Fresh Aquifers Research Articles

Mathematical modeling of pollution of underground aquifers due to mining of minerals

Purpose. The research aims to create a mathematical model of salt contamination spreading through underground aquifers in the event of depressurization of the hydrocarbon production well crater for further assessment of environmental and economic damage from these processes. Methods. To predict the environmental and economic damage from salt contamination, the distribution of concentrations of harmful substances was investigated, taking into account the number of supply sources and their intensity over time, based on situ studies at the Rybalske Oil Field, Okhtyrskyi District of Sumska Oblast in Ukraine, where there were technological failures wells, accompanied by open fountains with the release of large amounts of highly mineralized water and the formation of craters. Mathematical modelling methods were used to process the data from the study of accidental technogenic pollution of underground aquifers. Findings. Based on real data from the study of the processes of potential salt contamination spread in fresh aquifers as a result of accidents at hydrocarbon production facilities, a mathematical model of salt contamination spreading in drinking groundwater in the event of depressurization of an oil field well crater has been developed. Potential economic losses in case of possible groundwater contamination with highly mineralized solution, which can into drinking groundwater aquifers, are substantiated. It has been established that in connection with the occurrence of an emergency situation due to the release of formation water to the surface in the territory of oil and gas fields, the formation of technogenic meromictic reservoirs is possible, which is confirmed by the example of the Rybalske Oil Field. It is proved that the total mineralization of crater water increases linearly with depth of the reservoir occurrence, and a similar dependence is characteristic of the chloride ion content. Originality. For the first time, a multicomponent mathematical model of mineral salt migration processes in underground freshwater aquifers in the case of depressurization of a meromictic reservoir has been developed. Practical implications. The research results obtained using numerical methods make it possible to predict the processes of spreading harmful substances in drinking underground aquifers as a result of emergencies at oil and gas fields, taking into account the number of sources of pollutants penetrating the study area, the heterogeneity of properties of the environment into which the harmful substance enters, and to assess the dynamics of changes in the concentration of these substances and time with further assessment of environmental and economic damage from these processes.

Vertical leaching of paleo-saltwater in a coastal aquifer–aquitard system of the Pearl River Delta

Marine transgressive and regressive processes have promoted the formation of deltas and estuaries from the postglacial period, and the coastal aquifer-aquitard system can be identified based on the complicated sedimentary environments in the river delta. The groundwater system is usually composed of freshwater and paleo saltwater, and the vertical leaching of paleo saltwater from aquitard to fresh aquifer occurs due to density difference and gravity effect. In this study, radium quartet and radon were used as the tracers for groundwater due to their different half-lives. We constructed a radium reactive transport model considering the vertical leaching of paleo saltwater in a deltaic aquifer-aquitard system and then applied it in the Pearl River Delta (PRD). The activity ratio of 224Ra to 228Ra was used to characterize whether the groundwater system was controlled by α-recoil or sufficient 232Th under fully weathered condition, and results showed that the deltaic system was well weathered and the vertical leaching of paleo saltwater inhibited the α-recoil input and increased the decay of the sorbed parent nuclide in the aquifer. After incorporating the vertical leaching of saltwater in the model, the value of retardation factor in the shallow aquitard evidently increased, meaning that the leaching of salty porewater into the aquifer greatly affected the adsorption–desorption process of radium isotopes in the aquitard, and the value of retardation factor reduced to the lower limit in the basal aquifer, indicating that the desorption process was determined by the vertical leaching of saltwater here. After considering the effect of vertical leaching, the estimated water transit time in the aquifer was decreased and the groundwater discharge rate was increased, and the converse results were obtained in the aquitard. The proposed radium reactive transport model advances the understanding of the salinization process in coastal aquifers through vertical migration and facilitates the understanding of freshening process of paleo saltwater in the river delta with similar hydrogeological settings.

