pump) using only a single storage and recovery cycle appears to be complicated. Nevertheless, there is room for aquifer thermal energy storage optimization in space and time with regard to improving both the energy recovery rates and the recovered absolute temperatures.

Behavior of major and trace elements in a transient surface water/groundwater system following removal of a long-term wastewater treatment facility source

In many aquatic environments, municipal wastewater treatment facility (WWTF) effluent discharges influence local hydrologic and chemical connectivity between the surface-water and adjacent alluvial shallow-groundwater systems. Fourmile Creek located in Polk County, Iowa received effluent from the Ankeny WWTF for nearly forty years before it was shut down in November 2013. The decommissioning of the municipal WWTF provided a unique opportunity to characterize the recovery from impacts of treated wastewater discharge on water quality at the surface-water/groundwater interface in a shallow, unconfined alluvial aquifer.Dissolved major element and trace element concentrations in Fourmile Creek surface water, hyporheic-zone water, and shallow, unconfined groundwater were monitored upstream and downstream from the WWTF discharge before and after the shutdown. Multivariate statistical techniques including principal component analysis (PCA) and agglomerative hierarchical clustering (AHC) were used to differentiate source-water contributions, characterize elemental components, and describe surface-water/groundwater interaction dynamics. During the post-closure assessment, there was subsurface attenuation of wastewater constituents including Al, B, Cu, Gd, K, Mo, Na, P, Pb, Sb, and Zn. During the same time, groundwater concentrations increased for As, Ba, Ca, Fe, Mg, Mn, SiO2, Sr, and U and represented a profile characteristic of the shallow alluvial aquifer. Hydrologic conditions transitioned from predominantly wastewater infiltration and hyporheic exchange before the WWTF shutdown, to predominantly discharge of native groundwater. Precipitation-driven streamflow events created fluctuations in the groundwater water-table elevations, resulting in variable contact between the saturated and unsaturated zones within the unconfined, alluvial aquifer and intermittent exposure to constituents stored in the sediments. The inorganic fingerprint of municipal wastewater was flushed relatively quickly (≤19 weeks) from the hyporheic zone indicating that processes like diffusion or sorption/desorption that might extend recovery may not be important for many trace elements in this system.

Chlorine isotopes as tracers of solute origin and age of groundwaters from the Eastern Desert of Egypt

Chlorine-36 abundances and stable chlorine isotope ratios (37Cl/35Cl) were analyzed to decipher sources of chloride and to estimate subsurface residence times of groundwaters from the Nubian Sandstone Aquifer System (NSAS), alluvial aquifers, and fractured basement aquifers in the Eastern Desert of Egypt. Chlorine-36 isotopic abundances (36Cl/Cl) ranged from 5 × 10−15 to 343 × 10−15. The range in δ37Cl values was −0.61 to +0.90‰. Groundwater solute compositions were dominated by Na, Ca, Cl, and SO4 with total dissolved solids ranging from 445 to 13,700 mg/L. Chemical and isotopic data indicate that dry fallout of marine aerosols and evaporated vadose-zone residues from precipitation that recharged the aquifers may have been the main sources of groundwater solutes. Apparent groundwater 36Cl model ages range from 0 (+/−40) to 1300 (+300/−180) kyr. Groundwater from the fractured basement aquifers in the southwestern part of the study area had the youngest apparent ages, while that from deep wells tapping the Nubian aquifer had the oldest apparent ages. Shallow alluvial aquifers having anomalously old apparent 36Cl model ages indicate mixing of old Nubian aquifer water with modern recharge in alluvial aquifers. Stable isotope ratios of hydrogen and oxygen support this inferred mixing relationship and allowed quantitative estimation of old/young water mixing fractions.

