Groundwater resources evaluation in calcareous limestone using geoelectrical and VLF-EM surveys (El Salloum Basin,Egypt)

Understanding and developing groundwater resources in arid regions such as El Salloum basin, along the northwestern coast of Egypt, remains a challenging issue. One-dimensional (1D) electrical sounding (ES), two-dimensional (2D) electrical resistivity imaging (ERI), and very low frequency electromagnetic (VLF-EM) measurements were used to investigate the hydrogeological framework of El Salloum basin with the aim of determining the potential for extraction of potable water. 1D resistivity sounding models were used to delineate geoelectric sections and water-bearing layers. 2D ERI highlighted decreases in resistivity with depth, attributed to clay-rich limestone combined with seawater intrusion towards the coast. A depth of investigation (DOI) index was used to constrain the information content of the images at depths up to 100 m. The VLF-EM survey identified likely faults/fractured zones across the study area. A combined analysis of the datasets of the 1D ES, 2D ERI, and VLF-EM methods identified potential zones of groundwater, the extent of seawater intrusion, and major hydrogeological structures (fracture zones) in El Salloum basin. The equivalent geologic layers suggest that the main aquifer in the basin is the fractured chalky limestone middle Miocene) south of the coastal plain of the study area. Sites likely to provide significant volumes of potable water were identified based on relatively high resistivity and thickness of laterally extensive layers. The most promising locations for drilling productive wells are in the south and southeastern parts of the region, where the potential for potable groundwater increases substantially.

     

Sequential extraction and leaching characteristics of heavy metals in abandoned tungsten mine tailings sediments

The chemical speciation of potentially toxic elements (As, Cd, Cu, Pb, and Zn) in the contaminated soils and sulfides-rich tailings sediments of an abandoned tungsten mine in Korea was evaluated by conducting modified BCR sequential extraction tests. Kinetic and static batch leaching tests were also conducted to evaluate the potential release of As and other heavy metals by acidic rain water and the leaching behaviors of these heavy metals. The major sources of the elements were As-, Zn- and Pb-bearing sulfides, Pb carbonates (i.e., cerussite), and Pb sulfates (i.e., anglesite). The biggest pollutant fraction in these soil and tailing samples consists of metals bound to the oxidizable host phase, which can be released into the environment if conditions become oxidative, and/or to residual fractions. No significant difference in total element concentrations was observed between the tailings sediments and contaminated soils. For both sample types, almost no changes occurred in the mobility of As and the other heavy metals at 7 days, but the mobility increased afterwards until the end of the tests at 30 days, regardless of the initial pH. However, the mobility was approximately 5–10 times higher at initial pH 1.0 than at initial pHs of 3.0 and 5.0. The leached amounts of all the heavy metal contents were higher from tailings sediments than from contaminated soils at pH > 3.0, but were lower at pH < 3.0 except for As. Results of this study suggest that further dissolution of heavy metals from soil and tailing samples may occur during extended rainfall, resulting in a serious threat to surface and groundwater in the mine area.     

Landslide risk assessment and management: an overview

Landslides can result in enormous casualties and huge economic losses in mountainous regions. In order to mitigate landslide hazard effectively, new methodologies are required to develop a better understanding of landslide hazard and to make rational decisions on the allocation of funds for management of landslide risk. Recent advances in risk analysis and risk assessment are beginning to provide systematic and rigorous processes to enhance slope management. In recent years, risk analysis and assessment has become an important tool in addressing uncertainty inherent in landslide hazards.This article reviews recent advances in landslide risk assessment and management, and discusses the applicability of a variety of approaches to assessing landslide risk. Firstly, a framework for landslide risk assessment and management by which landslide risk can be reduced is proposed. This is followed by a critical review of the current state of research on assessing the probability of landsliding, runout behavior, and vulnerability. Effective management strategies for reducing economic and social losses due to landslides are described. Problems in landslide risk assessment and management are also examined.     