Delineation of Paleochannel and Groundwater Resources in the Khari River Basin, Kachchh using Transient Electromagnetics

Abstract The paleochannels are riverine geomorphic features, which are either buried or shifted due to tectonic, climate, and anthropogenic activities. In general, these channels serve as potential groundwater repositories, and their identification can help in developing potable groundwater sources. Here, the results of transient electromagnetic (TEM) study carried out near and around the Khari river basin of the tectonically active Kachchh intraplate region, western India are presented. The TEM investigations at 22 sites along three traverses have been carried out in the river basin that cut the present-day river channel and its presumed paleochannel. The geoelectric sections of the three profiles decipher information down to 300-350m and suggest a multilayer aquifer system. The sub-surface model infers a deeper confined aquifer at variable depths from 100-150m associated with the river as well as its paleochannel. The paleochannel aquifer is observed to be buried under 15-20m thick unconsolidated sediments that overlie a Mesozoic sandstone layer of the Bhuj Formation. The resistivity sections across the paleochannel suggest a relatively fresh aquifer layer with higher storage capacity. A vertical bedrock offset of 100-120m and the discontinuity of lithostratigraphic layers observed from the study suggest the dominant tectonic control in the formation of the paleochannel that correlated with the location of the reactivated splay of the Katrol Hill Fault.

High spatial heterogeneity and low connectivity of bacterial communities along a Mediterranean subterranean estuary.

Subterranean estuaries are biogeochemically active coastal sites resulting from the underground mixing of fresh aquifer groundwater and seawater. In these systems, microbial activity can largely transform the chemical elements that may reach the sea through submarine groundwater discharge (SGD), but little is known about the microorganisms thriving in these land-sea transition zones. We present the first spatially-resolved characterization of the bacterial assemblages along a coastal aquifer in the NW Mediterranean, considering the entire subsurface salinity gradient. Combining bulk heterotrophic activity measurements, flow cytometry, microscopy and 16S rRNA gene sequencing we find large variations in prokaryotic abundances, cell size, activity and diversity at both the horizontal and vertical scales that reflect the pronounced physicochemical gradients. The parts of the transect most influenced by freshwater were characterized by smaller cells and lower prokaryotic abundances and heterotrophic production, but some activity hotspots were found at deep low-oxygen saline groundwater sites enriched in nitrite and ammonium. Diverse, heterogeneous and highly endemic communities dominated by Proteobacteria, Patescibacteria, Desulfobacterota and Bacteroidota were observed throughout the aquifer, pointing to clearly differentiated prokaryotic niches across these transition zones and little microbial connectivity between groundwater and Mediterranean seawater habitats. Finally, experimental manipulations unveiled large increases in community heterotrophic activity driven by fast growth of some rare and site-specific groundwater Proteobacteria. Our results indicate that prokaryotic communities within subterranean estuaries are highly heterogeneous in terms of biomass, activity and diversity, suggesting that their role in transforming nutrients will also vary spatially within these terrestrial-marine transition zones.

Intensified salinity intrusion in coastal aquifers due to groundwater overextraction: a case study in the Mekong Delta, Vietnam.

Groundwater salinization is one of the most severe environmental problems in coastal aquifers worldwide, causing exceeding salinity in groundwater supply systems for many purposes. High salinity concentration in groundwater can be detected several kilometers inland and may result in an increased risk for coastal water supply systems and human health problems. This study investigates the impacts of groundwater pumping practices and regional groundwater flow dynamics on groundwater flow and salinity intrusion in the coastal aquifers of the Vietnamese Mekong Delta using the SEAWAT model-a variable-density groundwater flow and solute transport model. The model was constructed in three dimensions (3D) and accounted for multi-aquifers, variation of groundwater levels in neighboring areas, pumping, and paleo-salinity. Model calibration was carried for 13 years (2000 to 2012), and validation was conducted for 4 years (2013 to 2016). The best-calibrated model was used to develop prediction models for the next 14 years (2017 to 2030). Six future scenarios were introduced based on pumping rates and regional groundwater levels. Modeling results revealed that groundwater pumping activities and variation of regional groundwater flow systems strongly influence groundwater level depletion and saline movement from upper layers to lower layers. High salinity (>2.0 g/L) was expected to expand downward up to 150 m in depth and 2000 m toward surrounding areas in the next 14 years under increasing groundwater pumping capacity. A slight recovery in water level was also observed with decreasing groundwater exploitation. The reduction in the pumping rate from both local and regional scales will be necessary to recover groundwater levels and protect fresh aquifers from expanding paleo-saline in groundwater.