Significance of the connection between bedrock, alluvium and streams: A spatial and temporal hydrogeological and hydrogeochemical assessment from Queensland, Australia

Catchment-scale hydrological and hydrogeological investigations commonly conclude by finding that particular stream reaches are either gaining or losing; they also often assume that the influence of bedrock aquifers on catchment water balances and water quality is insignificant. However, in many cases, such broad findings are likely to oversimplify the spatial and temporal complexity of the connections between the different hydrological system components, particularly in regions dominated by cycles of droughts and flooding. From a modelling perspective, such oversimplifications can have serious implications on the process of identifying the magnitude and direction of the exchange fluxes between the surface and groundwater systems.In this study, we use 3D geological modelling and historic water chemistry and hydraulic records to identify the origins of groundwater at different locations in the alluvium and along the course of streams in the Lockyer Valley (Queensland, Australia), a catchment impacted by a severe drought (‘Millennium Drought’) from 1998 to 2009, followed by extensive flooding in 2011. We also demonstrate how discharge from the sub-alluvial regional-scale volcanic and sedimentary bedrock influences the water balance and water quality of the alluvium and streams. The investigation of aquifer geometry via development of a three-dimensional geological model combined with an assessment of hydraulic data provided important insights on groundwater flow paths and helped to identify areas where bedrock aquifers interact with shallow alluvial aquifers and streams. Multivariate statistical techniques were then applied as an additional line of evidence to groundwater and surface water hydrochemical data from large historical datasets. This confirmed that most sub-catchments within the Lockyer Valley have distinct water chemistry patterns, which result from mixing of different water sources, including discharge from the sub-alluvial bedrock. Importantly, in addition to the observed spatial variability, time-series hydrochemical groundwater and surface water data further demonstrated that the hydraulic connection between alluvial aquifers, streams and sub-alluvial bedrock aquifers is temporally dynamic with very significant changes occurring at the transition from normal to drought conditions and following flooding, affecting both catchment water quality and water balances.

Seasonal microbial variation accounts for arsenic dynamics in shallow alluvial aquifer systems.

Determining the temporal variation of microbial communities in groundwater systems is essential to improve our understanding of hydrochemical dynamics in aquifers, particularly as it relates to the fate of redox-sensitive contaminants like arsenic (As). Therefore, a high-resolution hydrobiogeochemical investigation was conducted in the As-affected alluvial aquifer systems of the Jianghan Plain. In two 25 m-deep monitoring wells, the seasonal variation in the composition of groundwater microbial communities was positively correlated with the change in groundwater level (R = 0.47 and 0.39 in NH03B and NH05B, respectively, P < 0.01), implying that the latter could be a primary driver of the seasonal microbial dynamics. In response to the fluctuating groundwater level, iron (Fe) reducers within the Desulfuromonadales were dominant (9.9 ± 4.7% among different sampling sites) in groundwater microbial communities during the monsoon season and associated with high concentrations of Fe(II) and As, while the predominance (16.7 ± 15.2% among different sampling sites) of iron-oxidizers the Gallionellaceae was accompanied by low Fe(II) and As in the non-monsoon season. These results suggest that microbially-mediated iron reduction/oxidation may have governed the seasonal mobilization/scavenging of As in groundwater. Our results provide new insights into mechanisms responsible for seasonal variations in groundwater As concentrations in similar aquifer systems.

Combinations of geoenvironmental data underline coastal aquifer anthropogenic nitrate legacy through groundwater vulnerability mapping methods

Groundwater quality is strongly dependent on land use. Past and current anthropogenic activities can lead to the diffusion of contaminants in aquifers. This diffusion can threaten the resource exploitation for decades, thereby endangering the ecological health of groundwater dependent ecosystems. Thus, groundwater stakeholders need methods for long-term management which integrate groundwater vulnerability. This study was conducted on the shallow alluvial aquifer of the groundwater-dependent Biguglia lagoon on Corsica Island, France. The aquifer is exposed to anthropogenic contamination for many decades with nitrate contamination legacy linked to agricultural activities, uncontrolled urbanization and sewage leakages.In most cases, vulnerability mapping is done in the objective of comparing groundwater situation regarding an on-going contamination process. But the question is still pending for aquifers where contamination is inherited from past practices or contaminations and where anthropogenic influences have changed through time.To propose an effective and innovative method for territorial management in Mediterranean alluvial aquifers, four index-based groundwater vulnerability mapping methods were tested and compared: two intrinsic vulnerability mapping methods (DRASTIC and SINTACS) and two specific vulnerability mapping methods (Modified-DRASTIC and SI), the latter integrating land use in the accuracy of groundwater vulnerability. Novelty is coming from the comparison between vulnerability maps and their application and validation in a hydrosystem affected by nitrate legacy-type contamination. The specific vulnerability mapping methods are more likely to represent the current pressures to which groundwater are subject. Thus, specific vulnerability methods such as the SI one revealed here very relevant to assess groundwater quality and to react retrospectively. The comparison between groundwater nitrate legacy and intrinsic groundwater vulnerability methods appeared also useful to define priority protection areas in long-term territorial management planning (EU Water Framework Direction). In this sense, the SINTACS method seems to be the more appropriate in the Mediterranean and alluvial context of this study.