Distribution and Removal of Silver and Lead in the Nearshore Waters of Western Taiwan

Concentrations of Al, Mn, Fe, Ag, and Pb in dissolved and particulate phases of the surface water were determined at 15 stations along the coastline off western Taiwan in April of 2007. This study presents the first set of data for Al, Ag, and Pb in the nearshore waters. Latitudinal distribution of these metals showed that high values were present in the regions affected by high fluvial discharge from the Dan-Sui River and the Cho-Sui River. Using the particle fluxes from ²¹⁰Po/²¹⁰Pb disequilibria, the removal fluxes and the residence times of the trace metals were calculated. Based on the K _d values, the sequence of particle affinity of trace metals, Fe ~ Al >> Pb > Mn > Ag, was found. The correlation of the residence times and of the partitioning coefficients of multiple metals in the nearshore waters implies that the affinities to the particles determine the geochemical cycling of metals in the coastal water.     

Probabilistic Analysis of Fracture Reactivation Associated with Deep Underground CO2 Injection

In the context of carbon capture and storage, deep underground injection of CO₂ induces the geomechanical changes within and around the injection zone and their impact on CO₂ storage security should be evaluated. In this study, we conduct coupled multiphase fluid flow and geomechanical modeling to investigate such geomechanical changes, focusing on probabilistic analysis of injection-induced fracture reactivation (such as shear slip) that could lead to enhanced permeability and CO₂ migration across otherwise low-permeability caprock formations. Fracture reactivation in terms of shear slip was analyzed by implicitly considering the fracture orientations generated using the Latin hypercube sampling method, in one case using published fracture statistics from a CO₂ storage site. The analysis was conducted by a coupled multiphase fluid flow and geomechanical simulation to first calculate the three-dimensional stress evolution during a hypothetical CO₂ injection operation and then evaluate the probability of shear slip considering the statistical fracture distribution and a Coulomb failure analysis. We evaluate the probability of shear slip at different points within the injection zone and in the caprock just above the injection zone and relate this to the potential for opening of new flow paths through the caprock. Our analysis showed that a reverse faulting stress field would be most favorable for avoiding fracture shear reactivation, but site-specific analyses will be required because of strong dependency of the local stress field and fracture orientations.     

Preservation of organic matter in mound-forming coral skeletons

This study demonstrates that intracrystalline organic matter in coral skeletons is well preserved over century timescales. The extent of preservation of organic matter in coral skeletons was investigated by measuring total organic carbon (TOC), total hydrolyzable amino acid (THAA), chloropigment, and lipid concentrations in 0-300 year old annual growth bands from Montastraea annularis (Florida Keys) and Porites lutea (Red Sea). Organic matter intrinsic to the calcium carbonate mineral (intracrystalline) was analyzed separately from total skeletal organic matter. The Red Sea coral had less TOC (0.02-0.04 wt%) than the Florida Keys coral (0.04-0.11 wt%), but a higher percent of intracrystalline organic matter in all annual bands measured. Carbon in the form of THAA, most likely from mineral-precipitating proteins, contributed 30-45% of the TOC in both corals. Carbon in lipids represented about 3% of the TOC in the coral skeletons. Chlorophyll-a and b were present in annual bands where endolithic algae were present, but these compounds were minor contributors to TOC. The distribution of specific organic compounds showed that organic matter was well preserved throughout the time period sampled in both the total and intracrystalline pools. Variations in THAA were not correlated with TOC over time, suggesting that organic matter that is involved in biomineralization, like amino acids, may be deposited in response to different environmental factors than are other components of skeletal organic matter. Differences in the quantity and composition of organic matter between the two corals investigated here were assessed using principal components analysis and suggest that location, species and skeletal structure may all influence organic matter content and possibly the degree of physical protection of organic matter by the coral skeleton. Further, our study suggests that intracrystalline organic matter may be better protected from diagenesis than non-intracrystalline organic matter and may therefore be a more reliable source of organic matter for paleoceanographic studies than total skeletal organic matter.     