Did water-saving irrigation protect water resources over the past 40 years? A global analysis based on water accounting framework

Water-saving technologies have long been seen as an effective method to reduce irrigation water use and alleviate regional water shortage. However, growing reports of more severe water shortage and increasing application of water-saving technologies across the world have necessitated reassessment of agricultural water-saving. This study develops a simple method based on satellite-based ET partitions to estimate water withdrawal, water consumption and return flow from the 1980s to 2010s, and quantifies water-savings across globe and four hot-spot irrigated areas at both field and regional scales based on water accounting framework. The results show that global irrigation water flows keep increasing from the 1980s to 2010s, with over 50% increase from the expansion in irrigated lands. While water-saving technologies are found mainly applied in originally old irrigated lands, traditional flooding irrigation is still dominant in newly-developed irrigated lands. Non-beneficial water consumption (soil evaporation) is effectively reduced by water-saving technologies, but return flow has increased at the same time. At field scale, water-saving technologies fail to save water because the accumulated increased return flow is more than the accumulated decreased non-beneficial water consumption. At regional scale, however, water is saved because the return flow percolated to fresh aquifers is seen as beneficial rather than loss. At the same time, the accumulated increase of beneficial water consumption (crop transpiration) exceeds regional water savings, which explains the paradox between wide application of water-saving technologies and more severe regional water shortage. This study provides key new evidence for the paradox of irrigation efficiency and helps reconsidering water-saving technologies and their impacts on regional water resources.

New Generation of Pulsed-Neutron Multidetector Comparison in a Challenging Multistack Clastic Reservoir: A Case Study in Brown Field, Malaysia

Running pulsed-neutron logs in Malaysia has previously been plagued by results with high uncertainties, especially in brown fields with complex multistacked clastic reservoirs. Together with a wide range of porosities and permeabilities, the acquired logs quite often tended to yield inconclusive results. In addition, the relatively fresh aquifer water (where salinity varies from 5,000 to 40,000 ppm) makes reservoir fluid typing and distinguishing between oil and water even more challenging. As a result, the inconsistencies and uncertainties of the results tend to leave more questions than answers. Confidence in using pulsed-neutron logging, especially to validate fluid contacts for updating static and dynamic reservoir models, deteriorated within the various study teams. Due to this fact, the petrophysics team took the initiative to conduct a three-tool log off in one of their wells with the objective of making a detailed comparison of three pulsed-neutron tools in Malaysia’s market today. The main criteria selected for comparisons were the consistency of the data, repeatability, and statistical variations. With recent advancements in pulsed-neutron (multidetector) tool technology, newer tools are being equipped with more efficient scintillation crystals, improving the repeatability of the measurements as well as the number of gamma ray (GR) count rates associated with the neutron interactions. In addition, the newer tools now have up to five detectors per tool, with the farthest detector supposedly being able to “see” deeper into the formation, albeit at a lower resolution. With these new features in mind, the log off was conducted in a single well with a relatively simple completion string (single tubing, single casing), logged during shut-in conditions only, and the logs were acquired directly one after the other (back to back) to avoid bias to any particular tool. Both sigma and spectroscopy measurements were acquired to compare the capabilities of each tool. Due to the relatively freshwater salinity, the carbon-oxygen (C/O) ratio from the spectroscopy measurements is used to identify the remaining oil located in the reservoirs, while the sigma measurements determine the gas-oil or gas-water contact, if present. This paper will illustrate the steps taken by Petronas Carigali Sdn Bhd (PCSB) to compare the raw data and interpreted results from the three pulsed-neutron tools. Consequently, a comparison from all the tools was made to the current understanding of the reservoir assessed. The points from these comparisons will then show which tools are favored over the rest.