A study on the role of hydrogeology on the distribution of uranium in alluvial aquifers of northwest India.

A study was undertaken to decipher the uranium distribution in relation to a number of hydrogeological factors in groundwater of southwest Punjab. Existing geological information for the region suggests that the shallow alluvial aquifer extends up to 50-70m below ground level (bgl) and is in turn underlain by a deeper aquifer which extends to a depth of 250mbgl. The presence of clayey units limits the vertical mixing of groundwater between the shallow and deep aquifers. Water level data (averaged over 5years period) indicates that the south and southwestern regions of the study area have shallow water levels (3-5mbgl) while the north and northeast regions have deep water levels (20-28mbgl). This difference in water levels is found to be increasing with time. Higher concentrations of uranium occur in the central, southern, and southwestern parts of the study area where the water table occurs at shallow depth. Groundwater in the northern and northeastern parts of the study area shows U concentration within permissible levels for potable use (< 30μg/L) while the highest concentration of U (341μg/L) was found in the central part of the study area. Seasonal variation in dissolved U concentration is found to be statistically significant. The observed increases in U concentrations during the post-monsoon season are due to the addition of bicarbonate from the root zone as well as increased dissolved oxygen, nitrate, and sulphate concentration (oxic condition) in the groundwater while the decrease in U concentration is attributed to quick recharge by precipitation through sand dunes and contribution of surface water. Deeper groundwater does not show much seasonal variation in dissolved U concentration. Correlation between U and other hydrochemical parameters was evaluated. Cluster analysis of the data also indicates the oxidative mobilization of U from the sediments. Based on the lithological, hydrogeological, and dissolved U data, a schematic map is prepared depicting the various factors affecting the U distribution in alluvial aquifers, which can also be applied to other regions of similar hydrogeological setup. Graphical abstract ᅟ.

Hydrochemical and Multivariate Statistical Evaluation of Heavy Metals in Shallow Alluvial Aquifers of North Brahmaputra Plain, India

The aim of this study was to display distribution and relationships of heavy elements in the unconfined, shallow alluvial aquifers of the lower Jia Bharali catchment and adjoining areas in central part of North Brahmaputra Plain (NBP), India using hydrochemical as well as multivariate statistical techniques such as principal component analysis (PCA) and cluster analysis. The original matrix was made up of 10 trace elements (As, Cd, Cu, Co, Cr, Fe, Mn, Pb, Ni and Zn) estimated from 50 shallow alluvial dug wells in both the wet and the dry season for a duration of 3 hydrological years (2008–2011). Except As, Cu and Zn all the other toxic metals in the shallow aquifers were found exceeding the WHO maximum permissible limits for drinking water. PCA extracted five varimax factors as geogenic, agricultural and anthropogenic explaining about 71.2% of the total variance in the wet season and 69.3% total variance in the dry season. Hierarchical cluster analysis classified the dug wells into two groups in the wet season and three groups in the dry season with respect to the heavy elements. The results emphasized the need for routine monitoring and management in order to avoid contamination of groundwater sources in the NBP with respect to the dissolved trace elements.