The imprinting of aridity upon a lateritic landscape: an illustration from southwestern Australia

The southwestern region of Australia contains the Yilgarn Craton that has been exposed to subaerial weathering since mid-Proterozoic. The gently undulating landscape experienced lateritic weathering so that today variably dissected, deep in situ isovolumetrically weathered regolith is widespread. Imposition of a more arid climate since the Miocene with the cessation of effective external drainage has resulted in substantial geochemical modification of the highly porous regolith. This vast pore volume acts as a reservoir for complex solutions that may be highly saline, extremely acid to alkaline and reducing. Diverse precipitates have formed in the regolith including widespread occurrence of silcrete, calcrete, dolocrete, ferricrete and gypcrete together with localised occurrences of pyrite, alunite, jarosite, barite, halite and other salts. Clearing of bush land for agriculture in the 20th century increased recharge so that rising chemically active groundwaters are damaging farmland and infrastructure throughout the region. To cite this article: B. Gilkes et al., C. R. Geoscience 335 (2003).     

Hydrogeochemical characterization of major factors affecting the quality of shallow groundwater in the coastal area at Kimje in South Korea

This study has evaluated the main hydrogeochemical characteristics that affect the quality of shallow groundwater in the coastal area at Kimje in South Korea. In this area, the chemical composition of groundwater is mostly classified into Na⁺?Cl^? and Ca²⁺+Mg²⁺?NO₃^-+Cl^? types. These types are affected by three major factors: seawater intrusion, fertilizers and redox processes. The Na⁺?Cl^? type, which is generally localized in the coastal area, shows typical characteristics of groundwater affected not only by modern seawater but also by old seawater residing in the reclaimed land. In contrast, the Ca²⁺+Mg²⁺?NO₃^-+Cl^? type, which is usually found inland, is very contaminated by fertilizers. As groundwater flows from the inland area to the coast, the redox condition changes from an oxic condition to a suboxic/anoxic condition. In addition, the reclamation has caused a large amount of underlying organic matter. These effects provide optimum conditions for the occurrence of redox processes in the coastal area.     

Evaluation of remedial alternatives for a petroleum contaminated unconfined aquifer with fluctuating groundwater level

This study evaluated remedial alternatives for a petroleum-contaminated site where an unconfined aquifer composed of a sandy layer of about 3–3.5 m thickness is covered by alluvial deposits and reclaimed soil of about 1.5 m thickness. Precambrian gneiss, of low permeability, lies below the sandy layer. The shallow water table is about 3 m below the surface, but shows high fluctuations of up to 1.5 m in response to precipitation events. The unsaturated soil near the water table and the groundwater are highly contaminated with petroleum hydrocarbons, especially toluene, which have apparently leaked from storage tanks. Selection of the remedial alternatives required consideration of the relevant laws on soil and groundwater conservation in Korea, the results of risk analysis and the hydrogeological conditions. The contaminated area has been divided into zones in which different remediation goals are set based on risk analysis and the degree of natural attenuation. It is estimated that the clean-up goal can be achieved in two years by the combined use of a trench drain and well point pumping to collect the contaminated groundwater for treatment, and a dual air injection system for the contaminated soil.     

Effects of natural and calcined oyster shells on Cd and Pb immobilization in contaminated soils

In Korea, soils adjacent to abandoned mines are commonly contaminated by heavy metals present in mine tailings. Further, the disposal of oyster shell waste by oyster farm industries has been associated with serious environmental problems. In this study, we attempted to remediate cadmium (Cd)- and lead (Pb)-contaminated soils typical of those commonly found adjacent to abandoned mines using oyster shell waste as a soil stabilizer. Natural oyster shell powder (NOSP) and calcined oyster shell powder (COSP) were applied as soil amendments to immobilize Cd and Pb. The primary components of NOSP and COSP are calcium carbonate (CaCO₃) and calcium oxide (CaO), respectively. X-ray diffraction, X-ray fluorescence and scanning electron microscope analyses conducted in this study revealed that the calcination of NOSP at 770°C converted the less reactive CaCO₃ to the more reactive CaO. The calcination process also decreased the sodium content in COSP, indicating that it was advantageous to use COSP as a liming material in agricultural soil. After 30 days of incubation, we found that the 0.1 N HCl-extractable Cd and Pb contents in soil decreased significantly as a result of an increase in the soil pH and the formation of metal hydroxides. COSP was more effective in immobilizing Cd and Pb in the contaminated soil than NOSP. Overall, the results of this study suggest that oyster shell waste can be recycled into an effective soil ameliorant.