Assessment of Groundwater Resources in Coastal Areas of Pakistan for Sustainable Water Quality Management Using Joint Geophysical and Geochemical Approach: A Case Study

Delineation of fresh/saline groundwater is essential for sustainable water quality management, especially in the coastal areas all around the globe. Seawater intrusion causes substantial degradation in quality of freshwater resources in the coastal areas. The main reason for saltwater intrusion is the changing environment in terms of sea-level rise, climate change, and over-extraction of freshwater resources to meet the growing demands. In this study, an integrated approach of geophysical and geochemical methods was used to assess saltwater intrusion in the coastal areas of Bela Plain, Pakistan. The inverted electrical resistivity computed from 50 vertical electrical sounding (VES) constrained the subsurface into five layers and two aquifers through 3D imaging, such as silty clay and sandy clay containing saline water, and sand, sandy gravel, and gravel containing freshwater. However, the narrow range of resistivity values shows an overlap of saline/fresh groundwater. Such ambiguity in the resistivity interpretation was removed by Dar-Zarrouk (D-Z) parameters. D-Z parameters, namely transverse unit resistance (Tr), longitudinal unit conductance (Sc), and longitudinal resistivity (ρL) estimated from VES, marked a clear distinction between saline and fresh aquifers with a wide range of values. The geochemical method was performed using 20 water samples for the main cations (K+, Ca2+ Na+, and Mg2+), anions (SO42−, HCO3−, Cl−, and NO3−), and other parameters (TDS, EC, and pH). Fresh/saline aquifers revealed by D-Z parameters are in good agreement with those delineated by physicochemical parameters and local hydrogeological conditions. This study delineates seawater intrusion of about 13–42 km from Sonmiani Bay in the Arabian Sea towards the inlands of Bela Plain. Therefore, it is expected that this investigation will be helpful in future planning for the management and exploitation of freshwater resources in the study area. Our study suggests that D-Z parameters can be used as the most inexpensive alternative to the traditional geotechnical and environmental tests for the demarcation of fresh/saline groundwater with a large coverage in any coastal or contaminated area under a homogeneous or heterogeneous setting.

Magnetic and Geo-electrical Geophysical Techniques for Subsurface Delineation and Groundwater Assessment in Ras Matarma, Sinai

Groundwater constitutes the main source of the freshwater in Ras-Matarma, Sinai, which necessitates optimized management of it. In this context, geophysical ground magnetic, Schlumberger resistivity inversion, remote sensing (RS), geographic information system (GIS), and pumping tests were conducted. The magnetic survey comprised 56 profiles, whereas, Schlumberger resistivity survey were 27 VES. GIS and RS were implemented for watershed analyses in the area. Interpretation of the magnetic data separated significantly the shallow and deep structures with depths ranged from 300 to 1400 m. Qualitative and quantitative modelling of the inverted resistivity data demarcated effectively the fresh aquifer with true resistivity and thickness ranged from 22 to 210 ohm.m and 2 to 80 m, respectively. GIS aggregated all the aforementioned results along with electric and hydraulic parameters of the fresh aquifer.

Volcanic glass leaching and the groundwater geochemistry on the semi-arid Atlantic island of Porto Santo