In Situ and GRACE‐Based Groundwater Observations: Similarities, Discrepancies, and Evaluation in the High Plains Aquifer in Kansas

AbstractRelating Gravity Recovery and Climate Experiment (GRACE)‐derived terrestrial water storage anomaly (aTWS) variations to in situ groundwater data is important to understanding GRACE data utility. Here GRACE‐derived annual changes in aTWS (ΔTWS) from National Aeronautics and Space Administration's Jet Propulsion Laboratory and Goddard Space Flight Center are compared to annual changes in saturated groundwater volumes (ΔGW) in the High Plains aquifer (HPA) and overlying alluvial aquifers in Kansas. Regression analysis suggests that trends in ΔTWS are strongly related to trends in ΔGWalluvial and weakly related to trends in ΔGWHPA, although the magnitude of ΔTWS is much larger than ΔGWalluvial and is similar to ΔGWHPA. Unlike alluvial aquifers, a thick vadose zone overlies the HPA. Estimates of changes in vadose zone water content (ΔVZ) using GRACE products are similar in magnitude to annual variations in North American Land Data Assimilation soil moisture data, suggesting an unexpected dominance of ΔVZ in ΔTWS despite significant groundwater depletion. Results demonstrate that water storage changes in shallow alluvial aquifers, the root zone, the deep vadose zone, and the HPA itself are all significant in the HPA region of Kansas. Consequently, GRACE observations cannot, alone, be taken to reflect variations in saturated zone groundwater storage in the HPA, or other large, heavily used aquifers subject to substantial groundwater depletion, when deep unsaturated zones exist. GRACE can best provide guidance on regional aquifer storage changes where water storage changes in the vadose zone and perched or adjacent aquifers are well constrained.

Biotic distribution within groundwater- is it really unpredictable?

Distribution of biota within groundwater is often patchy, and attributed to the heterogeneity of the aquifer environment. Geology and hydrological connectivity are often the factors that most influence water chemistry and habitat availability thus biota, however phreatophytic trees, other sources of carbon and nutrients may also influence biotic distribution. Critically, limited knowledge on the relative importance of such factors on the distribution of groundwater biota makes it difficult to distinguish natural variation from human impacts on groundwater ecosystems, thus inpact our ability to undertake biomonitoring of ecosystem health. This study uses complementary field surveys and laboratory studies to unravel the relative influence of water quality, climate, and sediment size on biotic communities. Field surveys combined traditional pumping and net collections with eDNA community profiling (metabarcoding) of 16S rDNA to characterise groundwater microbes in shallow alluvial aquifers within the Murray-Darling Basin, Australia. Laboratory studies examined the influence of sediment size on stygobiotic amphipods, syncarids and copepods. For stygofauna, sediment size, and thus size of interstitial voids, is a key limiting factor. For microbes, water chemistry influences microbial activity and functional processes, which may in turn influence biogeochemical cycling and ecosystem services provided by groundwater ecosystems.

What happens to groundwater ecosystems when you take out the groundwater?

The removal of groundwater results in the lowering of water tables, which, for groundwater organisms, translates to reduced habitat availability and changed environmental conditions in the habitat that remains. While changes in groundwater levels may be well modelled and predicted, the impacts on groundwater ecosystems remain poorly known. There are three key processes associated with groundwater drawdown in shallow alluvial aquifers that may threaten groundwater ecosystems. These processes are 1. the physical decline of water levels, from which fauna can be stranded in isolated or unsaturated sediments; 2. the loss of or change to habitat, particularly as water levels move through different geological strata and 3. changes in hydrological connectivity, that may influence water quality as a result of increasing distance or disconnection from the surface and other water sources. Results from laboratory studies show the variable capacity for stygobiotic invertebrates to move with declining water tables, dependent on both drawdown rate and sediment attributes. Once isolated in unsaturated habitats, our tests show that survival of fauna is limited beyond 48 h. Invertebrates are constrained by sediment size and unable to use those with relatively small pore spaces and may not be able to use all available saturated habitats. This talk will present a framework that identifies the key threats of groundwater drawdown to groundwater ecosystems and will highlight the current state of knowledge of each of these threatening processes. We present the results of empirical studies on the response of stygobiotic invertebrates to specific elements of the framework.

Shallow alluvial aquifers for drinking and agricultural purposes: a case study from Jia Bharali River Basin, North Brahmaputra Plain, India

A preliminary assessment of groundwater quality for drinking and irrigational purposes in the lower Jia Bharali river catchment and adjoining areas of North Brahmaputra Plain, India, was carried out with respect to major cations, anions, and trace elements. Water samples from 50 shallow alluvial dug wells were collected in wet and dry seasons for a period of 3 hydrological years (2008–2011). Seasonal analysis showed major cation and anion contents in a definite trend across the basin as Ca: 4.2–68.9 mg/L > Na 1.9–62.5 mg/L > Mg:1.0–29.2 mg/L > K (1.3–26.1 mg/L) and HCO3 (16–118 mg/L) > Cl (2.8–138.3 mg/L) > SO4 (1.2–99.5 mg/L) > PO4 (BDL—1.50 mg/L) > NO3 (BDL—1.20 mg/L) within WHO acceptable limit for drinking water in all the seasons. Low SAR ( 60% and Kelly’s Index > 1. However, majority of the wells were found not suitable for drinking as well as irrigational purposes due to the presence of trace elements Cd (BDL—0.070 mg/L), Cr (BDL—0.24 mg/L), Fe (0.10–11.76 mg/L), Mn (BDL—1.37 mg/L), Ni (BDL—0.18 mg/L), and Pb (BDL—0.22 mg/L) beyond their respective standard limits. Piper trilinear diagram identified the major hydrochemical facies of the groundwater as alkaline earths (Ca, Mg) and weak acids (HCO3) over alkalis (Na, K) and strong acids (SO4, Cl).

Assessments of seasonal groundwater recharge and discharge using environmental stable isotopes at Lower Muda River Basin, Malaysia

An accurate estimation of groundwater recharge is required to properly manage aquifers, especially for riverbank filtration method (RBF) purposes. The isotopes correlations and differences in different water bodies were studied to assess the sources of groundwater recharge and preliminary tools in understanding of the surface water and groundwater interactions in the Lower Muda River Basin. The environmental isotope and hydrochemical sampling results had emphasised that the area near Lower Muda River Basin had a connection with the river and was actively recharging the near-river shallow alluvial aquifer, via RBF method. Furthermore, the shallow groundwater that was close to Muda River from groundwater signatures had indicated the recharge of the shallow aquifer system by Muda River based on the plots along LMWL on a δ2H versus δ18O. The comparisons between like δ2H and δ18O isotopes in the rainwater revealed the variations in the rainfall amount and the 18O-depleted water of those isotopes for wet season precipitation as compared to dry seasons. Furthermore, the groundwater δ2H and δ18O isotopes exhibited a slight deviation from the δ2H and δ18O isotopic meteoric water line in Lower Muda River. Therefore, in this basin, the groundwater could be a combination of river water and precipitation, which had led to the recharge of river water being more than the recharge of rainfall infiltration.

Uranium Retention in a Bioreduced Region of an Alluvial Aquifer Induced by the Influx of Dissolved Oxygen.

Reduced zones in the subsurface represent biogeochemically active hotspots enriched in buried organic matter and reduced metals. Within a shallow alluvial aquifer located near Rifle, CO, reduced zones control the fate and transport of uranium (U). Though an influx of dissolved oxygen (DO) would be expected to mobilize U, we report U immobilization. Groundwater U concentrations decreased following delivery of DO (21.6 mg O2/well/h). After 23 days of DO delivery, injection of oxygenated groundwater was paused and resulted in the rebound of groundwater U concentrations to preinjection levels. When DO delivery resumed (day 51), groundwater U concentrations again decreased. The injection was halted on day 82 again and resulted in a rebound of groundwater U concentrations. DO delivery rate was increased to 54 mg O2/well/h (day 95) whereby groundwater U concentrations increased. Planktonic cell abundance remained stable throughout the experiment, but virus-to-microbial cell ratio increased 1.8-3.4-fold with initial DO delivery, indicative of microbial activity in response to DO injection. Together, these results indicate that the redox-buffering capacity of reduced sediments can prevent U mobilization, but could be overcome as delivery rate or oxidant concentration increases, mobilizing U.