The groundwater chemistry of the semi-arid volcanic island of Porto Santo, part of the Madeira archipelago, Atlantic Ocean, was investigated. Generally, the groundwater was brackish, containing 2–10 mol % seawater. Groundwater with up to 20 mM alkalinity and a Na enrichment of up to 30 mM, as compared to the Na concentration predicted by the seawater Na/Cl ratio, was found in the main aquifer. Also notable are the high concentrations of F (up to 0.3 mM), B (up to 0.55 mM), As (up to 0.35 μM), all in excess of WHO recommendations, as well as up to 6 μM V. Geochemical modeling, using the PHREEQC code, was used to explore different scenarios that could explain the genesis of the observed bulk groundwater chemistry. First, a model for aquifer freshening with the displacement of resident seawater from the aquifer by infiltrating freshwater, was tested. This scenario leads to the development of NaHCO3 waters as observed in many coastal aquifers. However, the measured alkalinity concentration in the groundwater was far higher than the concentration predicted by the freshening model. In addition, the behavior of modelled pH and PCO2 were at variance with their distributions in the field data. The second model explored the possible effect of volcanic glass leaching on the groundwater chemistry. Using insight derived from studies of volcanic glass surface alteration as well as experimental work on water-volcanic glass interactions, a geochemical model was developed in which the exchange of H+ for Na+ on the volcanic glass surface is the main mechanism but the exchange of other cations on the volcanic glass surface is also included. The uptake of H+ by the glass surface causes the dissociation of carbonic acid, generating bicarbonate. This model is consistent with the local geology and the field data. It requires, however, volcanic glass leaching to occur in the unsaturated zone where there is an unlimited supply of CO2. The exchange reaction of H+ for Na+ is confined to the surface layer of volcanic glass as otherwise the process becomes limited by slow solid state diffusion of H+ into the glass and Na+ out of the glass. Therefore, volcanic ash deposits, with their high volcanic glass surface areas and matrix flow, are the aquifers where this type of high NaHCO3 waters can be expected, rather than in basalts, which predominantly feature fracture flow. The trace components F, B, As and V are believed to originate from hyaloclastites, consisting of predominantly (90%) of trachy-rhyolite volcanic glass. Although stratigraphically older than the main calcarenite aquifer, topographically they are often located at higher altitudes, above the phreatic level and located along the main recharge flow path. In addition, the semi-arid climate conditions provide a long groundwater residence time for the reactions as well as limited aquifer flushing.

Boron toxicity in higher plants: an update.

In this review, emphasis is given to the most recent updates about morpho-anatomical, physiological, biochemical and molecular responses adopted by plants to cope with B excess. Boron (B) is a unique micronutrient for plants given that the range of B concentration from its essentiality to toxicity is extremely narrow, and also because it occurs as an uncharged molecule (boric acid) which can pass lipid bilayers without any degree of controls, as occurs for other ionic nutrients. Boron frequently exceeds the plant's requirement in arid and semiarid environments due to poor drainage, and in agricultural soils close to coastal areas due to the intrusion of B-rich seawater in fresh aquifer or because of dispersion of seawater aerosol. Global releases of elemental B through weathering, volcanic and geothermal processes are also relevant in enriching B concentration in some areas. Considerable progress has been made in understanding how plants react to B toxicity and relevant efforts have been made to investigate: (I) B uptake and in planta partitioning, (II) physiological, biochemical, and molecular changes induced by B excess, with particular emphasis to the effects on the photosynthetic process, the B-triggered oxidative stress and responses of the antioxidant apparatus to B toxicity, and finally (III) mechanisms of B tolerance. Recent findings addressing the effects of B toxicity are reviewed here, intending to clarify the effect of B excess and to propose new perspectives aimed at driving future researches on the topic.

Application of VES and ERT for delineation of fresh-saline interface in alluvial aquifers of Lower Bari Doab, Pakistan

Geophysical methods are effectively used to delineate intrusion boundary between the fresh and saline aquifers because of their intrinsic capability to assess the lateral variations in the pore-water salinity. In this study, an integrated geophysical approach of vertical electrical sounding (VES) and electrical resistivity tomography (ERT) has been conducted to delineate the contaminated aquifers in the Lower Bari Doab, Pakistan. Electrical resistivity tomography (ERT) using Schlumberger array with 5 m electrode spacing was conducted along eleven profiles at three selected sites (LBD1, LBD2 and LBD3) in the investigated area. The surface geoelectrical method was performed by sixty electrical resistivity soundings using the same array with maximum current electrode spacing (AB = 150 m). The integration of formation resistivity with ten boreholes reveals four discrete subsurface layers i.e., clay having saline aquifer, clay-sand containing brackish aquifer, sand with fresh aquifer and gravel-sand containing fresh aquifer. Estimation of Dar-Zarrouk Parameters (i.e., longitudinal resistivity, transverse resistance and longitudinal conductance) from different combinations of aquifer thickness and resistivity delineated the fresh, brackish and saline water zones with specific values range through mapping and graphical analysis. Geochemical method was performed on forty wells for main cations (K+, Na+, Ca2+ and Mg2+), anions (SO42−, Cl−, HCO3– and NO3−) and other parameters (As, EC, TDS and pH) to validate the results obtained from the geophysical methods. The fresh/saline aquifers delineated by the inclusion of ERT and geoelectrical method are in good agreement with those revealed by the physicochemical analysis and the local hydrogeological data. The results suggest that the use of non-invasive geophysical methods can reduce the number of expensive boreholes to obtain an interface between the fresh and saline water for the exploitation of fresh groundwater resources in any large area of homogeneous or heterogeneous aquifers.

Recharge process of a dune aquifer (Roman coast, Italy)

The urban development plan of left bank of the Tiber river Delta preserved a 9 km2 stretch of dune belt with a monumental coastal pine forest (Castelfusano forest), which is nowadays portion of a natural reserve managed by Municipality of Rome. The forest was largely destroyed by a first huge fire in July 2000 and by another one in July 2017. A reforestation project involved the installation of a monitoring network composed by 21 piezometers to check the groundwater depth and its degree of salinization after the 2000 fire. By examining series of water head measurements and chemical -physical parameters carried out from 2002 up today, the current research aims to analyse the effects of 2000 and 2017 fires on the recharge process. The first result consists in the definition of the hydrogeological conceptual models of the dune aquifer: a shallow fresh aquifer overlapping two deeper confined salinized aquifers. The comparison between the amount of the yearly recharge, evaluated in different periods, showed a significant recharge rate decrease (about 36%) to be attributed likely at the 2000 fire effect. The research is still ongoing in order to verify and detail the changes of the recharge processes induced by the 2000 and 2017 fires.

Numerical studies of CO2 and brine leakage into a shallow aquifer through an open wellbore

Industrial-scale geological storage of CO2 in saline aquifers may cause CO2 and brine leakage from abandoned wells into shallow fresh aquifers. This leakage problem involves the flow dynamics in both the wellbore and the storage reservoir. T2Well/ECO2N, a coupled wellbore-reservoir flow simulator, was used to analyze CO2 and brine leakage under different conditions with a hypothetical simulation model in water-CO2-brine systems. Parametric studies on CO2 and brine leakage, including the salinity, excess pore pressure (EPP) and initially dissolved CO2 mass fraction, are conducted to understand the mechanism of CO2 migration. The results show that brine leakage rates increase proportionally with EPP and inversely with the salinity when EPP varies from 0.5 to 1.5 MPa; however, there is no CO2 leakage into the shallow freshwater aquifer if EPP is less than 0.5 MPa. The dissolved CO2 mass fraction shows an important influence on the CO2 plume, as part of the dissolved CO2 becomes a free phase. Scenario simulation shows that the gas lifting effect will significantly increase the brine leakage rate into the shallow freshwater aquifer under the scenario of 3.89% dissolved CO2 mass fraction. The equivalent porous media (EPM) approach used to model the wellbore flow has been evaluated and results show that the EPM approach could either under- or over-estimate brine leakage rates under most scenarios. The discrepancies become more significant if a free CO2 phase evolves. Therefore, a model that can correctly describe the complex flow dynamics in the wellbore is necessary for investigating the leakage problems.

ASSESSMENT OF SEAWATER INTRUSION IN FUSHE KUQE AQUIFER, ALBANIA

The Fushë Kuqe costal aquifer is a typical confined alluvial aquifer. The aquifer medium consists of alternating and discontinuous layers of gravel and sand-gravel with and silt-clay impermeable layers which have conditioned its multilayer character. The aquifer recharge occurs mainly through water infiltration from the Mat river in the North, and from Droja river in the South, while its natural discharge proceeds to the Adriatic sea. As from the variation of chloride and TDS content in groundwater, an advancement of sea water intrusion into aquifer fresh water was evidenced. The direction of sea water wedge from coastal southwestern sectors towards the Gorre and Fushe Kuqe where pumping station are located, favors the opinion that it was caused by a decrease of groundwater pressure due to the groundwater pumping. The increase of chloride content in groundwater through time confirms that sea water intrusion towards the fresh aquifer water is still ad-vancing and is caused by both intensification of groundwater pumping for public water supply and by the drilling of artesian private wells.