Delayed nitrate dispersion within a coastal aquifer provides constraints on land-use evolution and nitrate contamination in the past

Identifying sources of anthropogenic pollution, and assessing the fate and residence time of pollutants in aquifers is important for the management of groundwater resources, and the ecological health of groundwater dependent ecosystems. This study investigates anthropogenic contamination in the shallow alluvial aquifer of the Marana-Casinca, hydraulically connected to the Biguglia lagoon (Corsica, France). A multi-tracer approach, combining geochemical and environmental isotopic data (δ18O-H2O, δ2H-H2O, 3H, δ15N-NO3−, δ18O-NO3−, δ11B), and groundwater residence-time tracers (3H and CFCs) was carried out in 2016, and integrated with a study of land use evolution in the catchment during the last century. Groundwater NO3− concentrations, ranged between 2 mg/L and up to 30 mg/L, displaying the degradation of groundwater quality induced by anthropogenic activities (agricultural activities). Comparatively high δ15N-NO3− values (up to 19.7‰) in combination with δ11B values that were significantly lower (between 23‰ and 26‰) than the seawater background are indicative of sewage contamination. The ongoing deterioration of groundwater quality can be attributed to the uncontrolled urbanization development all over the alluvial plain, with numerous sewage leakages from the sanitation network and private sewage systems. Integration of contaminant and water-residence time data revealed a progressive accumulation of pollutants with time in the groundwater, particularly in areas with major anthropogenic pressure and slow dynamic groundwater flow. Our approach provides time-dependent insight into nitrogen pollution in the studied aquifer over the past decades, revealing a systematic change in the dominant NO3− source, from agricultural to sewage contamination. Yet, today's low groundwater quality is to large parts due to legacy pollution from land-use practices several decades ago, underlining the poor self-remediating capacity of this hydrosystem. Our results can be taken as warning that groundwater pollution that happened in the recent past, or today, may have dire impacts on the quality of groundwater-dependent ecosystems in the future.

Hydrogeochemical characterization of a shallow alluvial aquifer: 1 baseline for groundwater quality assessment and resource management

Considering the progressive depletion of groundwater quantity and the alteration of superficial and groundwater quality in the Madrid region, a highly populated area with extended urbanizations in the north and agricultural activities in the south, we conducted a monitoring study over a period of 2.5 years (2015–2017). The study was conducted in the Jarama-Tajuña shallow alluvial aquifer system located southeast of Madrid, where the exploitation of the aquifer and the Jarama river have increased exponentially in the last decade being affected by both urban and agricultural activities. Our aims were to provide: i) a geochemical characterization of the surface and groundwater properties; ii) identify the process responsible for the geochemical evolution and mineralization of the waters; iii) assess the water quality (i.e. nitrates, ammonia, sodium and chloride as potential contaminants) and the water suitability for irrigation (SAR, Wilcox, KI and MH indexes); and iv) identify the main sources of contamination in the area.A set of plots, ion ratios, correlation coefficients, multivariate statistical analyses and indexes were performed. Results indicated that rock weathering largely controls the hydrogeochemistry of the system and that wastewater treatment plant discharges and agricultural practices significantly affect the composition of the water, causing an important decline of both surface and groundwater chemical quality. Nonetheless, water suitability for irrigation is admissible. Thus, taking additional measures to increase its quality are not necessary.With this study we aimed to establish a base line to evaluate future changes in the groundwater properties from the Madrid region enabling the planners and policy makers to develop a strategy to mitigate the impact of the exponential increase of urban and agriculture activities on groundwater resources.

Radionuclide geochemistry of groundwater in the Eastern Desert, Egypt

Radionuclides have been recognized as a limiting factor of groundwater quality in the Middle East and Northeastern Africa. High levels of naturally occurring radioactivity, mostly from radium and radon isotopes, have been reported in waters from the Nubian Sandstone Aquifer System (NSAS) in several countries in the Middle East including the Sinai Peninsula of Egypt. This study aims at extending the existing data coverage by investigating radionuclide concentrations and their potential geological and hydrogeochemical controls in groundwater of the NSAS and the overlying alluvial aquifers in the Eastern Desert of Egypt. Radium isotope activities (226Ra and 228Ra) and uranium concentrations were analyzed in 39 groundwater samples from these aquifers. The shallow Nubian aquifer has 226Ra and 228Ra activities ranging from 0.016 to 0.750 and 0.018–1.421 Bq/L, respectively. The deep Nubian aquifer has 226Ra and 228Ra activities ranging from 0.019 to 0.051 and 0.014–0.248 Bq/L, respectively. The shallow alluvial aquifers have 226Ra and 228Ra activities ranging from 0.008 to 0.086 and 0.006–0.081 Bq/L, respectively. Groundwater in the Nubian aquifer may have Ra activities substantially in excess of the drinking water MCL values of the US Environmental Protection Agency (EPA), the European Union (EU), and the World Health Organization (WHO). The concentration of U varies from 0.06 to 33.06 μg/L, 0.06–15.46 μg/L, and 0.01–13.19 μg/L for the shallow Nubian aquifer, the deep Nubian aquifer, and the shallow alluvial aquifers, respectively. U concentrations exceed the EPA and WHO MCL values in some wells, mostly from the shallow Nubian aquifer.