Unstable convection flow as a controlling process of increasing salinity in the saline lake coastal aquifers: case of Maharlu Lake coastal aquifer

Deterioration of freshwater aquifers adjacent to saline lakes is a serious environmental and water resources management problem. Generally, different phenomena including saltwater intrusion, upconing, free and forced convection flow can lead to the salinization of fresh aquifers in the vicinity of saline lakes. The severity of this problem depends on hydrogeological and hydrogeochemical conditions of coastal saline lake aquifers. Accordingly, Maharlu Lake in the southeast of Shiraz plain is one of these saline lakes and has an important impact on its adjacent fresh aquifers so that the salinity of these aquifers has increased in recent years. Since the lake has special conditions such as very flat and low permeable floor and variable water level fluctuation during a year, with the onset of the rainy season after a long-term well pumping in the adjacent aquifer, the lake water covers a wide extent of the lake area in a short time. Then, because of the higher permeability of the surface of the lake in its southeast margin, conditions for convection flow are provided there. In this study, salinity distribution in one of the aquifers (Bokat aquifer) in the southeast of the lake is investigated using resistivity tomography along several profiles. Interpretation of inverse models of these profiles showed that convection flow is an important process in increasing the salinity of fresh aquifer. Comparison of the results of geo-tomography sections with convection index map of the Bokat aquifer showed that getting closer to the lake, free convection flow becomes the dominant process in the salinity distribution. In addition, in farther distances relative to the lake, due to increasing the pumping rate of the extraction wells, forced convection flow is an important process.

Hydraulic and electric anisotropy of shallow fresh coastal aquifer in Nabq, Sinai, Egypt

The prospective of this research is to investigate the hydraulic and electric anisotropy of the fresh coastal aquifer. In this context, 44 Schlumberger DC soundings associated with the available boreholes data and numbers of measured and/or calculated hydraulic and electric parameters were carried out in Nabq area, Sinai. The inverted DC soundings revealed high potentiality of the fresh coastal aquifer toward the western part of the Quaternary and Pre-Quaternary. An increased tortuosity (T) toward the west direction was associated with coarser grains size and increase in resistivity (ρ) hydraulic conductivity (K), transmissivity (T), and a decrease in porosity (ϕ). The longitudinal hydraulic conductivity (K l ) was found to be greater than the transverse hydraulic conductivity (K t) which implied a lower tortuosity in the horizontal direction than in the vertical direction. The decrease in the hydraulic anisotropy (λ H) was associated by an increase in transmissivity. Minor variation in electric anisotropy (λ e) could be observed as a result of alternating layers and intercalation of different grain sizes. Resistivity of the fresh aquifer was recognized by a liner direct relation with λ H, whereas, no clear relation could be observed with λ E. A polynomial relation with poor correlation coefficient could be observed between λ H and λ E.

Hydro/Engineering Geophysical Parameters and Design Response Spectrum for Sustainable Development in Ras Muhammed National Park, Sinai

The Egyptian government is preparing a sustainable development master plan for the Ras Muhammed National Park (RMNP), south Sinai. Noteworthy, the scarcity of the freshwater resources and close proximity to the active seismic zones of the Gulf of Aqaba implicate geophysical investigations for the fresh groundwater aquifers and construct a design response spectrum, respectively. Accordingly, 14 VESs, hydro/engineering geophysical analysis, pumping tests, downhole seismic test, a design response spectrum for buildings, and borehole data were carried out in the study area. The unconfined freshwater aquifer was effectively depicted with true resistivities, thickness, and EC ranged from 56 to 135 Ω m, 11 to 112 m, and 1.4 to 7.1 mS/m, respectively. The Northeastern part was characterized by higher aquifer potentiality, where coarser grains size, highest thickness (112 m), high true resistivity (135 Ω m), groundwater flow (0.074 m3/day), tortuosity (1.293–1.312), formation resistivity factor (4.1–4.6), and storativity (0.281–0.276). An increase in pumping rate was accompanied by an increase in well loss, increase in aquifer losses, decrease in well specific capacity, and decrease in well efficiency. Design response spectrum prognosticated the short buildings (<7 floors) in RMNP to be suffering from a high peak horizontal acceleration and shear forces for acceleration between 0.25 and 0.35 g. Therefore, appropriate detailing of shear reinforcement is indispensable to reduce the risk of structural damages at RMNP.

Geochemical responses of a saline aquifer to CO2 injection: experimental study on Guantao formation of Bohai Bay Basin, East China

AbstractGeochemical responses of saline aquifers toward large quantities of CO2 injection are important to the monitoring and safety assessment of CO2 storage. Detailed studies on water‐rock‐CO2 interactions of non‐marine saline aquifers through three batch‐reaction experiments were carried out under simulated reservoir conditions (T = 100°C, P = 10 MPa). pH decreased by 1∼2 and TDS increased by 268 mg/L ∼561 mg/L. Water type evolved from original Cl·SO4‐Na to HCO3Cl·SO4‐Na with a water/rock ratio of 3:1. Chemical components of HCO3, Ca, Mg and K and trace elements of Al, Cr, Mn, Ni and Zn showed a significant increase post CO2 injection. Heavy metals including Cr, Mn, Ni, and Zn in the post‐reaction water exceeded drinking water standards, indicating potential pollution to shallow fresh aquifers by brine/CO2 leakage. K‐feldspar and albite were variably dissolved and kaolinite, chlorite, and Fe‐bearing minerals of pyrite and hematite were newly formed, confirmed by suspended materials in the post‐reaction water, red sediments on the bottom of the reactor, and mineral saturation indexes. δ2HH2O shift was observed and discussed, which was not reported in previous water‐rock‐CO2 interactions studies. One possible reason is geochemical processes of new clay minerals formation under low temperature causing water consumption and δ2HH2O enriched in the residual water. The CO2 saturation and fraction of DIC from CO2 dissolution were calculated to be 23%–36% and 33%–49% under experimental conditions and it is suggested that they can be used for CO2 storage capacity assessment.

The effect of salinization and freshening events in coastal aquifers on nutrient characteristics as deduced from field data

Summary The effect of seawater intrusion and freshening events in coastal aquifers on nutrient (dissolved inorganic nitrogen species, phosphate and silica) dynamics across the fresh–saline groundwater interface (FSI) were quantified using field data. Seasonal vertical profiles revealed a clear transition between nutrient species across the FSI, which is also an oxycline. In view of the results of our experimental simulations, it is clear that the major process controlling the nutrient dynamics at the FSI, besides the mixing that takes place between the two different water bodies, is the seasonal variation between seawater intrusion (salinization) in summer and flushing of the aquifer (freshening) in winter. Aquifer salinization during the summer shifts the FSI and the anaerobic depth-location upwards and leads to the enrichment of NH4+, PO43− and DSi (dissolved silica) in the saline groundwater. NH4+ and PO43− are enriched due to ion exchange, and DSi is enriched either by ion exchange (as PO43−) or as a result of dissolution of biogenic silica. Denitrification occurs at the base of the FSI, as indicated by the slight NO3− depletion and the enrichment in δ15N of NO3−. Aquifer freshening during the winter shifts the FSI downward and the water becomes suboxic with the influence of the oxic fresh groundwater. This leads to nitrification of the NH4+, enrichment of NO2− and depletion of 15N in the residual NO3− in the FSI. These cyclic processes generate a certain depletion of N and enrichment of P in the saline groundwater. Circulation of the saline groundwater below the FSI back to the sea can serve as a partial counterbalance to the high anthropogenic load of N impacting the coastal groundwater system.