Monitoring well utility in a heterogeneous DNAPL source zone area: Insights from proximal multilevel sampler wells and sampling capture-zone modelling

Groundwater-quality assessment at contaminated sites often involves the use of short-screen (1.5 to 3 m) monitoring wells. However, even over these intervals considerable variation may occur in contaminant concentrations in groundwater adjacent to the well screen. This is especially true in heterogeneous dense non-aqueous phase liquid (DNAPL) source zones, where cm-scale contamination variability may call into question the effectiveness of monitoring wells to deliver representative data. The utility of monitoring wells in such settings is evaluated by reference to high-resolution multilevel sampler (MLS) wells located proximally to short-screen wells, together with sampling capture-zone modelling to explore controls upon well sample provenance and sensitivity to monitoring protocols. Field data are analysed from the highly instrumented SABRE research site that contained an old trichloroethene source zone within a shallow alluvial aquifer at a UK industrial facility. With increased purging, monitoring-well samples tend to a flow-weighted average concentration but may exhibit sensitivity to the implemented protocol and degree of purging. Formation heterogeneity adjacent to the well-screen particularly, alongside pump-intake position and water level, influence this sensitivity. Purging of low volumes is vulnerable to poor reproducibility arising from concentration variability predicted over the initial 1 to 2 screen volumes purged. Marked heterogeneity may also result in limited long-term sample concentration stabilization. Development of bespoke monitoring protocols, that consider screen volumes purged, alongside water-quality indicator parameter stabilization, is recommended to validate and reduce uncertainty when interpreting monitoring-well data within source zone areas. Generalised recommendations on monitoring well based protocols are also developed. A key monitoring well utility is their proportionately greater sample draw from permeable horizons constituting a significant contaminant flux pathway and hence representative fraction of source mass flux. Acquisition of complementary, high-resolution, site monitoring data, however, vitally underpins optimal interpretation of monitoring-well datasets and appropriate advancement of a site conceptual model and remedial implementation.

Assessment of well performance criteria and aquifer characteristics using step-drawdown tests and hydrogeochemical data, west of Qena area, Egypt

A groundwater investigation was performed to characterize hydrogeological conditions and well performance in a shallow alluvial aquifer using well logs, step-drawdown tests, and hydrogeochemical data. Results from three single-well step-drawdown tests conducted in three recently drilled boreholes located west of the Qena area in Upper Egypt and were analyzed by the Rorabaugh (1953) graphical method. A total of 47 groundwater wells were sampled and analyzed to detect the main hydrochemical facies associated geochemical processes. Results of the step-drawdown tests indicated well losses between 1.5% and 27.7% (14.2% avg.) and aquifer losses of between 72.3% and 98.5% (85.8% avg.), reflective of high well efficiencies. Specific capacity values varied from 183.4 m3/day/m to 278.4 m3/day/m while well efficiency values varied from 72.3% to 98.5%, indicating that the wells had been properly designed and developed. Estimated aquifer transmissivity ranges from 1103.7 m2/day to 1459.7 m2/day (1314.9 m2/day avg.), indicating high yields and water accessibility to the wells. Results indicated laminar flow at the aquifer/well-face contact with negligible turbulent flow. Gibbs and various scatter ionic ratios plots of the geochemical data indicate that water-rock interaction followed by evaporation are the most dominant processes controlling groundwater composition, while a Piper plot reflects mixing with irrigation-return flows subject to evapotranspiration. The approach demonstrates the practical applications of the single-well step-drawdown tests for estimating of the safe and sustained well yields for future groundwater extraction.